diff --git a/packages/business/src/system-config-problem.mjs b/packages/business/src/system-config-problem.mjs
new file mode 100644
index 000000000..7f1324563
--- /dev/null
+++ b/packages/business/src/system-config-problem.mjs
@@ -0,0 +1,2 @@
+// Old path of packages/organization/src/system-config-problem.mjs (rename design r2, stage B).
+export * from "../../organization/src/system-config-problem.mjs";
diff --git a/packages/cli/src/cli.mjs b/packages/cli/src/cli.mjs
index 314ff713f..d8fbeda92 100644
--- a/packages/cli/src/cli.mjs
+++ b/packages/cli/src/cli.mjs
@@ -519,7 +519,8 @@ async function processingCommand(verb, rest, io, deps) {
     if (!result || typeof result !== 'object' || (typeof result.halted !== 'boolean' && !result.invalid))
       throw new CliError('processing outcome unknown; use mosaic processing status before trying again', 1);
     if (verb === 'halt' && result.quiescent !== true)
-      throw new CliError(`halt gate is on for instance ${system.dataRoot}; ${result.remaining ?? 'unknown'} stops unconfirmed. Use mosaic processing status`, 1);
+      // #1873: the refusal names the instance, never its data root; a count that is not a count is unknown.
+      throw new CliError(`halt gate is on for this instance; ${Number.isSafeInteger(result.remaining) && result.remaining >= 0 ? result.remaining : 'unknown'} stops unconfirmed. Use mosaic processing status`, 1);
     if (parsed.flags.has('--json')) { io.stdout.write(JSON.stringify(result, null, 2) + '\n'); return; }
     const status = verb === 'resume' ? 'resumed' : result.halted ? 'halted' : result.invalid ? 'uninitialized' : 'running';
     io.stdout.write(`processing ${status} for instance ${system.dataRoot}\n`);
diff --git a/packages/cli/src/config.mjs b/packages/cli/src/config.mjs
index 36fee7d83..e34d81a8c 100644
--- a/packages/cli/src/config.mjs
+++ b/packages/cli/src/config.mjs
@@ -13,6 +13,7 @@ import { BusinessError, accessFilePath, configDir, loadAccess, loadBusiness, loa
 import { loadRootAgents } from "../../organization/src/agent-levels.mjs";
 import { materializeCopies, withCopies } from "../../organization/src/agent-copies.mjs";
 import { organizationWriter } from "../../organization/src/organization.mjs";
+import { systemConfigProblem } from "../../organization/src/system-config-problem.mjs";
 import { businessFilePath } from "../../organization/src/organization-config.mjs";
 import { busOrganization } from "../../bus/src/organization-context.mjs";
 import { BusError } from "../../bus/src/broker.mjs";
@@ -41,13 +42,40 @@ export function orgPaths(root) {
     threads: join(root, "threads"), hostDir };
 }
 
+// #1873: mosaic-config's stderr can quote the config's path, the data root or a config value, so
+// it is never relayed. An instance refusal keeps its code and the instance names, which passed
+// the instance pattern; a missing config keeps its bootstrap hint; anything else reads as
+// `mosaic org config` reads it: a known field and its constraint, the config named by label.
+const INSTANCE = "[a-z][a-z0-9]{1,15}";
+function instanceProblem(problem, label) {
+  const body = problem.replace(/^mosaic-config: /, "");
+  let m = new RegExp(`^instance-root-mismatch: .+ is claimed by instance (${INSTANCE})(?:, not (${INSTANCE})|; select it with --instance \\1)$`).exec(body);
+  if (m) return `instance-root-mismatch: the data root is claimed by instance ${m[1]}${m[2] ? `, not ${m[2]}` : `; select it with --instance ${m[1]}`}`;
+  m = new RegExp(`^instance-root-unclaimed: .+ holds no instance\\.json naming (${INSTANCE}) \\(scripts/bootstrap\\.sh --instance \\1 claims a new root\\)$`).exec(body);
+  if (m) return `instance-root-unclaimed: the data root holds no instance.json naming ${m[1]} (scripts/bootstrap.sh --instance ${m[1]} claims a new root)`;
+  if (body.startsWith("instance-root-unclaimed: ")) return "instance-root-unclaimed: the data root's instance.json is not a readable, valid marker";
+  m = new RegExp(`^instance-config-mismatch: --instance (${INSTANCE}) names `).exec(body);
+  if (m) return `instance-config-mismatch: --instance ${m[1]} names its own config, but MOSAIC_CONFIG names another`;
+  if (body.startsWith("instance-config-mismatch: ")) return "instance-config-mismatch: --instance names its own config, but MOSAIC_CONFIG names another";
+  if (body.startsWith("instance-name-invalid: ")) return `instance-name-invalid: an instance name must match /^${INSTANCE}$/`;
+  if (body.startsWith("configuration not found: ")) {
+    m = new RegExp(`\\(run (scripts/bootstrap\\.sh(?: --instance ${INSTANCE})?) to create it\\)$`).exec(body);
+    return `configuration not found: ${label}${m ? ` (run ${m[1]} to create it)` : ""}`;
+  }
+  return null;
+}
+
 export function loadSystem({ env = process.env, instance = null } = {}) {
   const proc = spawnSync(process.execPath, [join(REPO, "scripts", "mosaic-config.mjs"), "validate", ...(instance === null ? [] : ["--instance", instance])], {
     encoding: "utf8",
     maxBuffer: 1024 * 1024,
     env,
   });
-  if (proc.status !== 0) throw new CliError(`system config problem (mosaic-config exit ${proc.status}): ${proc.stderr.trim()}`, 3);
+  if (proc.status !== 0) {
+    const label = instance !== null && instance !== "dev" ? `the config of instance ${instance}` : env.MOSAIC_CONFIG ? "the system config MOSAIC_CONFIG names" : "the default system config";
+    const known = instanceProblem(String(proc.stderr ?? "").trim(), label);
+    throw new CliError(known ? `system config problem (mosaic-config exit ${proc.status}): ${known}` : systemConfigProblem(proc, env, label), 3);
+  }
   try {
     return JSON.parse(proc.stdout);
   } catch {
@@ -90,7 +118,7 @@ function trackerFor(system, b, warn, dataRoot) {
     if (dataRoot && managedState({ dataRoot, business: b.id, project: id, entry }) === 'reserved') continue;
     if (!existsSync(projectFilePath(entry.root))) continue;
     const project = loadProject(entry.root);
-    if (project.id !== id) throw new CliError(`project file ${project.file} has id that does not match the declared project key`, 3);
+    if (project.id !== id) throw new CliError(`project file of project ${id} has id that does not match the declared project key`, 3);
     const vars = resolveInstance({ system, business: b, project, instance: first }).vars;
     if (vars["tracker.project"] !== undefined) named.push({ id, vars });
   }
@@ -127,17 +155,20 @@ function accessFor(system, env, warn) {
   try {
     context = accessContextFor(system, env);
   } catch (e) {
-    warn(`access.json is present but its context can't be read, so no granted user binds: ${e.message}`);
+    // #1873: the error's message can quote a path; only a plain code is relayed.
+    const code = typeof e?.code === "string" && /^[A-Za-z][A-Za-z0-9_-]{0,63}$/.test(e.code) ? ` (${e.code})` : "";
+    warn(`access.json is present but its context can't be read, so no granted user binds${code}`);
     return null;
   }
   // sage-3153: one line at boot when the loader refuses the file, so the owner sees why no user
-  // binds. The loader's messages can quote the file, so the line names only the path and a code
-  // from its exit code: 4 is a file it could not open as a regular file, anything else invalid.
+  // binds. The loader's messages can quote the file, so the line names only the file, by label, and
+  // a code from its exit code: 4 is a file it could not open as a regular file, anything else
+  // invalid. #1873: no host path.
   try {
     loadAccess(file, context);
   } catch (e) {
     const code = e instanceof BusinessError && e.exitCode !== 4 ? "access-invalid" : "access-unreadable";
-    warn(`access file refused at boot (${code}), no granted user binds until it is fixed: ${file}`);
+    warn(`access file refused at boot (${code}), no granted user binds until it is fixed: access.json in the config directory`);
   }
   return { file, context };
 }
diff --git a/packages/cli/src/launcher.mjs b/packages/cli/src/launcher.mjs
index 49299f2c5..8ba047a9f 100644
--- a/packages/cli/src/launcher.mjs
+++ b/packages/cli/src/launcher.mjs
@@ -145,6 +145,7 @@ import { chmodSync, existsSync, lstatSync, mkdirSync, readFileSync, renameSync,
 import { dirname, join, relative } from "node:path";
 import { configDir, resolveInstance, systemVars } from "../../organization/src/index.mjs";
 import { organizationWriter } from "../../organization/src/organization.mjs";
+import { quietMessage } from "../../organization/src/org-registry.mjs";
 import { businessFilePath } from "../../organization/src/organization-config.mjs";
 import { copyOf, copyRefusal, loadWithCopies, projectRefusal, withCopies } from "../../organization/src/agent-copies.mjs";
 import { selectModelProvider } from "../../plugins/src/model-provider-selection.mjs";
@@ -201,13 +202,24 @@ class Refusal extends Error {
   }
 }
 
+// #1873: a refusal's reason never quotes a host path. A Node system error's message names one,
+// so it reads as the call and its code (org-registry quietMessage). Any other message is the
+// host's own text or text relayed from a module (a preflight, the loader, a bundle or checkout
+// error); relay() replaces every absolute or home path and file: URL in it with "a host path".
+const HOST_PATH = /(^|[\s'"(=:,[<])(?:~?\/(?!\/)|file:)[^\s'"),\]>;]*/gi;
+export const relay = (text) => String(text).replace(HOST_PATH, (_, before) => `${before}a host path`);
+const reason = (e) => quietMessage(e, "a host file") ?? relay(e?.message ?? e);
+const relayed = (failed) => failed && (typeof failed.message === "string" ? { ...failed, message: relay(failed.message) } : failed);
+
 // A harness module runs with the host's authority, and anything it throws refuses the launch
-// and names the module rather than escaping the host.
+// and names the module rather than escaping the host. What it threw is named by its system code
+// or its class, never its message, which the host didn't write (#1873).
 function call(name, what, fn) {
   try {
     return fn();
   } catch (e) {
-    throw new Refusal("harness-failed", `harness ${name} ${what}: ${e.message}`);
+    const thrown = quietMessage(e, "a host file") ?? `threw ${/^[A-Za-z][A-Za-z0-9]{0,39}$/.test(String(e?.name)) ? e.name : "a value"} without a system code`;
+    throw new Refusal("harness-failed", `harness ${name} ${what}: ${thrown}`);
   }
 }
 
@@ -272,7 +284,8 @@ export function createLauncher({
   try {
     leftover = readSessions(dataRoot).filter((s) => s.business === b.id);
   } catch (e) {
-    throw new CliError(`${e.message}; check which sessions still run, then move the file aside`, 3);
+    // readSessions names the file by its place under the data root (#1873); anything else is unreadable.
+    throw new CliError(`${e?.name === "SeatError" ? e.message : "sessions file is unreadable"}; check which sessions still run, then move the file aside`, 3);
   }
   const registry = new Registry(dataRoot, { readOnly: !launches });
   // Row 269: earlier-host runs still live after recover(). check() sees each while it lives.
@@ -386,7 +399,7 @@ export function createLauncher({
       // org-defscan (#1873): the entry the contract came from, taken before any await lets another check replace b.
       definitionEntry = String(resolved.definition).startsWith("org:") ? b.definitions?.[resolved.definition] : undefined;
     } catch (e) {
-      throw new Refusal(e.code === "plugin-disabled" ? "plugin-disabled" : "unsupported-harness", e.code === "plugin-disabled" ? e.plugin : e.message);
+      throw new Refusal(e.code === "plugin-disabled" ? "plugin-disabled" : "unsupported-harness", e.code === "plugin-disabled" ? e.plugin : relay(e.message));
     }
     // Resolve the business's current provider modules with a fresh loader; a refused
     // load never inherits a previous business's authority.
@@ -409,7 +422,7 @@ export function createLauncher({
         return sessionModel(resolved, b.launch.models, which, { proxy: Boolean(system.proxy || proxyContext), resolver });
       } catch (e) {
         const code = e instanceof BundleError && (e.code === "no-route" || e.code.startsWith("proxy-") || e.code.startsWith("model-")) ? e.code : "unsupported-harness";
-        throw new Refusal(code, e.message);
+        throw new Refusal(code, relay(e.message));
       }
     };
     const primary = routeOf("primary");
@@ -425,7 +438,7 @@ export function createLauncher({
     try {
       readSkills(resolved.skills, skillsDir);
     } catch (e) {
-      if (e instanceof BundleError) throw new Refusal(e.code === "skill-not-enabled" ? "skill-not-enabled" : "skill-refused", e.message);
+      if (e instanceof BundleError) throw new Refusal(e.code === "skill-not-enabled" ? "skill-not-enabled" : "skill-refused", relay(e.message));
       throw e;
     }
     // Both of a launch's harnesses must be switched on, whichever it takes.
@@ -437,7 +450,9 @@ export function createLauncher({
     const harnessOf = async (m) => {
       const loader = makeLoader({ dataRoot:system.instanceRoot ?? dataRoot, log: (entry) => record({ ...entry, instance }) });
       const { refused } = await loader.load({ harness: [m.harness] });
-      if (refused.length) throw new Refusal("harness-refused", `harness ${m.harness}: ${refused.map((r) => `${r.code}: ${r.message}`).join("; ")}`);
+      // #1873: a loader message can quote the module's path or its load error; only a
+      // missing-export one, which names the export, is relayed. Any other refusal names its code.
+      if (refused.length) throw new Refusal("harness-refused", `harness ${m.harness}: ${refused.map((r) => r.code === "missing-export" ? `${r.code}: ${relay(r.message)}` : String(r.code)).join("; ")}`);
       const module = loader.modules("harness")[0];
       const levels = call(m.harness, "levels", () => module.levels());
       if (!levels.includes(m.thinking)) throw new Refusal("thinking-unsupported", `harness ${m.harness} takes thinking ${levels.join(", ")}, not ${m.thinking}`);
@@ -484,7 +499,7 @@ export function createLauncher({
         }
       }
       const unavailable = sandboxProblem({ bwrap });
-      if (unavailable) throw new Refusal("sandbox-unavailable", unavailable);
+      if (unavailable) throw new Refusal("sandbox-unavailable", relay(unavailable));
       const hit=limitHit(registry.sessions,b.id,b.launch.limits,model);
       if(hit){const error=new Refusal("capacity-full",JSON.stringify(hit));error.limit=hit;throw error;}
       // Row 125 (#1619, REQ-LIMIT-4): the limit checks. An answer that isn't an allow refuses,
@@ -532,7 +547,8 @@ export function createLauncher({
     // and the helper returns the last one they saw.
     const pickRoute = async (proxyOf) => {
       let sessionProxy = await proxyOf(primary);
-      const failed = call(primary.harness, "preflight", () => harness.preflight({ env: sessionProxy ? sessionEnv(env, "preflight", sessionProxy) : env, proxy: sessionProxy }));
+      // #1873: a preflight's message is the module's own text, relayed with host paths replaced.
+      const failed = relayed(call(primary.harness, "preflight", () => harness.preflight({ env: sessionProxy ? sessionEnv(env, "preflight", sessionProxy) : env, proxy: sessionProxy })));
       if (failed) {
         if (!fallback) throw new Refusal(failed.code, failed.message);
         // The fallback only on a failed primary preflight, and only at launch (row 65). Any refusal of
@@ -542,7 +558,7 @@ export function createLauncher({
           throw e;
         });
         sessionProxy = await proxyOf(fallback);
-        const also = call(fallback.harness, "preflight", () => second.preflight({ env: sessionProxy ? sessionEnv(env, "preflight", sessionProxy) : env, proxy: sessionProxy }));
+        const also = relayed(call(fallback.harness, "preflight", () => second.preflight({ env: sessionProxy ? sessionEnv(env, "preflight", sessionProxy) : env, proxy: sessionProxy })));
         if (also) throw new Refusal(also.code, `fallback ${fallback.harness}: ${also.message} (primary ${primary.harness}: ${failed.message})`);
         [model, harness, route, routeReason] = [fallback, second, "fallback", failed.code];
       }
@@ -664,7 +680,7 @@ export function createLauncher({
         return ensureCheckouts({ workspace, projects: codeProjects, env });
       });
     } catch (e) {
-      if (e instanceof CheckoutError) throw new Refusal("checkout-failed", `${e.project}: ${e.message}`);
+      if (e instanceof CheckoutError) throw new Refusal("checkout-failed", `${e.project}: ${relay(e.message)}`);
       throw e;
     }
     for (const c of checkouts) {
@@ -861,7 +877,7 @@ export function createLauncher({
       unregisterRuntime(dataRoot, managed.id);
       if (e instanceof Refusal) throw e;
       if (e.code?.startsWith('proxy-')) throw new Refusal(e.code, e.code);
-      throw new Refusal("launch-failed", e.message);
+      throw new Refusal("launch-failed", reason(e));
     }
     children.set(run, exited);
     const outputWatch = admittedProxy ? watchModelOutput({ runDir, armAtFirstTurn: true, keyId: modelKeyId, seconds: system.proxy.firstOutputSeconds ?? 120,
@@ -1041,7 +1057,7 @@ export function createLauncher({
           if (refusedThreads.get(key) === code) return;
           refusedThreads.set(key, code);
           log(`thread ${t.thread} session ${t.session} (${t.instance}): start refused: ${code}`);
-          record({ event: "refused", by: b.human, instance: t.instance, thread: t.thread, session: t.session, code, why: e.message, ...(e.limit?{limit:e.limit}:{}) });
+          record({ event: "refused", by: b.human, instance: t.instance, thread: t.thread, session: t.session, code, why: reason(e), ...(e.limit?{limit:e.limit}:{}) });
         }
       });
     }
@@ -1143,7 +1159,7 @@ export function createLauncher({
           if (clearLogged.get(c.op) === code) return;
           clearLogged.set(c.op, code);
           log(`clear ${c.op}: successor ${c.successor} (${c.instance}): start ${CLEAR_HELD.has(code) ? "held" : "refused"}: ${code}`);
-          record({ event: "refused", by: b.human, instance: c.instance, thread: c.thread, session: c.successor, code, why: e.message, ...(e.limit ? { limit: e.limit } : {}) });
+          record({ event: "refused", by: b.human, instance: c.instance, thread: c.thread, session: c.successor, code, why: reason(e), ...(e.limit ? { limit: e.limit } : {}) });
           await host.op({ op: "sessionClearStart", record: { ...where, start: CLEAR_HELD.has(code) ? "held" : "refused", refusal: code } });
           return;
         }
@@ -1203,7 +1219,7 @@ export function createLauncher({
           if (refusedLand.get(h.decision) === code) return;
           refusedLand.set(h.decision, code);
           log(`decision ${h.decision} (${h.instance}): landing start refused: ${code}`);
-          record({ event: "refused", by: b.human, instance: h.instance, decision: h.decision, code, why: e.message, ...(e.limit ? { limit: e.limit } : {}) });
+          record({ event: "refused", by: b.human, instance: h.instance, decision: h.decision, code, why: reason(e), ...(e.limit ? { limit: e.limit } : {}) });
         }
       });
     }
@@ -1248,7 +1264,7 @@ export function createLauncher({
     try {
       done = await act(take);
     } catch (e) {
-      done = { refusal: e instanceof Refusal ? e.code : "launch-failed", why: e.message, limit: e.limit };
+      done = { refusal: e instanceof Refusal ? e.code : "launch-failed", why: reason(e), limit: e.limit };
     }
     const { why, limit, ...closing } = done;
     if (closing.refusal) record({ event: "refused", by: r.by, instance: r.instance, request: r.request, code: closing.refusal, ...(why ? { why } : {}), ...(limit ? { limit } : {}) });
@@ -1356,18 +1372,19 @@ export function createLauncher({
     const bot = out.bot ? { bot: out.bot } : {};
     // The old instance workspace, then (row 269) the instance's session workspaces, each moved
     // whole. A retry moves whichever is still in place.
-    for (const from of [workspaceDir(dataRoot, b.id, r.instance), join(dataRoot, "session-workspaces", b.id, r.instance)]) {
+    for (const [from, label] of [[workspaceDir(dataRoot, b.id, r.instance), "the instance workspace"], [join(dataRoot, "session-workspaces", b.id, r.instance), "the session workspaces"]]) {
       if (!existsSync(from)) continue;
       const to = join(dirname(from), ".retired", `${r.instance}-${transaction}`);
       try {
         mkdirSync(dirname(to), { recursive: true, mode: 0o700 });
         chmodSync(dirname(to), 0o700);
-        if (existsSync(to)) throw new Error(`${to} exists`);
+        if (existsSync(to)) throw new Error("its .retired name already exists");
         renameSync(from, to);
         chmodSync(to, 0o700);
       } catch (e) {
         log(`request ${r.request} (${r.instance}): workspace rename failed: ${e.message}; left at ${from}`);
-        return { transaction, ...bot, refusal: "workspace-rename-failed", why: `${e.message}; left at ${from}` };
+        // #1873: the reason names the workspace by label and the error by code, never a path.
+        return { transaction, ...bot, refusal: "workspace-rename-failed", why: `${quietMessage(e, label) ?? `${label}: ${relay(e.message)}`}; left in place` };
       }
       record({ event: "workspace-retired", instance: r.instance, request: r.request, transaction, path: to });
     }
@@ -1438,7 +1455,7 @@ export function createLauncher({
       } catch (e) {
         if (!(e instanceof Refusal)) throw e;
         await host.op({ op: "refuse", cap, code: e.code }).catch(() => {});
-        record({ event: "refused", by: who.role, instance, code: e.code, why: e.message, ...(e.limit?{limit:e.limit}:{}) });
+        record({ event: "refused", by: who.role, instance, code: e.code, why: reason(e), ...(e.limit?{limit:e.limit}:{}) });
         return reply({ ok: false, error: e.code });
       }
       try {
@@ -1453,7 +1470,7 @@ export function createLauncher({
         const code = e instanceof Refusal ? e.code : "launch-failed";
         log(`launch of ${instance} for ${who.role} failed: ${e.message}`);
         await host.op({ op: "refuse", cap, code }).catch(() => {});
-        record({ event: "refused", by: who.role, instance, code, why: e.message, ...(e.limit?{limit:e.limit}:{}) });
+        record({ event: "refused", by: who.role, instance, code, why: reason(e), ...(e.limit?{limit:e.limit}:{}) });
         return reply({ ok: false, error: code });
       }
     });
@@ -1467,8 +1484,8 @@ export function createLauncher({
         return await start({ instance: b.launch.by, launchedBy: b.human, ...(await check(b.launch.by, { pm: true })) });
       } catch (e) {
         if (!(e instanceof Refusal)) throw e;
-        record({ event: "refused", by: b.human, instance: b.launch.by, code: e.code, why: e.message, ...(e.limit?{limit:e.limit}:{}) });
-        const error = new CliError(`PM launch refused: ${e.code}${e.message !== e.code ? ` (${e.message})` : ""}`, 3);
+        record({ event: "refused", by: b.human, instance: b.launch.by, code: e.code, why: reason(e), ...(e.limit?{limit:e.limit}:{}) });
+        const error = new CliError(`PM launch refused: ${e.code}${reason(e) !== e.code ? ` (${reason(e)})` : ""}`, 3);
         error.code = e.code;
         throw error;
       }
@@ -1519,7 +1536,7 @@ export function createLauncher({
     await recover();
     const path = launchSocketPath(dataRoot);
     if (existsSync(path)) {
-      if (!lstatSync(path).isSocket()) throw new CliError(`${path} exists and isn't a socket`, 3);
+      if (!lstatSync(path).isSocket()) throw new CliError("launch socket path exists and isn't a socket", 3);
       rmSync(path);
     }
     server = createServer((socket) => {
diff --git a/packages/cli/tests/access-boot.test.mjs b/packages/cli/tests/access-boot.test.mjs
index c9337d6a4..d573d0931 100644
--- a/packages/cli/tests/access-boot.test.mjs
+++ b/packages/cli/tests/access-boot.test.mjs
@@ -91,7 +91,9 @@ test("R6 B3 a boot with a file R1's loader refuses still boots, binds no user an
     const s = await boot(t, file);
     assert.equal(s.config.access.file, s.path, why);
     assert.equal(s.bind("alice"), "access-revoked", why);
-    assert.deepEqual(s.warnings, [TRACKER, `access file refused at boot (${code}), no granted user binds until it is fixed: ${s.path}`], why);
+    // #1873: the warning names access.json by its place, never by host path.
+    assert.deepEqual(s.warnings, [TRACKER, `access file refused at boot (${code}), no granted user binds until it is fixed: access.json in the config directory`], why);
+    assert.ok(!s.warnings.join("\n").includes(s.path), why);
     assert.doesNotMatch(s.warnings.join("\n"), /secret-marker/, why);
   }
 });
diff --git a/packages/cli/tests/json-redaction.test.mjs b/packages/cli/tests/json-redaction.test.mjs
index bbcffd626..8c57cc046 100644
--- a/packages/cli/tests/json-redaction.test.mjs
+++ b/packages/cli/tests/json-redaction.test.mjs
@@ -22,7 +22,7 @@ function fixture(t) {
   return { root, file, env, run, boot };
 }
 // label: the CLI refusal names the file by this label and never by host path (PR #1916).
-// Without it, the refusal comes from scripts/mosaic-config.mjs, which still names the file.
+// scripts/mosaic-config.mjs names it by label too (#1873 redact6).
 function redacted(result, file, status, label) {
   assert.equal(result.status, status, result.stderr);
   assert.equal(result.stdout, '');
@@ -37,10 +37,12 @@ function redacted(result, file, status, label) {
 test('system config parse refusal and CLI relay omit parser bytes', t => {
   const f = fixture(t);
   mkdirSync(dirname(f.file), { recursive: true }); writeFileSync(f.file, secret);
-  redacted(f.run(configScript, 'validate', '--instance', 'redacttest'), f.file, 2);
+  redacted(f.run(configScript, 'validate', '--instance', 'redacttest'), f.file, 2, 'configuration is not valid JSON (the config of instance redacttest)');
   assert.throws(() => loadSystem({ env: f.env, instance: 'redacttest' }), error => {
     assert.equal(error.exitCode, 3);
-    assert.ok(error.message.includes(f.file));
+    // #1873: the cli relay names the instance's config by label, never its path.
+    assert.ok(!error.message.includes(f.file), error.message);
+    assert.ok(error.message.includes('configuration is not valid JSON; expected readable JSON: the config of instance redacttest'), error.message);
     assert.match(error.message, /not valid JSON/);
     assert.doesNotMatch(error.message, /sk-test|Unexpected token/);
     return true;
@@ -52,7 +54,7 @@ test('named instance marker parse refusal omits parser bytes', t => {
   const f = fixture(t); f.boot();
   const { dataRoot } = JSON.parse(readFileSync(f.file, 'utf8'));
   const marker = join(dataRoot, 'instance.json'); writeFileSync(marker, secret);
-  redacted(f.run(configScript, 'validate', '--instance', 'redacttest'), marker, 3);
+  redacted(f.run(configScript, 'validate', '--instance', 'redacttest'), marker, 3, "instance-root-unclaimed: the data root's instance marker is not a valid marker (not valid JSON)");
 });
 
 for (const operation of ['validate', 'create', 'update']) test(`org ${operation} document refusal omits parser bytes`, t => {
diff --git a/packages/cli/tests/last-values.test.mjs b/packages/cli/tests/last-values.test.mjs
index f7e823f3c..e529b80c2 100644
--- a/packages/cli/tests/last-values.test.mjs
+++ b/packages/cli/tests/last-values.test.mjs
@@ -89,7 +89,12 @@ test('CLI boot project id mismatch omits the configured value and keeps exit 3',
  const root = scratch(t), f = fixture(root), file = join(f.doc.projects.stack.root, '.mosaic', 'project.json');
  mkdirSync(join(f.doc.projects.stack.root, '.mosaic'));
  writeFileSync(file, JSON.stringify({ projectVersion: 1, id: secret.toLowerCase() }));
- assert.throws(() => bootConfig({ system: loadSystem({ env: f.env }), businessId: 'acme', env: f.env }), safe(file, CliError, { exitCode: 3 }, secret.toLowerCase()));
+ assert.throws(() => bootConfig({ system: loadSystem({ env: f.env }), businessId: 'acme', env: f.env }), error => {
+  // #1873: the refusal names the project by its key, never the project file's path.
+  safe('project file of project stack has id that does not match the declared project key', CliError, { exitCode: 3 }, secret.toLowerCase())(error);
+  assert.ok(!error.message.includes(file) && !error.message.includes(f.doc.projects.stack.root), error.message);
+  return true;
+ });
 });
 
 for (const mission of [false, true]) test(`duplicate ${mission ? 'mission' : 'task'} tool rejects an unknown value before naming it`, t => {
diff --git a/packages/cli/tests/launch-routes.test.mjs b/packages/cli/tests/launch-routes.test.mjs
index a945cd9a2..de2cdb2fc 100644
--- a/packages/cli/tests/launch-routes.test.mjs
+++ b/packages/cli/tests/launch-routes.test.mjs
@@ -120,7 +120,7 @@ test('row 65 the loader refusing a module refuses harness-refused and names it;
  }
  const s=await setup(t,route('throws','claude-sonnet-5-5','high'));
  assert.deepEqual(await s.launch(),{ok:false,error:'harness-failed'});
- assert.equal(s.last().why,'harness throws preflight: fixture preflight threw');
+ assert.equal(s.last().why,'harness throws preflight: threw Error without a system code');
 });
 
 test('row 65 a thinking level the route harness does not apply refuses thinking-unsupported, on the primary or a fallback taken',async t=>{
diff --git a/packages/cli/tests/launcher.test.mjs b/packages/cli/tests/launcher.test.mjs
index 5ec0b06e9..2dc8277fd 100644
--- a/packages/cli/tests/launcher.test.mjs
+++ b/packages/cli/tests/launcher.test.mjs
@@ -768,9 +768,10 @@ test("a missing or failing bwrap refuses sandbox-unavailable before anything sta
   const bad = join(given.root, "bwrap");
   writeFileSync(bad, "#!/bin/sh\necho 'bwrap: setting up uid map: Permission denied' >&2\nexit 1\n", { mode: 0o755 });
   const { f, launcher, cto } = await setup(t, undefined, given, { bwrap: bad });
-  await assert.rejects(launcher.launchPm(), (e) => e.message === `PM launch refused: sandbox-unavailable (${bad} failed: bwrap: setting up uid map: Permission denied)`);
+  // #1873: the sandbox by name, never the binary's host path.
+  await assert.rejects(launcher.launchPm(), (e) => e.message === "PM launch refused: sandbox-unavailable (the sandbox (bwrap) failed: bwrap: setting up uid map: Permission denied)");
   rmSync(bad);
-  await assert.rejects(launcher.launchPm(), (e) => e.message === `PM launch refused: sandbox-unavailable (${bad} is missing)`);
+  await assert.rejects(launcher.launchPm(), (e) => e.message === "PM launch refused: sandbox-unavailable (the sandbox (bwrap) is missing)");
   // A session's launch request gets the same code, through refuse().
   assert.deepEqual(await launcher.fromSession(cto.cap, "coder"), { ok: false, error: "sandbox-unavailable" });
   assert.deepEqual(log(f).map((e) => e.code), ["sandbox-unavailable", "sandbox-unavailable", "sandbox-unavailable"]);
@@ -791,7 +792,7 @@ test("row 64 a role skill that isn't enabled refuses skill-not-enabled, and one
   assert.deepEqual(await launcher.fromSession(cto.cap, "coder"), { ok: false, error: "skill-not-enabled" });
   // A symlink in skills-enabled is refused, not followed.
   symlinkSync(join(REPO, "skills", "ms-unslop"), join(enabled, "ms-unslop"));
-  await assert.rejects(launcher.launchPm(), (e) => e.exitCode === 3 && e.message === `PM launch refused: skill-refused (skill ms-unslop isn't a plain directory under ${enabled})`);
+  await assert.rejects(launcher.launchPm(), (e) => e.exitCode === 3 && e.message === "PM launch refused: skill-refused (skill ms-unslop isn't a plain directory under the enabled skills directory)");
   assert.deepEqual(await launcher.fromSession(cto.cap, "coder"), { ok: false, error: "skill-refused" });
   assert.deepEqual(log(f).map((e) => [e.event, e.code]), [["refused", "skill-not-enabled"], ["refused", "skill-not-enabled"], ["refused", "skill-refused"], ["refused", "skill-refused"]]);
   assert.deepEqual(readSessions(f.dataRoot), []);
@@ -832,7 +833,9 @@ test("row 213 a creative instance's persona is read from <configDir>/personas: o
   const e = entries[1];
   assert.deepEqual([e.event, e.code], ["refused", "launch-failed"]);
   assert.equal(e.thread, thread);
-  assert.equal(e.why, `instance bean: persona file ${join(dir, "bean.md")} isn't the file persona.sha256 names`);
+  // #1873: the file by its place under the persona directory, never its host path.
+  assert.equal(e.why, "instance bean: persona file acme/bean.md in the persona directory isn't the file persona.sha256 names");
+  assert.ok(!e.why.includes(dir));
   assert.ok(!JSON.stringify(log(f)).includes("PERSONA-MARKER-d2"));
   assert.deepEqual(readSessions(f.dataRoot), []);
   // The run directory exists by then (BUILD.md residual); the persona is read before any bundle file.
diff --git a/packages/cli/tests/lifecycle.test.mjs b/packages/cli/tests/lifecycle.test.mjs
index 7548107d6..bf417882f 100644
--- a/packages/cli/tests/lifecycle.test.mjs
+++ b/packages/cli/tests/lifecycle.test.mjs
@@ -404,6 +404,10 @@ test("row 194 V5: delete retires the name, renames the workspace to .retired/I-<
   const del = s.call("instances.set", { revision: revision(), instance: "sec-1", op: "delete" }).request;
   const failed = await s.carry(del);
   assert.equal(failed.done.refusal, "workspace-rename-failed");
+  // #1873: the refused event's reason names the workspace by label and the error by code, never a path.
+  const refused = launchLog(p.f).filter((e) => e.event === "refused" && e.code === "workspace-rename-failed");
+  assert.deepEqual(refused.map((e) => e.why), ["cannot mkdir the instance workspace (EEXIST); left in place"]);
+  assert.ok(!JSON.stringify(refused).includes(p.f.dataRoot));
   const transaction = failed.done.transaction;
   assert.ok(transaction);
   const file = JSON.parse(readFileSync(join(p.root, "config", "businesses", "acme.json"), "utf8"));
diff --git a/packages/cli/tests/org-recovery.test.mjs b/packages/cli/tests/org-recovery.test.mjs
index e2309f03e..bdab8aa28 100644
--- a/packages/cli/tests/org-recovery.test.mjs
+++ b/packages/cli/tests/org-recovery.test.mjs
@@ -84,7 +84,8 @@ test('lock recovery reports fences and recovers a dead clearer while refusing li
   assert.equal(shown.fence.pid, process.pid);
   await assert.rejects(f.call('org', 'lock', 'clear', 'alpha'), new RegExp(`recovery is already in progress.*${process.pid}`));
   writeFileSync(fence, '');
-  await assert.rejects(f.call('org', 'lock', 'clear', 'alpha'), e => e.message.includes(fence) && /remove.*hand/i.test(e.message));
+  // #1873: the fence is named by label in the config directory, never by its path.
+  await assert.rejects(f.call('org', 'lock', 'clear', 'alpha'), e => !e.message.includes(f.ctx.configDir) && e.message.includes('recovery fence org-lifecycle-alpha.lock.clear in the config directory') && /remove.*hand/i.test(e.message));
   unlinkSync(fence);
   const registry = new URL('../../organization/src/org-registry.mjs', import.meta.url).href;
   const code = `import fs from 'node:fs'; import { syncBuiltinESMExports } from 'node:module';
diff --git a/packages/cli/tests/path-redaction-labels.test.mjs b/packages/cli/tests/path-redaction-labels.test.mjs
new file mode 100644
index 000000000..16a528381
--- /dev/null
+++ b/packages/cli/tests/path-redaction-labels.test.mjs
@@ -0,0 +1,242 @@
+// #1873 (redact6): a cli refusal names the file, the instance or the field, never a host path,
+// and never relays mosaic-config's stderr or a Node system error's message. The sentinel is a
+// component of every scratch path, so a refusal that quotes a path quotes the sentinel too; each
+// test also checks the scratch root and the label. The launcher cases need no bus: a bus socket
+// under a sentinel path would pass the Unix socket length limit, so they use a stub host.
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { mkdirSync, readFileSync, symlinkSync, writeFileSync } from 'node:fs';
+import { spawnSync } from 'node:child_process';
+import { join } from 'node:path';
+import { createLauncher, relay } from '../src/launcher.mjs';
+import { CliError } from '../src/errors.mjs';
+import { loadSystem } from '../src/config.mjs';
+import { main } from '../src/cli.mjs';
+import { initializeControl } from '../../processing-control/src/state.mjs';
+import { launchLogFile } from '../../seat/src/session.mjs';
+import { fakeHarnesses, fixture, io, tmp, withoutHostCredentials } from './helpers.mjs';
+
+const secret = 'sk-test-NOT-A-SECRET-1234';
+function scratch(t) {
+  const root = tmp(t, 'r6-');
+  const dir = join(root, secret);
+  mkdirSync(dir, { mode: 0o700 });
+  return { root, dir };
+}
+function clean(text, root) {
+  assert.ok(!text.includes(root), text);
+  assert.doesNotMatch(text, /sk-test|NOT-A-SECRET/);
+}
+const PI = JSON.stringify(new URL('../../plugins/harness/pi/index.mjs', import.meta.url).href);
+
+function stubLauncher(t, { op = async () => ({}) } = {}) {
+  const { root, dir } = scratch(t);
+  const f = fixture(dir, 'acme');
+  initializeControl(f.dataRoot);
+  withoutHostCredentials(f.env, { piKey: true });
+  const system = JSON.parse(readFileSync(f.config, 'utf8'));
+  const host = { business: 'acme', beforeClose: () => {}, op };
+  return { root, f, make: () => createLauncher({ host, system, env: f.env, bwrap: '/usr/bin/true', log: () => {} }) };
+}
+
+test('an unreadable sessions file refuses exit 3 naming bus-host/sessions.json under the data root, never its path', t => {
+  const s = stubLauncher(t);
+  mkdirSync(join(s.f.dataRoot, 'bus-host'), { recursive: true, mode: 0o700 });
+  writeFileSync(join(s.f.dataRoot, 'bus-host', 'sessions.json'), '{not json');
+  assert.throws(() => s.make(), e => {
+    assert.ok(e instanceof CliError, e.stack);
+    assert.equal(e.exitCode, 3);
+    assert.equal(e.message, 'sessions file is unreadable: bus-host/sessions.json under the data root; check which sessions still run, then move the file aside');
+    clean(e.message, s.root);
+    return true;
+  });
+  writeFileSync(join(s.f.dataRoot, 'bus-host', 'sessions.json'), JSON.stringify({ sessionsVersion: 999, sessions: [] }));
+  assert.throws(() => s.make(), e => e.exitCode === 3 && e.message.startsWith('sessions file is malformed: bus-host/sessions.json under the data root;') && !e.message.includes(s.root));
+});
+
+test('a launch socket path that is not a socket refuses exit 3 by label, never its path', async t => {
+  const s = stubLauncher(t);
+  mkdirSync(join(s.f.dataRoot, 'bus-host'), { recursive: true, mode: 0o700 });
+  writeFileSync(join(s.f.dataRoot, 'bus-host', 'launch.sock'), 'in the way\n');
+  const launcher = s.make();
+  t.after(() => launcher.close?.());
+  await assert.rejects(launcher.listen(), e => {
+    assert.ok(e instanceof CliError, e.stack);
+    assert.equal(e.exitCode, 3);
+    assert.equal(e.message, "launch socket path exists and isn't a socket");
+    clean(e.message, s.root);
+    return true;
+  });
+});
+
+// The launch-routes pattern: a stub host stops each launch at authorizeLaunch, and the launch
+// log's refused event carries the reason.
+async function routed(t, harness) {
+  const { root, dir } = scratch(t);
+  const f = fixture(dir, 'acme', doc => {
+    doc.roles.coder.vars = { harness, model: 'claude-sonnet-5-5', thinking: 'high' };
+    doc.plugins = { ...doc.plugins, harness: ['pi', 'claude-code', harness] };
+    return doc;
+  });
+  initializeControl(f.dataRoot);
+  withoutHostCredentials(f.env, { piKey: true });
+  const host = { business: 'acme', beforeClose: () => {}, op: async x => {
+    if (x.op === 'identity') return { business: 'acme', role: 'pm' };
+    if (x.op === 'mayLaunch') return { allow: true };
+    if (x.op === 'authorizeLaunch') throw Object.assign(Error('fixture authorization stop'), { code: 'fixture-policy' });
+    return {};
+  } };
+  const absent = join(dir, 'absent.json');
+  const makeLoader = await fakeHarnesses(t, { pi: null, 'claude-code': null }, write => {
+    // fsthrows: its preflight reads a missing file, so the error's message quotes the path.
+    write('harness', 'fsthrows', `export * from ${PI};\nimport { readFileSync } from "node:fs";\nexport function preflight() { readFileSync(${JSON.stringify(absent)}); }\n`);
+    // plainthrows: a plain Error whose message quotes a host path, as a module's own text.
+    write('harness', 'plainthrows', `export * from ${PI};\nexport function preflight() { throw new Error(${JSON.stringify(`cannot read ${absent}`)}); }\n`);
+    // pathfails: a preflight that returns a failure whose message quotes a host path.
+    write('harness', 'pathfails', `export * from ${PI};\nexport function preflight() { return { code: "harness-binary-missing", message: ${JSON.stringify(`no binary at ${absent}; see file://${absent}`)} }; }\n`);
+  });
+  const system = JSON.parse(readFileSync(f.config, 'utf8'));
+  const launcher = createLauncher({ host, system, env: f.env, makeLoader, bwrap: '/usr/bin/true', log: () => {} });
+  const last = () => readFileSync(launchLogFile(f.dataRoot, 'acme'), 'utf8').trim().split('\n').map(l => JSON.parse(l)).at(-1);
+  return { root, f, launch: () => launcher.fromSession('fixture-cap', 'coder'), last };
+}
+
+test('a harness whose preflight throws a plain Error naming a path refuses harness-failed by its class, never its message', async t => {
+  const s = await routed(t, 'plainthrows');
+  assert.deepEqual(await s.launch(), { ok: false, error: 'harness-failed' });
+  assert.equal(s.last().why, 'harness plainthrows preflight: threw Error without a system code');
+  clean(JSON.stringify(s.last()), s.root);
+});
+
+test('a preflight failure whose message quotes a path keeps its code and relays the text with the path replaced', async t => {
+  const s = await routed(t, 'pathfails');
+  assert.deepEqual(await s.launch(), { ok: false, error: 'harness-binary-missing' });
+  assert.equal(s.last().why, 'no binary at a host path; see a host path');
+  clean(JSON.stringify(s.last()), s.root);
+});
+
+test('the claude-code preflight names MOSAIC_CLAUDE_BIN, never its value', async t => {
+  const { root, dir } = scratch(t);
+  const f = fixture(dir, 'acme', doc => {
+    doc.roles.coder.vars = { harness: 'claude-code', model: 'claude-sonnet-5-5', thinking: 'high' };
+    return doc;
+  });
+  initializeControl(f.dataRoot);
+  withoutHostCredentials(f.env);
+  f.env.CLAUDE_CODE_OAUTH_TOKEN = 'fixture-only';
+  f.env.MOSAIC_CLAUDE_BIN = join(dir, 'absent-claude');
+  const host = { business: 'acme', beforeClose: () => {}, op: async x => x.op === 'identity' ? { business: 'acme', role: 'pm' } : x.op === 'mayLaunch' ? { allow: true } : {} };
+  const makeLoader = await fakeHarnesses(t, { pi: null, 'claude-code': null });
+  const launcher = createLauncher({ host, system: JSON.parse(readFileSync(f.config, 'utf8')), env: f.env, makeLoader, bwrap: '/usr/bin/true', log: () => {} });
+  assert.deepEqual(await launcher.fromSession('fixture-cap', 'coder'), { ok: false, error: 'harness-binary-missing' });
+  const last = JSON.parse(readFileSync(launchLogFile(f.dataRoot, 'acme'), 'utf8').trim().split('\n').at(-1));
+  assert.equal(last.why, "MOSAIC_CLAUDE_BIN isn't an executable file at an absolute path");
+  clean(JSON.stringify(last), root);
+});
+
+test('relay replaces absolute, home and file: paths and keeps the rest of the text', () => {
+  assert.equal(relay(`bad ${'/srv/x/' + secret} and ~/y, (file:///z) here`), 'bad a host path and a host path, (a host path) here');
+  assert.equal(relay('fatal: not a git repository: .git; see https://example.test/a'), 'fatal: not a git repository: .git; see https://example.test/a');
+});
+
+test('a harness whose preflight throws a system error refuses harness-failed naming the call and code, never the path', async t => {
+  const s = await routed(t, 'fsthrows');
+  assert.deepEqual(await s.launch(), { ok: false, error: 'harness-failed' });
+  assert.equal(s.last().why, 'harness fsthrows preflight: cannot open a host file (ENOENT)');
+  clean(JSON.stringify(s.last()), s.root);
+});
+
+test('a harness the loader refuses names its code only, never the loader message or a path', async t => {
+  const s = await routed(t, 'absent');
+  assert.deepEqual(await s.launch(), { ok: false, error: 'harness-refused' });
+  assert.match(s.last().why, /^harness absent: [a-z][a-z0-9-]*$/);
+  clean(JSON.stringify(s.last()), s.root);
+});
+
+test('the halt gate refusal names the instance, never its data root, and keeps exit 1 and the count', async t => {
+  const { root, dir } = scratch(t);
+  const result = { version: 1, generation: '11111111-1111-4111-8111-111111111111', operation: '11111111-1111-4111-8111-111111111111', business: 'demo', human: 'jason', at: '2026-10-20T00:00:00.000Z', recovered: false, halted: true, quiescent: false, remaining: 2, stopped: 0 };
+  const x = io();
+  await assert.rejects(main(['halt', '--business', 'demo'], x, { system: { dataRoot: join(dir, 'data') }, transport: () => async () => result }), e => {
+    assert.equal(e.exitCode, 1);
+    assert.equal(e.message, 'halt gate is on for this instance; 2 stops unconfirmed. Use mosaic processing status');
+    clean(e.message, root);
+    return true;
+  });
+  const odd = io();
+  await assert.rejects(main(['halt', '--business', 'demo'], odd, { system: { dataRoot: join(dir, 'data') }, transport: () => async () => ({ ...result, remaining: join(dir, 'x') }) }), e => {
+    assert.equal(e.message, 'halt gate is on for this instance; unknown stops unconfirmed. Use mosaic processing status');
+    clean(e.message, root);
+    return true;
+  });
+});
+
+test('a system config problem names the config by label and never relays mosaic-config stderr', t => {
+  const { root, dir } = scratch(t);
+  // Missing: the label for where it came from, with the bootstrap hint.
+  assert.throws(() => loadSystem({ env: { PATH: process.env.PATH, HOME: dir, MOSAIC_CONFIG: join(dir, 'absent.json') } }), e => {
+    assert.ok(e instanceof CliError, e.stack);
+    assert.equal(e.exitCode, 3);
+    assert.equal(e.message, 'system config problem (mosaic-config exit 3): configuration not found: the system config MOSAIC_CONFIG names (run scripts/bootstrap.sh to create it)');
+    clean(e.message, root);
+    return true;
+  });
+  assert.throws(() => loadSystem({ env: { PATH: process.env.PATH, HOME: dir } }), e => {
+    assert.match(e.message, /^system config problem \(mosaic-config exit 3\): configuration not found: the default system config \(run scripts\/bootstrap\.sh to create it\)$/);
+    clean(e.message, root);
+    return true;
+  });
+  // A field whose value quotes the sentinel: the field and its constraint, never the value.
+  const f = fixture(dir, 'acme');
+  const doc = JSON.parse(readFileSync(f.config, 'utf8'));
+  writeFileSync(f.config, JSON.stringify({ ...doc, dataRoot: `relative/${secret}` }));
+  assert.throws(() => loadSystem({ env: f.env }), e => {
+    assert.equal(e.exitCode, 3);
+    assert.match(e.message, /^system config problem \(mosaic-config exit \d+\): dataRoot: expected a canonical absolute instance data path: the system config MOSAIC_CONFIG names$/);
+    clean(e.message, root);
+    return true;
+  });
+});
+
+// scripts/mosaic-config.mjs run standalone: every refusal names the config by where it came from,
+// the data root and its marker by their roles, and a key only when it is a plain name. Exit codes
+// are unchanged: 2 invalid, 3 missing or unclaimed, 4 usage.
+const CONFIG_SCRIPT = new URL('../../../scripts/mosaic-config.mjs', import.meta.url).pathname;
+function mosaicConfig(home, env, ...args) {
+  return spawnSync(process.execPath, [CONFIG_SCRIPT, ...args], { encoding: 'utf8', env: { PATH: process.env.PATH, HOME: home, ...env } });
+}
+function refusedBy(r, status, text, root) {
+  assert.equal(r.status, status, r.stderr);
+  assert.equal(r.stdout, '');
+  assert.ok(r.stderr.includes(text), r.stderr);
+  clean(r.stderr, root);
+}
+
+test('mosaic-config refusals name the config, data root and keys by label, never a host path or value', t => {
+  const { root, dir } = scratch(t);
+  const file = join(dir, 'config.json');
+  const env = { MOSAIC_CONFIG: file };
+  writeFileSync(file, 'not json');
+  refusedBy(mosaicConfig(dir, env, 'validate'), 2, 'mosaic-config: configuration is not valid JSON (the system config MOSAIC_CONFIG names)', root);
+  const good = { configVersion: 1, environment: 'development', dataRoot: join(dir, 'data'), execution: { backend: 'docker', provider: 'zai', model: 'glm-5.3-flash' } };
+  writeFileSync(file, JSON.stringify({ ...good, [join(dir, 'k')]: 1 }));
+  refusedBy(mosaicConfig(dir, env, 'validate'), 2, 'unsupported configuration key: that is not a plain name', root);
+  writeFileSync(file, JSON.stringify({ ...good, console: { [join(dir, 'k')]: 1 } }));
+  refusedBy(mosaicConfig(dir, env, 'validate'), 2, 'console has a key that is not a plain name', root);
+  writeFileSync(file, JSON.stringify({ ...good, dataRoot: dir }));
+  refusedBy(mosaicConfig(dir, env, 'validate'), 2, 'execution "dataRoot" must not be or contain the home directory', root);
+  writeFileSync(join(dir, 'real.json'), JSON.stringify(good));
+  const link = join(dir, 'link.json');
+  symlinkSync(join(dir, 'real.json'), link);
+  refusedBy(mosaicConfig(dir, { MOSAIC_CONFIG: link }, 'validate'), 2, 'configuration path must be a regular, non-symbolic-link file: the system config MOSAIC_CONFIG names', root);
+  // A named instance: MOSAIC_CONFIG naming another file is usage (4); an unmarked root is 3.
+  refusedBy(mosaicConfig(dir, env, 'validate', '--instance', 'alpha'), 4, 'instance-config-mismatch: --instance alpha names its own config, but MOSAIC_CONFIG names another file', root);
+  refusedBy(mosaicConfig(dir, {}, 'validate', '--instance', join(dir, 'x')), 4, 'instance-name-invalid: that name must match', root);
+  const named = join(dir, '.config', 'mosaic-alpha');
+  mkdirSync(named, { recursive: true, mode: 0o700 });
+  mkdirSync(join(dir, '.mosaic-alpha'), { mode: 0o700 });
+  writeFileSync(join(named, 'config.json'), JSON.stringify({ ...good, dataRoot: join(dir, '.mosaic-alpha') }));
+  refusedBy(mosaicConfig(dir, {}, 'validate', '--instance', 'alpha'), 3, 'instance-root-unclaimed: the data root holds no instance.json naming alpha', root);
+  mkdirSync(join(dir, '.mosaic-alpha', 'instance.json'));
+  refusedBy(mosaicConfig(dir, {}, 'validate', '--instance', 'alpha'), 3, "instance-root-unclaimed: the data root's instance marker must be a regular, non-symbolic-link file", root);
+});
diff --git a/packages/cli/tests/proxy-launch-order.test.mjs b/packages/cli/tests/proxy-launch-order.test.mjs
index 3461fd3e3..4e00713f9 100644
--- a/packages/cli/tests/proxy-launch-order.test.mjs
+++ b/packages/cli/tests/proxy-launch-order.test.mjs
@@ -130,7 +130,8 @@ test('#774 F1 proxy launch of an agent with no key yet passes the first check un
 // claude-code module on claude-opus-5-5 (provider anthropic); MOSAIC_CLAUDE_BIN decides whether its
 // preflight passes. The stated fallback is pi on glm-5.3-flash (provider zai).
 const NO_CLAUDE = '/nonexistent-774/claude';
-const NO_CLAUDE_WHY = `MOSAIC_CLAUDE_BIN ${NO_CLAUDE} isn't an executable file at an absolute path`;
+// #1873: names the variable, never its value (was `MOSAIC_CLAUDE_BIN ${NO_CLAUDE} isn't ...`).
+const NO_CLAUDE_WHY = "MOSAIC_CLAUDE_BIN isn't an executable file at an absolute path";
 const routed = (t, bin) => managedLaunchFixture(t, { harness: 'claude-code', extra: ['pi'], real: ['claude-code'], hostEnv: { MOSAIC_CLAUDE_BIN: bin } });
 const withFallback = (doc, harness = 'pi', model = 'glm-5.3-flash') => {
   claudeCoder(doc);
diff --git a/packages/cli/tests/rename-b-commands.test.mjs b/packages/cli/tests/rename-b-commands.test.mjs
index a72605092..a41e2a754 100644
--- a/packages/cli/tests/rename-b-commands.test.mjs
+++ b/packages/cli/tests/rename-b-commands.test.mjs
@@ -112,7 +112,7 @@ test("rename r2 B2: a credential problem, an expiry warning and a system config
   for (const args of [["validate", "acme"], ["resolve", "acme", "coder"]]) {
     const { old, now } = await sameAcrossSpellings(args, bad.env, bad.root, 2);
     assert.equal(now.stderr, old.stderr, "a refusal is byte for byte the same, unnormalized");
-    assert.match(old.stderr, /^mosaic business: .*coder-gitea\.token.*mode 644/m);
+    assert.match(old.stderr, /^mosaic business: (?:roles\.coder\.credentials\.gitea|coder gitea) file: mode 644/m);
     assert.match(old.stderr, /credential reference problem\(s\)\n$/);
   }
   const soon = new Date(Date.now() + 3 * 86400000).toISOString().slice(0, 10);
diff --git a/packages/cli/tests/stack-instances.test.mjs b/packages/cli/tests/stack-instances.test.mjs
index ff028b5cd..8476b2c84 100644
--- a/packages/cli/tests/stack-instances.test.mjs
+++ b/packages/cli/tests/stack-instances.test.mjs
@@ -133,7 +133,9 @@ test("T-I1 bootstrap --instance creates each instance's config, root and marker
     for (const name of ["gamma", "worktrees", "delta"]) {
       const r = bootstrap(home, "--instance", name);
       assert.equal(r.code, 3, r.err);
-      assert.match(r.err, new RegExp(`instance-root-unclaimed: ${join(home, `.mosaic-${name}`)} exists, is not empty and holds no instance.json naming ${name}; nothing was written`));
+      // #1873: the data root by its role, never its path.
+      assert.match(r.err, new RegExp(`instance-root-unclaimed: the instance's data root exists, is not empty and holds no instance.json naming ${name}; nothing was written`));
+      assert.ok(!r.err.includes(home), r.err);
       assert.equal(existsSync(join(home, ".config", `mosaic-${name}`)), false);
     }
     assert.deepEqual(snapshot(home), before);
@@ -154,7 +156,8 @@ test("T-I1 bootstrap --instance creates each instance's config, root and marker
     const before = snapshot(home);
     const r = bootstrap(home, "--instance", "alpha");
     assert.equal(r.code, 3);
-    assert.match(r.err, /instance-root-unclaimed: .*\.mosaic-alpha holds no instance\.json naming alpha/);
+    assert.match(r.err, /instance-root-unclaimed: the data root holds no instance\.json naming alpha/);
+    assert.ok(!r.err.includes(home), r.err);
     assert.deepEqual(snapshot(home), before);
   });
 
@@ -262,7 +265,8 @@ test("T-I2 selection: the four rows of D1 through the instance op and through an
         const r = config(home, { MOSAIC_CONFIG: given }, op, "--instance", "alpha");
         assert.equal(r.code, 4, `${op} ${given}: ${r.err}`);
         assert.equal(r.out, "");
-        assert.match(r.err, new RegExp(`instance-config-mismatch: --instance alpha names ${cfgOf(home, "alpha")}, but MOSAIC_CONFIG names ${given}`));
+        assert.match(r.err, /instance-config-mismatch: --instance alpha names its own config, but MOSAIC_CONFIG names another file/);
+        assert.ok(!r.err.includes(home) && !r.err.includes(given), r.err);
       }
     }
   });
@@ -270,7 +274,9 @@ test("T-I2 selection: the four rows of D1 through the instance op and through an
   await t.test("a named instance with no config exits 3 with its own bootstrap hint", () => {
     const r = config(home, {}, "instance", "--instance", "gamma");
     assert.equal(r.code, 3);
-    assert.match(r.err, /configuration not found: .*mosaic-gamma\/config\.json \(run scripts\/bootstrap\.sh --instance gamma to create it\)/);
+    // #1873: the refusal names the config by its instance, never by host path.
+    assert.match(r.err, /configuration not found: the config of instance gamma \(run scripts\/bootstrap\.sh --instance gamma to create it\)/);
+    assert.ok(!r.err.includes(cfgOf(home, "gamma")) && !r.err.includes(home), r.err);
   });
 
   await t.test("an entry point takes --instance in any position, once, and refuses a mismatch before it prints", () => {
@@ -326,7 +332,8 @@ test("T-I7 claims: the instance op refuses a root another instance claims, and a
       const r = config(home, {}, op, "--instance", "alpha");
       assert.equal(r.code, 3, `${op}: ${r.err}`);
       assert.equal(r.out, "");
-      assert.match(r.err, new RegExp(`instance-root-mismatch: ${join(home, ".mosaic-beta")} is claimed by instance beta, not alpha`));
+      assert.match(r.err, /instance-root-mismatch: the data root is claimed by instance beta, not alpha/);
+      assert.ok(!r.err.includes(home), r.err);
     }
     edit("alpha", join(home, ".mosaic-alpha"));
     assert.equal(config(home, {}, "instance", "--instance", "alpha").code, 0);
@@ -336,7 +343,8 @@ test("T-I7 claims: the instance op refuses a root another instance claims, and a
     for (const op of ["instance"]) {
       const r = config(home, { MOSAIC_CONFIG: cfgOf(home, "alpha") }, op);
       assert.equal(r.code, 3, r.err);
-      assert.match(r.err, new RegExp(`instance-root-mismatch: ${join(home, ".mosaic-alpha")} is claimed by instance alpha; select it with --instance alpha`));
+      assert.match(r.err, /instance-root-mismatch: the data root is claimed by instance alpha; select it with --instance alpha/);
+      assert.ok(!r.err.includes(home), r.err);
     }
   });
 
diff --git a/packages/control-board/src/scan.mjs b/packages/control-board/src/scan.mjs
index 9854812b2..a8307880e 100644
--- a/packages/control-board/src/scan.mjs
+++ b/packages/control-board/src/scan.mjs
@@ -18,7 +18,7 @@ import { existsSync, readFileSync, readdirSync, statSync, mkdirSync, writeFileSy
 import { join, basename, isAbsolute, resolve } from "node:path";
 import { homedir } from "node:os";
 import { spawnSync } from "node:child_process";
-import { readRegistration, samePath, SeatError, LAYOUTS } from "../../seat/src/seat.mjs";
+import { readRegistration, samePath, SeatError, LAYOUTS, plainKey } from "../../seat/src/seat.mjs";
 
 import { discoverDiscordAgents, inspectDiscord, newestDiscordSession } from './discord.mjs';
 
@@ -32,17 +32,18 @@ export function defaultConfigPath() {
 }
 
 // Fail closed: the config must exist, parse, and name an absolute dataRoot.
+// Refusals name the config, never its path (#1873).
 export function loadConfig(path = defaultConfigPath()) {
-  if (!existsSync(path)) throw new ConfigError(`config not found: ${path}`);
+  if (!existsSync(path)) throw new ConfigError("config not found");
   let raw;
   try {
     raw = parseJsonFileText(readFileSync(path, "utf8"), path);
   } catch (error) {
-    throw new ConfigError(`config is not valid JSON: ${path}${error.code ? ` (${error.code})` : ""}`);
+    throw new ConfigError(`config is not valid JSON${error.code ? ` (${error.code})` : ""}`);
   }
-  if (!raw || typeof raw !== "object" || Array.isArray(raw)) throw new ConfigError(`config is not an object: ${path}`);
+  if (!raw || typeof raw !== "object" || Array.isArray(raw)) throw new ConfigError("config is not an object");
   if (typeof raw.dataRoot !== "string" || !isAbsolute(raw.dataRoot)) {
-    throw new ConfigError(`config.dataRoot must be an absolute path: ${path}`);
+    throw new ConfigError("config.dataRoot must be an absolute path");
   }
   return { dataRoot: raw.dataRoot };
 }
@@ -230,11 +231,11 @@ export function loadSeen(boardDir) {
   try {
     parsed = parseJsonFileText(readFileSync(path, "utf8"), path);
   } catch (error) {
-    throw new ConfigError(`seen marks file is not valid JSON: ${path}${error.code ? ` (${error.code})` : ""}`);
+    throw new ConfigError(`seen marks file seen.json is not valid JSON${error.code ? ` (${error.code})` : ""}`);
   }
-  if (!parsed || typeof parsed !== "object" || Array.isArray(parsed)) throw new ConfigError(`seen marks file must be a JSON object: ${path}`);
+  if (!parsed || typeof parsed !== "object" || Array.isArray(parsed)) throw new ConfigError("seen marks file seen.json must be a JSON object");
   for (const [k, v] of Object.entries(parsed)) {
-    if (typeof v !== "string") throw new ConfigError(`seen marks file has a non-string value for ${JSON.stringify(k)}: ${path}`);
+    if (typeof v !== "string") throw new ConfigError(`seen marks file seen.json has a non-string value for ${plainKey(k)}`);
   }
   return parsed;
 }
diff --git a/packages/control-board/tests/path-redaction-labels.test.mjs b/packages/control-board/tests/path-redaction-labels.test.mjs
new file mode 100644
index 000000000..29167ba50
--- /dev/null
+++ b/packages/control-board/tests/path-redaction-labels.test.mjs
@@ -0,0 +1,98 @@
+// #1873 (redact6): a control-board refusal names the config, the seen marks file or the seat
+// by label, never a host path. The sentinel is a component of every scratch path, so a refusal
+// that quotes a path quotes the sentinel too; each test also checks the scratch root and the label.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { dirname, join } from 'node:path';
+import { ConfigError, loadConfig, loadRegistrations, loadSeen } from '../src/scan.mjs';
+import { readRegistration, registrationPath, SeatError } from '../../seat/src/seat.mjs';
+import { startServer } from '../src/serve.mjs';
+
+const secret = 'sk-test-NOT-A-SECRET-1234';
+function scratch(t) {
+  const root = mkdtempSync(join(tmpdir(), 'r6-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+  const dir = join(root, secret);
+  mkdirSync(dir);
+  return { root, dir };
+}
+function clean(text, root) {
+  assert.ok(!text.includes(root), text);
+  assert.doesNotMatch(text, /sk-test|NOT-A-SECRET/);
+}
+function labelled(label, root) {
+  return error => {
+    assert.ok(error instanceof ConfigError, error.stack);
+    assert.equal(error.message, label);
+    clean(error.message, root);
+    return true;
+  };
+}
+function write(file, text) {
+  mkdirSync(dirname(file), { recursive: true });
+  writeFileSync(file, text);
+  return file;
+}
+
+test('config refusals name the config, not its path', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => loadConfig(join(dir, 'config.json')), labelled('config not found', root));
+  assert.throws(() => loadConfig(write(join(dir, 'array.json'), '[]')), labelled('config is not an object', root));
+  assert.throws(() => loadConfig(write(join(dir, 'relative.json'), '{"dataRoot":"data"}')), labelled('config.dataRoot must be an absolute path', root));
+});
+
+test('seen marks refusals name seen.json, not its path', t => {
+  const { root, dir } = scratch(t);
+  write(join(dir, 'seen.json'), '[]');
+  assert.throws(() => loadSeen(dir), labelled('seen marks file seen.json must be a JSON object', root));
+  write(join(dir, 'seen.json'), '{"a":1}');
+  assert.throws(() => loadSeen(dir), labelled('seen marks file seen.json has a non-string value for "a"', root));
+});
+
+test('a bad registration is reported by layout and seat, never by its path', t => {
+  const { root, dir } = scratch(t);
+  write(registrationPath(dir, 'builder', 'repo'), '{}');
+  const { registrations, errors } = loadRegistrations(dir);
+  assert.deepEqual(registrations, []);
+  assert.equal(errors.length, 1);
+  assert.match(errors[0], /^seat repo\/builder: .*: registration repo\/builder$/);
+  clean(errors[0], root);
+});
+
+// Review round (#1873): a key or name that could be a host path is described, never echoed.
+test('a seen marks key or a registration field that is not a plain name is described, never echoed', t => {
+  const { root, dir } = scratch(t);
+  writeFileSync(join(dir, 'seen.json'), JSON.stringify({ [join(dir, 'host')]: 1 }));
+  assert.throws(() => loadSeen(dir), labelled('seen marks file seen.json has a non-string value for that is not a plain name', root));
+  const f = registrationPath(dir, 'builder', 'repo');
+  mkdirSync(dirname(f), { recursive: true });
+  writeFileSync(f, JSON.stringify({ [join(dir, 'host')]: 1 }));
+  assert.throws(() => readRegistration(dir, 'builder', 'repo'), e => {
+    assert.ok(e instanceof SeatError, e.stack);
+    assert.equal(e.exitCode, 2);
+    assert.equal(e.message, 'registration has an unknown field: that is not a plain name: registration repo/builder');
+    clean(e.message, root);
+    return true;
+  });
+});
+
+test('an invalid seat name or layout states the constraint, never the value, and keeps exit 4', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => registrationPath(dir, join(dir, 'x'), 'repo'), e => e instanceof SeatError && e.exitCode === 4 && e.message === 'invalid seat name (lowercase letters, digits, ., _ or -, at most 64)' && (clean(e.message, root), true));
+  assert.throws(() => registrationPath(dir, 'builder', join(dir, 'x')), e => e instanceof SeatError && e.exitCode === 4 && e.message === 'invalid layout (one of repo, fleet, unknown)' && (clean(e.message, root), true));
+});
+
+// The board API returns a scan refusal in its JSON body, so the HTTP body carries the label too.
+test('a seen marks refusal reaches the board API body by label, never by path', async t => {
+  const { root, dir } = scratch(t);
+  write(join(dir, 'seen.json'), '[]');
+  const server = await startServer({ host: '127.0.0.1', port: 0, specs: [], boardDir: dir, isAlive: () => true, page: '<html></html>' });
+  t.after(() => new Promise(done => server.close(done)));
+  const res = await fetch(`http://127.0.0.1:${server.address().port}/api/board`);
+  const body = await res.text();
+  assert.equal(res.status, 500);
+  assert.deepEqual(JSON.parse(body), { error: 'seen marks file seen.json must be a JSON object' });
+  clean(body, root);
+});
diff --git a/packages/control-board/tests/refusal-redaction.test.mjs b/packages/control-board/tests/refusal-redaction.test.mjs
index 171af624b..dbbcc5f59 100644
--- a/packages/control-board/tests/refusal-redaction.test.mjs
+++ b/packages/control-board/tests/refusal-redaction.test.mjs
@@ -6,10 +6,13 @@ import { dirname, join } from 'node:path';
 const secret = 'sk-test-NOT-A-SECRET-1234';
 // JSON.parse quotes a prefix near this fault on Node 26; check partial leaks too.
 const malformed = secret;
+// #1873: the sentinel is a path component, so a refusal that quotes a path quotes it too.
 function scratch(t) {
   const root = mkdtempSync(join(tmpdir(), 'r3-'));
   t.after(() => rmSync(root, { recursive: true, force: true }));
-  return root;
+  const dir = join(root, secret);
+  mkdirSync(dir);
+  return dir;
 }
 function write(file, text = malformed) {
   mkdirSync(dirname(file), { recursive: true });
@@ -21,6 +24,7 @@ function safe(label, ErrorType, properties = {}) {
     assert.ok(error instanceof ErrorType);
     for (const [key, value] of Object.entries(properties)) assert.equal(error[key], value);
     assert.ok(error.message.includes(label), error.message);
+    assert.ok(!error.message.includes(tmpdir()), error.message);
     assert.doesNotMatch(error.message, /sk-test|Unexpected token/);
     assert.doesNotMatch(error.stack, /sk-test/);
     assert.equal(error.cause, undefined);
@@ -30,13 +34,13 @@ function safe(label, ErrorType, properties = {}) {
 import { ConfigError, loadConfig, loadSeen } from '../src/scan.mjs';
 for (const kind of ['config', 'seen']) test(`${kind} JSON refusal names only the file`, t => {
   const root = scratch(t), file = write(join(root, kind === 'config' ? 'config.json' : 'seen.json'));
-  assert.throws(() => kind === 'config' ? loadConfig(file) : loadSeen(root), safe(file, ConfigError));
+  assert.throws(() => kind === 'config' ? loadConfig(file) : loadSeen(root), safe(kind === 'config' ? 'config is not valid JSON' : 'seen marks file seen.json is not valid JSON', ConfigError));
 });
 for (const kind of ['config', 'seen']) test(`${kind} read refusal retains the filesystem code`, t => {
   const root = scratch(t), file = join(root, kind === 'config' ? 'config.json' : 'seen.json');
   mkdirSync(file);
   assert.throws(() => kind === 'config' ? loadConfig(file) : loadSeen(root), error => {
-    safe(file, ConfigError)(error);
+    safe(kind === 'config' ? 'config is not valid JSON' : 'seen marks file seen.json is not valid JSON', ConfigError)(error);
     assert.match(error.message, /\(EISDIR\)$/);
     assert.doesNotMatch(error.message, /illegal operation/);
     return true;
diff --git a/packages/discord/src/approvals.mjs b/packages/discord/src/approvals.mjs
index 516af3d65..d714d9482 100644
--- a/packages/discord/src/approvals.mjs
+++ b/packages/discord/src/approvals.mjs
@@ -22,7 +22,7 @@
 import { parseJsonFileText } from "../../organization/src/util.mjs";
 import { appendFileSync, existsSync, readFileSync } from "node:fs";
 import { join } from "node:path";
-import { DiscordError } from "./errors.mjs";
+import { DiscordError, quietFs, quietRead } from "./errors.mjs";
 
 export const APPROVE_WORD = "approve";
 export const CUSTOM_ID_PREFIX = "approve:";
@@ -95,19 +95,29 @@ export function appendApproval(dir, entry) {
   if (!isObject(entry) || typeof entry.kind !== "string") throw new DiscordError("approvals: entry needs a kind", 1);
   const line = JSON.stringify(entry);
   if (line.includes("\n")) throw new DiscordError("approvals: line must not contain a newline", 1);
-  appendFileSync(approvalsPath(dir), line + "\n", { mode: 0o600 });
+  try {
+    appendFileSync(approvalsPath(dir), line + "\n", { mode: 0o600 });
+  } catch (e) {
+    throw quietFs(e, "approvals.jsonl", "append to");
+  }
 }
 
 export function readApprovals(dir) {
   const path = approvalsPath(dir);
   if (!existsSync(path)) return [];
   const out = [];
-  for (const [i, line] of readFileSync(path, "utf8").split("\n").entries()) {
+  let text;
+  try {
+    text = readFileSync(path, "utf8");
+  } catch (e) {
+    throw quietRead(e, "approvals.jsonl");
+  }
+  for (const [i, line] of text.split("\n").entries()) {
     if (line.length === 0) continue;
     try {
       out.push(parseJsonFileText(line, `${path}:${i + 1}`));
     } catch {
-      throw new DiscordError(`${path}:${i + 1}: not valid JSON`);
+      throw new DiscordError(`approvals.jsonl:${i + 1}: not valid JSON`);
     }
   }
   return out;
diff --git a/packages/discord/src/binding.mjs b/packages/discord/src/binding.mjs
index 6076f52ee..359aa2534 100644
--- a/packages/discord/src/binding.mjs
+++ b/packages/discord/src/binding.mjs
@@ -22,14 +22,14 @@ import { parseJsonFileText } from "../../organization/src/util.mjs";
 import { existsSync, lstatSync, readFileSync, realpathSync, statSync } from "node:fs";
 import { loadWebConfig } from "./web.mjs";
 import { loadSetsparkConfig } from "./setspark.mjs";
-import { isAbsolute, join, resolve, sep } from "node:path";
+import { basename, isAbsolute, join, resolve, sep } from "node:path";
 import { homedir } from "node:os";
-import { DiscordError } from "./errors.mjs";
+import { BINDING_NAME, DiscordError, plainKey, quietRead } from "./errors.mjs";
 import { TOOL_DEFAULTS } from "./tools.mjs";
 import { loadGitConfig } from "./git.mjs";
 
 export const BINDING_VERSION = 1;
-export const BINDING_NAME = /^[a-z0-9][a-z0-9._-]{0,63}$/;
+export { BINDING_NAME };
 export const SNOWFLAKE = /^[0-9]{17,20}$/;
 export const CHANNEL_MODES = Object.freeze(["open", "mention"]);
 export const THINKING_LEVELS = Object.freeze(["off", "minimal", "low", "medium", "high", "xhigh", "max"]);
@@ -56,16 +56,17 @@ export function defaultConfigPath(env = process.env) {
 }
 
 // Only dataRoot is read here; scripts/mosaic-config.mjs owns full validation.
+// Refusals name the config, never its path (#1873).
 export function loadDataRoot(path = defaultConfigPath()) {
-  if (!existsSync(path)) throw new DiscordError(`config not found: ${path}`);
+  if (!existsSync(path)) throw new DiscordError("config not found");
   let raw;
   try {
     raw = parseJsonFileText(readFileSync(path, "utf8"), path);
   } catch (error) {
-    throw new DiscordError(`config is not valid JSON: ${path}${error.code ? ` (${error.code})` : ""}`);
+    throw new DiscordError(`config is not valid JSON${error.code ? ` (${error.code})` : ""}`);
   }
-  if (!raw || typeof raw !== "object" || Array.isArray(raw)) throw new DiscordError(`config is not an object: ${path}`);
-  if (typeof raw.dataRoot !== "string" || !isAbsolute(raw.dataRoot)) throw new DiscordError(`config.dataRoot must be an absolute path: ${path}`);
+  if (!raw || typeof raw !== "object" || Array.isArray(raw)) throw new DiscordError("config is not an object");
+  if (typeof raw.dataRoot !== "string" || !isAbsolute(raw.dataRoot)) throw new DiscordError("config.dataRoot must be an absolute path");
   return raw.dataRoot;
 }
 
@@ -73,13 +74,16 @@ export function discordDir(dataRoot) {
   return join(dataRoot, "discord");
 }
 
+// The name is checked, never echoed: a bad one could be a host path (#1873).
+const INVALID_BINDING_NAME = "invalid binding name (lowercase letters, digits, ., _ or -, at most 64)";
+
 export function bindingPath(dataRoot, name) {
-  if (!BINDING_NAME.test(String(name))) throw new DiscordError(`invalid binding name: ${JSON.stringify(name)}`, 4);
+  if (!BINDING_NAME.test(String(name))) throw new DiscordError(INVALID_BINDING_NAME, 4);
   return join(discordDir(dataRoot), `${name}.json`);
 }
 
 export function bindingDataDir(dataRoot, name) {
-  if (!BINDING_NAME.test(String(name))) throw new DiscordError(`invalid binding name: ${JSON.stringify(name)}`, 4);
+  if (!BINDING_NAME.test(String(name))) throw new DiscordError(INVALID_BINDING_NAME, 4);
   return join(discordDir(dataRoot), name);
 }
 
@@ -89,7 +93,7 @@ function isObject(v) {
 
 function onlyKeys(obj, allowed, where) {
   for (const key of Object.keys(obj)) {
-    if (!allowed.includes(key)) throw new DiscordError(`${where}: unknown key ${JSON.stringify(key)}`);
+    if (!allowed.includes(key)) throw new DiscordError(`${where}: unknown key ${plainKey(key)}`);
   }
 }
 
@@ -274,38 +278,49 @@ export function reloadDiff(current, next) {
 }
 
 // A private file: regular, not a symlink, owner-only (0600), non-empty.
+// `what` is the label a refusal names; the path never appears (#1873).
 export function checkPrivateFile(path, what) {
   let st;
   try {
     st = lstatSync(path);
   } catch {
-    throw new DiscordError(`${what} not found: ${path}`);
+    throw new DiscordError(`${what} not found`);
   }
-  if (st.isSymbolicLink()) throw new DiscordError(`${what} must not be a symlink: ${path}`);
-  if (!st.isFile()) throw new DiscordError(`${what} is not a regular file: ${path}`);
+  if (st.isSymbolicLink()) throw new DiscordError(`${what} must not be a symlink`);
+  if (!st.isFile()) throw new DiscordError(`${what} is not a regular file`);
   const mode = st.mode & 0o777;
-  if (mode !== 0o600) throw new DiscordError(`${what} must be mode 0600, is ${mode.toString(8).padStart(4, "0")}: ${path}`);
-  if (st.size === 0) throw new DiscordError(`${what} is empty: ${path}`);
+  if (mode !== 0o600) throw new DiscordError(`${what} must be mode 0600, is ${mode.toString(8).padStart(4, "0")}`);
+  if (st.size === 0) throw new DiscordError(`${what} is empty`);
   return st;
 }
 
+// The binding is named by its file's name when that is a valid binding name
+// (bindingPath() makes it so), never by its path.
 export function loadBinding(path) {
-  checkPrivateFile(path, "binding");
+  const name = basename(String(path), ".json");
+  const label = BINDING_NAME.test(name) ? `binding ${name}` : "binding";
+  checkPrivateFile(path, label);
   let raw;
   try {
     raw = parseJsonFileText(readFileSync(path, "utf8"), path);
   } catch (error) {
-    throw new DiscordError(`binding is not valid JSON: ${path}${error.code ? ` (${error.code})` : ""}`);
+    throw new DiscordError(`${label} is not valid JSON${error.code ? ` (${error.code})` : ""}`);
   }
-  return validateBinding(raw, `binding ${path}`);
+  return validateBinding(raw, label);
 }
 
 // The token is read once into memory and handed to the REST and gateway
 // clients. It is never printed, journaled, or put on a command line.
 export function readToken(binding) {
   checkPrivateFile(binding.tokenFile, "token file");
-  const token = readFileSync(binding.tokenFile, "utf8").trim();
-  if (!/^[A-Za-z0-9._-]{20,}$/.test(token)) throw new DiscordError(`token file does not hold a bot token: ${binding.tokenFile}`);
+  // A file that changes after its check fails with a native error that carries the path (#1873).
+  let token;
+  try {
+    token = readFileSync(binding.tokenFile, "utf8").trim();
+  } catch (e) {
+    throw quietRead(e, "token file");
+  }
+  if (!/^[A-Za-z0-9._-]{20,}$/.test(token)) throw new DiscordError("token file does not hold a bot token");
   return token;
 }
 
@@ -315,22 +330,34 @@ export function readToken(binding) {
 // the model's prompt, so this is the boundary that keeps host files out of
 // Discord Sage (Q14, Q16). Every file must be a regular non-empty file.
 export function resolveContextFiles(binding, repo) {
-  const root = realpathSync(repo);
-  return binding.context.files.map((f) => {
+  let root;
+  try {
+    root = realpathSync(repo);
+  } catch (e) {
+    throw quietRead(e, "the repository");
+  }
+  // Refusals name the entry by its index in context.files, never its path (#1873).
+  return binding.context.files.map((f, i) => {
+    const at = `context.files[${i}]`;
     if (typeof f !== "string" || f.length === 0) throw new DiscordError("context file must be a non-empty string");
-    if (isAbsolute(f)) throw new DiscordError(`context file must be repository-relative: ${f}`);
-    if (f.split(/[\\/]/).includes("..")) throw new DiscordError(`context file must not escape the repository: ${f}`);
+    if (isAbsolute(f)) throw new DiscordError(`context file must be repository-relative: ${at}`);
+    if (f.split(/[\\/]/).includes("..")) throw new DiscordError(`context file must not escape the repository: ${at}`);
     const path = resolve(root, f);
     let st;
     try {
       st = lstatSync(path);
     } catch {
-      throw new DiscordError(`missing context file: ${path}`);
+      throw new DiscordError(`missing context file: ${at}`);
     }
-    if (st.isSymbolicLink()) throw new DiscordError(`context file must not be a symlink: ${path}`);
-    if (!st.isFile() || st.size === 0) throw new DiscordError(`context file is not a regular non-empty file: ${path}`);
-    const real = realpathSync(path);
-    if (real !== path || !real.startsWith(root + sep)) throw new DiscordError(`context file resolves outside the repository: ${f}`);
+    if (st.isSymbolicLink()) throw new DiscordError(`context file must not be a symlink: ${at}`);
+    if (!st.isFile() || st.size === 0) throw new DiscordError(`context file is not a regular non-empty file: ${at}`);
+    let real;
+    try {
+      real = realpathSync(path);
+    } catch (e) {
+      throw quietRead(e, `context file ${at}`);
+    }
+    if (real !== path || !real.startsWith(root + sep)) throw new DiscordError(`context file resolves outside the repository: ${at}`);
     return path;
   });
 }
@@ -363,18 +390,28 @@ function webConfig(raw, where) {
 
 export function resolveToolRoots(binding, { dataRoot }) {
   if (!binding.tools) return null;
-  const data = existsSync(dataRoot) ? realpathSync(dataRoot) : resolve(dataRoot);
+  let data;
+  try {
+    data = existsSync(dataRoot) ? realpathSync(dataRoot) : resolve(dataRoot);
+  } catch (e) {
+    throw quietRead(e, "the data root");
+  }
   const roots = binding.tools.roots.map((r) => {
     let st;
     try {
       st = lstatSync(r.path);
     } catch {
-      throw new DiscordError(`tool root ${r.name} does not exist: ${r.path}`);
+      throw new DiscordError(`tool root ${r.name} does not exist`);
     }
-    if (st.isSymbolicLink()) throw new DiscordError(`tool root ${r.name} must not be a symlink: ${r.path}`);
-    if (!st.isDirectory()) throw new DiscordError(`tool root ${r.name} is not a directory: ${r.path}`);
-    const real = realpathSync(r.path);
-    if (real === data || real.startsWith(data + sep) || data.startsWith(real + sep)) throw new DiscordError(`tool root ${r.name} overlaps the data root: ${r.path}`);
+    if (st.isSymbolicLink()) throw new DiscordError(`tool root ${r.name} must not be a symlink`);
+    if (!st.isDirectory()) throw new DiscordError(`tool root ${r.name} is not a directory`);
+    let real;
+    try {
+      real = realpathSync(r.path);
+    } catch (e) {
+      throw quietRead(e, `tool root ${r.name}`);
+    }
+    if (real === data || real.startsWith(data + sep) || data.startsWith(real + sep)) throw new DiscordError(`tool root ${r.name} overlaps the data root`);
     return { name: r.name, path: real, write: r.write, ...(r.git ? { git: { branch: r.git.branch, identity: r.git.identity, tokenFile: r.git.tokenFile, author: `${r.git.author.name} <${r.git.author.email}>`, ...(r.git.protocol ? { protocol: r.git.protocol } : {}) } } : {}) };
   });
   // setspark carries only the keys loadSetsparkConfig accepts; the extension
diff --git a/packages/discord/src/cli.mjs b/packages/discord/src/cli.mjs
index e291d8c03..11726a514 100755
--- a/packages/discord/src/cli.mjs
+++ b/packages/discord/src/cli.mjs
@@ -46,22 +46,22 @@
 // 3 refused by a brake (STOP present or the binding held; a supervisor must
 // not retry); 4 usage.
 
-import { existsSync, mkdirSync, mkdtempSync, writeFileSync, statSync, readdirSync } from "node:fs";
+import { existsSync, mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
 import { dirname, join, resolve } from "node:path";
 import { createHash } from "node:crypto";
-import { DiscordError } from "./errors.mjs";
+import { DiscordError, printable } from "./errors.mjs";
 import { assertProcessing, processingStatus, ProcessingError } from "../../processing-control/src/state.mjs";
 import { registerRuntime, updateRuntime, unregisterRuntime, processIdentity } from "../../processing-control/src/runtimes.mjs";
 import { loadSeatSets } from "../../organization/src/library-seats.mjs";
 import { defaultConfigPath, loadDataRoot, bindingPath, bindingDataDir, loadBinding, readToken, resolveContextFiles, resolveToolRoots, reloadDiff } from "./binding.mjs";
 import { createRest } from "./rest.mjs";
 import { createGateway, CONNECTOR_INTENTS } from "./gateway.mjs";
-import { createEngine, buildPiArgs } from "./engine-pi.mjs";
+import { createEngine, buildPiArgs, sessionContinues } from "./engine-pi.mjs";
 import { TOOLS_ENV, enabledToolNames } from "./tools.mjs";
 import { createSetsparkApi } from "./setspark.mjs";
 import { assembleContext } from "./context.mjs";
 import { createConnector } from "./connector.mjs";
-import { ensureJournal, requestStop, requestProcessingStop, stopRequested, readPid, stopTarget, writePid, clearPid, unlock, recover, appendReload, BRAKE_EXIT } from "./journal.mjs";
+import { ensureJournal, requestStop, requestProcessingStop, stopRequested, readPid, stopTarget, writePid, clearPid, unlock, recover, appendReload, journalLabel, BRAKE_EXIT } from "./journal.mjs";
 
 const USAGE = [
   "usage: mosaic-discord check <binding> [--config PATH] [--repo PATH] [--offline]",
@@ -114,7 +114,7 @@ function checkLibraryEngine(configDirectory, binding) {
   try {
     sets = loadSeatSets({ dir: configDirectory });
   } catch (err) {
-    throw new DiscordError(`discord-business-unreadable: ${err.message}`, 2);
+    throw new DiscordError(`discord-business-unreadable: ${printable(err, "a business file")}`, 2);
   }
   if (!sets.librarySeats.has(binding.seat)) return;
   if (binding.engine.provider !== "mosaic-bus") {
@@ -135,7 +135,7 @@ function prepare(opts) {
   const contextFiles = resolveContextFiles(binding, opts.repo);
   const toolRoots = resolveToolRoots(binding, { dataRoot });
   const pi = join(opts.repo, "node_modules", ".bin", "pi");
-  if (!existsSync(pi)) throw new DiscordError(`pi not found at ${pi}; run npm ci in the repository`);
+  if (!existsSync(pi)) throw new DiscordError("pi not found at node_modules/.bin/pi in the repository; run npm ci in the repository");
   const journalDir = bindingDataDir(dataRoot, binding.name);
   const sessionDir = join(dataRoot, "sessions", `discord-${binding.name}`);
   return { dataRoot, bindingFile, binding, contextFiles, toolRoots, pi, journalDir, sessionDir };
@@ -205,7 +205,7 @@ async function run(opts) {
     const outcome = recover(journalDir);
     if (outcome === "cleared") warn("supervised start: run.lock left by a process that is gone was removed");
   }
-  if (stopRequested(journalDir)) throw new DiscordError(`STOP is present in ${journalDir}; remove it to run`, BRAKE_EXIT);
+  if (stopRequested(journalDir)) throw new DiscordError(`STOP is present in ${journalLabel(journalDir)}; remove it to run`, BRAKE_EXIT);
   writePid(journalDir, process.pid);
   let managed = null;
   const cleanupPid = () => {
@@ -234,7 +234,7 @@ async function run(opts) {
     const promptFile = join(launch, "context.md");
     writeFileSync(promptFile, snapshot.text, { mode: 0o600 });
     writeFileSync(join(launch, "context.sha256"), `${snapshot.sha256}  context.md\n`, { mode: 0o600 });
-    const continueSession = existsSync(sessionDir) && statSync(sessionDir).isDirectory() && hasJsonl(sessionDir);
+    const continueSession = sessionContinues(sessionDir);
 
     const rest = createRest({ token, log: warn });
     const gw = await rest.getGatewayBot();
@@ -272,7 +272,7 @@ async function run(opts) {
       clearInterval(processingWatch);
       exitCode = code;
       warn(immediate ? 'stopping: processing halted' : "stopping: finishing in-flight turns");
-      connector.stop({ immediate }).catch((err) => warn(`stop failed: ${err.message}`)).finally(() => {
+      connector.stop({ immediate }).catch((err) => warn(`stop failed: ${printable(err)}`)).finally(() => {
         cleanupPid();
         process.exit(exitCode);
       });
@@ -317,8 +317,8 @@ async function run(opts) {
         const n = (d) => `+${d.added.length} -${d.removed.length} ~${d.changed.length}`;
         warn(`reload applied: channels ${n(diff.channels)}, users ${n(diff.users)}, limits ${diff.limits.length ? diff.limits.join(",") : "unchanged"}${diff.guildName ? ", guildName" : ""}`);
       } catch (err) {
-        appendReload(journalDir, { at, outcome: "refused", error: err.message });
-        warn(`reload refused, binding unchanged: ${err.message}`);
+        appendReload(journalDir, { at, outcome: "refused", error: printable(err) });
+        warn(`reload refused, binding unchanged: ${printable(err)}`);
       }
     };
     let reloadChain = Promise.resolve();
@@ -332,13 +332,6 @@ async function run(opts) {
   }
 }
 
-function hasJsonl(dir) {
-  try {
-    return readdirSync(dir).some((f) => f.endsWith(".jsonl"));
-  } catch {
-    return false;
-  }
-}
 
 function stop(opts) {
   const dataRoot = loadDataRoot(opts.config);
@@ -413,7 +406,8 @@ main().then((code) => {
   if (code !== null) process.exit(code);
 }).catch((err) => {
   const code = err instanceof ProcessingError ? BRAKE_EXIT : err instanceof DiscordError ? err.exitCode : 1;
-  warn(err.message);
+  // Never a native error's message: it carries the path (#1873).
+  warn(printable(err));
   if (err.details && err.details.nonces) warn(`nonces: ${err.details.nonces.join(", ")}`);
   process.exit(code);
 });
diff --git a/packages/discord/src/connector.mjs b/packages/discord/src/connector.mjs
index a99a96794..74833e4c3 100644
--- a/packages/discord/src/connector.mjs
+++ b/packages/discord/src/connector.mjs
@@ -35,7 +35,7 @@ import { reloadDiff } from "./binding.mjs";
 import { envelope, splitReply } from "./context.mjs";
 import {
   ensureJournal, appendInbox, readInboxIds, appendOutbox, unresolvedOutbox, appendDrop,
-  writeTurn, appendAdmission, countAdmissionsOn, appendNotice, noticeOn, utcDate, stopRequested,
+  writeTurn, appendAdmission, countAdmissionsOn, appendNotice, noticeOn, utcDate, stopRequested, journalLabel,
 } from "./journal.mjs";
 import { RestOutcome } from "./rest.mjs";
 import { DiscordError } from "./errors.mjs";
@@ -596,7 +596,7 @@ ${status === "not-posted" ? APPROVAL_LINES.pressAgain : APPROVAL_LINES.failed}`;
     async start() {
       processing();
       if (state.started) throw new DiscordError("connector already started", 1);
-      if (stopRequested(journalDir)) throw new DiscordError(`STOP is present in ${journalDir}; remove it to run`, 1);
+      if (stopRequested(journalDir)) throw new DiscordError(`STOP is present in ${journalLabel(journalDir)}; remove it to run`, 1);
       const reconciled = await reconcile();
       const approvals = await reconcileApprovals();
       processing();
diff --git a/packages/discord/src/engine-pi.mjs b/packages/discord/src/engine-pi.mjs
index 96b4aa118..087e4355e 100644
--- a/packages/discord/src/engine-pi.mjs
+++ b/packages/discord/src/engine-pi.mjs
@@ -32,8 +32,9 @@
 // without the connector noticing: the contract is start(), prompt(), stop().
 
 import { spawn as nodeSpawn } from "node:child_process";
+import { existsSync, readdirSync, statSync } from "node:fs";
 import { fileURLToPath } from "node:url";
-import { DiscordError } from "./errors.mjs";
+import { DiscordError, printable, quietFs } from "./errors.mjs";
 import { enabledToolNames } from "./tools.mjs";
 import { assertProcessing, processingStatus } from "../../processing-control/src/state.mjs";
 import { registerRuntime, updateRuntime, unregisterRuntime, processIdentity, runtime, runtimeGroupState, createRuntimeSignaller } from "../../processing-control/src/runtimes.mjs";
@@ -51,6 +52,25 @@ export const TOOLS_EXTENSION = fileURLToPath(new URL("../extension/tools.mjs", i
 // Older name, kept for the tests and docs that still use it.
 export const READONLY_TOOLS_EXTENSION = TOOLS_EXTENSION;
 
+// Whether pi continues the session in sessionDir: it is a directory holding a
+// .jsonl session file. A stat that fails names the binding's session directory,
+// never its path (#1873); a listing that fails means a new session, as before.
+export function sessionContinues(sessionDir) {
+  if (!existsSync(sessionDir)) return false;
+  let st;
+  try {
+    st = statSync(sessionDir);
+  } catch (e) {
+    throw quietFs(e, "the binding's session directory");
+  }
+  if (!st.isDirectory()) return false;
+  try {
+    return readdirSync(sessionDir).some((f) => f.endsWith(".jsonl"));
+  } catch {
+    return false;
+  }
+}
+
 export function buildPiArgs({ provider, model, thinking, sessionDir, appendSystemPromptFile, continueSession, tools = null }) {
   const args = [...PI_FIXED_ARGS];
   if (tools) args.push("--no-builtin-tools", "--extension", TOOLS_EXTENSION, "--tools", enabledToolNames(tools).join(","));
@@ -393,9 +413,11 @@ export function createEngine({
       child.stderr.on("data", (chunk) => log(`pi: ${chunk.trimEnd()}`));
       child.on("error", (err) => {
         releaseRuntime();
-        log(`engine spawn error: ${err.message}`);
-        state.exited = { code: null, signal: null, error: err.message };
-        failAll("engine-down", `engine failed: ${err.message}`);
+        // A spawn error's message carries the command's path (#1873).
+        const why = printable(err, "pi");
+        log(`engine spawn error: ${why}`);
+        state.exited = { code: null, signal: null, error: why };
+        failAll("engine-down", `engine failed: ${why}`);
         onExit(state.exited);
       });
       child.on("exit", (code, signal) => {
diff --git a/packages/discord/src/errors.mjs b/packages/discord/src/errors.mjs
index f15f12477..dbeb46fe7 100644
--- a/packages/discord/src/errors.mjs
+++ b/packages/discord/src/errors.mjs
@@ -1,6 +1,48 @@
 // One error class for the package. exitCode follows docs/TOOLS.md: 1 operation
 // failed, 2 invalid data or configuration, 3 refused by a brake (STOP or a
 // held binding; a supervisor must not retry), 4 usage.
+// A refusal that names an unknown key quotes it only when it is a plain name;
+// a key that could carry a host path or a secret is described, never echoed (#1873).
+export const plainKey = (k) => (/^[A-Za-z_][A-Za-z0-9_-]{0,63}$/.test(String(k)) ? JSON.stringify(k) : "that is not a plain name");
+// A binding (and seat) name. Defined here, not in binding.mjs, so journal.mjs can label a
+// journal directory without importing binding.mjs and its config readers; copies of
+// journal.mjs + errors.mjs (the queue test repo) stay self-contained. binding.mjs re-exports it.
+export const BINDING_NAME = /^[a-z0-9][a-z0-9._-]{0,63}$/;
+
+// A filesystem call that fails names the file by label, the call and the
+// error code, never the path Node puts in the message. The same error object
+// is rethrown, so its type, code and the exit it maps to are unchanged, and
+// it is marked so the CLI's top-level handler prints it as it is (#1873).
+const QUIET = Symbol("discord.quiet");
+const SYSCALL = /^[a-z][a-z0-9_]{0,31}$/;
+const CODE = /^[A-Z][A-Z0-9_]{0,63}$/;
+const callOf = (e) => {
+  const word = typeof e.syscall === "string" ? e.syscall.split(" ")[0] : "";
+  return SYSCALL.test(word) ? word : "access";
+};
+const codeOf = (e) => (typeof e.code === "string" && CODE.test(e.code) ? e.code : "UNKNOWN");
+export function quietFs(e, label, verb = null) {
+  if (e && typeof e === "object" && typeof e.code === "string") {
+    e.message = `cannot ${verb ?? callOf(e)} ${label} (${codeOf(e)})`;
+    e[QUIET] = true;
+  }
+  return e;
+}
+export const quietRead = (e, label) => quietFs(e, label, "read");
+
+// What a top-level handler prints for an error (#1873). Our refusals and an
+// error already labelled at its source print their own message. A native
+// Node error (it carries a syscall, or a code and a path) that slipped past
+// every source label prints only its call and code, never its message,
+// which carries the path; `label` names the file when the error has one.
+export function printable(err, label = "a discord file") {
+  if (err instanceof DiscordError || (err && err[QUIET] === true)) return String(err.message);
+  if (err && typeof err === "object" && (typeof err.syscall === "string" || (typeof err.code === "string" && typeof err.path === "string"))) {
+    return typeof err.path === "string" ? `cannot ${callOf(err)} ${label} (${codeOf(err)})` : `cannot ${callOf(err)} (${codeOf(err)})`;
+  }
+  return err && typeof err.message === "string" ? err.message : String(err);
+}
+
 export class DiscordError extends Error {
   constructor(message, exitCode = 2, details = undefined) {
     super(message);
diff --git a/packages/discord/src/git.mjs b/packages/discord/src/git.mjs
index 2351b4270..44c8dda13 100644
--- a/packages/discord/src/git.mjs
+++ b/packages/discord/src/git.mjs
@@ -46,6 +46,7 @@
 import { spawnSync } from "node:child_process";
 import { existsSync, lstatSync } from "node:fs";
 import { join } from "node:path";
+import { plainKey } from "./errors.mjs";
 import { fileURLToPath } from "node:url";
 
 export const GIT_TOOL_NAMES = Object.freeze(["git_status", "git_commit", "git_pull", "git_push"]);
@@ -109,7 +110,7 @@ const AUTHOR = /^([^<>\r\n]{1,64}?) <([^<>\s@]+@[^<>\s@]+)>$/;
 export function loadGitConfig(raw, where, real) {
   if (!isObject(raw)) throw new Error(`${where}: not an object`);
   for (const k of Object.keys(raw)) {
-    if (!["branch", "identity", "tokenFile", "author", "protocol"].includes(k)) throw new Error(`${where}: unknown key ${JSON.stringify(k)}`);
+    if (!["branch", "identity", "tokenFile", "author", "protocol"].includes(k)) throw new Error(`${where}: unknown key ${plainKey(k)}`);
   }
   if (typeof raw.branch !== "string" || !BRANCH_NAME.test(raw.branch) || raw.branch.includes("..")) throw new Error(`${where}.branch: must be a branch name`);
   if (typeof raw.identity !== "string" || !IDENTITY.test(raw.identity)) throw new Error(`${where}.identity: must match ${IDENTITY}`);
@@ -125,7 +126,7 @@ export function loadGitConfig(raw, where, real) {
     } catch {
       // handled below
     }
-    if (!st || !(st.isDirectory() || st.isFile())) throw new Error(`${where}: ${real} is not a git work tree`);
+    if (!st || !(st.isDirectory() || st.isFile())) throw new Error(`${where}: the root is not a git work tree`);
   }
   if (process.execPath.includes("'") || CREDENTIAL_HELPER.includes("'")) throw new Error(`${where}: the node or helper path holds a quote and cannot be a credential helper`);
   return Object.freeze({
@@ -139,12 +140,12 @@ function checkPrivateFile(path, what) {
   try {
     st = lstatSync(path);
   } catch {
-    throw new Error(`${what}: not found: ${path}`);
+    throw new Error(`${what}: not found`);
   }
-  if (st.isSymbolicLink()) throw new Error(`${what}: must not be a symlink: ${path}`);
-  if (!st.isFile()) throw new Error(`${what}: not a regular file: ${path}`);
-  if ((st.mode & 0o777) !== 0o600) throw new Error(`${what}: must be mode 0600: ${path}`);
-  if (st.size === 0) throw new Error(`${what}: is empty: ${path}`);
+  if (st.isSymbolicLink()) throw new Error(`${what}: must not be a symlink`);
+  if (!st.isFile()) throw new Error(`${what}: not a regular file`);
+  if ((st.mode & 0o777) !== 0o600) throw new Error(`${what}: must be mode 0600`);
+  if (st.size === 0) throw new Error(`${what}: is empty`);
 }
 
 // The environment every child sees. No global or system git configuration,
@@ -201,7 +202,7 @@ function cap(text) {
 function run(cmd, args, cwd, env, spawn) {
   const r = spawn(cmd, args, { cwd, env, encoding: "utf8", timeout: GIT_TIMEOUT_MS, maxBuffer: 4 * 1024 * 1024, stdio: ["ignore", "pipe", "pipe"] });
   if (r.error && r.error.code === "ETIMEDOUT") throw new GitRefusal(GIT_REFUSAL.TIMEOUT, `${cmd} ${args[0] || ""}`);
-  if (r.error) throw new GitRefusal(GIT_REFUSAL.NO_GIT, `${cmd} could not start (${r.error.code || r.error.message})`);
+  if (r.error) throw new GitRefusal(GIT_REFUSAL.NO_GIT, `${cmd} could not start (${r.error.code || "error"})`);
   return { status: r.status, stdout: cap(r.stdout || ""), stderr: cap(r.stderr || "") };
 }
 
@@ -209,8 +210,12 @@ function git(root, gitCfg, args, { remote = false, spawn = spawnSync } = {}) {
   return run("git", args, root.real, gitEnv(gitCfg, { remote }), spawn);
 }
 
+// git output reaches a refusal detail, the journal and Discord. A line that
+// carries a host path (an absolute or home path, or a file: URL) is dropped,
+// never relayed; repo-relative lines such as a lock owner or a conflict stay (#1873).
+const HOST_PATH = /(^|[\s'"(=:,[<])~?\/(?!\/)|file:/i;
 function firstLines(text, n = 5) {
-  return text.split("\n").filter((l) => l.trim().length > 0).slice(0, n).join("\n");
+  return text.split("\n").filter((l) => l.trim().length > 0 && !HOST_PATH.test(l)).slice(0, n).join("\n");
 }
 
 // The guard every verb runs first: on the named branch, nothing in
diff --git a/packages/discord/src/journal.mjs b/packages/discord/src/journal.mjs
index a8a31dde7..ff1fb376b 100644
--- a/packages/discord/src/journal.mjs
+++ b/packages/discord/src/journal.mjs
@@ -25,8 +25,16 @@ import {
   appendFileSync, closeSync, constants, existsSync, fstatSync, fsyncSync, mkdirSync, openSync, readdirSync, readFileSync, readSync, renameSync, rmdirSync, rmSync,
   unlinkSync, writeFileSync, writeSync,
 } from "node:fs";
-import { join } from "node:path";
-import { DiscordError } from "./errors.mjs";
+import { basename, join } from "node:path";
+import { BINDING_NAME, DiscordError, quietFs, quietRead } from "./errors.mjs";
+
+// Where a refusal says a binding's journal is: its place under the data root
+// when the directory carries a valid binding name (bindingDataDir() makes it
+// so), never the host path (#1873).
+export function journalLabel(dir) {
+  const name = basename(String(dir));
+  return BINDING_NAME.test(name) ? `discord/${name} under the data root` : "the binding's journal directory";
+}
 
 export const OUTBOX_STATUS = Object.freeze(["intent", "confirmed", "refused", "unknown"]);
 
@@ -38,19 +46,28 @@ export function ensureJournal(dir) {
 function appendLine(path, record) {
   const line = JSON.stringify(record);
   if (line.includes("\n")) throw new DiscordError("journal line must not contain a newline", 1);
-  appendFileSync(path, line + "\n", { mode: 0o600 });
+  try {
+    appendFileSync(path, line + "\n", { mode: 0o600 });
+  } catch (e) {
+    throw quietFs(e, basename(path), "append to");
+  }
 }
 
 function readLines(path) {
   if (!existsSync(path)) return [];
   const out = [];
-  const text = readFileSync(path, "utf8");
+  let text;
+  try {
+    text = readFileSync(path, "utf8");
+  } catch (e) {
+    throw quietRead(e, basename(path));
+  }
   for (const [i, line] of text.split("\n").entries()) {
     if (line.length === 0) continue;
     try {
       out.push(parseJsonFileText(line, `${path}:${i + 1}`));
     } catch {
-      throw new DiscordError(`${path}:${i + 1}: not valid JSON`);
+      throw new DiscordError(`${basename(path)}:${i + 1}: not valid JSON`);
     }
   }
   return out;
@@ -109,42 +126,61 @@ export function readDrops(dir) {
 const TURN_ID = /^[A-Za-z0-9][A-Za-z0-9._-]{0,127}$/;
 
 export function turnPath(dir, id) {
-  if (!TURN_ID.test(String(id))) throw new DiscordError(`invalid turn id: ${JSON.stringify(id)}`, 1);
+  if (!TURN_ID.test(String(id))) throw new DiscordError("invalid turn id (letters, digits, ., _ or -, at most 128)", 1);
   return join(dir, "turns", `${id}.json`);
 }
 
+// A parse refusal or a failed read or write names the turn by its id, never by
+// host path (PR #1916, #1873); a listed file's id is named only when it passes TURN_ID.
+const turnLabel = (id) => (TURN_ID.test(id) ? `turn record ${id}` : "turn record");
+
 export function writeTurn(dir, id, record) {
   const path = turnPath(dir, id);
   let fd;
   try {
     fd = openSync(path, "wx", 0o600);
   } catch (err) {
-    if (err.code === "EEXIST") throw new DiscordError(`turn record already exists: ${path}`, 1);
-    throw err;
+    if (err.code === "EEXIST") throw new DiscordError(`turn record already exists: ${id}`, 1);
+    throw quietFs(err, turnLabel(String(id)), "write");
   }
   try {
-    writeSync(fd, JSON.stringify({ ...record, id }, null, 2) + "\n");
-  } finally {
-    closeSync(fd);
+    try {
+      writeSync(fd, JSON.stringify({ ...record, id }, null, 2) + "\n");
+    } finally {
+      closeSync(fd);
+    }
+  } catch (err) {
+    throw quietFs(err, turnLabel(String(id)), "write");
   }
   return path;
 }
 
-// A parse refusal names the turn by its id, never by host path (PR #1916); a
-// listed file's id is named only when it passes TURN_ID.
-const turnLabel = (id) => (TURN_ID.test(id) ? `turn record ${id}` : "turn record");
+function readTurnFile(path, id) {
+  let text;
+  try {
+    text = readFileSync(path, "utf8");
+  } catch (e) {
+    throw quietRead(e, turnLabel(id));
+  }
+  return parseJsonFileText(text, path, turnLabel(id));
+}
 
 export function readTurn(dir, id) {
-  const path = turnPath(dir, id);
-  return parseJsonFileText(readFileSync(path, "utf8"), path, turnLabel(String(id)));
+  return readTurnFile(turnPath(dir, id), String(id));
 }
 
 export function listTurns(dir) {
   const turns = join(dir, "turns");
   if (!existsSync(turns)) return [];
-  return readdirSync(turns)
+  let names;
+  try {
+    names = readdirSync(turns);
+  } catch (e) {
+    throw quietRead(e, `the turns directory in ${journalLabel(dir)}`);
+  }
+  return names
     .filter((f) => f.endsWith(".json"))
-    .map((f) => parseJsonFileText(readFileSync(join(turns, f), "utf8"), join(turns, f), turnLabel(f.slice(0, -".json".length))));
+    .map((f) => readTurnFile(join(turns, f), f.slice(0, -".json".length)));
 }
 
 // The daily ceiling counts admissions on the current UTC date. An admission
@@ -189,21 +225,38 @@ function stopLock(dir, action) {
   const lock = join(dir, '.stop.lock');
   try { mkdirSync(lock, { mode: 0o700 }); }
   catch { throw new DiscordError('STOP update is locked; refusing', 1); }
-  try { return action(); } finally { rmdirSync(lock); }
+  try { return action(); } finally {
+    try { rmdirSync(lock); } catch (e) { throw quietFs(e, `.stop.lock in ${journalLabel(dir)}`, "remove"); }
+  }
 }
 
+// A STOP write or removal that fails names STOP in the journal, never its path (#1873).
+const stopLabel = (dir) => `STOP in ${journalLabel(dir)}`;
+
 function appendStop(dir, reason) {
   const path = stopPath(dir);
-  const fd = openSync(path, constants.O_WRONLY | constants.O_APPEND | constants.O_CREAT | constants.O_NOFOLLOW, 0o600);
   try {
-    writeSync(fd, JSON.stringify({ at: new Date().toISOString(), reason }) + "\n");
-    fsyncSync(fd);
-  } finally {
-    closeSync(fd);
+    const fd = openSync(path, constants.O_WRONLY | constants.O_APPEND | constants.O_CREAT | constants.O_NOFOLLOW, 0o600);
+    try {
+      writeSync(fd, JSON.stringify({ at: new Date().toISOString(), reason }) + "\n");
+      fsyncSync(fd);
+    } finally {
+      closeSync(fd);
+    }
+  } catch (e) {
+    throw quietFs(e, stopLabel(dir), "write");
   }
   return path;
 }
 
+function removeStop(dir) {
+  try {
+    unlinkSync(stopPath(dir));
+  } catch (e) {
+    throw quietFs(e, stopLabel(dir), "remove");
+  }
+}
+
 const PROCESSING_GENERATION = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
 function processingStops(dir) {
   let fd;
@@ -235,14 +288,13 @@ export function clearProcessingStop(dir, generation) {
     if (!rows?.length || rows.some(r => !r || Object.keys(r).sort().join(',') !== 'at,reason' ||
         r.reason !== `processing:${generation}` || !Number.isFinite(Date.parse(r.at)) ||
         new Date(r.at).toISOString() !== r.at)) return false;
-    unlinkSync(stopPath(dir));
+    removeStop(dir);
     return true;
   });
 }
 
 export function clearStop(dir) {
-  const path = stopPath(dir);
-  if (existsSync(path)) unlinkSync(path);
+  if (existsSync(stopPath(dir))) removeStop(dir);
 }
 
 // The STOP lines as written, oldest first. A line that does not parse is
@@ -250,7 +302,13 @@ export function clearStop(dir) {
 // treated as ours.
 export function readStop(dir) {
   if (!stopRequested(dir)) return [];
-  return readFileSync(stopPath(dir), "utf8").split("\n").filter((l) => l.trim() !== "").map((l) => {
+  let text;
+  try {
+    text = readFileSync(stopPath(dir), "utf8");
+  } catch (e) {
+    throw quietRead(e, stopLabel(dir));
+  }
+  return text.split("\n").filter((l) => l.trim() !== "").map((l) => {
     try {
       const v = JSON.parse(l);
       return v && typeof v === "object" && typeof v.reason === "string" ? v : { reason: null };
@@ -396,7 +454,7 @@ function lockRefusal(dir, opts) {
   const existing = readPid(dir);
   const state = ownerState(existing, opts);
   if (state === "absent") return new DiscordError(`run.lock exists without an owner record: a start is in progress or was interrupted; ${UNLOCK_HINT}`, BRAKE_EXIT);
-  if (state === "invalid") return new DiscordError(`run.lock has an owner record that cannot be read; refusing. Inspect ${ownerPath(dir)} by hand`, BRAKE_EXIT);
+  if (state === "invalid") return new DiscordError(`run.lock has an owner record that cannot be read; refusing. Inspect run.lock/owner.json in ${journalLabel(dir)} by hand`, BRAKE_EXIT);
   if (state === "live") return new DiscordError(`another connector is running for this binding (pid ${existing.pid})`, BRAKE_EXIT);
   if (state === "unknown") return new DiscordError(`run.lock belongs to pid ${existing.pid}, which is alive but whose identity cannot be verified; refusing`, BRAKE_EXIT);
   return new DiscordError(`run.lock belongs to pid ${existing.pid}, which is gone or is a different process now; ${UNLOCK_HINT}`, BRAKE_EXIT);
@@ -409,17 +467,21 @@ export function writePid(dir, pid, { now = Date.now(), identity = identityOf } =
   try {
     mkdirSync(lock, { mode: 0o700 });
   } catch (err) {
-    if (err.code !== "EEXIST") throw err;
+    if (err.code !== "EEXIST") throw quietFs(err, `run.lock in ${journalLabel(dir)}`, "create");
     throw lockRefusal(dir, { identity });
   }
   const tmp = join(lock, "owner.json.tmp");
-  writeFileSync(tmp, JSON.stringify({ pid, start, boot, at: new Date(now).toISOString() }) + "\n", { mode: 0o600 });
-  renameSync(tmp, ownerPath(dir));
+  try {
+    writeFileSync(tmp, JSON.stringify({ pid, start, boot, at: new Date(now).toISOString() }) + "\n", { mode: 0o600 });
+    renameSync(tmp, ownerPath(dir));
+  } catch (e) {
+    throw quietFs(e, `run.lock/owner.json in ${journalLabel(dir)}`, "write");
+  }
   // The gate: STOP written before this point (by `stop` or `unlock`) means
   // this claim must not stand, however it interleaved with an unlock.
   if (stopRequested(dir)) {
     clearPid(dir, pid);
-    throw new DiscordError(`STOP is present in ${dir}; remove it to run`, BRAKE_EXIT);
+    throw new DiscordError(`STOP is present in ${journalLabel(dir)}; remove it to run`, BRAKE_EXIT);
   }
 }
 
@@ -439,9 +501,9 @@ export function unlock(dir, { beforeRemove = null, identity = identityOf, reason
   const state = ownerState(rec, { identity });
   if (state === "live") throw new DiscordError(`refusing to unlock: the connector is running (pid ${rec.pid}); use stop, and unlock only a lock whose owner is gone`, 1);
   if (state === "unknown") throw new DiscordError(`refusing to unlock: pid ${rec.pid} is alive and its identity cannot be verified; nothing removed. Stop that process first`, 1);
-  if (state === "invalid") throw new DiscordError(`refusing to unlock: the owner record cannot be read; nothing removed. Inspect ${ownerPath(dir)} by hand`, 1);
+  if (state === "invalid") throw new DiscordError(`refusing to unlock: the owner record cannot be read; nothing removed. Inspect run.lock/owner.json in ${journalLabel(dir)} by hand`, 1);
   if (beforeRemove) beforeRemove();
-  rmSync(lock, { recursive: true, force: true, maxRetries: 10, retryDelay: 20 });
+  removeLock(dir, { maxRetries: 10, retryDelay: 20 });
   return rec;
 }
 
@@ -468,14 +530,14 @@ export function unlock(dir, { beforeRemove = null, identity = identityOf, reason
 export function recover(dir, { identity = identityOf, beforeRemove = null } = {}) {
   const ours = (lines) => lines.length === 1 && lines[0].reason === RECOVER_REASON;
   if (stopRequested(dir)) {
-    if (!ours(readStop(dir))) throw new DiscordError(`STOP is present in ${dir}; the brake is on. Remove it to run`, BRAKE_EXIT);
+    if (!ours(readStop(dir))) throw new DiscordError(`STOP is present in ${journalLabel(dir)}; the brake is on. Remove it to run`, BRAKE_EXIT);
     clearStop(dir);
   }
   if (!existsSync(lockPath(dir))) return "clean";
   const state = ownerState(readPid(dir), { identity });
   if (state === "live" || state === "unknown" || state === "invalid") throw lockRefusal(dir, { identity });
   unlock(dir, { identity, reason: RECOVER_REASON, beforeRemove });
-  if (!ours(readStop(dir))) throw new DiscordError(`STOP was written by an operator while recovering ${dir}; the brake stays. Remove it to run`, BRAKE_EXIT);
+  if (!ours(readStop(dir))) throw new DiscordError(`STOP was written by an operator while recovering ${journalLabel(dir)}; the brake stays. Remove it to run`, BRAKE_EXIT);
   clearStop(dir);
   return "cleared";
 }
@@ -489,7 +551,15 @@ export function stopTarget(dir, opts) {
 
 export function clearPid(dir, pid) {
   const rec = readPid(dir);
-  if (rec !== null && !rec.invalid && rec.pid === pid) rmSync(lockPath(dir), { recursive: true, force: true });
+  if (rec !== null && !rec.invalid && rec.pid === pid) removeLock(dir);
+}
+
+function removeLock(dir, retry = {}) {
+  try {
+    rmSync(lockPath(dir), { recursive: true, force: true, ...retry });
+  } catch (e) {
+    throw quietFs(e, `run.lock in ${journalLabel(dir)}`, "remove");
+  }
 }
 
 // --- reloads ---
diff --git a/packages/discord/src/setspark.mjs b/packages/discord/src/setspark.mjs
index 41b0c95de..aceabe88c 100644
--- a/packages/discord/src/setspark.mjs
+++ b/packages/discord/src/setspark.mjs
@@ -28,6 +28,7 @@
 import { lstatSync, readFileSync } from "node:fs";
 import { request as httpsRequest } from "node:https";
 import { request as httpRequest } from "node:http";
+import { plainKey, quietRead } from "./errors.mjs";
 
 export const SETSPARK_DEFAULTS = Object.freeze({ timeoutMs: 15000, maxResponseBytes: 262144 });
 export const USER_AGENT = "mosaic-discord-sage/1 (Mosaic Stack Discord connector; setspark client)";
@@ -69,7 +70,7 @@ const isObject = (v) => v !== null && typeof v === "object" && !Array.isArray(v)
 export function loadSetsparkConfig(raw, where = "setspark") {
   if (!isObject(raw)) throw new Error(`${where}: not an object`);
   for (const k of Object.keys(raw)) {
-    if (!["baseUrl", "keyFile", "principal", "timeoutMs", "approvers"].includes(k)) throw new Error(`${where}: unknown key ${JSON.stringify(k)}`);
+    if (!["baseUrl", "keyFile", "principal", "timeoutMs", "approvers"].includes(k)) throw new Error(`${where}: unknown key ${plainKey(k)}`);
   }
   if (typeof raw.baseUrl !== "string") throw new Error(`${where}.baseUrl: must be a url string`);
   let u;
@@ -108,12 +109,12 @@ function checkPrivateFile(path, what) {
   try {
     st = lstatSync(path);
   } catch {
-    throw new Error(`${what}: not found: ${path}`);
+    throw new Error(`${what}: not found`);
   }
-  if (st.isSymbolicLink()) throw new Error(`${what}: must not be a symlink: ${path}`);
-  if (!st.isFile()) throw new Error(`${what}: not a regular file: ${path}`);
-  if ((st.mode & 0o777) !== 0o600) throw new Error(`${what}: must be mode 0600: ${path}`);
-  if (st.size === 0) throw new Error(`${what}: is empty: ${path}`);
+  if (st.isSymbolicLink()) throw new Error(`${what}: must not be a symlink`);
+  if (!st.isFile()) throw new Error(`${what}: not a regular file`);
+  if ((st.mode & 0o777) !== 0o600) throw new Error(`${what}: must be mode 0600`);
+  if (st.size === 0) throw new Error(`${what}: is empty`);
 }
 
 // Read the key for one call. The file is re-checked every time, so a key
@@ -132,7 +133,14 @@ export function readKey(config) {
     throw new SetsparkRefusal(SETSPARK_REFUSAL.KEY_FILE);
   }
   if (st.size > KEY_MAX_BYTES) throw new SetsparkRefusal(SETSPARK_REFUSAL.KEY_SHAPE);
-  const text = readFileSync(config.keyFile, "utf8");
+  // A file that changes after its checks fails with a native error that carries the path: it
+  // keeps its type and code and names the field (#1873).
+  let text;
+  try {
+    text = readFileSync(config.keyFile, "utf8");
+  } catch (e) {
+    throw quietRead(e, "keyFile");
+  }
   // Either one bare key line, or the mint's own JSON output
   // ({"key_id", "key", "note"}) stored as is; only "key" is used.
   let key = text;
diff --git a/packages/discord/tests/binding.test.mjs b/packages/discord/tests/binding.test.mjs
index 0e6b07df8..4d5816c9d 100644
--- a/packages/discord/tests/binding.test.mjs
+++ b/packages/discord/tests/binding.test.mjs
@@ -177,7 +177,8 @@ test("cli: check refuses a missing context file and a missing binding with exit
   assert.match(r.stderr, /missing context file/);
   r = runCli(["check", "other-seat", "--config", dep.config, "--repo", repo]);
   assert.equal(r.status, 2);
-  assert.match(r.stderr, /binding not found/);
+  assert.match(r.stderr, /binding other-seat not found/);
+  assert.ok(!r.stderr.includes(root), r.stderr);
   r = runCli(["check"]);
   assert.equal(r.status, 4);
   r = runCli(["frobnicate", "x"]);
diff --git a/packages/discord/tests/connector.test.mjs b/packages/discord/tests/connector.test.mjs
index a12018c33..f8aab191d 100644
--- a/packages/discord/tests/connector.test.mjs
+++ b/packages/discord/tests/connector.test.mjs
@@ -230,7 +230,7 @@ test("restart: an inbox with three ids and a replay of the same three produces z
 test("stop: STOP present refuses start; STOP written while running refuses new turns and the current one finishes", async () => {
   const { journalDir, rest, engine, connector } = setup({ replies: [{ text: "done", delayMs: 30 }] });
   requestStop(journalDir, "test");
-  await assert.rejects(connector.start(), /STOP is present/);
+  await assert.rejects(connector.start(), (err) => /STOP is present/.test(err.message) && !err.message.includes(journalDir));
   assert.equal(engine.started, false);
   writeFileSync(join(journalDir, "STOP"), ""); // still present; clear it
   const { unlinkSync } = await import("node:fs");
diff --git a/packages/discord/tests/native-fs-labels.test.mjs b/packages/discord/tests/native-fs-labels.test.mjs
new file mode 100644
index 000000000..93deda873
--- /dev/null
+++ b/packages/discord/tests/native-fs-labels.test.mjs
@@ -0,0 +1,225 @@
+// #1873 (redact6, re-check 2): a native fs error never prints its path. The journal and
+// approvals readers and writers name the file by label at the source, and the CLI's
+// top-level handler prints any native error that slipped through as its call and code
+// only. The sentinel is a component of every scratch path, so an error message that
+// quotes a path quotes the sentinel too.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import fs, { existsSync, mkdtempSync, mkdirSync, writeFileSync, rmSync } from 'node:fs';
+import { syncBuiltinESMExports } from 'node:module';
+import { spawnSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { appendApproval } from '../src/approvals.mjs';
+import { DiscordError } from '../src/errors.mjs';
+import {
+  appendInbox, clearStop, ensureJournal, listTurns, lockPath, readTurn, recover, requestStop, stopPath, turnPath, writePid, writeTurn,
+} from '../src/journal.mjs';
+import { makeDeployment, makeRepo } from './helpers.mjs';
+import { initializeControl } from '../../processing-control/src/state.mjs';
+
+const secret = 'sk-test-NOT-A-SECRET-1234';
+const cli = fileURLToPath(new URL('../src/cli.mjs', import.meta.url));
+
+// A journal directory named like a binding, under a sentinel path component, so its
+// label is "discord/seat under the data root".
+function scratch(t) {
+  const root = mkdtempSync(join(tmpdir(), 'r6n-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+  const dir = join(root, secret, 'seat');
+  mkdirSync(dir, { recursive: true });
+  return { root, dir };
+}
+const where = 'discord/seat under the data root';
+function quiet(text, root) {
+  assert.ok(text.includes(root) === false, text);
+  assert.doesNotMatch(text, /sk-test|NOT-A-SECRET/);
+}
+function labelled(label, root) {
+  return error => {
+    assert.ok(error instanceof Error, String(error));
+    assert.equal(error instanceof DiscordError, false, 'a native fs error keeps its type');
+    assert.ok(error.message.includes(label), error.message);
+    quiet(error.message, root);
+    return true;
+  };
+}
+
+// Swap one node:fs function so the target goes away right before the real call, which
+// then fails with a genuine error that names the path. One swap per test.
+function race(t, fn, target, remove) {
+  const original = fs[fn];
+  const swapped = function (p, ...rest) {
+    if (String(p) === target) remove();
+    return original.call(this, p, ...rest);
+  };
+  if (original.native) swapped.native = original.native;
+  fs[fn] = swapped;
+  syncBuiltinESMExports();
+  t.after(() => {
+    fs[fn] = original;
+    syncBuiltinESMExports();
+  });
+}
+
+// --- the four named sites ---
+
+test('recover: a STOP removed between its check and its read names STOP in the journal', t => {
+  const { root, dir } = scratch(t);
+  ensureJournal(dir);
+  writeFileSync(stopPath(dir), JSON.stringify({ at: new Date().toISOString(), reason: 'cli stop' }) + '\n', { mode: 0o600 });
+  race(t, 'readFileSync', stopPath(dir), () => rmSync(stopPath(dir)));
+  assert.throws(() => recover(dir), labelled(`cannot read STOP in ${where} (ENOENT)`, root));
+});
+
+test('readTurn: a turn record removed before its read names the turn by id', t => {
+  const { root, dir } = scratch(t);
+  ensureJournal(dir);
+  writeTurn(dir, 't1', { startedAt: new Date().toISOString() });
+  race(t, 'readFileSync', turnPath(dir, 't1'), () => rmSync(turnPath(dir, 't1')));
+  assert.throws(() => readTurn(dir, 't1'), labelled('cannot read turn record t1 (ENOENT)', root));
+});
+
+test('listTurns: a turns directory removed between its check and its listing names the turns directory', t => {
+  const { root, dir } = scratch(t);
+  ensureJournal(dir);
+  const turns = join(dir, 'turns');
+  race(t, 'readdirSync', turns, () => rmSync(turns, { recursive: true }));
+  assert.throws(() => listTurns(dir), labelled(`cannot read the turns directory in ${where} (ENOENT)`, root));
+});
+
+test('listTurns: a turn record removed between the listing and its read names the turn by id', t => {
+  const { root, dir } = scratch(t);
+  ensureJournal(dir);
+  writeTurn(dir, 't1', { startedAt: new Date().toISOString() });
+  race(t, 'readFileSync', turnPath(dir, 't1'), () => rmSync(turnPath(dir, 't1')));
+  assert.throws(() => listTurns(dir), labelled('cannot read turn record t1 (ENOENT)', root));
+});
+
+test("run: a session directory removed between its check and its stat names the binding's session directory", async t => {
+  const { root, dir } = scratch(t);
+  const { sessionContinues } = await import('../src/engine-pi.mjs');
+  assert.equal(typeof sessionContinues, 'function', 'engine-pi.mjs exports sessionContinues');
+  const session = join(dir, 'session');
+  assert.equal(sessionContinues(session), false, 'no directory: a new session');
+  mkdirSync(session);
+  assert.equal(sessionContinues(session), false, 'an empty directory: a new session');
+  writeFileSync(join(session, 'a.jsonl'), '');
+  assert.equal(sessionContinues(session), true, 'a .jsonl file: the session continues');
+  race(t, 'statSync', session, () => rmSync(session, { recursive: true }));
+  assert.throws(() => sessionContinues(session), labelled("cannot stat the binding's session directory (ENOENT)", root));
+});
+
+// --- journal and approvals writers (the connector logs err.message at runtime) ---
+
+test('a journal line that cannot be appended names the journal file, never its path', t => {
+  const { root, dir } = scratch(t);
+  ensureJournal(dir);
+  mkdirSync(join(dir, 'inbox.jsonl'));
+  assert.throws(() => appendInbox(dir, { id: '1' }), labelled('cannot append to inbox.jsonl (EISDIR)', root));
+});
+
+test('an approvals line that cannot be appended names approvals.jsonl, never its path', t => {
+  const { root, dir } = scratch(t);
+  ensureJournal(dir);
+  mkdirSync(join(dir, 'approvals.jsonl'));
+  assert.throws(() => appendApproval(dir, { kind: 'opened' }), labelled('cannot append to approvals.jsonl (EISDIR)', root));
+});
+
+test('a turn record that cannot be created names the turn by id; an existing one keeps its refusal', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => writeTurn(dir, 't1', {}), labelled('cannot write turn record t1 (ENOENT)', root));
+  ensureJournal(dir);
+  writeTurn(dir, 't1', {});
+  assert.throws(() => writeTurn(dir, 't1', {}), e => e instanceof DiscordError && e.exitCode === 1 && /turn record already exists: t1/.test(e.message));
+});
+
+test('a STOP that cannot be written names STOP in the journal; the lock is released', t => {
+  const { root, dir } = scratch(t);
+  mkdirSync(stopPath(dir));
+  assert.throws(() => requestStop(dir, 'cli stop'), labelled(`cannot write STOP in ${where} (EISDIR)`, root));
+  assert.equal(existsSync(join(dir, '.stop.lock')), false);
+});
+
+test('a STOP removed between its check and its removal names STOP in the journal', t => {
+  const { root, dir } = scratch(t);
+  writeFileSync(stopPath(dir), '{}\n', { mode: 0o600 });
+  race(t, 'unlinkSync', stopPath(dir), () => rmSync(stopPath(dir)));
+  assert.throws(() => clearStop(dir), labelled(`cannot remove STOP in ${where} (ENOENT)`, root));
+});
+
+test('a run.lock that cannot be created names run.lock in the journal', t => {
+  const { root, dir } = scratch(t);
+  const gone = join(dir, 'gone');
+  assert.throws(() => writePid(gone, process.pid), e => {
+    assert.ok(e.message.includes('cannot create run.lock in discord/gone under the data root (ENOENT)'), e.message);
+    quiet(e.message, root);
+    return true;
+  });
+  assert.equal(existsSync(lockPath(gone)), false);
+});
+
+test('engine: a pi that cannot be spawned is logged and recorded as "cannot spawn pi", never its path', async t => {
+  const { root, dir } = scratch(t);
+  const { createEngine } = await import('../src/engine-pi.mjs');
+  const logs = [];
+  let exited = null;
+  const engine = createEngine({ command: join(dir, 'pi'), args: [], cwd: dir, env: {}, log: (m) => logs.push(m), onExit: (e) => (exited = e) });
+  engine.start();
+  for (let i = 0; i < 200 && exited === null; i += 1) await new Promise((res) => setTimeout(res, 10));
+  assert.ok(exited, 'the spawn error reached onExit');
+  assert.equal(exited.error, 'cannot spawn pi (ENOENT)');
+  assert.ok(logs.includes('engine spawn error: cannot spawn pi (ENOENT)'), logs.join('\n'));
+  quiet(JSON.stringify({ logs, exited }), root);
+});
+
+// --- the choke point ---
+
+test('printable: a native error prints its call and code, a refusal or a labelled error its own message', async () => {
+  const { printable, quietRead } = await import('../src/errors.mjs');
+  assert.equal(typeof printable, 'function', 'errors.mjs exports printable');
+  const path = `/x/${secret}/discord/seat/STOP`;
+  const native = Object.assign(new Error(`ENOENT: no such file or directory, open '${path}'`), { code: 'ENOENT', syscall: 'open', path, errno: -2 });
+  assert.equal(printable(native), 'cannot open a discord file (ENOENT)');
+  const pathOnly = Object.assign(new Error(`EACCES ${path}`), { code: 'EACCES', path });
+  assert.equal(printable(pathOnly), 'cannot access a discord file (EACCES)');
+  const spawn = Object.assign(new Error(`spawn ${path} ENOENT`), { code: 'ENOENT', syscall: `spawn ${path}`, path });
+  assert.equal(printable(spawn), 'cannot spawn a discord file (ENOENT)');
+  const net = Object.assign(new Error('connect ECONNREFUSED 127.0.0.1:1'), { code: 'ECONNREFUSED', syscall: 'connect' });
+  assert.equal(printable(net), 'cannot connect (ECONNREFUSED)');
+  const odd = Object.assign(new Error(path), { code: `X ${path}`, syscall: path, path });
+  assert.equal(printable(odd), 'cannot access a discord file (UNKNOWN)');
+  const labelledRead = quietRead(Object.assign(new Error(path), { code: 'ENOENT', syscall: 'open', path }), 'token file');
+  assert.equal(printable(labelledRead), 'cannot read token file (ENOENT)');
+  assert.equal(printable(new DiscordError('STOP is present in discord/seat under the data root; remove it to run', 3)), 'STOP is present in discord/seat under the data root; remove it to run');
+  assert.equal(printable(new Error('plain refusal')), 'plain refusal');
+  for (const v of [native, pathOnly, spawn, odd]) assert.doesNotMatch(printable(v), /sk-test|NOT-A-SECRET/);
+});
+
+test('cli: a native fs error reaching the top-level handler prints its call and code, never the path, and exits 1', t => {
+  const { root } = scratch(t);
+  const base = join(root, secret, 'dep');
+  mkdirSync(base, { recursive: true });
+  const repo = makeRepo(base);
+  const dep = makeDeployment(base);
+  initializeControl(dep.dataRoot);
+  const run = (args) => spawnSync(process.execPath, [cli, ...args, '--config', dep.config, '--repo', repo], { encoding: 'utf8' });
+
+  // stop: the journal directory is a regular file, so ensureJournal's mkdir fails.
+  writeFileSync(dep.journalDir, 'not a directory');
+  let r = run(['stop', 'test-seat']);
+  assert.equal(r.status, 1, r.stderr);
+  assert.equal(r.stderr, 'discord: cannot mkdir a discord file (ENOTDIR)\n');
+  quiet(r.stderr + r.stdout, root);
+  rmSync(dep.journalDir);
+
+  // run: the sessions directory is a regular file, so the claimed run's mkdir fails
+  // after the claim; the claim is released and the exit stays 1.
+  writeFileSync(join(dep.dataRoot, 'sessions'), 'not a directory');
+  r = run(['run', 'test-seat']);
+  assert.equal(r.status, 1, r.stderr);
+  assert.equal(r.stderr, 'discord: cannot mkdir a discord file (ENOTDIR)\n');
+  quiet(r.stderr + r.stdout, root);
+  assert.equal(existsSync(lockPath(dep.journalDir)), false, 'the claim is released');
+});
diff --git a/packages/discord/tests/notify.test.mjs b/packages/discord/tests/notify.test.mjs
index f793eeaa0..024aaa88e 100644
--- a/packages/discord/tests/notify.test.mjs
+++ b/packages/discord/tests/notify.test.mjs
@@ -75,6 +75,6 @@ test("notify: no dmRecipient, a non-0600 binding or token, or a missing binding
   assert.throws(() => openDirect({ dataRoot: none.dataRoot, name: "test-seat", fetch }), (e) => e instanceof DiscordError && e.exitCode === 2 && /no dmRecipient/.test(e.message));
   const loose = makeDeployment(makeRoot(), { dmRecipient: IDS.owner }, { tokenMode: 0o644 });
   assert.throws(() => openDirect({ dataRoot: loose.dataRoot, name: "test-seat", fetch }), (e) => e instanceof DiscordError && /mode 0600/.test(e.message) && !e.message.includes(TOKEN));
-  assert.throws(() => openDirect({ dataRoot: none.dataRoot, name: "absent", fetch }), (e) => e instanceof DiscordError && /binding not found/.test(e.message));
+  assert.throws(() => openDirect({ dataRoot: none.dataRoot, name: "absent", fetch }), (e) => e instanceof DiscordError && /binding absent not found/.test(e.message) && !e.message.includes(none.dataRoot));
   assert.equal(calls, 0);
 });
diff --git a/packages/discord/tests/path-redaction-labels.test.mjs b/packages/discord/tests/path-redaction-labels.test.mjs
new file mode 100644
index 000000000..46a8a74e6
--- /dev/null
+++ b/packages/discord/tests/path-redaction-labels.test.mjs
@@ -0,0 +1,204 @@
+// #1873 (redact6): a discord refusal names the file, field or binding, never a host path.
+// The sentinel is a component of every scratch path, so a refusal that quotes a path
+// quotes the sentinel too; each test also checks the scratch root and the label.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import fs, { mkdtempSync, mkdirSync, writeFileSync, rmSync } from 'node:fs';
+import { syncBuiltinESMExports } from 'node:module';
+import { readApprovals } from '../src/approvals.mjs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { DiscordError } from '../src/errors.mjs';
+import { bindingDataDir, bindingPath, loadDataRoot, readToken, resolveContextFiles, resolveToolRoots, validateBinding } from '../src/binding.mjs';
+import { ensureJournal, lockPath, ownerPath, readInboxIds, recover, requestStop, turnPath, unlock, writeTurn } from '../src/journal.mjs';
+import { gitPull, loadGitConfig } from '../src/git.mjs';
+import { loadSetsparkConfig, readKey } from '../src/setspark.mjs';
+
+const secret = 'sk-test-NOT-A-SECRET-1234';
+function scratch(t) {
+  const root = mkdtempSync(join(tmpdir(), 'r6-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+  const dir = join(root, secret);
+  mkdirSync(dir);
+  return { root, dir };
+}
+function labelled(label, root, Type = DiscordError) {
+  return error => {
+    assert.ok(error instanceof Type, error.stack);
+    assert.ok(error.message.includes(label), error.message);
+    assert.ok(!error.message.includes(root), error.message);
+    assert.doesNotMatch(error.message, /sk-test|NOT-A-SECRET/);
+    return true;
+  };
+}
+
+test('config not found names the config, not its path', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => loadDataRoot(join(dir, 'config.json')), labelled('config not found', root));
+});
+
+test('token file refusals name the token file, not its path', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => readToken({ tokenFile: join(dir, 'token') }), labelled('token file not found', root));
+  const short = join(dir, 'short');
+  writeFileSync(short, 'x', { mode: 0o600 });
+  assert.throws(() => readToken({ tokenFile: short }), labelled('token file does not hold a bot token', root));
+  const open = join(dir, 'open');
+  writeFileSync(open, 'x'.repeat(30), { mode: 0o644 });
+  assert.throws(() => readToken({ tokenFile: open }), labelled('token file must be mode 0600, is 0644', root));
+});
+
+test('a context file refusal names its index in context.files', t => {
+  const { root, dir } = scratch(t);
+  const repo = join(dir, 'repo');
+  mkdirSync(repo);
+  assert.throws(() => resolveContextFiles({ context: { files: [join(dir, 'abs.md')] } }, repo), labelled('context file must be repository-relative: context.files[0]', root));
+  assert.throws(() => resolveContextFiles({ context: { files: ['ok.md', `${secret}.md`] } }, repo), labelled('missing context file: context.files[0]', root));
+});
+
+test('a tool root refusal names the root, not its path', t => {
+  const { root, dir } = scratch(t);
+  const binding = { tools: { roots: [{ name: 'docs', path: join(dir, 'docs'), write: false }] } };
+  assert.throws(() => resolveToolRoots(binding, { dataRoot: join(dir, 'data') }), labelled('tool root docs does not exist', root));
+  mkdirSync(join(dir, 'data', 'docs'), { recursive: true });
+  binding.tools.roots[0].path = join(dir, 'data', 'docs');
+  assert.throws(() => resolveToolRoots(binding, { dataRoot: join(dir, 'data') }), labelled('tool root docs overlaps the data root', root));
+});
+
+test('git and setspark key file refusals name the field', t => {
+  const { root, dir } = scratch(t);
+  const git = { branch: 'main', identity: 'sage', tokenFile: join(dir, 'gitea'), author: 'Sage <sage@mosaicstack.dev>' };
+  assert.throws(() => loadGitConfig(git, 'tools.roots[0].git'), labelled('tools.roots[0].git.tokenFile: not found', root, Error));
+  const setspark = { baseUrl: 'https://setspark.example', keyFile: join(dir, 'key'), principal: 'sage' };
+  assert.throws(() => loadSetsparkConfig(setspark), labelled('setspark.keyFile: not found', root, Error));
+});
+
+for (const [name, label] of [['bot', 'discord/bot under the data root'], [secret, "the binding's journal directory"]]) {
+  test(`journal refusals name ${label}`, t => {
+    const { root, dir } = scratch(t);
+    const journal = join(dir, name);
+    ensureJournal(journal);
+    requestStop(journal, 'operator');
+    assert.throws(() => recover(journal), labelled(`STOP is present in ${label}`, root));
+    rmSync(join(journal, 'STOP'));
+    mkdirSync(lockPath(journal));
+    writeFileSync(ownerPath(journal), secret, { mode: 0o600 });
+    assert.throws(() => unlock(journal), labelled(`Inspect run.lock/owner.json in ${label} by hand`, root));
+    writeTurn(journal, 't1', {});
+    assert.throws(() => writeTurn(journal, 't1', {}), labelled('turn record already exists: t1', root));
+  });
+}
+
+// Review round (#1873): keys, names, read errors and git output that could carry a host path.
+test('an unknown key that is not a plain name is described, never echoed; a plain one is still quoted', t => {
+  const { root, dir } = scratch(t);
+  const doc = { [join(dir, 'host')]: 1 };
+  assert.throws(() => validateBinding(doc), labelled('unknown key that is not a plain name', root));
+  assert.throws(() => loadGitConfig(doc, 'tools.roots[0].git'), labelled('tools.roots[0].git: unknown key that is not a plain name', root, Error));
+  assert.throws(() => loadSetsparkConfig(doc, 'setspark'), labelled('setspark: unknown key that is not a plain name', root, Error));
+  assert.throws(() => validateBinding({ colour: 1 }), labelled('unknown key "colour"', root));
+});
+
+test('an invalid binding name or turn id states the constraint, never the value, and keeps its exit', t => {
+  const { root, dir } = scratch(t);
+  for (const f of [bindingPath, bindingDataDir]) {
+    assert.throws(() => f(dir, join(dir, 'bad')), e => labelled('invalid binding name (lowercase letters, digits, ., _ or -, at most 64)', root)(e) && e.exitCode === 4);
+  }
+  assert.throws(() => turnPath(dir, join(dir, 'bad')), e => labelled('invalid turn id (letters, digits, ., _ or -, at most 128)', root)(e) && e.exitCode === 1);
+});
+
+test('an unreadable journal or approvals file, or a missing repository, names the file and code, never the path', t => {
+  const { root, dir } = scratch(t);
+  writeFileSync(join(dir, 'approvals.jsonl'), '{}\n', { mode: 0o000 });
+  writeFileSync(join(dir, 'inbox.jsonl'), '{}\n', { mode: 0o000 });
+  assert.throws(() => readApprovals(dir), e => labelled('cannot read approvals.jsonl (EACCES)', root, Error)(e) && e.code === 'EACCES' && !(e instanceof DiscordError));
+  assert.throws(() => readInboxIds(dir), e => labelled('cannot read inbox.jsonl (EACCES)', root, Error)(e) && e.code === 'EACCES');
+  assert.throws(() => resolveContextFiles({ context: { files: ['x'] } }, join(dir, 'missing')), e => labelled('cannot read the repository (ENOENT)', root, Error)(e) && e.code === 'ENOENT');
+});
+
+test('a git refusal drops stderr lines that carry a host path and a spawn failure names only its code', t => {
+  const { root, dir } = scratch(t);
+  const rootCfg = { real: dir, name: 'docs', git: { branch: 'main', identity: 'sage', tokenFile: join(dir, 'never-read'), author: { name: 'Sage', email: 'sage@example.test' } } };
+  let calls = 0;
+  const spawn = () => ++calls === 1 ? { status: 0, stdout: 'main\n', stderr: '' } : { status: 128, stdout: '', stderr: `fatal: cannot access ${join(dir, 'repo')}\n` };
+  assert.throws(() => gitPull(rootCfg, { spawn }), e => {
+    assert.equal(e.reason, 'that root has no git');
+    assert.equal(e.message, e.reason);
+    assert.ok(!e.detail, String(e.detail));
+    return labelled(e.reason, root, Error)(e);
+  });
+  assert.equal(calls, 2);
+  // A repo-relative line survives: the detail still says what git said.
+  calls = 0;
+  const kept = () => ++calls === 1 ? { status: 0, stdout: 'main\n', stderr: '' } : { status: 128, stdout: '', stderr: `fatal: not a git repository: .git\n` };
+  assert.throws(() => gitPull(rootCfg, { spawn: kept }), e => e.detail === 'fatal: not a git repository: .git');
+  const failed = () => ({ error: Object.assign(new Error(`spawn ${join(dir, 'git')} ENOENT`), { code: 'ENOENT' }) });
+  assert.throws(() => gitPull(rootCfg, { spawn: failed }), e => labelled('git could not start (ENOENT)', root, Error)(e));
+});
+
+// Re-check (#1873): a file removed between its check and its read surfaces a native
+// error. Each site names the file by label and code; the error's path never reaches the
+// message. `race` swaps one node:fs function so the target goes away right before the
+// real call, which then fails with a genuine ENOENT that names the path.
+function race(t, fn, target, remove) {
+  const original = fs[fn];
+  const swapped = function (p, ...rest) {
+    if (String(p) === target) remove();
+    return original.call(this, p, ...rest);
+  };
+  if (original.native) swapped.native = original.native;
+  fs[fn] = swapped;
+  syncBuiltinESMExports();
+  t.after(() => {
+    fs[fn] = original;
+    syncBuiltinESMExports();
+  });
+}
+
+test('a token file removed between its check and its read names the token file', t => {
+  const { root, dir } = scratch(t);
+  const tokenFile = join(dir, 'token');
+  writeFileSync(tokenFile, 'x'.repeat(30), { mode: 0o600 });
+  race(t, 'readFileSync', tokenFile, () => rmSync(tokenFile));
+  assert.throws(() => readToken({ tokenFile }), labelled('cannot read token file (ENOENT)', root, Error));
+});
+
+test('a context file removed between its check and its realpath names its index', t => {
+  const { root, dir } = scratch(t);
+  const repo = join(dir, 'repo');
+  mkdirSync(repo);
+  writeFileSync(join(repo, 'ok.md'), 'ok');
+  writeFileSync(join(repo, `${secret}.md`), 'x');
+  const target = join(repo, `${secret}.md`);
+  race(t, 'realpathSync', target, () => rmSync(target));
+  assert.throws(() => resolveContextFiles({ context: { files: ['ok.md', `${secret}.md`] } }, repo), labelled('cannot read context file context.files[1] (ENOENT)', root, Error));
+});
+
+test('a tool root removed between its check and its realpath names the root', t => {
+  const { root, dir } = scratch(t);
+  const docs = join(dir, 'docs');
+  mkdirSync(docs);
+  const binding = { tools: { roots: [{ name: 'docs', path: docs, write: false }] } };
+  race(t, 'realpathSync', docs, () => rmSync(docs, { recursive: true }));
+  assert.throws(() => resolveToolRoots(binding, { dataRoot: join(dir, 'data') }), labelled('cannot read tool root docs (ENOENT)', root, Error));
+});
+
+test('a data root removed between its check and its realpath names the data root', t => {
+  const { root, dir } = scratch(t);
+  const docs = join(dir, 'docs');
+  mkdirSync(docs);
+  const binding = { tools: { roots: [{ name: 'docs', path: docs, write: false }] } };
+  const data = join(dir, 'data');
+  mkdirSync(data);
+  race(t, 'realpathSync', data, () => rmSync(data, { recursive: true }));
+  assert.throws(() => resolveToolRoots(binding, { dataRoot: data }), labelled('cannot read the data root (ENOENT)', root, Error));
+});
+
+test('a setspark key file removed between its check and its read names keyFile', t => {
+  const { root, dir } = scratch(t);
+  const keyFile = join(dir, 'key');
+  writeFileSync(keyFile, 'ssk_' + 'a'.repeat(40), { mode: 0o600 });
+  const config = loadSetsparkConfig({ baseUrl: 'https://setspark.example', keyFile, principal: 'sage' });
+  race(t, 'readFileSync', keyFile, () => rmSync(keyFile));
+  assert.throws(() => readKey(config), labelled('cannot read keyFile (ENOENT)', root, Error));
+});
diff --git a/packages/discord/tests/refusal-redaction.test.mjs b/packages/discord/tests/refusal-redaction.test.mjs
index 12ad349be..415628cf6 100644
--- a/packages/discord/tests/refusal-redaction.test.mjs
+++ b/packages/discord/tests/refusal-redaction.test.mjs
@@ -6,10 +6,13 @@ import { dirname, join } from 'node:path';
 const secret = 'sk-test-NOT-A-SECRET-1234';
 // JSON.parse quotes a prefix near this fault on Node 26; check partial leaks too.
 const malformed = secret;
+// #1873: the sentinel is a path component, so a refusal that quotes a path quotes it too.
 function scratch(t) {
   const root = mkdtempSync(join(tmpdir(), 'r3-'));
   t.after(() => rmSync(root, { recursive: true, force: true }));
-  return root;
+  const dir = join(root, secret);
+  mkdirSync(dir);
+  return dir;
 }
 function write(file, text = malformed) {
   mkdirSync(dirname(file), { recursive: true });
@@ -21,6 +24,7 @@ function safe(label, ErrorType, properties = {}) {
     assert.ok(error instanceof ErrorType);
     for (const [key, value] of Object.entries(properties)) assert.equal(error[key], value);
     assert.ok(error.message.includes(label), error.message);
+    assert.ok(!error.message.includes(tmpdir()), error.message);
     assert.doesNotMatch(error.message, /sk-test|Unexpected token/);
     assert.doesNotMatch(error.stack, /sk-test/);
     assert.equal(error.cause, undefined);
@@ -33,15 +37,15 @@ import { readApprovals } from '../src/approvals.mjs';
 import { readInboxIds } from '../src/journal.mjs';
 import extension from '../extension/tools.mjs';
 import { TOOLS_ENV } from '../src/tools.mjs';
-for (const [name, read, relative] of [
-  ['config', (file) => loadDataRoot(file), 'config.json'],
-  ['binding', (file) => loadBinding(file), 'binding.json'],
-  ['approvals', (_file, root) => readApprovals(root), 'approvals.jsonl'],
-  ['journal', (_file, root) => readInboxIds(root), 'inbox.jsonl'],
+for (const [name, read, relative, label] of [
+  ['config', (file) => loadDataRoot(file), 'config.json', 'config is not valid JSON'],
+  ['binding', (file) => loadBinding(file), 'binding.json', 'binding binding is not valid JSON'],
+  ['approvals', (_file, root) => readApprovals(root), 'approvals.jsonl', 'approvals.jsonl:2: not valid JSON'],
+  ['journal', (_file, root) => readInboxIds(root), 'inbox.jsonl', 'inbox.jsonl:2: not valid JSON'],
 ]) test(`${name} JSON refusal omits parser bytes`, t => {
   const root = scratch(t), ledger = name === 'approvals' || name === 'journal';
   const file = write(join(root, relative), ledger ? '{}\n' + malformed : malformed);
-  assert.throws(() => read(file, root), safe(ledger ? `${file}:2` : file, DiscordError, { exitCode: 2 }));
+  assert.throws(() => read(file, root), safe(label, DiscordError, { exitCode: 2 }));
 });
 test('tools environment JSON refusal names the config key without its bytes', () => {
   const previous = process.env[TOOLS_ENV];
@@ -52,7 +56,7 @@ test('tools environment JSON refusal names the config key without its bytes', ()
 test('config read refusal retains the filesystem code', t => {
   const file = scratch(t);
   assert.throws(() => loadDataRoot(file), error => {
-    safe(file, DiscordError, { exitCode: 2 })(error);
+    safe('config is not valid JSON', DiscordError, { exitCode: 2 })(error);
     assert.match(error.message, /\(EISDIR\)$/);
     return true;
   });
diff --git a/packages/harness/src/bundle.mjs b/packages/harness/src/bundle.mjs
index 93bdb2257..d0cd080e2 100644
--- a/packages/harness/src/bundle.mjs
+++ b/packages/harness/src/bundle.mjs
@@ -159,7 +159,7 @@ function readSkill(name, root, size) {
     try { return lstatSync(path); } catch (e) { if (e.code === "ENOENT") throw skillNotEnabled(name); throw e; }
   };
   // scripts/skill.sh activate moves a real directory in, so a symlink here is refused, not followed.
-  if (!found(join(root, name)).isDirectory()) throw new BundleError(`skill ${name} isn't a plain directory under ${root}`);
+  if (!found(join(root, name)).isDirectory()) throw new BundleError(`skill ${name} isn't a plain directory under the enabled skills directory`);
   if (!found(join(root, name, "SKILL.md")).isFile()) throw new BundleError(`skill ${name}: SKILL.md isn't a plain file`);
   walk(join(root, name), "");
   return files;
@@ -222,34 +222,36 @@ function readPersona(resolved, personaDir) {
     throw new BundleError(`instance ${resolved.instance} has a persona, but the bundle has no persona directory`, "persona-invalid");
   }
   const path = join(personaDir, resolved.business, `${resolved.instance}.md`);
+  // #1873: a refusal names the file under the persona directory, never its host path.
+  const shown = `${resolved.business}/${resolved.instance}.md in the persona directory`;
   let fd;
   try {
     fd = openSync(path, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK);
   } catch (e) {
     if (e.code === "ENOENT" && digest === undefined) return null;
-    if (e.code === "ENOENT") throw new BundleError(`instance ${resolved.instance}: persona file ${path} doesn't exist`, "persona-invalid");
-    if (e.code === "ELOOP") throw new BundleError(`instance ${resolved.instance}: persona file ${path} is a symlink`, "persona-invalid");
-    throw new BundleError(`instance ${resolved.instance}: persona file ${path} can't be opened (${e.code})`, "persona-invalid");
+    if (e.code === "ENOENT") throw new BundleError(`instance ${resolved.instance}: persona file ${shown} doesn't exist`, "persona-invalid");
+    if (e.code === "ELOOP") throw new BundleError(`instance ${resolved.instance}: persona file ${shown} is a symlink`, "persona-invalid");
+    throw new BundleError(`instance ${resolved.instance}: persona file ${shown} can't be opened (${e.code})`, "persona-invalid");
   }
   let data;
   try {
     const stat = fstatSync(fd);
-    if (!stat.isFile()) throw new BundleError(`instance ${resolved.instance}: persona file ${path} isn't a regular file`, "persona-invalid");
-    if (stat.uid !== process.getuid()) throw new BundleError(`instance ${resolved.instance}: persona file ${path} isn't owned by uid ${process.getuid()}`, "persona-invalid");
-    if (stat.mode & 0o077) throw new BundleError(`instance ${resolved.instance}: persona file ${path} has group or other mode bits`, "persona-invalid");
+    if (!stat.isFile()) throw new BundleError(`instance ${resolved.instance}: persona file ${shown} isn't a regular file`, "persona-invalid");
+    if (stat.uid !== process.getuid()) throw new BundleError(`instance ${resolved.instance}: persona file ${shown} isn't owned by uid ${process.getuid()}`, "persona-invalid");
+    if (stat.mode & 0o077) throw new BundleError(`instance ${resolved.instance}: persona file ${shown} has group or other mode bits`, "persona-invalid");
     // Four bytes is the most one character takes in UTF-8.
-    if (stat.size > PERSONA_CHARS * 4) throw new BundleError(`instance ${resolved.instance}: persona file ${path} is over ${PERSONA_CHARS} characters`, "persona-invalid");
+    if (stat.size > PERSONA_CHARS * 4) throw new BundleError(`instance ${resolved.instance}: persona file ${shown} is over ${PERSONA_CHARS} characters`, "persona-invalid");
     data = readFileSync(fd);
   } finally {
     closeSync(fd);
   }
   if (sha256(data) !== digest) {
-    throw new BundleError(`instance ${resolved.instance}: persona file ${path} isn't the file persona.sha256 names`, "persona-mismatch");
+    throw new BundleError(`instance ${resolved.instance}: persona file ${shown} isn't the file persona.sha256 names`, "persona-mismatch");
   }
   let text;
-  try { text = utf8.decode(data); } catch { throw new BundleError(`instance ${resolved.instance}: persona file ${path} isn't UTF-8 text`, "persona-invalid"); }
+  try { text = utf8.decode(data); } catch { throw new BundleError(`instance ${resolved.instance}: persona file ${shown} isn't UTF-8 text`, "persona-invalid"); }
   const fault = personaTextFault(text);
-  if (fault) throw new BundleError(`instance ${resolved.instance}: persona file ${path} ${fault}`, "persona-invalid");
+  if (fault) throw new BundleError(`instance ${resolved.instance}: persona file ${shown} ${fault}`, "persona-invalid");
   return { name: resolved.vars["persona.name"], sha256: digest, text };
 }
 // Between the contract and "## This session". The contract wins on a conflict, and the broker's
diff --git a/packages/organization/src/config-command.mjs b/packages/organization/src/config-command.mjs
index 2395f5aec..45da727cd 100644
--- a/packages/organization/src/config-command.mjs
+++ b/packages/organization/src/config-command.mjs
@@ -27,6 +27,7 @@ import { configDir, loadOrganization } from "./organization-config.mjs";
 import { loadProject, projectFilePath } from "./project.mjs";
 import { checkCredentialRef } from "./credentials.mjs";
 import { systemVars, resolveInstance } from "./resolve.mjs";
+import { systemConfigProblem } from "./system-config-problem.mjs";
 
 const REPO = resolve(dirname(fileURLToPath(import.meta.url)), "..", "..", "..");
 
@@ -67,21 +68,7 @@ export function runConfigCommand(argv, { stdout = process.stdout, stderr = proce
       maxBuffer: 1024 * 1024,
       env,
     });
-    // Render known key paths with fixed constraints; never relay child stderr.
-    if (proc.status !== 0) {
-      const problem = proc.stderr.trim();
-      const field = problem.startsWith('mosaic-config: execution "dataRoot"') ? "dataRoot"
-        : /^mosaic-config: (?:unsupported )?"?((?:configVersion|environment|dataRoot|execution|console|federation|compactionReadBytes|compactionStreams)(?:\.[A-Za-z][A-Za-z0-9]*|\[\d+\])*)"?(?=[: ])/u.exec(problem)?.[1];
-      const name = "a 1-200 character name starting with a letter or digit and containing only letters, digits, . _ : / -";
-      const expected = { configVersion: "1", environment: "development or production", dataRoot: "a canonical absolute instance data path",
-        "execution.backend": "docker", "execution.adapter": "pi or mock", "execution.provider": name, "execution.model": name };
-      const detail = problem.startsWith("mosaic-config: configuration is not valid JSON (")
-        ? "configuration is not valid JSON; expected readable JSON: "
-        : field ? `${field}: expected ${expected[field] ?? "a value satisfying the system configuration schema"}: `
-          : "expected valid system configuration: ";
-      // Name the config by where it came from, never by host path (PR #1916).
-      fail(3, `system config problem (mosaic-config exit ${proc.status}): ${detail}${env.MOSAIC_CONFIG ? "the system config MOSAIC_CONFIG names" : "the default system config"}${proc.error?.code ? ` (${proc.error.code})` : ""}`);
-    }
+    if (proc.status !== 0) fail(3, systemConfigProblem(proc, env));
     try {
       return JSON.parse(proc.stdout);
     } catch {
@@ -90,19 +77,23 @@ export function runConfigCommand(argv, { stdout = process.stdout, stderr = proce
   };
   const load = (id) => loadOrganization(id, { dir: configDir(env), rolesDir: resolve(env.MOSAIC_ROLES_DIR || join(REPO, "roles")) });
 
-  // Check credential references; return the problems and warnings.
+  // Check credential references, each a [field, ref] pair; return the problems
+  // and warnings. They name the field and the roots by label, never a path (#1873).
   const checkRefs = (refs, forbiddenRoots) => {
     const problems = [];
     const warnings = [];
-    for (const ref of refs) {
-      const result = checkCredentialRef(ref, { forbiddenRoots, env });
+    for (const [where, ref] of refs) {
+      const result = checkCredentialRef(ref, { forbiddenRoots, env, where });
       problems.push(...result.problems);
       warnings.push(...result.warnings);
     }
     return { problems, warnings };
   };
-  const forbiddenRoots = (config, organization) =>
-    [REPO, config.dataRoot, ...Object.values(organization.projects).filter((p) => p.kind !== "library").map((p) => p.root)];
+  const forbiddenRoots = (config, organization) => [
+    { path: REPO, label: "the repository" },
+    { path: config.dataRoot, label: "the data root" },
+    ...Object.entries(organization.projects).filter(([, p]) => p.kind !== "library").map(([id, p]) => ({ path: p.root, label: `the root of project ${id}` })),
+  ];
 
   const validate = (args) => {
     if (args.length !== 1) usage();
@@ -125,8 +116,8 @@ export function runConfigCommand(argv, { stdout = process.stdout, stderr = proce
       projects[id] = "valid";
     }
     const refs = [
-      ...Object.values(organization.tracker?.sync?.credentials ?? {}),
-      ...Object.values(organization.roles).flatMap((r) => Object.values(r.credentials)),
+      ...Object.entries(organization.tracker?.sync?.credentials ?? {}).map(([service, ref]) => [`tracker.sync.credentials.${service}`, ref]),
+      ...Object.entries(organization.roles).flatMap(([instance, r]) => Object.entries(r.credentials).map(([service, ref]) => [`roles.${instance}.credentials.${service}`, ref])),
     ];
     const checked = checkRefs(refs, forbiddenRoots(config, organization));
     warnings.push(...checked.warnings);
@@ -159,11 +150,12 @@ export function runConfigCommand(argv, { stdout = process.stdout, stderr = proce
     let loaded = null;
     if (project !== null) {
       const entry = Object.hasOwn(organization.projects, project) ? organization.projects[project] : null;
-      if (!entry) fail(2, `business ${organization.id} declares no project ${JSON.stringify(project)}`);
+      // The flag is quoted only when it is a plain name, never a path (#1873).
+      if (!entry) fail(2, `business ${organization.id} declares no project ${/^[a-z0-9][a-z0-9._-]{0,63}$/.test(project) ? JSON.stringify(project) : "by that name"}`);
       if (entry.kind !== "library") loaded = loadProject(entry.root);
     }
     const resolved = resolveInstance({ system: systemVars(config), business: organization, project: loaded, instance });
-    const checked = checkRefs(Object.values(resolved.credentials), forbiddenRoots(config, organization));
+    const checked = checkRefs(Object.entries(resolved.credentials).map(([service, ref]) => [`${instance} ${service}`, ref]), forbiddenRoots(config, organization));
     for (const w of checked.warnings) say(`warning: ${w}`);
     if (checked.problems.length > 0) {
       for (const p of checked.problems) say(p);
diff --git a/packages/organization/src/credentials.mjs b/packages/organization/src/credentials.mjs
index 02e53e219..9958bcc80 100644
--- a/packages/organization/src/credentials.mjs
+++ b/packages/organization/src/credentials.mjs
@@ -44,7 +44,7 @@ export function parseCredentialRef(ref, service, where, { store = null } = {}) {
     }
     out.file = ref.file;
     if (store && inside(join(store.configDir, "secrets", "agents"), ref.file) && ref.file !== storePath(store, service)) {
-      refuse(`${where}.file credential-not-yours: ${ref.file} is in the agents' store but not this agent's path`);
+      refuse(`${where}.file credential-not-yours: the file is in the agents' store but not this agent's path`);
     }
   } else {
     if (typeof ref.env !== "string" || !ENV_NAME.test(ref.env)) refuse(`${where}.env must match ${ENV_NAME}`);
@@ -68,11 +68,16 @@ function inside(root, path) {
 // Check a parsed reference against the filesystem and the calendar.
 // Returns { problems: [...], warnings: [...] }; a caller that finds any
 // problem refuses. `forbiddenRoots` are directories a token file must not
-// sit in (the repository, dataRoot). `now` is a Date.
-export function checkCredentialRef(ref, { forbiddenRoots = [], now = new Date(), env = process.env, uid = process.getuid() } = {}) {
+// sit in (the repository, dataRoot): each a path, or { path, label } so a
+// problem can name it. `where` is the reference's field (for example
+// roles.coder.credentials.gitea). `now` is a Date.
+// A problem or warning names the reference by its field, its service and its
+// kind, and an env reference by its checked variable name. It never quotes the
+// token file's path or a root's path (#1873).
+export function checkCredentialRef(ref, { forbiddenRoots = [], now = new Date(), env = process.env, uid = process.getuid(), where = null } = {}) {
   const problems = [];
   const warnings = [];
-  const label = `${ref.service} ${ref.file ? `file ${ref.file}` : `env ${ref.env}`}`;
+  const label = `${where ?? ref.service} ${ref.store ? "store file" : ref.file ? "file" : `env ${ref.env}`}`;
   let notIssued = false;
   if (ref.file) {
     let stat = null;
@@ -96,14 +101,16 @@ export function checkCredentialRef(ref, { forbiddenRoots = [], now = new Date(),
         } catch {
           problems.push(`${label}: path can't be resolved`);
         }
-        for (const root of forbiddenRoots) {
+        for (const entry of forbiddenRoots) {
+          const root = typeof entry === "string" ? entry : entry.path;
+          const name = typeof entry === "string" ? "a forbidden root" : entry.label;
           let realRoot = root;
           try {
             realRoot = realpathSync(root);
           } catch {
             // A root that doesn't exist yet can't contain the file.
           }
-          if (inside(realRoot, real)) problems.push(`${label}: inside ${root}; token files live outside the repository and dataRoot`);
+          if (inside(realRoot, real)) problems.push(`${label}: inside ${name}; token files live outside the repository and dataRoot`);
         }
       }
     }
diff --git a/packages/organization/src/org-registry.mjs b/packages/organization/src/org-registry.mjs
index 6bd757909..6ef935bec 100644
--- a/packages/organization/src/org-registry.mjs
+++ b/packages/organization/src/org-registry.mjs
@@ -6,34 +6,56 @@ import { processState } from '../../seat/src/process-state.mjs';
 import { ID_PATTERN } from './vocabulary.mjs';
 import { parseJsonFileText } from './util.mjs';
 
+// `path` is kept only when it is a document field ($.projects.alpha.root): a
+// host path never rides on the error, where a caller could print or serialise
+// it (#1873).
 export class OrgError extends Error {
-  constructor(code, message, path) { super(message); this.name = 'OrgError'; this.code = code; if (path) this.path = path; }
+  constructor(code, message, path) { super(message); this.name = 'OrgError'; this.code = code; if (typeof path === 'string' && path.startsWith('$')) this.path = path; }
 }
+// A Node system error names the host path in its message, and a spawn's syscall names the
+// program. quietMessage is the call's first word, the file's label and the error code, or null
+// for an error that is not a system error; quiet puts it in the message. The code and syscall
+// fields stay (#1873, from PR #1916's org-service quiet).
+const quieted = new WeakSet();
+export function quietMessage(e, what) {
+  if (!e || typeof e !== 'object') return null;
+  if (quieted.has(e)) return e.message;
+  return typeof e.syscall === 'string' && typeof e.code === 'string' ? `cannot ${e.syscall.split(' ')[0]} ${what} (${e.code})` : null;
+}
+export function quiet(e, what) {
+  const message = quietMessage(e, what);
+  if (message !== null && !quieted.has(e)) { e.message = message; quieted.add(e); }
+  return e;
+}
+// A filesystem call's error keeps its code and loses its path: rethrow(what) for a promise,
+// quiet(e, what) in a catch.
+const rethrow = what => e => { throw quiet(e, what); };
+const CONFIG = 'the config directory';
 const fail = (code, message, path) => { throw new OrgError(code, message, path); };
 function idCheck(id) { if (typeof id !== 'string' || !ID_PATTERN.test(id)) fail('org-invalid', 'invalid organization id'); }
 export function orgRoot(dataRoot, id) { idCheck(id); if (!isAbsolute(dataRoot) || normalize(dataRoot) !== dataRoot) fail('org-invalid', 'data root must be a normalized absolute path'); return join(dataRoot, 'org-runtime', id); }
-async function safeDir(path, create = false) {
+async function safeDir(path, create = false, what = 'a directory') {
   if (!isAbsolute(path) || resolve(path) !== path) fail('org-mismatch', 'directory must be a normalized absolute path', path);
   let current = parse(path).root;
   for (const part of path.slice(current.length).split('/').filter(Boolean)) {
     current = join(current, part);
     try { const st = await fs.lstat(current); if (!st.isDirectory() || st.isSymbolicLink()) fail('org-mismatch', 'directory path contains a symlink or non-directory', current); }
-    catch (e) { if (e.code !== 'ENOENT' || !create) throw e; await fs.mkdir(current, { mode: 0o700 }).catch(err => { if (err.code !== 'EEXIST') throw err; }); const st = await fs.lstat(current); if (!st.isDirectory() || st.isSymbolicLink()) fail('org-mismatch', 'unsafe directory', current); }
+    catch (e) { if (e.code !== 'ENOENT' || !create) throw quiet(e, what); await fs.mkdir(current, { mode: 0o700 }).catch(err => { if (err.code !== 'EEXIST') throw quiet(err, what); }); const st = await fs.lstat(current).catch(rethrow(what)); if (!st.isDirectory() || st.isSymbolicLink()) fail('org-mismatch', 'unsafe directory', current); }
   }
 }
 async function readPrivate(file) {
   const fd = await fs.open(file, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK);
   try { const st = await fd.stat(); if (!st.isFile() || st.uid !== process.getuid() || (st.mode & 0o777) !== 0o600) fail('org-mismatch', 'unsafe metadata file', file); return parseJsonFileText(await fd.readFile('utf8'), file, 'metadata file'); } finally { await fd.close(); }
 }
-async function privateDir(path) { const st = await fs.lstat(path); if (!st.isDirectory() || st.isSymbolicLink() || st.uid !== process.getuid() || (st.mode & 0o077)) fail('org-mismatch', 'unsafe private directory', path); }
+async function privateDir(path, what = 'a directory') { const st = await fs.lstat(path).catch(rethrow(what)); if (!st.isDirectory() || st.isSymbolicLink() || st.uid !== process.getuid() || (st.mode & 0o077)) fail('org-mismatch', 'unsafe private directory', path); }
 function validateRegistry(doc, file) {
   if (!doc || doc.version !== 1 || typeof doc.instance !== 'string' || !doc.orgs || typeof doc.orgs !== 'object' || Array.isArray(doc.orgs)) fail('org-mismatch', 'invalid registry', file);
   for (const [id, entry] of Object.entries(doc.orgs)) { idCheck(id); if (!entry || entry.id !== id || typeof entry.root !== 'string' || !['reserved', 'active', 'deleting', 'archived'].includes(entry.state) || !Number.isSafeInteger(entry.revision) || entry.revision < 1 || typeof entry.created !== 'string') fail('org-mismatch', 'invalid registry entry', file); }
   return doc;
 }
 export async function readRegistry({ configDir }) {
-  await safeDir(configDir); await privateDir(configDir); const file = join(configDir, 'org-runtime.json'); let doc;
-  try { doc = await readPrivate(file); } catch (e) { if (e.code === 'ENOENT') return null; if (e instanceof OrgError) throw e; fail('org-mismatch', `invalid registry: ${e.message}`, file); }
+  await safeDir(configDir, false, CONFIG); await privateDir(configDir, CONFIG); const file = join(configDir, 'org-runtime.json'); let doc;
+  try { doc = await readPrivate(file); } catch (e) { if (e.code === 'ENOENT') return null; if (e instanceof OrgError) throw e; fail('org-mismatch', `invalid registry: ${e instanceof SyntaxError ? e.message : quiet(e, 'registry file').message}`); }
   return validateRegistry(doc, file);
 }
 export async function listOrgs(ctx) { const doc = await readRegistry(ctx); return doc ? Object.values(doc.orgs) : []; }
@@ -49,8 +71,8 @@ export async function readRegistryLocked(registry, ctx) {
   return validateRegistry(registry, join(held.ctx.configDir, 'org-runtime.json'));
 }
 export async function withRegistry(ctx, fn, { write = true } = {}) {
-  await safeDir(ctx.configDir); await privateDir(ctx.configDir); const lock = join(ctx.configDir, 'org-runtime.lock'); let fd;
-  for (let n = 0; n < 200; n++) { try { fd = await fs.open(lock, 'wx', 0o600); break; } catch (e) { if (e.code !== 'EEXIST') throw e; await new Promise(r => setTimeout(r, 10)); } }
+  await safeDir(ctx.configDir, false, CONFIG); await privateDir(ctx.configDir, CONFIG); const lock = join(ctx.configDir, 'org-runtime.lock'); let fd;
+  for (let n = 0; n < 200; n++) { try { fd = await fs.open(lock, 'wx', 0o600); break; } catch (e) { if (e.code !== 'EEXIST') throw quiet(e, 'the registry lock'); await new Promise(r => setTimeout(r, 10)); } }
   if (!fd) fail('org-locked', 'registry lock is held', lock);
   try {
     const persisted = await readRegistry(ctx);
@@ -62,10 +84,10 @@ export async function withRegistry(ctx, fn, { write = true } = {}) {
     finally { heldRegistries.delete(registry); }
     if (write) {
       const file = join(ctx.configDir, 'org-runtime.json'); const temp = join(ctx.configDir, `.org-runtime-${randomBytes(12).toString('hex')}`);
-      try { await fs.writeFile(temp, JSON.stringify(registry, null, 2) + '\n', { mode: 0o600, flag: 'wx' }); await fs.rename(temp, file); } finally { await fs.rm(temp, { force: true }); }
+      try { await fs.writeFile(temp, JSON.stringify(registry, null, 2) + '\n', { mode: 0o600, flag: 'wx' }); await fs.rename(temp, file); } catch (e) { throw quiet(e, 'the registry file'); } finally { await fs.rm(temp, { force: true }).catch(rethrow('the registry file')); }
     }
     return result;
-  } finally { await fd.close(); await fs.unlink(lock); }
+  } finally { await fd.close(); await fs.unlink(lock).catch(rethrow('the registry lock')); }
 }
 // The broker's existing organization writer is synchronous. It shares the
 // registry lock with the async service and refuses contention rather than
@@ -74,16 +96,16 @@ export function withRegistryWriter(configDir, fn) {
   const file = join(configDir, 'org-runtime.json');
   const lock = join(configDir, 'org-runtime.lock'); let lockFd;
   try { lockFd = openSync(lock, constants.O_WRONLY | constants.O_CREAT | constants.O_EXCL | constants.O_NOFOLLOW, 0o600); }
-  catch (e) { if (e.code === 'EEXIST') fail('org-locked', 'registry lock is held', lock); throw e; }
-  const release = () => { closeSync(lockFd); unlinkSync(lock); };
+  catch (e) { if (e.code === 'EEXIST') fail('org-locked', 'registry lock is held', lock); throw quiet(e, 'the registry lock'); }
+  const release = () => { closeSync(lockFd); try { unlinkSync(lock); } catch (e) { throw quiet(e, 'the registry lock'); } };
   let pending = false;
   try {
     let fd, registry = null;
     try { fd = openSync(file, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK); }
-    catch (e) { if (e.code !== 'ENOENT') throw e; }
+    catch (e) { if (e.code !== 'ENOENT') throw quiet(e, 'the registry file'); }
     if (fd !== undefined) {
       try {
-        const dir = lstatSync(configDir);
+        let dir; try { dir = lstatSync(configDir); } catch (e) { throw quiet(e, CONFIG); }
         if (!dir.isDirectory() || dir.isSymbolicLink() || dir.uid !== process.getuid() || (dir.mode & 0o077)) fail('org-mismatch', 'unsafe private directory', configDir);
         const st = fstatSync(fd);
         if (!st.isFile() || st.uid !== process.getuid() || (st.mode & 0o777) !== 0o600) fail('org-mismatch', 'unsafe metadata file', file);
@@ -93,7 +115,8 @@ export function withRegistryWriter(configDir, fn) {
     const publish = () => {
       const temp = join(configDir, `.org-runtime-${randomBytes(12).toString('hex')}`);
       try { writeFileSync(temp, JSON.stringify(registry, null, 2) + '\n', { mode: 0o600, flag: 'wx' }); renameSync(temp, file); }
-      finally { try { unlinkSync(temp); } catch (e) { if (e.code !== 'ENOENT') throw e; } }
+      catch (e) { throw quiet(e, 'the registry file'); }
+      finally { try { unlinkSync(temp); } catch (e) { if (e.code !== 'ENOENT') throw quiet(e, 'the registry file'); } }
     };
     const result = fn(registry, publish);
     if (result !== null && typeof result === 'object' && typeof result.then === 'function') {
@@ -108,10 +131,10 @@ export async function reserveOrg(ctx, id) {
   return withRegistry(ctx, async registry => {
     if (Object.hasOwn(registry.orgs, id)) fail('org-exists', 'organization already reserved', root);
     for (const entry of Object.values(registry.orgs)) if (entry.root === root || root.startsWith(entry.root + '/') || entry.root.startsWith(root + '/')) fail('org-overlap', 'organization roots overlap', root);
-    await safeDir(ctx.dataRoot); await privateDir(ctx.dataRoot);
-    await safeDir(dirname(root), true); await privateDir(dirname(root));
-    try { await fs.mkdir(root, { mode: 0o700 }); } catch (e) { if (e.code === 'EEXIST') fail('org-exists', 'organization root already exists', root); throw e; }
-    await fs.writeFile(join(root, '.mosaic-org.json'), JSON.stringify({ instance: ctx.instance, id }) + '\n', { mode: 0o600, flag: 'wx' });
+    await safeDir(ctx.dataRoot, false, 'the data root'); await privateDir(ctx.dataRoot, 'the data root');
+    await safeDir(dirname(root), true, 'org-runtime under the data root'); await privateDir(dirname(root), 'org-runtime under the data root');
+    try { await fs.mkdir(root, { mode: 0o700 }); } catch (e) { if (e.code === 'EEXIST') fail('org-exists', 'organization root already exists', root); throw quiet(e, 'the organization root'); }
+    await fs.writeFile(join(root, '.mosaic-org.json'), JSON.stringify({ instance: ctx.instance, id }) + '\n', { mode: 0o600, flag: 'wx' }).catch(rethrow('the organization marker'));
     const entry = { id, root, state: 'reserved', created: new Date().toISOString(), revision: 1 }; registry.orgs[id] = entry; return { ...entry };
   });
 }
@@ -132,14 +155,14 @@ export async function activateOrg(ctx, id) {
     // no document yet; preserve the registry's existing activation contract.
     const dir = join(ctx.configDir, 'businesses'), file = join(dir, `${id}.json`);
     try {
-      await safeDir(dir);
+      await safeDir(dir, false, 'businesses in the config directory');
       const fd = await fs.open(file, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK);
       try {
         const st = await fd.stat();
         if (!st.isFile() || st.uid !== process.getuid() || (st.mode & 0o022)) fail('org-mismatch', 'unsafe organization document', file);
         registry.orgs[id].digest = createHash('sha256').update(await fd.readFile()).digest('hex');
       } finally { await fd.close(); }
-    } catch (e) { if (e.code !== 'ENOENT') throw e; }
+    } catch (e) { if (e.code !== 'ENOENT') throw quiet(e, 'the organization document'); }
     registry.orgs[id].state = 'active';
     return { ...registry.orgs[id] };
   });
@@ -148,12 +171,12 @@ export async function activateOrg(ctx, id) {
 // Serialize bus launch with organization lifecycle operations.
 // A leftover lock is never guessed stale; the operator must inspect it.
 export async function withOrgLifecycle(ctx, id, fn) {
-  idCheck(id); await safeDir(ctx.configDir); await privateDir(ctx.configDir);
+  idCheck(id); await safeDir(ctx.configDir, false, CONFIG); await privateDir(ctx.configDir, CONFIG);
   const path = join(ctx.configDir, `org-lifecycle-${id}.lock`); let fd;
   try { fd = await fs.open(path, 'wx', 0o600); }
-  catch (e) { if (e.code === 'EEXIST') fail('org-locked', 'organization lifecycle lock is held; inspect the lock and resume'); throw e; }
+  catch (e) { if (e.code === 'EEXIST') fail('org-locked', 'organization lifecycle lock is held; inspect the lock and resume'); throw quiet(e, 'the lifecycle lock'); }
   try { await fd.writeFile(JSON.stringify({ pid: process.pid, at: new Date().toISOString() }) + '\n'); return await fn(); }
-  finally { await fd.close(); await fs.unlink(path); }
+  finally { await fd.close(); await fs.unlink(path).catch(rethrow('the lifecycle lock')); }
 }
 
 // Lifecycle locks carry {pid, at}; registry locks are empty and cannot be
@@ -173,7 +196,7 @@ function inspectRecoveryFence(path) {
   } finally { closeSync(fd); }
 }
 export async function orgLock(ctx, id, { clear = false } = {}) {
-  idCheck(id); await safeDir(ctx.configDir); await privateDir(ctx.configDir);
+  idCheck(id); await safeDir(ctx.configDir, false, CONFIG); await privateDir(ctx.configDir, CONFIG);
   const path = join(ctx.configDir, `org-lifecycle-${id}.lock`);
   const guard = `${path}.clear`; let guardFd, self;
   if (clear) {
@@ -182,16 +205,16 @@ export async function orgLock(ctx, id, { clear = false } = {}) {
     for (;;) {
       try { guardFd = openSync(guard, constants.O_WRONLY | constants.O_CREAT | constants.O_EXCL | constants.O_NOFOLLOW, 0o600); break; }
       catch (e) {
-        if (e.code !== 'EEXIST') throw e;
+        if (e.code !== 'EEXIST') throw quiet(e, 'the recovery fence');
         const holder = inspectRecoveryFence(guard);
         if (!holder) continue;
-        if (holder.unreadable) fail('org-locked', `unreadable recovery fence ${guard}; remove it by hand`, guard);
+        if (holder.unreadable) fail('org-locked', `unreadable recovery fence org-lifecycle-${id}.lock.clear in the config directory; remove it by hand`);
         if (holder.alive !== false) fail('org-locked', `lock recovery is already in progress by pid ${holder.pid}`, guard);
-        let current; try { current = lstatSync(guard); } catch (err) { if (err.code === 'ENOENT') continue; throw err; }
+        let current; try { current = lstatSync(guard); } catch (err) { if (err.code === 'ENOENT') continue; throw quiet(err, 'the recovery fence'); }
         if (current.dev !== holder.dev || current.ino !== holder.ino) fail('org-locked', 'recovery fence changed during recovery', guard);
         const stamp = new Date().toISOString().replace(/[:.]/g, '-');
         try { renameSync(guard, `${guard}.stale-${stamp}-${randomBytes(4).toString('hex')}`); }
-        catch (err) { if (err.code === 'ENOENT') continue; throw err; }
+        catch (err) { if (err.code === 'ENOENT') continue; throw quiet(err, 'the recovery fence'); }
       }
     }
   }
@@ -201,7 +224,7 @@ export async function orgLock(ctx, id, { clear = false } = {}) {
     const reportFence = result => { if (fence) { const { dev, ino, ...visible } = fence; result.fence = visible; } return result; };
     let fd;
     try { fd = openSync(path, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK); }
-    catch (e) { if (e.code === 'ENOENT') return reportFence(clear ? { held: false, cleared: false } : { held: false }); throw e; }
+    catch (e) { if (e.code === 'ENOENT') return reportFence(clear ? { held: false, cleared: false } : { held: false }); throw quiet(e, 'the lifecycle lock'); }
     try {
       const st = fstatSync(fd);
       if (!st.isFile() || st.uid !== process.getuid() || (st.mode & 0o777) !== 0o600 || st.nlink !== 1) fail('org-mismatch', 'unsafe lifecycle lock', path);
@@ -210,10 +233,11 @@ export async function orgLock(ctx, id, { clear = false } = {}) {
       let status; try { status = processState(holder.pid); } catch { fail('org-mismatch', 'lifecycle lock holder is uncertain', path); }
       const result = { held: true, pid: holder.pid, start: holder.at, alive: status.alive };
       if (clear) {
-        if (status.alive) fail('org-locked', `lifecycle lock held by pid ${holder.pid} since ${holder.at} (alive)`, path);
-        const current = lstatSync(path);
+        if (status.alive) fail('org-locked', `lifecycle lock held by pid ${holder.pid} since ${new Date(holder.at).toISOString()} (alive)`, path);
+        let current; try { current = lstatSync(path); } catch (e) { throw quiet(e, 'the lifecycle lock'); }
         if (current.dev !== st.dev || current.ino !== st.ino) fail('org-locked', 'lifecycle lock changed during recovery', path);
-        unlinkSync(path); result.cleared = true;
+        try { unlinkSync(path); } catch (e) { throw quiet(e, 'the lifecycle lock'); }
+        result.cleared = true;
       }
       return reportFence(result);
     } finally { closeSync(fd); }
@@ -221,9 +245,9 @@ export async function orgLock(ctx, id, { clear = false } = {}) {
     if (guardFd !== undefined) {
       const owned = fstatSync(guardFd);
       try {
-        const current = lstatSync(guard);
+        let current; try { current = lstatSync(guard); } catch (e) { throw quiet(e, 'the recovery fence'); }
         if (owned.dev !== current.dev || owned.ino !== current.ino) fail('org-locked', 'recovery fence changed during recovery', guard);
-        unlinkSync(guard);
+        try { unlinkSync(guard); } catch (e) { throw quiet(e, 'the recovery fence'); }
       } finally { closeSync(guardFd); }
     }
   }
diff --git a/packages/organization/src/org-service.mjs b/packages/organization/src/org-service.mjs
index 4b384d9b6..161ad969b 100644
--- a/packages/organization/src/org-service.mjs
+++ b/packages/organization/src/org-service.mjs
@@ -6,7 +6,7 @@ import { dirname, join, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { validateBusinessDocument, httpsUrl } from './organization-config.mjs';
 import { ID_PATTERN } from './vocabulary.mjs';
-import { OrgError, orgRoot, readRegistry, reserveOrg, resolveOrg, withRegistry, withOrgLifecycle } from './org-registry.mjs';
+import { OrgError, orgRoot, quiet, readRegistry, reserveOrg, resolveOrg, withRegistry, withOrgLifecycle } from './org-registry.mjs';
 import { loadInstalled } from '../../plugins/src/loader.mjs';
 import { BINDING_NAME } from '../../discord/src/binding.mjs';
 import { parseJsonFileText } from './util.mjs';
@@ -21,11 +21,6 @@ function authorize(ctx) { if (!ctx || typeof ctx.instance !== 'string' || !/^[a-
 function checkId(id) { if (typeof id !== 'string' || !ID_PATTERN.test(id)) fail('org-invalid', 'invalid id'); }
 // A filesystem error names the operation, the file by label and the error code, never the
 // host path Node puts in its message (PR #1916). code, syscall and the other fields stay.
-const quieted = new WeakSet();
-function quiet(e, what) {
-  if (e && typeof e === 'object' && typeof e.syscall === 'string' && typeof e.code === 'string' && !quieted.has(e)) { e.message = `cannot ${e.syscall} ${what} (${e.code})`; quieted.add(e); }
-  return e;
-}
 async function privateRead(file, what = 'organization file') { let fd; try { fd = await fs.open(file, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK); } catch (e) { throw quiet(e, what); } try { const st = await fd.stat(); if (!st.isFile() || st.uid !== process.getuid() || (st.mode & 0o077)) fail('org-mismatch', 'unsafe file', file); return await fd.readFile('utf8'); } catch (e) { throw quiet(e, what); } finally { await fd.close(); } }
 async function atomic(file, content, exclusive = false) {
   const tmp = join(dirname(file), `.org-write-${randomBytes(12).toString('hex')}`);
diff --git a/packages/organization/src/system-config-problem.mjs b/packages/organization/src/system-config-problem.mjs
new file mode 100644
index 000000000..6864cfcc8
--- /dev/null
+++ b/packages/organization/src/system-config-problem.mjs
@@ -0,0 +1,21 @@
+// One refusal line for a failed `mosaic-config.mjs validate`, shared by `mosaic business` /
+// `mosaic org config` and the cli's system config load (#1873). Its own module, so the
+// config-command module's export list stays what importers pin.
+
+// A failed `mosaic-config.mjs validate` as one refusal line. Render known key paths with fixed
+// constraints; never relay the child's stderr, which can quote a host path or a config value.
+// The config is named by where it came from, never by host path (PR #1916): `label` when the
+// caller knows it (the cli's --instance load, #1873), else from MOSAIC_CONFIG.
+export function systemConfigProblem(proc, env, label = null) {
+  const problem = String(proc.stderr ?? "").trim();
+  const field = problem.startsWith('mosaic-config: execution "dataRoot"') ? "dataRoot"
+    : /^mosaic-config: (?:unsupported )?"?((?:configVersion|environment|dataRoot|execution|console|federation|compactionReadBytes|compactionStreams)(?:\.[A-Za-z][A-Za-z0-9]*|\[\d+\])*)"?(?=[: ])/u.exec(problem)?.[1];
+  const name = "a 1-200 character name starting with a letter or digit and containing only letters, digits, . _ : / -";
+  const expected = { configVersion: "1", environment: "development or production", dataRoot: "a canonical absolute instance data path",
+    "execution.backend": "docker", "execution.adapter": "pi or mock", "execution.provider": name, "execution.model": name };
+  const detail = problem.startsWith("mosaic-config: configuration is not valid JSON (")
+    ? "configuration is not valid JSON; expected readable JSON: "
+    : field ? `${field}: expected ${expected[field] ?? "a value satisfying the system configuration schema"}: `
+      : "expected valid system configuration: ";
+  return `system config problem (mosaic-config exit ${proc.status}): ${detail}${label ?? (env.MOSAIC_CONFIG ? "the system config MOSAIC_CONFIG names" : "the default system config")}${proc.error?.code ? ` (${proc.error.code})` : ""}`;
+}
diff --git a/packages/organization/tests/cli.test.mjs b/packages/organization/tests/cli.test.mjs
index 111632347..d921c8b0a 100644
--- a/packages/organization/tests/cli.test.mjs
+++ b/packages/organization/tests/cli.test.mjs
@@ -124,8 +124,8 @@ test("validate: credential reference problems exit 2 and name each one", () => {
   const r = run(s, "validate", "acme");
   assert.equal(r.code, 2);
   assert.equal(r.out, "");
-  assert.match(r.err, /cto-gitea\.token: mode 644/);
-  assert.match(r.err, /coder\.token: inside .*data/);
+  assert.match(r.err, /roles\.cto\.credentials\.gitea file: mode 644/);
+  assert.match(r.err, /roles\.coder\.credentials\.vikunja file: inside the data root/);
   assert.match(r.err, /expired on 2026-01-01/);
   assert.match(r.err, /3 credential reference problem/);
 });
@@ -140,8 +140,8 @@ test("validate: a not-issued store agent dated today passes, and an issued one w
   });
   const r = run(s, "validate", "acme");
   assert.equal(r.code, 0, r.err);
-  assert.match(r.err, /gitea file .*secrets\/agents\/acme\/coder\/gitea: not issued/);
-  assert.match(r.err, /vikunja file .*secrets\/agents\/acme\/coder\/vikunja: not issued/);
+  assert.match(r.err, /roles\.coder\.credentials\.gitea store file: not issued/);
+  assert.match(r.err, /roles\.coder\.credentials\.vikunja store file: not issued/);
   assert.doesNotMatch(r.err, /expire|rotation/);
 
   const issued = setup((doc) => {
@@ -150,7 +150,7 @@ test("validate: a not-issued store agent dated today passes, and an issued one w
   tokenFile(join(issued.root, "config", "secrets", "agents", "acme", "coder"), "vikunja");
   const e = run(issued, "validate", "acme");
   assert.equal(e.code, 2);
-  assert.match(e.err, /vikunja file .*coder\/vikunja: expired on 2026-01-01/);
+  assert.match(e.err, /roles\.coder\.credentials\.vikunja store file: expired on 2026-01-01/);
 });
 
 test("validate: a token file inside the repository is refused", () => {
@@ -211,5 +211,10 @@ test("resolve: refusals", () => {
   assert.equal(run(s, "resolve", "acme", "ghost").code, 2);
   assert.equal(run(s, "resolve", "acme", "constructor").code, 2);
   assert.match(run(s, "resolve", "acme", "pm", "--project", "ghost").err, /declares no project "ghost"/);
+  // #1873: a --project value that is not a plain name is never echoed.
+  const odd = run(s, "resolve", "acme", "pm", "--project", "/srv/sk-test-NOT-A-SECRET-1234/x");
+  assert.equal(odd.code, 2);
+  assert.match(odd.err, /declares no project by that name/);
+  assert.doesNotMatch(odd.err, /sk-test|NOT-A-SECRET|\/srv\//);
   assert.equal(run(s, "resolve", "acme", "pm", "--project", "stack").code, 4);
 });
diff --git a/packages/organization/tests/instance-settings.test.mjs b/packages/organization/tests/instance-settings.test.mjs
index 993f2a7fa..617d054d9 100644
--- a/packages/organization/tests/instance-settings.test.mjs
+++ b/packages/organization/tests/instance-settings.test.mjs
@@ -177,7 +177,7 @@ test("T19 add of a credentialed definition writes store references dated today,
   });
   const validated = f.validate();
   assert.equal(validated.status, 0, validated.stderr);
-  assert.match(validated.stderr, /reviewer-2\/vikunja: not issued/);
+  assert.match(validated.stderr, /roles\.reviewer-2\.credentials\.vikunja store file: not issued/);
   // The Console's create form keeps listing it as not accepted.
   assert.equal(f.settings.read("acme").definitions.reviewer.accepted, false);
 });
diff --git a/packages/organization/tests/path-redaction-labels.test.mjs b/packages/organization/tests/path-redaction-labels.test.mjs
new file mode 100644
index 000000000..749ffa3b6
--- /dev/null
+++ b/packages/organization/tests/path-redaction-labels.test.mjs
@@ -0,0 +1,113 @@
+// #1873 (redact6): an organization refusal names the field, the file or the root by label,
+// never a host path. The sentinel is a component of every scratch path, so a refusal that
+// quotes a path quotes the sentinel too; each test also checks the scratch root and the label.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { chmodSync, mkdirSync, mkdtempSync, rmSync, symlinkSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { checkCredentialRef, parseCredentialRef, storePath } from '../src/credentials.mjs';
+import { OrgError, orgLock, quietMessage, readRegistry, withRegistryWriter } from '../src/org-registry.mjs';
+
+const secret = 'sk-test-NOT-A-SECRET-1234';
+function scratch(t) {
+  const root = mkdtempSync(join(tmpdir(), 'r6-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+  const dir = join(root, secret);
+  mkdirSync(dir, { mode: 0o700 });
+  return { root, dir };
+}
+function clean(text, root) {
+  assert.ok(!text.includes(root), text);
+  assert.doesNotMatch(text, /sk-test|NOT-A-SECRET/);
+}
+
+test('a credential problem names the field and the root by label, never the token file or the root', t => {
+  const { root, dir } = scratch(t);
+  const file = join(dir, 'gitea');
+  writeFileSync(file, 'token', { mode: 0o644 });
+  const ref = { service: 'gitea', file, rotateBy: '2999-01-01' };
+  const { problems } = checkCredentialRef(ref, { forbiddenRoots: [{ path: dir, label: 'the data root' }, root], where: 'roles.coder.credentials.gitea' });
+  assert.deepEqual(problems, [
+    'roles.coder.credentials.gitea file: mode 644 gives group or other access; use 600',
+    'roles.coder.credentials.gitea file: inside the data root; token files live outside the repository and dataRoot',
+    'roles.coder.credentials.gitea file: inside a forbidden root; token files live outside the repository and dataRoot',
+  ]);
+  for (const p of problems) clean(p, root);
+  const missing = checkCredentialRef({ service: 'gitea', file: join(dir, 'absent'), rotateBy: '2999-01-01' });
+  assert.deepEqual(missing.problems, ['gitea file: not found']);
+  const store = checkCredentialRef({ service: 'gitea', store: true, file: join(dir, 'absent'), rotateBy: '2999-01-01' }, { where: 'roles.coder.credentials.gitea' });
+  assert.deepEqual(store.warnings, ['roles.coder.credentials.gitea store file: not issued']);
+});
+
+test('credential-not-yours names the field, not the file', t => {
+  const { root, dir } = scratch(t);
+  const store = { configDir: dir, business: 'acme', agent: 'coder' };
+  const other = storePath({ ...store, agent: 'pm' }, 'gitea');
+  assert.throws(() => parseCredentialRef({ file: other, rotateBy: '2999-01-01' }, 'gitea', 'roles.coder.credentials.gitea', { store }), error => {
+    assert.match(error.message, /^roles\.coder\.credentials\.gitea\.file credential-not-yours: the file is in the agents' store/);
+    clean(error.message, root);
+    return true;
+  });
+});
+
+test('an OrgError keeps a document field but drops a host path', t => {
+  const { dir } = scratch(t);
+  assert.equal(new OrgError('org-mismatch', 'unsafe file', join(dir, 'org.json')).path, undefined);
+  assert.equal(new OrgError('org-invalid', 'bad root', '$.projects.alpha.root').path, '$.projects.alpha.root');
+  const error = Object.assign(new Error(`ENOENT: no such file or directory, open '${join(dir, 'x')}'`), { code: 'ENOENT', syscall: 'open' });
+  assert.equal(quietMessage(error, 'the registry file'), 'cannot open the registry file (ENOENT)');
+  assert.equal(quietMessage(Object.assign(new Error('x'), { code: 'ENOENT', syscall: `spawn ${join(dir, 'git')}` }), 'git'), 'cannot spawn git (ENOENT)');
+});
+
+test('an unreadable registry names the registry file and the error code, never its path', async t => {
+  const { root, dir } = scratch(t);
+  writeFileSync(join(dir, 'real.json'), '{}', { mode: 0o600 });
+  symlinkSync(join(dir, 'real.json'), join(dir, 'org-runtime.json'));
+  await assert.rejects(readRegistry({ configDir: dir }), error => {
+    assert.ok(error instanceof OrgError, error.stack);
+    assert.equal(error.code, 'org-mismatch');
+    assert.equal(error.message, 'invalid registry: cannot open registry file (ELOOP)');
+    assert.equal(error.path, undefined);
+    clean(error.message, root);
+    clean(JSON.stringify(error), root);
+    return true;
+  });
+});
+
+test('an unreadable recovery fence names the fence in the config directory, never its path', async t => {
+  const { root, dir } = scratch(t);
+  writeFileSync(join(dir, 'org-lifecycle-acme.lock.clear'), '{}', { mode: 0o600 });
+  chmodSync(join(dir, 'org-lifecycle-acme.lock.clear'), 0o644);
+  await assert.rejects(orgLock({ configDir: dir }, 'acme', { clear: true }), error => {
+    assert.ok(error instanceof OrgError, error.stack);
+    assert.equal(error.code, 'org-locked');
+    assert.equal(error.message, 'unreadable recovery fence org-lifecycle-acme.lock.clear in the config directory; remove it by hand');
+    assert.equal(error.path, undefined);
+    clean(error.message, root);
+    return true;
+  });
+});
+
+// Review round (#1873): the registry's own filesystem calls name the directory or file by label.
+test('a missing config directory names it by label and code, never its path, and keeps the system code', async t => {
+  const { root, dir } = scratch(t);
+  await assert.rejects(readRegistry({ configDir: join(dir, 'absent') }), error => {
+    assert.equal(error.code, 'ENOENT');
+    assert.equal(error.message, 'cannot lstat the config directory (ENOENT)');
+    clean(error.message, root);
+    return true;
+  });
+});
+
+test('the registry writer names the registry file by label when it cannot open it, never its path', t => {
+  const { root, dir } = scratch(t);
+  writeFileSync(join(dir, 'real'), '{}', { mode: 0o600 });
+  symlinkSync(join(dir, 'real'), join(dir, 'org-runtime.json'));
+  assert.throws(() => withRegistryWriter(dir, () => {}), error => {
+    assert.equal(error.code, 'ELOOP');
+    assert.equal(error.message, 'cannot open the registry file (ELOOP)');
+    clean(error.message, root);
+    return true;
+  });
+});
diff --git a/packages/plugins/harness/claude-code/index.mjs b/packages/plugins/harness/claude-code/index.mjs
index e65f38c57..e72a4b2e6 100644
--- a/packages/plugins/harness/claude-code/index.mjs
+++ b/packages/plugins/harness/claude-code/index.mjs
@@ -63,7 +63,8 @@ export function preflight({ env, proxy = null }) {
   if (!binary(env)) {
     return {
       code: "harness-binary-missing",
-      message: env.MOSAIC_CLAUDE_BIN ? `MOSAIC_CLAUDE_BIN ${env.MOSAIC_CLAUDE_BIN} isn't an executable file at an absolute path` : "no claude on the bus host's PATH",
+      // Names the variable, never its value, which is a host path (#1873).
+      message: env.MOSAIC_CLAUDE_BIN ? "MOSAIC_CLAUDE_BIN isn't an executable file at an absolute path" : "no claude on the bus host's PATH",
     };
   }
   return null;
diff --git a/packages/plugins/harness/pi/index.mjs b/packages/plugins/harness/pi/index.mjs
index 28ae7cc1b..4e07d0c33 100644
--- a/packages/plugins/harness/pi/index.mjs
+++ b/packages/plugins/harness/pi/index.mjs
@@ -37,7 +37,7 @@ export function preflight({ env = {}, proxy = null } = {}) {
     && !["ANTHROPIC_API_KEY", "OPENAI_API_KEY", "OPENROUTER_API_KEY", "ZAI_API_KEY"].some(name => Boolean(env[name]))) {
     return { code: "no-session-credential", message: "pi needs its own provider key or a session proxy key" };
   }
-  if (!existsSync(BIN)) return { code: "harness-binary-missing", message: `pi isn't installed at ${BIN}; run npm ci in the repository` };
+  if (!existsSync(BIN)) return { code: "harness-binary-missing", message: "pi isn't installed in the repository's node_modules; run npm ci in the repository" };
   return null;
 }
 
diff --git a/packages/seat/src/sandbox.mjs b/packages/seat/src/sandbox.mjs
index 2232afa76..f401bc99e 100644
--- a/packages/seat/src/sandbox.mjs
+++ b/packages/seat/src/sandbox.mjs
@@ -194,9 +194,10 @@ export function sandboxArgv(list, runDir, command, { business, role, bwrap = BWR
 // Whether bwrap runs here at all: the namespaces and the system binds, then
 // setpriv and `true`. Returns null, or why not.
 export function sandboxProblem({ bwrap = BWRAP } = {}) {
-  if (!existsSync(bwrap)) return `${bwrap} is missing`;
+  // #1873: names the sandbox, never the binary's host path; a launch refusal carries this text.
+  if (!existsSync(bwrap)) return "the sandbox (bwrap) is missing";
   const r = spawnSync(bwrap, [...NAMESPACES, ...argsOf(systemBinds()), "--remount-ro", "/", "--", ...KILL_WITH_PARENT, "/usr/bin/true"], { encoding: "utf8", timeout: 10000 });
   if (r.status === 0) return null;
   const why = (r.stderr ?? "").trim().split("\n")[0] || (r.error ? r.error.code : `exit ${r.status ?? r.signal}`);
-  return `${bwrap} failed: ${why}`;
+  return `the sandbox (bwrap) failed: ${why}`;
 }
diff --git a/packages/seat/src/seat.mjs b/packages/seat/src/seat.mjs
index 6549daeaf..e95ab6611 100644
--- a/packages/seat/src/seat.mjs
+++ b/packages/seat/src/seat.mjs
@@ -50,16 +50,17 @@ export function defaultConfigPath(env = process.env) {
 
 // Fail closed: the config must exist, parse, and name an absolute dataRoot.
 // Only dataRoot is read here; scripts/mosaic-config.mjs owns full validation.
+// Refusals name the config, never its path (#1873).
 export function loadDataRoot(path = defaultConfigPath()) {
-  if (!existsSync(path)) throw new SeatError(`config not found: ${path}`);
+  if (!existsSync(path)) throw new SeatError("config not found");
   let raw;
   try {
     raw = parseJsonFileText(readFileSync(path, "utf8"), path);
   } catch (error) {
-    throw new SeatError(`config is not valid JSON: ${path}${error.code ? ` (${error.code})` : ""}`);
+    throw new SeatError(`config is not valid JSON${error.code ? ` (${error.code})` : ""}`);
   }
-  if (!raw || typeof raw !== "object" || Array.isArray(raw)) throw new SeatError(`config is not an object: ${path}`);
-  if (typeof raw.dataRoot !== "string" || !isAbsolute(raw.dataRoot)) throw new SeatError(`config.dataRoot must be an absolute path: ${path}`);
+  if (!raw || typeof raw !== "object" || Array.isArray(raw)) throw new SeatError("config is not an object");
+  if (typeof raw.dataRoot !== "string" || !isAbsolute(raw.dataRoot)) throw new SeatError("config.dataRoot must be an absolute path");
   return raw.dataRoot;
 }
 
@@ -69,11 +70,15 @@ export function seatsDir(dataRoot) {
 
 export const LAYOUTS = Object.freeze(["repo", "fleet", "unknown"]);
 
+// A refusal quotes a key or name only when it is a plain name; anything that
+// could carry a host path or a secret is described, never echoed (#1873).
+export const plainKey = (k) => (/^[A-Za-z_][A-Za-z0-9_.-]{0,63}$/.test(String(k)) ? JSON.stringify(k) : "that is not a plain name");
+
 // Keyed by layout and seat, because a seat name is not unique across
 // layouts (this repository and the fleet both have a "darkwing").
 export function registrationPath(seats, seat, layout) {
-  if (!SEAT_NAME.test(String(seat))) throw new SeatError(`invalid seat name: ${JSON.stringify(seat)}`, 4);
-  if (!LAYOUTS.includes(layout)) throw new SeatError(`invalid layout: ${JSON.stringify(layout)}`, 4);
+  if (!SEAT_NAME.test(String(seat))) throw new SeatError("invalid seat name (lowercase letters, digits, ., _ or -, at most 64)", 4);
+  if (!LAYOUTS.includes(layout)) throw new SeatError(`invalid layout (one of ${LAYOUTS.join(", ")})`, 4);
   return join(seats, layout, seat, "registration.json");
 }
 
@@ -87,10 +92,11 @@ export function resolveSeat(arg, { repo = process.cwd() } = {}) {
   else throw new SeatError(`invalid seat name: ${JSON.stringify(arg)}`, 4);
   const seat = basename(seatDir);
   if (!SEAT_NAME.test(seat)) throw new SeatError(`invalid seat name: ${JSON.stringify(seat)}`, 4);
-  if (!existsSync(seatDir) || !statSync(seatDir).isDirectory()) throw new SeatError(`no such seat directory: ${seatDir}`);
+  // Named by the checked seat name, never the directory's path (#1873).
+  if (!existsSync(seatDir) || !statSync(seatDir).isDirectory()) throw new SeatError(`no such seat directory: seat ${seat}`);
   const launchScript = join(seatDir, "launch.sh");
-  if (!existsSync(launchScript) || !statSync(launchScript).isFile()) throw new SeatError(`seat has no launch.sh: ${seatDir}`);
-  if ((statSync(launchScript).mode & 0o111) === 0) throw new SeatError(`launch script is not executable: ${launchScript}`);
+  if (!existsSync(launchScript) || !statSync(launchScript).isFile()) throw new SeatError(`seat has no launch.sh: seat ${seat}`);
+  if ((statSync(launchScript).mode & 0o111) === 0) throw new SeatError(`launch script is not executable: launch.sh of seat ${seat}`);
 
   const parent = dirname(seatDir);
   const root = basename(parent) === "agents" ? dirname(parent) : null;
@@ -141,7 +147,7 @@ const isTimestamp = (v) => typeof v === "string" && Number.isFinite(Date.parse(v
 // SeatError with the failing field; never echoes the offending value.
 export function validateRegistration(record) {
   if (!record || typeof record !== "object" || Array.isArray(record)) throw new SeatError("registration is not an object");
-  for (const key of Object.keys(record)) if (!FIELDS.includes(key)) throw new SeatError(`registration has an unknown field: ${key}`);
+  for (const key of Object.keys(record)) if (!FIELDS.includes(key)) throw new SeatError(`registration has an unknown field: ${plainKey(key)}`);
   if (record.version !== REGISTRATION_VERSION) throw new SeatError("registration has an unsupported version");
   if (typeof record.seat !== "string" || !SEAT_NAME.test(record.seat)) throw new SeatError("registration.seat is invalid");
   if (typeof record.task !== "string" || record.task.length > TASK_LIMIT) throw new SeatError("registration.task must be a string");
@@ -205,14 +211,14 @@ export function readRegistration(seats, seat, layout) {
   try {
     parsed = parseJsonFileText(readFileSync(path, "utf8"), path);
   } catch (error) {
-    throw new SeatError(`registration is not valid JSON: ${path}${error.code ? ` (${error.code})` : ""}`);
+    throw new SeatError(`registration ${layout}/${seat} is not valid JSON${error.code ? ` (${error.code})` : ""}`);
   }
   try {
     const record = validateRegistration(parsed);
     if (record.seat !== seat || record.layout !== layout) throw new SeatError("registration does not match its path");
     return record;
   } catch (err) {
-    throw new SeatError(`${err.message}: ${path}`);
+    throw new SeatError(`${err.message}: registration ${layout}/${seat}`);
   }
 }
 
diff --git a/packages/seat/src/session.mjs b/packages/seat/src/session.mjs
index 060542a3e..60964627f 100644
--- a/packages/seat/src/session.mjs
+++ b/packages/seat/src/session.mjs
@@ -35,7 +35,7 @@ import { spawn } from "node:child_process";
 import { randomBytes } from "node:crypto";
 import { appendFileSync, closeSync, existsSync, linkSync, lstatSync, mkdirSync, openSync, readdirSync, readFileSync, realpathSync, renameSync, unlinkSync, writeFileSync } from "node:fs";
 import { constants } from "node:os";
-import { dirname, join, sep } from "node:path";
+import { basename, dirname, join, relative, sep } from "node:path";
 import { childrenOf, cmdlineOf, startTimeOf } from "./proc.mjs";
 import { binds, prepareRun, REPO, sandboxArgv } from "./sandbox.mjs";
 import { SeatError } from "./seat.mjs";
@@ -71,23 +71,33 @@ function segments(what, pairs, code) {
     if (!segment(x)) throw seatError(`${what}: ${name} ${JSON.stringify(x)} isn't an id`, code);
   }
 }
+// A directory under the data root is named by its path relative to the data root, never
+// its host path (#1873). Every segment below the root is a checked id or a fixed name.
+const under = (dataRoot, p) => `under the data root, ${relative(dataRoot, p) || "the root itself"}`;
 // Makes each directory in order, then checks it is ours, a real directory and private.
-function privateDirs(what, dirs, code) {
+function privateDirs(what, dataRoot, dirs, code) {
   for (const d of dirs) {
+    // A system error keeps its code and type; its message names the directory by label.
+    const quiet = (e) => Object.assign(e, { message: `${what}: cannot ${e.syscall ?? "use"} ${under(dataRoot, d)} (${e.code})` });
     try {
       mkdirSync(d, { mode: 0o700 });
     } catch (e) {
-      if (e.code !== "EEXIST") throw e;
+      if (e.code !== "EEXIST") throw quiet(e);
     }
-    const st = lstatSync(d);
-    if (st.isSymbolicLink() || !st.isDirectory() || st.uid !== process.getuid() || st.mode & 0o077) throw seatError(`${what}: ${d} is unsafe`, code);
+    let st;
+    try {
+      st = lstatSync(d);
+    } catch (e) {
+      throw quiet(e);
+    }
+    if (st.isSymbolicLink() || !st.isDirectory() || st.uid !== process.getuid() || st.mode & 0o077) throw seatError(`${what}: ${under(dataRoot, d)} is unsafe`, code);
   }
 }
 export function threadStore(dataRoot, business, thread) {
   segments("thread store", [["business", business], ["thread", thread]], "thread-store-refused");
   const dir = join(dataRoot, "threads", business, thread);
   const out = { dir, session: join(dir, "session"), projects: join(dir, "claude-projects") };
-  privateDirs("thread store", [join(dataRoot, "threads"), join(dataRoot, "threads", business), dir, out.session, out.projects], "thread-store-refused");
+  privateDirs("thread store", dataRoot, [join(dataRoot, "threads"), join(dataRoot, "threads", business), dir, out.session, out.projects], "thread-store-refused");
   return out;
 }
 
@@ -110,11 +120,11 @@ export function sessionStore(dataRoot, business, thread, session, { legacy = fal
       if (e.code !== "ENOENT") throw e;
       old = false;
     }
-    if (old) throw seatError(`thread store: ${join(threadDir, "session")} holds history no legacy session maps`, "legacy-store-unmapped");
+    if (old) throw seatError(`thread store: ${under(dataRoot, join(threadDir, "session"))} holds history no legacy session maps`, "legacy-store-unmapped");
   }
   const dir = join(threadDir, "sessions", session);
   const out = { dir, session: join(dir, "session"), projects: join(dir, "claude-projects") };
-  privateDirs("thread store", [join(dataRoot, "threads"), join(dataRoot, "threads", business), threadDir, join(threadDir, "sessions"), dir, out.session, out.projects], "thread-store-refused");
+  privateDirs("thread store", dataRoot, [join(dataRoot, "threads"), join(dataRoot, "threads", business), threadDir, join(threadDir, "sessions"), dir, out.session, out.projects], "thread-store-refused");
   return out;
 }
 
@@ -138,7 +148,7 @@ export function sessionWorkspace(dataRoot, business, instance, session, { live =
   segments("session workspace", [["business", business], ["instance", instance], ["session", session]], "session-workspace-unsafe");
   const root = join(dataRoot, "session-workspaces");
   const path = join(root, business, instance, session);
-  privateDirs("session workspace", [root, join(root, business), join(root, business, instance), path], "session-workspace-unsafe");
+  privateDirs("session workspace", dataRoot, [root, join(root, business), join(root, business, instance), path], "session-workspace-unsafe");
   const real = realpathSync(path);
   const legacy = join(dataRoot, "workspaces");
   const named = [legacy, join(legacy, business), join(legacy, business, instance)];
@@ -152,11 +162,11 @@ export function sessionWorkspace(dataRoot, business, instance, session, { live =
   };
   for (const p of [...named, ...entries(legacy), ...entries(join(legacy, business))]) {
     const other = realOrNull(p);
-    if (other && (inside(real, other) || inside(other, real))) throw seatError(`session workspace: ${path} overlaps the legacy workspace ${p}`, "session-workspace-overlap");
+    if (other && (inside(real, other) || inside(other, real))) throw seatError(`session workspace: ${under(dataRoot, path)} overlaps the legacy workspace ${relative(dataRoot, p)}`, "session-workspace-overlap");
   }
   for (const p of live) {
     const other = realOrNull(p);
-    if (other && other !== real && (inside(real, other) || inside(other, real))) throw seatError(`session workspace: ${path} overlaps the live workspace ${p}`, "session-workspace-overlap");
+    if (other && other !== real && (inside(real, other) || inside(other, real))) throw seatError(`session workspace: ${under(dataRoot, path)} overlaps a live workspace`, "session-workspace-overlap");
   }
   return path;
 }
@@ -171,7 +181,8 @@ export function lockSessionWorkspace(workspace, owner) {
   const file = `${workspace}.lock`;
   let held = { ...owner };
   const write = (flag) => writeFileSync(file, `${JSON.stringify(held)}\n`, { mode: 0o600, flag });
-  const busy = (why) => seatError(`session workspace ${workspace} is busy: ${why}`, "session-workspace-busy");
+  // Named by its session id (the workspace's last segment, a checked id), never its path (#1873).
+  const busy = (why) => seatError(`session workspace ${basename(workspace)} is busy: ${why}`, "session-workspace-busy");
   for (let attempt = 0; attempt < 2; attempt++) {
     try {
       write("wx");
@@ -209,7 +220,7 @@ export function lockSessionWorkspace(workspace, owner) {
       other = JSON.parse(raw);
     } catch {}
     // An unreadable lock may be one being written, so it counts as held.
-    if (!other || typeof other !== "object") throw busy(`${file} is unreadable`);
+    if (!other || typeof other !== "object") throw busy("its lock is unreadable");
     if (lockAlive(other.hostPid, other.hostStartTime)) throw busy(`host pid ${other.hostPid} holds it`);
     if (lockAlive(other.runPid, other.runStartTime)) throw busy(`run pid ${other.runPid} holds it`);
     // Stale. Move it aside; if what moved isn't what was judged stale, another
@@ -226,11 +237,11 @@ export function lockSessionWorkspace(workspace, owner) {
         linkSync(aside, file);
       } catch {}
       unlinkSync(aside);
-      throw busy(`another host took ${file} over`);
+      throw busy("another host took its lock over");
     }
     unlinkSync(aside);
   }
-  throw busy(`${file} could not be taken`);
+  throw busy("its lock could not be taken");
 }
 
 // The session's environment is an allowlist: nothing else from the host's
@@ -279,7 +290,7 @@ export function newRun(dataRoot, business) {
       if (e.code === "EEXIST") continue;
       throw e;
     }
-    if (Buffer.byteLength(join(runDir, "tools.sock")) > 107) throw new SeatError(`data root path too long for a socket: ${runDir}`, 2);
+    if (Buffer.byteLength(join(runDir, "tools.sock")) > 107) throw new SeatError(`data root path too long for a socket: run ${run}`, 2);
     return { run, runDir };
   }
   throw new SeatError("could not pick a free run id", 1);
@@ -399,9 +410,10 @@ export function readSessions(dataRoot) {
   try {
     doc = JSON.parse(readFileSync(file, "utf8"));
   } catch {
-    throw new SeatError(`sessions file is unreadable: ${file}`, 2);
+    throw new SeatError("sessions file is unreadable: bus-host/sessions.json under the data root", 2);
   }
-  if (!SESSIONS_READ.includes(doc?.sessionsVersion) || !Array.isArray(doc.sessions)) throw new SeatError(`sessions file is malformed: ${file}`, 2);
+  // #1873: named by its fixed place under the data root, never by host path.
+  if (!SESSIONS_READ.includes(doc?.sessionsVersion) || !Array.isArray(doc.sessions)) throw new SeatError("sessions file is malformed: bus-host/sessions.json under the data root", 2);
   return doc.sessions.map((s) => ({ ...s, live: startTimeOf(s.runnerPid) === s.runnerStartTime }));
 }
 
diff --git a/packages/seat/tests/path-redaction-labels.test.mjs b/packages/seat/tests/path-redaction-labels.test.mjs
new file mode 100644
index 000000000..21183a78b
--- /dev/null
+++ b/packages/seat/tests/path-redaction-labels.test.mjs
@@ -0,0 +1,120 @@
+// #1873 (redact6): a seat refusal names the config, the seat or the registration by label,
+// never a host path. The sentinel is a component of every scratch path, so a refusal that
+// quotes a path quotes the sentinel too; each test also checks the scratch root and the label.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { chmodSync, mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { dirname, join } from 'node:path';
+import { SeatError, loadDataRoot, readRegistration, registrationPath, resolveSeat } from '../src/seat.mjs';
+import { lockSessionWorkspace, newRun, readSessions, sessionStore, sessionWorkspace, sessionsFile, threadStore } from '../src/session.mjs';
+
+const secret = 'sk-test-NOT-A-SECRET-1234';
+function scratch(t) {
+  const root = mkdtempSync(join(tmpdir(), 'r6-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+  const dir = join(root, secret);
+  mkdirSync(dir);
+  return { root, dir };
+}
+function labelled(label, root) {
+  return error => {
+    assert.ok(error instanceof SeatError, error.stack);
+    assert.equal(error.message, label);
+    assert.ok(!error.message.includes(root), error.message);
+    assert.doesNotMatch(error.message, /sk-test|NOT-A-SECRET/);
+    return true;
+  };
+}
+function write(file, text) {
+  mkdirSync(dirname(file), { recursive: true });
+  writeFileSync(file, text);
+  return file;
+}
+
+test('config refusals name the config, not its path', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => loadDataRoot(join(dir, 'config.json')), labelled('config not found', root));
+  assert.throws(() => loadDataRoot(write(join(dir, 'array.json'), '[]')), labelled('config is not an object', root));
+  assert.throws(() => loadDataRoot(write(join(dir, 'relative.json'), '{"dataRoot":"data"}')), labelled('config.dataRoot must be an absolute path', root));
+});
+
+test('seat directory refusals name the seat, not its directory', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => resolveSeat(join(dir, 'agents', 'builder')), labelled('no such seat directory: seat builder', root));
+  mkdirSync(join(dir, 'agents', 'builder'), { recursive: true });
+  assert.throws(() => resolveSeat('builder', { repo: dir }), labelled('seat has no launch.sh: seat builder', root));
+  write(join(dir, 'agents', 'builder', 'launch.sh'), '#!/bin/sh\n');
+  chmodSync(join(dir, 'agents', 'builder', 'launch.sh'), 0o644);
+  assert.throws(() => resolveSeat('builder', { repo: dir }), labelled('launch script is not executable: launch.sh of seat builder', root));
+});
+
+test('a registration that does not validate is named by its layout and seat', t => {
+  const { root, dir } = scratch(t);
+  write(registrationPath(dir, 'builder', 'repo'), '{}');
+  assert.throws(() => readRegistration(dir, 'builder', 'repo'), error => {
+    assert.ok(error instanceof SeatError, error.stack);
+    assert.match(error.message, /: registration repo\/builder$/);
+    assert.ok(!error.message.includes(root), error.message);
+    assert.doesNotMatch(error.message, /sk-test|NOT-A-SECRET/);
+    return true;
+  });
+});
+
+test('an unreadable or malformed sessions file is named by its place under the data root', t => {
+  const { root, dir } = scratch(t);
+  write(sessionsFile(dir), 'not json');
+  assert.throws(() => readSessions(dir), labelled('sessions file is unreadable: bus-host/sessions.json under the data root', root));
+  write(sessionsFile(dir), '{"sessionsVersion":0}');
+  assert.throws(() => readSessions(dir), labelled('sessions file is malformed: bus-host/sessions.json under the data root', root));
+});
+
+// Review round (#1873): session stores, workspaces, locks and run directories are named under
+// the data root by their checked ids, never by host path; codes and exits are unchanged.
+function coded(label, root, code) {
+  return error => labelled(label, root)(error) && error.code === code && error.exitCode === 2;
+}
+
+test('an unsafe or unmakeable thread store directory is named under the data root, never by path', t => {
+  const { root, dir } = scratch(t);
+  mkdirSync(join(dir, 'threads'), { mode: 0o755 });
+  chmodSync(join(dir, 'threads'), 0o755);
+  assert.throws(() => threadStore(dir, 'acme', 't1'), coded('thread store: under the data root, threads is unsafe', root, 'thread-store-refused'));
+  // A system error keeps its code; its message names the directory by label.
+  assert.throws(() => threadStore(join(dir, 'absent'), 'acme', 't1'), error => {
+    assert.equal(error.code, 'ENOENT');
+    assert.equal(error.message, 'thread store: cannot mkdir under the data root, threads (ENOENT)');
+    assert.ok(!error.message.includes(root), error.message);
+    return true;
+  });
+});
+
+test('a legacy session store left behind is named under the data root, never by path', t => {
+  const { root, dir } = scratch(t);
+  mkdirSync(join(dir, 'threads', 'acme', 't1', 'session'), { recursive: true, mode: 0o700 });
+  assert.throws(() => sessionStore(dir, 'acme', 't1', 's1'), coded('thread store: under the data root, threads/acme/t1/session holds history no legacy session maps', root, 'legacy-store-unmapped'));
+});
+
+test('a session workspace that overlaps a live one is named under the data root, never by path', t => {
+  const { root, dir } = scratch(t);
+  sessionWorkspace(dir, 'acme', 'i1', 's1');
+  assert.throws(() => sessionWorkspace(dir, 'acme', 'i1', 's2', { live: [join(dir, 'session-workspaces', 'acme')] }), coded('session workspace: under the data root, session-workspaces/acme/i1/s2 overlaps a live workspace', root, 'session-workspace-overlap'));
+});
+
+test('a busy session workspace lock names the session, never the lock path', t => {
+  const { root, dir } = scratch(t);
+  const ws = join(dir, 's1');
+  writeFileSync(`${ws}.lock`, 'not json');
+  assert.throws(() => lockSessionWorkspace(ws, {}), coded('session workspace s1 is busy: its lock is unreadable', root, 'session-workspace-busy'));
+});
+
+test('a data root too long for a socket names the run, never its directory', t => {
+  const { root, dir } = scratch(t);
+  assert.throws(() => newRun(join(dir, 'a'.repeat(70)), 'acme'), error => {
+    assert.ok(error instanceof SeatError, error.stack);
+    assert.equal(error.exitCode, 2);
+    assert.match(error.message, /^data root path too long for a socket: run r[0-9a-f]{12}$/);
+    assert.ok(!error.message.includes(root), error.message);
+    return true;
+  });
+});
diff --git a/packages/seat/tests/refusal-redaction.test.mjs b/packages/seat/tests/refusal-redaction.test.mjs
index 74f9d96f7..9d340b7c9 100644
--- a/packages/seat/tests/refusal-redaction.test.mjs
+++ b/packages/seat/tests/refusal-redaction.test.mjs
@@ -6,10 +6,13 @@ import { dirname, join } from 'node:path';
 const secret = 'sk-test-NOT-A-SECRET-1234';
 // JSON.parse quotes a prefix near this fault on Node 26; check partial leaks too.
 const malformed = secret;
+// #1873: the sentinel is a path component, so a refusal that quotes a path quotes it too.
 function scratch(t) {
   const root = mkdtempSync(join(tmpdir(), 'r3-'));
   t.after(() => rmSync(root, { recursive: true, force: true }));
-  return root;
+  const dir = join(root, secret);
+  mkdirSync(dir);
+  return dir;
 }
 function write(file, text = malformed) {
   mkdirSync(dirname(file), { recursive: true });
@@ -21,6 +24,7 @@ function safe(label, ErrorType, properties = {}) {
     assert.ok(error instanceof ErrorType);
     for (const [key, value] of Object.entries(properties)) assert.equal(error[key], value);
     assert.ok(error.message.includes(label), error.message);
+    assert.ok(!error.message.includes(tmpdir()), error.message);
     assert.doesNotMatch(error.message, /sk-test|Unexpected token/);
     assert.doesNotMatch(error.stack, /sk-test/);
     assert.equal(error.cause, undefined);
@@ -30,13 +34,13 @@ function safe(label, ErrorType, properties = {}) {
 import { SeatError, loadDataRoot, readRegistration, registrationPath } from '../src/seat.mjs';
 for (const kind of ['config', 'registration']) test(`${kind} JSON refusal names only the file`, t => {
   const root = scratch(t), file = write(kind === 'config' ? join(root, 'config.json') : registrationPath(root, 'builder', 'repo'));
-  assert.throws(() => kind === 'config' ? loadDataRoot(file) : readRegistration(root, 'builder', 'repo'), safe(file, SeatError, { exitCode: 2 }));
+  assert.throws(() => kind === 'config' ? loadDataRoot(file) : readRegistration(root, 'builder', 'repo'), safe(kind === 'config' ? 'config is not valid JSON' : 'registration repo/builder is not valid JSON', SeatError, { exitCode: 2 }));
 });
 for (const kind of ['config', 'registration']) test(`${kind} read refusal retains the filesystem code`, t => {
   const root = scratch(t), file = kind === 'config' ? join(root, 'config.json') : registrationPath(root, 'builder', 'repo');
   mkdirSync(file, { recursive: true });
   assert.throws(() => kind === 'config' ? loadDataRoot(file) : readRegistration(root, 'builder', 'repo'), error => {
-    safe(file, SeatError, { exitCode: 2 })(error);
+    safe(kind === 'config' ? 'config is not valid JSON' : 'registration repo/builder is not valid JSON', SeatError, { exitCode: 2 })(error);
     assert.match(error.message, /\(EISDIR\)$/);
     return true;
   });
diff --git a/packages/seat/tests/sandbox.test.mjs b/packages/seat/tests/sandbox.test.mjs
index 08da8d152..c7377a1c8 100644
--- a/packages/seat/tests/sandbox.test.mjs
+++ b/packages/seat/tests/sandbox.test.mjs
@@ -66,11 +66,12 @@ test("row 331 mounts only the parsing validator and fixed marker code, never pro
 
 test("sandboxProblem names a missing bwrap and a bwrap that fails", (t) => {
   const root = scratch(t);
-  assert.equal(sandboxProblem({ bwrap: join(root, "nope") }), `${join(root, "nope")} is missing`);
+  // #1873: the sandbox by name, never the binary's host path.
+  assert.equal(sandboxProblem({ bwrap: join(root, "nope") }), "the sandbox (bwrap) is missing");
   const bad = join(root, "bwrap");
   writeFileSync(bad, "#!/bin/sh\necho 'bwrap: No permissions to create new namespace' >&2\nexit 1\n");
   chmodSync(bad, 0o755);
-  assert.equal(sandboxProblem({ bwrap: bad }), `${bad} failed: bwrap: No permissions to create new namespace`);
+  assert.equal(sandboxProblem({ bwrap: bad }), "the sandbox (bwrap) failed: bwrap: No permissions to create new namespace");
   if (!skip) assert.equal(sandboxProblem(), null);
 });
 
diff --git a/packages/webui/src/sso-config.mjs b/packages/webui/src/sso-config.mjs
index 1238d2842..04f7e7143 100644
--- a/packages/webui/src/sso-config.mjs
+++ b/packages/webui/src/sso-config.mjs
@@ -22,7 +22,8 @@ function refuse(where, why) {
 }
 function keys(value, where, allowed, required = allowed) {
   if (!object(value)) refuse(where, 'must be a JSON object');
-  for (const key of Object.keys(value)) if (!allowed.includes(key)) refuse(`${where}.${key}`, 'is not a supported key');
+  // #1873: an unknown key is named only when it is a plain name; a key can be anything, a host path too.
+  for (const key of Object.keys(value)) if (!allowed.includes(key)) refuse(/^[A-Za-z_][A-Za-z0-9_-]{0,63}$/.test(key) ? `${where}.${key}` : where, /^[A-Za-z_][A-Za-z0-9_-]{0,63}$/.test(key) ? 'is not a supported key' : 'has a key that is not a plain name');
   for (const key of required) if (!Object.hasOwn(value, key)) refuse(`${where}.${key}`, 'is required');
 }
 function httpsURL(value, where) {
diff --git a/scripts/mosaic-config.mjs b/scripts/mosaic-config.mjs
index a676242a5..6c8220c41 100755
--- a/scripts/mosaic-config.mjs
+++ b/scripts/mosaic-config.mjs
@@ -67,6 +67,16 @@ function fail(exitCode, message) {
   throw new Failure(exitCode, message);
 }
 
+// #1873: a refusal names the config by where it came from, the data root and its marker by
+// their roles, and a key or argument only when it is a plain name; never a host path or a raw
+// error message. CONFIG is set when the selection is made.
+let CONFIG = "the default system config";
+function configLabel(instance) {
+  return isNamed(instance) ? `the config of instance ${instance}` : process.env.MOSAIC_CONFIG ? "the system config MOSAIC_CONFIG names" : "the default system config";
+}
+const plain = (value, otherwise) => /^[A-Za-z_][A-Za-z0-9_.-]{0,63}$/.test(String(value)) ? JSON.stringify(String(value)) : otherwise;
+const MARKER_LABEL = "the data root's instance marker";
+
 function instancePath(name) {
   return path.join(os.homedir(), ".config", `mosaic-${name}`, "config.json");
 }
@@ -82,6 +92,7 @@ function realOrNull(file) {
 // The config file for a selection. Without --instance, as before. With it,
 // NAME's file; a $MOSAIC_CONFIG beside it must be the same file.
 function configPath(instance) {
+  CONFIG = configLabel(instance);
   if (instance === null) {
     return process.env.MOSAIC_CONFIG
       ? path.resolve(process.env.MOSAIC_CONFIG)
@@ -92,7 +103,7 @@ function configPath(instance) {
     const given = path.resolve(process.env.MOSAIC_CONFIG);
     const same = given === named || (realOrNull(given) !== null && realOrNull(given) === realOrNull(named));
     if (!same) {
-      fail(4, `instance-config-mismatch: --instance ${instance} names ${named}, but MOSAIC_CONFIG names ${given}`);
+      fail(4, `instance-config-mismatch: --instance ${instance} names its own config, but MOSAIC_CONFIG names another file`);
     }
   }
   return named;
@@ -106,7 +117,7 @@ function parseArgs(args) {
   }
   const name = args[1];
   if (!INSTANCE_PATTERN.test(name)) {
-    fail(4, `instance-name-invalid: ${JSON.stringify(name)} must match ${INSTANCE_PATTERN}`);
+    fail(4, `instance-name-invalid: ${plain(name, "that name")} must match ${INSTANCE_PATTERN}`);
   }
   return name;
 }
@@ -124,20 +135,20 @@ function readMarker(dataRoot) {
     stat = fs.lstatSync(file);
   } catch (error) {
     if (error.code === "ENOENT") return null;
-    fail(3, `instance-root-unclaimed: cannot read ${file} (${error.code})`);
+    fail(3, `instance-root-unclaimed: cannot read ${MARKER_LABEL} (${error.code})`);
   }
   if (!stat.isFile() || stat.isSymbolicLink()) {
-    fail(3, `instance-root-unclaimed: ${file} must be a regular, non-symbolic-link file`);
+    fail(3, `instance-root-unclaimed: ${MARKER_LABEL} must be a regular, non-symbolic-link file`);
   }
   let marker;
   try {
     marker = JSON.parse(fs.readFileSync(file, "utf8"));
   } catch (error) {
-    fail(3, `instance-root-unclaimed: ${file} is not a valid marker (${error instanceof SyntaxError ? 'not valid JSON' : error.message})`);
+    fail(3, `instance-root-unclaimed: ${MARKER_LABEL} is not a valid marker (${error instanceof SyntaxError ? 'not valid JSON' : `cannot read it, ${error.code ?? "error"}`})`);
   }
   if (!isPlainObject(marker) || Object.keys(marker).sort().join(",") !== "instanceVersion,name"
       || marker.instanceVersion !== 1 || typeof marker.name !== "string" || !INSTANCE_PATTERN.test(marker.name)) {
-    fail(3, `instance-root-unclaimed: ${file} is not a valid marker ({"instanceVersion":1,"name":NAME})`);
+    fail(3, `instance-root-unclaimed: ${MARKER_LABEL} is not a valid marker ({"instanceVersion":1,"name":NAME})`);
   }
   return marker.name;
 }
@@ -148,13 +159,13 @@ function checkClaim(dataRoot, instance) {
   const owner = readMarker(dataRoot);
   if (isNamed(instance)) {
     if (owner === null) {
-      fail(3, `instance-root-unclaimed: ${dataRoot} holds no ${MARKER} naming ${instance} (scripts/bootstrap.sh --instance ${instance} claims a new root)`);
+      fail(3, `instance-root-unclaimed: the data root holds no ${MARKER} naming ${instance} (scripts/bootstrap.sh --instance ${instance} claims a new root)`);
     }
     if (owner !== instance) {
-      fail(3, `instance-root-mismatch: ${dataRoot} is claimed by instance ${owner}, not ${instance}`);
+      fail(3, `instance-root-mismatch: the data root is claimed by instance ${owner}, not ${instance}`);
     }
   } else if (owner !== null && owner !== DEFAULT_INSTANCE) {
-    fail(3, `instance-root-mismatch: ${dataRoot} is claimed by instance ${owner}; select it with --instance ${owner}`);
+    fail(3, `instance-root-mismatch: the data root is claimed by instance ${owner}; select it with --instance ${owner}`);
   }
 }
 
@@ -166,19 +177,19 @@ function readRaw(file) {
     return null; // missing
   }
   if (!stat.isFile() || stat.isSymbolicLink()) {
-    fail(2, `configuration path must be a regular, non-symbolic-link file: ${file}`);
+    fail(2, `configuration path must be a regular, non-symbolic-link file: ${CONFIG}`);
   }
   try {
     return fs.readFileSync(file, "utf8");
   } catch {
-    fail(2, `configuration file is not readable: ${file}`);
+    fail(2, `configuration file is not readable: ${CONFIG}`);
   }
 }
 
 function rejectUnknownKeys(object, allowed, where) {
   for (const key of Object.keys(object)) {
     if (!allowed.includes(key)) {
-      fail(2, `unsupported ${where} key: "${key}"`);
+      fail(2, `unsupported ${where} key: ${plain(key, "that is not a plain name")}`);
     }
   }
 }
@@ -206,11 +217,11 @@ function validateDataRoot(value, file) {
   }
   const home = path.resolve(os.homedir());
   if (resolved === home || isAncestorOf(resolved, home)) {
-    fail(2, `execution "dataRoot" must not be or contain the home directory (${home})`);
+    fail(2, 'execution "dataRoot" must not be or contain the home directory');
   }
   const configDir = path.dirname(path.resolve(file));
   if (resolved === configDir || isAncestorOf(resolved, configDir)) {
-    fail(2, `execution "dataRoot" must not be or contain the configuration directory (${configDir})`);
+    fail(2, 'execution "dataRoot" must not be or contain the configuration directory');
   }
   return resolved;
 }
@@ -377,13 +388,14 @@ async function load(file, instance = null) {
   const raw = readRaw(file);
   if (raw === null) {
     const bootstrap = isNamed(instance) ? `scripts/bootstrap.sh --instance ${instance}` : "scripts/bootstrap.sh";
-    fail(3, `configuration not found: ${file} (run ${bootstrap} to create it)`);
+    // #1873: named by where it came from, never by host path.
+    fail(3, `configuration not found: ${configLabel(instance)} (run ${bootstrap} to create it)`);
   }
   let document;
   try {
     document = JSON.parse(raw);
   } catch {
-    fail(2, `configuration is not valid JSON (${file})`);
+    fail(2, `configuration is not valid JSON (${CONFIG})`);
   }
   return await validate(document, file);
 }
@@ -409,7 +421,7 @@ const DEFAULT_CONFIG = defaultConfig(path.join(os.homedir(), ".mosaic-dev"));
 
 // 'wx': creation is exclusive; an existing file is never overwritten, and a
 // symbolic link at the path is never followed.
-function createExclusive(file, text, label = file) {
+function createExclusive(file, text, label) {
   let fd;
   try {
     fd = fs.openSync(file, "wx", 0o644);
@@ -417,7 +429,7 @@ function createExclusive(file, text, label = file) {
     return true;
   } catch (error) {
     if (error.code === "EEXIST") return false;
-    fail(1, `unable to create ${label}: ${error.message}`);
+    fail(1, `unable to create ${label} (${error.code ?? "error"})`);
   } finally {
     if (fd !== undefined) fs.closeSync(fd);
   }
@@ -452,23 +464,23 @@ async function bootstrapNamed(file, instance) {
   let entries = null;
   try {
     const stat = fs.lstatSync(dataRoot);
-    if (!stat.isDirectory()) fail(3, `instance-root-unclaimed: ${dataRoot} exists and is not a directory; nothing was written`);
+    if (!stat.isDirectory()) fail(3, `instance-root-unclaimed: the instance's data root exists and is not a directory; nothing was written`);
     entries = fs.readdirSync(dataRoot);
   } catch (error) {
     if (error instanceof Failure) throw error;
-    if (error.code !== "ENOENT") fail(3, `instance-root-unclaimed: cannot read ${dataRoot} (${error.code}); nothing was written`);
+    if (error.code !== "ENOENT") fail(3, `instance-root-unclaimed: cannot read the instance's data root (${error.code}); nothing was written`);
   }
   if (entries !== null && entries.length > 0 && readMarker(dataRoot) !== instance) {
-    fail(3, `instance-root-unclaimed: ${dataRoot} exists, is not empty and holds no ${MARKER} naming ${instance}; nothing was written`);
+    fail(3, `instance-root-unclaimed: the instance's data root exists, is not empty and holds no ${MARKER} naming ${instance}; nothing was written`);
   }
   const configDir = path.dirname(file);
   fs.mkdirSync(path.dirname(configDir), { recursive: true });
   try {
     fs.mkdirSync(configDir, { mode: 0o700 });
   } catch (error) {
-    if (error.code !== "EEXIST") fail(1, `unable to create ${configDir}: ${error.message}`);
+    if (error.code !== "EEXIST") fail(1, `unable to create the config directory of instance ${instance} (${error.code ?? "error"})`);
   }
-  if (!createExclusive(file, `${JSON.stringify(defaultConfig(dataRoot), null, 2)}\n`)) {
+  if (!createExclusive(file, `${JSON.stringify(defaultConfig(dataRoot), null, 2)}\n`, CONFIG)) {
     const resolved = await load(file, instance);
     checkClaim(resolved.dataRoot, instance);
     return;
@@ -477,9 +489,9 @@ async function bootstrapNamed(file, instance) {
   try {
     fs.mkdirSync(resolved.dataRoot, { mode: 0o700 });
   } catch (error) {
-    if (error.code !== "EEXIST") fail(1, `unable to create ${resolved.dataRoot}: ${error.message}`);
+    if (error.code !== "EEXIST") fail(1, `unable to create the data root (${error.code ?? "error"})`);
   }
-  createExclusive(path.join(resolved.dataRoot, MARKER), `${JSON.stringify({ instanceVersion: 1, name: instance })}\n`);
+  createExclusive(path.join(resolved.dataRoot, MARKER), `${JSON.stringify({ instanceVersion: 1, name: instance })}\n`, MARKER_LABEL);
   checkClaim(resolved.dataRoot, instance);
   process.stderr.write(`mosaic-config: created configuration for instance ${instance}: ${file}, data root ${resolved.dataRoot}\n`);
 }
@@ -531,7 +543,7 @@ const operation = process.argv[2];
 
 try {
   if (!["bootstrap", "validate", "env", "instance"].includes(operation)) {
-    fail(1, `unknown operation: ${JSON.stringify(operation ?? "")} (expected bootstrap | validate | env | instance)`);
+    fail(1, `unknown operation: ${plain(operation ?? "", "that is not one")} (expected bootstrap | validate | env | instance)`);
   }
   const instance = parseArgs(process.argv.slice(3));
   switch (operation) {