diff --git a/packages/bus/README.md b/packages/bus/README.md
index b0c469263..18f3039dd 100644
--- a/packages/bus/README.md
+++ b/packages/bus/README.md
@@ -324,6 +324,8 @@ refuses `message-not-found`; malformed arguments refuse `invalid-request`.
 Roles get `human-required`. A successful read records nothing, so Console
 history reads never prevent a later `message.receive` from delivering it.
 
+A tester (row 110, #1604) is a PM test's sender, never the human. `src/tester-cli.mjs <socket>` is human-cli.mjs with its own nonce variable, `MOSAIC_BUS_TESTER_NONCE`, so neither shim's nonce proves the other. `verifyTester` (`src/tester.mjs`) checks the same process proof but walks the ancestry for a managed run only: a launch record, `MOSAIC_RUN_ID`, `MOSAIC_BUS_CAP` or `MOSAIC_AGENT_RUN` refuses `tester-required`. Claude and Codex markers pass, since a tester runs from inside Mos or a T3 seat. A role session can't bind: its shim reports a pid from the sandbox's PID namespace, and the seat sandbox test runs that case under bwrap. `bindTester` then binds only when the business var `bus.tester` is exactly `true`, read at bus start, else `tester-off`. A request carries exactly one of `cap`, `human` or `tester`. The session may use `message.send`, `message.receive` and `message.read`, plus the reader's views of `inbox`, `agents`, `tasks`, `trail`, `decisions`, `messages` and `replies`; every other verb refuses `tester-refused`. It sends only to a role, with a body that starts `[mos test]` (`tester-prefix`) and no `corrects` or `decision`. Its message is stored `from_role 'tester'`, `from_run 'tester-cli'`, with no request and no event, so no `human.input` backs it and `task_create` can't cite it. A role answers at the `tester` address, and only with `in_reply_to` naming a tester's message (`tester-reply-required`); the human can't send there. Those replies never reach the human's `message.receive` or `messages`.
+
 ## Shared reads and adapter boundary
 
 ```js
diff --git a/packages/bus/src/broker.mjs b/packages/bus/src/broker.mjs
index ddc18f21c..64a544d4b 100644
--- a/packages/bus/src/broker.mjs
+++ b/packages/bus/src/broker.mjs
@@ -50,6 +50,10 @@ const TASK_ARGS = ['done', 'assignee', 'label', 'requirement', 'limit', 'after',
 export const TASK_PAGE = 50;
 export const TASK_PAGE_MAX = 200;
 export const TASK_VERBS = Object.freeze(ACTIONS.filter((a) => a.startsWith('task.')));
+// Row 110 (#1604): what a tester session may do. Send to a role, receive and read the replies
+// sent to `tester`, and the human's read views. Every other verb refuses tester-refused.
+const TESTER_VERBS = ['message.send', 'message.receive', 'message.read', 'inbox', 'agents', 'tasks', 'trail', 'decisions', 'messages', 'replies'];
+const TESTER_PREFIX = '[mos test]';
 const SELF_KINDS = new Set(['task.created', 'task.assigned', 'task.state', 'task.closed', 'task.conflict']);
 const POLL_KINDS = new Set([
   'task.changed.external',
@@ -133,7 +137,7 @@ export class Broker {
       if (!id(name) || b.id !== name || !id(b.human) || !object(b.roles) || !object(b.arbiters))
         fail('invalid-business');
       for (const role of Object.keys(b.roles)) {
-        if (!id(role) || role === 'human') fail('invalid-business');
+        if (!id(role) || role === 'human' || role === 'tester') fail('invalid-business');
         const a = b.roles[role].authority;
         if (!object(a) || !Array.isArray(a.withinRole) || !Array.isArray(a.crossRole))
           fail('invalid-authority');
@@ -164,6 +168,7 @@ export class Broker {
     );
   }
   #agent(s) {
+    if (s.tester) fail('tester-refused');
     if (s.reader) fail('read-only');
     if (s.human) fail('agent-required');
     const h = this.#holder(s.business, s.role);
@@ -254,6 +259,14 @@ export class Broker {
       fail('human-required');
     return this.#cap({ ...record, role: null, run: null, human: b.human });
   }
+  // Row 110 (#1604): the trusted tester transport invokes this only after checking its CLI process
+  // and that no managed run is among its ancestors. The business turns testing on with the business
+  // var `bus.tester`, exactly true; anything else refuses tester-off.
+  bindTester(record) {
+    keys(record, ['business'], ['business']);
+    if (this.#business(record.business).vars?.['bus.tester'] !== true) fail('tester-off');
+    return this.#cap({ business: record.business, tester: true, role: 'tester', run: null, human: false });
+  }
   bindReader({ business }) {
     this.#business(business);
     return this.#cap({ business, reader: true, role: null, run: null, human: false });
@@ -656,7 +669,10 @@ export class Broker {
       return this.#store.transaction(() => {
         if (s.reader && !['inbox', 'agents', 'tasks', 'trail', 'decisions', 'credentials', 'replies', 'messages', 'state'].includes(request.verb))
           fail('read-only');
-        const result = this.#dispatch(s, request.verb, args);
+        if (s.tester && !TESTER_VERBS.includes(request.verb)) fail('tester-refused');
+        // A tester reads the human's views, as a reader does, and its message verbs are its own.
+        const view = s.tester && !request.verb.startsWith('message.') ? { ...s, reader: true } : s;
+        const result = this.#dispatch(view, request.verb, args);
         this.#secretCheck(result);
         return result;
       });
@@ -877,14 +893,29 @@ export class Broker {
       }
       case 'message.send': {
         keys(a, ['to', 'body', 'class', 'in_reply_to', 'corrects', 'decision'], ['to', 'body']);
-        if (!s.human) {
+        if (s.tester) {
+          // A tester writes to a role only, says so in its first words, and cites no decision.
+          // It consumes no authority and writes no human.input.
+          keys(a, ['to', 'body', 'class', 'in_reply_to'], ['to', 'body']);
+          if (!Object.hasOwn(b.roles, a.to)) fail('unknown-role');
+          if (typeof a.body !== 'string' || !a.body.startsWith(TESTER_PREFIX)) fail('tester-prefix');
+        } else if (!s.human) {
           const withinRole = this.#classification(s, 'message.send') === 'within-role';
           this.#consumeAuthority(s, 'message.send', {
             decision: withinRole ? null : (a.decision ?? null),
             target: a.to,
           });
-        } else this.#human(s);
-        if (a.to !== 'human' && !Object.hasOwn(b.roles, a.to)) fail('unknown-role');
+          // A role answers a tester only in reply to a tester's message.
+          if (
+            a.to === 'tester' &&
+            !(id(a.in_reply_to) && this.#store.get("SELECT 1 FROM messages WHERE id=? AND business=? AND from_role='tester'", a.in_reply_to, s.business))
+          )
+            fail('tester-reply-required');
+        } else {
+          this.#human(s);
+          if (a.to === 'tester') fail('unknown-role');
+        }
+        if (a.to !== 'human' && a.to !== 'tester' && !Object.hasOwn(b.roles, a.to)) fail('unknown-role');
         string(a.body, 32768);
         if (
           a.class !== undefined &&
@@ -915,7 +946,7 @@ export class Broker {
           this.#now(),
           s.business,
           s.human ? 'human' : s.role,
-          s.human ? 'human-cli' : s.run,
+          s.human ? 'human-cli' : s.tester ? 'tester-cli' : s.run,
           a.to,
           a.class ?? 'INFO',
           a.in_reply_to ?? null,
@@ -933,7 +964,7 @@ export class Broker {
       case 'message.receive': {
         keys(a, []);
         if (s.human) this.#human(s);
-        else this.#agent(s);
+        else if (!s.tester) this.#agent(s);
         const role = s.human ? 'human' : s.role;
         const rows = this.#store.all(
           "SELECT * FROM messages m WHERE business=? AND to_role=? AND NOT EXISTS(SELECT 1 FROM deliveries d WHERE d.message=m.id AND d.op IN ('delivered','read')) ORDER BY seq LIMIT 100",
@@ -944,8 +975,8 @@ export class Broker {
           this.#delivery(
             m.id,
             'delivered',
-            s.human ? null : this.#holder(s.business, s.role),
-            s.human ? 'cli' : 'broker',
+            s.human || s.tester ? null : this.#holder(s.business, s.role),
+            s.human || s.tester ? 'cli' : 'broker',
           );
         return rows.map((m) => ({
           ...m,
@@ -960,7 +991,7 @@ export class Broker {
       case 'message.read': {
         keys(a, ['id'], ['id']);
         if (s.human) this.#human(s);
-        else this.#agent(s);
+        else if (!s.tester) this.#agent(s);
         const m = this.#store.get('SELECT * FROM messages WHERE business=? AND id=?', s.business, a.id);
         if (!m || m.to_role !== (s.human ? 'human' : s.role)) fail('message-not-found');
         const delivery = this.#store.get(
@@ -969,7 +1000,7 @@ export class Broker {
         );
         if (!delivery || delivery.holder_run !== (s.run ?? null)) fail('not-recipient');
         if (!this.#store.get("SELECT seq FROM deliveries WHERE message=? AND op='read'", m.id))
-          this.#delivery(m.id, 'read', s.human ? null : this.#holder(s.business, s.role));
+          this.#delivery(m.id, 'read', s.human || s.tester ? null : this.#holder(s.business, s.role));
         return { read: true };
       }
       // Row 93 (#1587): the coder asks a reviewer role to review the task's latest pushed commit.
diff --git a/packages/bus/src/client.mjs b/packages/bus/src/client.mjs
index 52d46be3d..11543b5b3 100644
--- a/packages/bus/src/client.mjs
+++ b/packages/bus/src/client.mjs
@@ -1,15 +1,20 @@
 import { connect } from 'node:net';
 import { BusError } from './broker.mjs';
 export class Client {
-  constructor({ path, cap, human, timeout = 5000 }) {
+  constructor({ path, cap, human, tester, timeout = 5000 }) {
     this.path = path;
     this.cap = cap;
     this.human = human;
+    this.tester = tester;
     this.timeout = timeout;
   }
   call(verb, args = {}) {
     const request =
-      JSON.stringify({ ...(this.human ? { human: this.human } : { cap: this.cap }), verb, args }) + '\n';
+      JSON.stringify({
+        ...(this.human ? { human: this.human } : this.tester ? { tester: this.tester } : { cap: this.cap }),
+        verb,
+        args,
+      }) + '\n';
     if (Buffer.byteLength(request) > 65536) return Promise.reject(new BusError('request-too-large'));
     return new Promise((resolve, reject) => {
       const socket = connect(this.path);
diff --git a/packages/bus/src/runtime.mjs b/packages/bus/src/runtime.mjs
index a4912853f..dbb09e9b6 100644
--- a/packages/bus/src/runtime.mjs
+++ b/packages/bus/src/runtime.mjs
@@ -5,6 +5,7 @@ import { Broker, BusError } from './broker.mjs';
 import { Credentials } from './credentials.mjs';
 import { serve } from './server.mjs';
 import { verifyHuman } from './human.mjs';
+import { verifyTester } from './tester.mjs';
 // Trusted host API. S1 supplies resolved definitions, S6 supplies launch records and ends them.
 // Neither a business-file writer nor a socket-accessible configuration endpoint.
 // `tasks` is S3's adapter factory: ({broker, credentials, businesses}) => {handle, timeout, close}.
@@ -72,6 +73,15 @@ export async function startBroker({
         if (!human) throw new BusError('unknown-business');
         return broker.bindHuman({ business, human, via: 'cli', outsideAgent: true });
       },
+      // Row 110 (#1604): a tester proves its CLI process and that no managed run is above it.
+      // The broker then binds only if the business sets `bus.tester` to true.
+      authenticateTester: (proof) => {
+        const { business } = verifyTester(proof, {
+          cliPath: fileURLToPath(new URL('./tester-cli.mjs', import.meta.url)),
+          launches: launchRecords,
+        });
+        return broker.bindTester({ business });
+      },
     });
     // S6 launcher operations. The host decides capacity and the instance list; the broker
     // authorizes role.launch and keeps the evidence, refusals included.
diff --git a/packages/bus/src/server.mjs b/packages/bus/src/server.mjs
index 860d88bd0..b6517bfc3 100644
--- a/packages/bus/src/server.mjs
+++ b/packages/bus/src/server.mjs
@@ -4,7 +4,8 @@ import { BusError, TASK_VERBS } from './broker.mjs';
 const LIMIT = 65536;
 // One request per connection. There is deliberately no reconnect/retry or SQL verb.
 // `tasks` ({handle, timeout}) is the trusted S3 adapter; only the eight task verbs reach it.
-export async function serve({ broker, path, authenticateHuman = null, timeout = 5000, tasks = null }) {
+// A request carries exactly one of cap, human (row S4) and tester (row 110) proof.
+export async function serve({ broker, path, authenticateHuman = null, authenticateTester = null, timeout = 5000, tasks = null }) {
   try {
     lstatSync(path);
     throw new BusError('socket-exists');
@@ -44,9 +45,9 @@ export async function serve({ broker, path, authenticateHuman = null, timeout =
           !r ||
           Array.isArray(r) ||
           typeof r !== 'object' ||
-          Object.keys(r).some((k) => !['cap', 'human', 'verb', 'args'].includes(k)) ||
+          Object.keys(r).some((k) => !['cap', 'human', 'tester', 'verb', 'args'].includes(k)) ||
           typeof r.verb !== 'string' ||
-          Boolean(r.cap) === Boolean(r.human)
+          [r.cap, r.human, r.tester].filter(Boolean).length !== 1
         )
           throw new BusError('invalid-envelope');
         let cap = r.cap;
@@ -54,6 +55,10 @@ export async function serve({ broker, path, authenticateHuman = null, timeout =
           if (!authenticateHuman) throw new BusError('human-required');
           transient = cap = authenticateHuman(r.human);
         }
+        if (r.tester) {
+          if (!authenticateTester) throw new BusError('tester-required');
+          transient = cap = authenticateTester(r.tester);
+        }
         if (typeof cap !== 'string') throw new BusError('unauthenticated');
         if (tasks && TASK_VERBS.includes(r.verb)) {
           const own = transient;
diff --git a/packages/business/README.md b/packages/business/README.md
index 8c7a43350..f36ded9eb 100644
--- a/packages/business/README.md
+++ b/packages/business/README.md
@@ -141,6 +141,10 @@ each layer that sets one narrows it, and the result also narrows the role
 definition. `limits.authority` is an allowlist, so a role action it leaves
 out becomes gated.
 
+`bus.tester` is business-only and defaults to false. Set to `true`, the bus
+binds a tester from `tester-cli.mjs` for PM tests; it reads the value at bus
+start, so a change takes a bus restart.
+
 `resolve` prints `provenance` beside `vars`. For a plain key it's the
 layer that set the value (`default`, `system`, `business:<id>`,
 `project:<id>`, `project:<id>:roles.<instance>`,
diff --git a/packages/business/src/vars.mjs b/packages/business/src/vars.mjs
index 69b6ea575..c7e8d0a67 100644
--- a/packages/business/src/vars.mjs
+++ b/packages/business/src/vars.mjs
@@ -96,6 +96,8 @@ export const REGISTRY = Object.freeze({
     return v;
   }),
   "gitea.baseUrl": def(["business"], baseUrl),
+  // On: the bus binds a tester from tester-cli.mjs for PM tests (row 110). Read at bus start.
+  "bus.tester": def(["business"], boolean, { default: false }),
 
   // Project.
   "tracker.project": def(["project"], (v, key) => requirePositiveInt(v, `variable ${key}`)),
diff --git a/packages/business/tests/vars.test.mjs b/packages/business/tests/vars.test.mjs
index ab7d2b3cd..b5db7ef8c 100644
--- a/packages/business/tests/vars.test.mjs
+++ b/packages/business/tests/vars.test.mjs
@@ -33,7 +33,7 @@ test("unknown keys and wrong layers refuse", () => {
 
 test("types", () => {
   const ok = (vars, layer) => assert.deepEqual({ ...checkVars(vars, layer, "v") }, vars);
-  ok({ "tracker.baseUrl": "https://tasks.example:3456", "tracker.reconcileMinutes": 1, "tracker.pollSeconds": 10, "human.discordUserId": "123456789012345678" }, "business");
+  ok({ "tracker.baseUrl": "https://tasks.example:3456", "tracker.reconcileMinutes": 1, "tracker.pollSeconds": 10, "human.discordUserId": "123456789012345678", "bus.tester": true }, "business");
   ok({ "tracker.project": 3, "git.workingBranch": "refactor", "git.protectedBranches": ["main", "next"], suites: ["scripts/test-task.sh"], "issues.repo": "mosaicstack/stack", "tracker.descendants": true }, "project");
   ok({ harness: "claude-code", model: "claude-opus-5-5", thinking: "high", "limits.tools": [], "limits.network": "none", "limits.authority": ["message.send"] }, "agent");
 
@@ -53,6 +53,11 @@ test("types", () => {
     [{ "tracker.descendants": "true" }, "project", /true or false/],
     [{ "tracker.descendants": 1 }, "project", /true or false/],
     [{ "tracker.descendants": true }, "business", /business layer \(allowed: project\)/],
+    [{ "bus.tester": "true" }, "business", /true or false/],
+    [{ "bus.tester": 1 }, "business", /true or false/],
+    [{ "bus.tester": true }, "project", /project layer \(allowed: business\)/],
+    [{ "bus.tester": true }, "agent", /agent layer \(allowed: business\)/],
+    [{ "bus.tester": true }, "system", /system layer \(allowed: business\)/],
     [{ "git.workingBranch": "-x" }, "project", /git branch name/],
     [{ "git.workingBranch": "a..b" }, "project", /git branch name/],
     [{ "git.workingBranch": "x.lock" }, "project", /git branch name/],
@@ -83,6 +88,8 @@ test("merge: defaults, then the most specific layer wins", () => {
   assert.equal(vars["tracker.kind"], "vikunja");
   assert.equal(vars["tracker.descendants"], false);
   assert.equal(provenance["tracker.descendants"], "default");
+  assert.equal(vars["bus.tester"], false);
+  assert.equal(provenance["bus.tester"], "default");
   assert.equal(vars.harness, undefined);
   assert.equal(provenance.harness, undefined);
 });
diff --git a/packages/cli/README.md b/packages/cli/README.md
index 3111fe03d..e23d8fb0d 100644
--- a/packages/cli/README.md
+++ b/packages/cli/README.md
@@ -80,6 +80,16 @@ mosaic launches list [--json]
   the bus (see "Sessions" below). `stop` refuses inside an agent run;
   `launches list` does not, because the file is readable to the same user
   anyway.
+- `--tester` (row 110, #1604) runs `inbox`, `tasks`, `agents`, `trail`,
+  `talk` and `follow` as the business's tester through
+  `packages/bus/src/tester-cli.mjs` instead of as the human. It is the one
+  exception to the agent check above: Mos or a T3 seat may run it for a PM
+  test, and the broker still refuses it under a managed run
+  (`tester-required`) or while the business var `bus.tester` isn't `true`
+  (`tester-off`), each exit 3. `talk --tester` text must start with
+  `[mos test]`, else exit 2 before any call. The role's reply comes back to
+  the tester, not to the human's inbox. `decide`, `stop` and `launches`
+  take no `--tester` (exit 4).
 
 ## The app
 
diff --git a/packages/cli/src/cli.mjs b/packages/cli/src/cli.mjs
index fcd7c0132..a547e36c7 100644
--- a/packages/cli/src/cli.mjs
+++ b/packages/cli/src/cli.mjs
@@ -15,7 +15,7 @@ import { fileURLToPath } from "node:url";
 import { BINDING_NAME } from "../../discord/src/binding.mjs";
 import { CliError } from "./errors.mjs";
 import { bootConfig, loadSystem, socketPath } from "./config.mjs";
-import { humanTransport, refuseInsideAgent } from "./transport.mjs";
+import { humanTransport, refuseInsideAgent, testerTransport } from "./transport.mjs";
 import { formatAgents, formatDecision, formatInbox, formatTasks, formatTrail, shortId } from "./format.mjs";
 import { hostStatus, readHostState, startHost, stopHost } from "./host.mjs";
 import { createLauncher } from "./launcher.mjs";
@@ -24,13 +24,13 @@ import { readSessions, stopSession } from "../../seat/src/session.mjs";
 import { SeatError } from "../../seat/src/seat.mjs";
 
 export const USAGE = `usage:
-  mosaic inbox [--business <id>] [--json]
+  mosaic inbox [--business <id>] [--json] [--tester]
   mosaic decide <decision> <option> [--note <text>] [--yes] [--business <id>]
-  mosaic tasks [--business <id>] [--json]
-  mosaic agents [--business <id>] [--json]
-  mosaic trail <task|decision> [--business <id>] [--json]
-  mosaic talk <role> <text> [--wait <seconds> | --follow] [--business <id>]
-  mosaic follow [--business <id>]
+  mosaic tasks [--business <id>] [--json] [--tester]
+  mosaic agents [--business <id>] [--json] [--tester]
+  mosaic trail <task|decision> [--business <id>] [--json] [--tester]
+  mosaic talk <role> <text> [--wait <seconds> | --follow] [--business <id>] [--tester]
+  mosaic follow [--business <id>] [--tester]
   mosaic stop <run>
   mosaic launches off|on [--business <id>]
   mosaic launches list [--json]
@@ -155,13 +155,22 @@ export async function resolveDecision({ call, ref, choice, note, write, ask }) {
   return d;
 }
 
-async function human(verb, rest, io, deps) {
-  const spec = verb === "decide" ? { flags: ["--yes"], values: ["--business", "--note"] } : { flags: ["--json"], values: ["--business"] };
-  const parsed = parse(rest, spec);
-  refuseInsideAgent(io.env);
+// The bus call for one command. --tester (row 110) binds as the business's
+// tester through tester-cli.mjs instead of as the human, and may run inside
+// an agent; the broker refuses it under a managed run or with bus.tester off.
+function callFor(parsed, io, deps) {
+  const tester = parsed.flags.has("--tester");
+  if (!tester) refuseInsideAgent(io.env);
   const system = deps.system ?? loadSystem({ env: io.env });
   const business = businessFor(parsed, system.dataRoot);
-  const call = deps.transport ? deps.transport(business) : humanTransport({ socket: socketPath(system.dataRoot), business, env: io.env });
+  if (tester) return deps.testerTransport ? deps.testerTransport(business) : testerTransport({ socket: socketPath(system.dataRoot), business, env: io.env, spawn: deps.testerSpawn });
+  return deps.transport ? deps.transport(business) : humanTransport({ socket: socketPath(system.dataRoot), business, env: io.env });
+}
+
+async function human(verb, rest, io, deps) {
+  const spec = verb === "decide" ? { flags: ["--yes"], values: ["--business", "--note"] } : { flags: ["--json", "--tester"], values: ["--business"] };
+  const parsed = parse(rest, spec);
+  const call = callFor(parsed, io, deps);
   if (verb === "decide") return decide(parsed, call, io);
   const json = parsed.flags.has("--json");
   const print = (value, text) => io.stdout.write(json ? `${JSON.stringify(value, null, 2)}\n` : text(value));
@@ -189,6 +198,7 @@ async function human(verb, rest, io, deps) {
 }
 
 const TALK_WAIT_S = 900;
+const TESTER_PREFIX = "[mos test]";
 const TALK_POLL_MS = 2000;
 
 function formatMessage(m) {
@@ -200,18 +210,17 @@ function formatMessage(m) {
 // until the reply arrives or --wait runs out. --follow keeps receiving after
 // that reply; follow starts the same receive loop without sending.
 async function talk(rest, io, deps, receiveOnly = false) {
-  const parsed = parse(rest, { flags: ["--follow"], values: ["--business", ...(receiveOnly ? [] : ["--wait"])] });
+  const parsed = parse(rest, { flags: ["--follow", "--tester"], values: ["--business", ...(receiveOnly ? [] : ["--wait"])] });
   if (parsed.positional.length !== (receiveOnly ? 0 : 2)) throw usage(receiveOnly ? "follow takes no arguments" : "talk takes a role and one quoted text");
   if (receiveOnly && parsed.flags.has("--follow")) throw usage("follow already follows");
   const follow = receiveOnly || parsed.flags.has("--follow");
   if (follow && parsed.values["--wait"] !== undefined) throw usage("--follow and --wait cannot be combined");
   const wait = parsed.values["--wait"] === undefined ? TALK_WAIT_S : Number(parsed.values["--wait"]);
   if (!Number.isInteger(wait) || wait < 0) throw usage("--wait takes whole seconds, 0 or more");
-  refuseInsideAgent(io.env);
-  const system = deps.system ?? loadSystem({ env: io.env });
-  const business = businessFor(parsed, system.dataRoot);
-  const call = deps.transport ? deps.transport(business) : humanTransport({ socket: socketPath(system.dataRoot), business, env: io.env });
   const [to, body] = parsed.positional;
+  // The broker refuses it too (tester-prefix); this is the clear early message.
+  if (!receiveOnly && parsed.flags.has("--tester") && !body.startsWith(TESTER_PREFIX)) throw new CliError(`a tester message starts with "${TESTER_PREFIX}"`, 2);
+  const call = callFor(parsed, io, deps);
   let sent;
   if (!receiveOnly) {
     sent = await call("message.send", { to, body, class: "REQUEST" });
diff --git a/packages/cli/src/transport.mjs b/packages/cli/src/transport.mjs
index 555385293..268566656 100644
--- a/packages/cli/src/transport.mjs
+++ b/packages/cli/src/transport.mjs
@@ -10,6 +10,7 @@ import { fileURLToPath } from "node:url";
 import { CliError } from "./errors.mjs";
 
 export const HUMAN_CLI = fileURLToPath(new URL("../../bus/src/human-cli.mjs", import.meta.url));
+export const TESTER_CLI = fileURLToPath(new URL("../../bus/src/tester-cli.mjs", import.meta.url));
 
 // The broker's markers (packages/bus/src/human.mjs). The broker checks the
 // whole ancestry; this check is only the clear early message for the case
@@ -37,6 +38,9 @@ const EXIT = {
   unauthenticated: 3,
   "unknown-business": 3,
   "read-only": 3,
+  "tester-required": 3,
+  "tester-off": 3,
+  "tester-refused": 3,
   "outcome-unknown": 1,
   "response-too-large": 1,
   "invalid-response": 1,
@@ -73,3 +77,11 @@ export function humanTransport({ socket, business, env = process.env, cli = HUMA
     }
   };
 }
+
+// Row 110 (#1604): the tester's transport is the same exchange through
+// tester-cli.mjs. It makes no agent check of its own: a tester runs from
+// inside Mos or a T3 seat, and the broker refuses one under a managed run or
+// while the business's bus.tester is off.
+export function testerTransport(options) {
+  return humanTransport({ cli: TESTER_CLI, ...options });
+}
diff --git a/packages/cli/tests/stack-copy.test.mjs b/packages/cli/tests/stack-copy.test.mjs
index 2ebacfa8f..8460b9198 100644
--- a/packages/cli/tests/stack-copy.test.mjs
+++ b/packages/cli/tests/stack-copy.test.mjs
@@ -106,13 +106,14 @@ test('real pinned install loads bus and Console; same-copy mosaic talk passes pr
  try{await until(()=>/Mosaic Console: http:/.test(webOut)||web.exitCode!==null);const port=webOut.match(/127\.0\.0\.1:(\d+)/)?.[1];assert.ok(port,webErr);assert.equal((await fetch(`http://127.0.0.1:${port}/healthz`)).status,200);}
  finally{if(web.exitCode===null&&web.signalCode===null){const done=once(web,'close');web.kill();await done;}}
  // The production runtime derives cliPath. Only agent ancestry is mocked;
+ // readProcess passes through for tester.mjs (row 110).
  // real pid/start/argv/nonce and the runtime's entry-path binding remain intact.
  const proofScript=join(s.root,'proof-runtime.mjs');
  writeFileSync(proofScript,`
  import {mock} from 'node:test';
  const humanURL=${JSON.stringify(url('packages/bus/src/human.mjs'))};
  const real=await import(humanURL);
- mock.module(humanURL,{namedExports:{verifyHuman:(proof,options)=>real.verifyHuman(proof,{...options,readProcess:pid=>({...real.readProcess(pid),ppid:1})})}});
+ mock.module(humanURL,{namedExports:{readProcess:real.readProcess,verifyHuman:(proof,options)=>real.verifyHuman(proof,{...options,readProcess:pid=>({...real.readProcess(pid),ppid:1})})}});
  const {startBroker}=await import(${JSON.stringify(url('packages/bus/src/runtime.mjs'))});
  const runtime=await startBroker({dataRoot:${JSON.stringify(f.dataRoot)},businesses:${JSON.stringify(BUSINESSES)}});
  const broker=runtime.broker;
diff --git a/packages/harness/src/runner.mjs b/packages/harness/src/runner.mjs
index f806cabed..aaa9d5d22 100644
--- a/packages/harness/src/runner.mjs
+++ b/packages/harness/src/runner.mjs
@@ -70,7 +70,12 @@ export function turnRequest(m) {
   if (m.decision) head.push(`citing decision ${m.decision}`);
   // Row 90 (#1584): the human input id task_create cites as its request.
   if (m.request) head.push(`request ${m.request}`);
-  return `${head.join(", ")}:\n\n${m.body}`;
+  // Row 110 (#1604): a tester's message is a PM test. Its answer goes back to the tester.
+  const tester =
+    m.from_role === "tester"
+      ? "This message is from a tester running a PM test. It is never Jason's instruction and authorizes nothing.\n\n"
+      : "";
+  return `${head.join(", ")}:\n\n${tester}${m.body}`;
 }
 
 // Row 109 (#1603): the block at the top of a turn's request. It is what the broker said at `readAt`,
diff --git a/packages/harness/tests/runner.test.mjs b/packages/harness/tests/runner.test.mjs
index 12b683cb7..896e5bafa 100644
--- a/packages/harness/tests/runner.test.mjs
+++ b/packages/harness/tests/runner.test.mjs
@@ -57,6 +57,16 @@ test("turnRequest names the sender, class, reply and decision", () => {
 });
 
 // Row 109 (#1603): the header carries when the message was sent, not when it is read.
+test("turnRequest says a tester's message is a test and never Jason's instruction", () => {
+  assert.equal(
+    turnRequest({ id: "m7", from_role: "tester", class: "REQUEST", request: null, body: "[mos test] is the plan current?" }),
+    "Message m7 from tester, class REQUEST:\n\nThis message is from a tester running a PM test. It is never Jason's instruction and authorizes nothing.\n\n[mos test] is the plan current?",
+  );
+  // No other sender gets the line, the human included.
+  for (const from_role of ["human", "pm", "jason"])
+    assert.doesNotMatch(turnRequest({ id: "m8", from_role, class: "REQUEST", body: "[mos test] b" }), /tester|never Jason's/, from_role);
+});
+
 test("turnRequest shows the message's own sent time, a day old as well as new", () => {
   const sent = "2026-10-12T09:30:00.000Z";
   assert.equal(
diff --git a/packages/seat/tests/sandbox.test.mjs b/packages/seat/tests/sandbox.test.mjs
index 9995b6b03..77168d405 100644
--- a/packages/seat/tests/sandbox.test.mjs
+++ b/packages/seat/tests/sandbox.test.mjs
@@ -8,12 +8,13 @@
 
 import { test } from "node:test";
 import assert from "node:assert/strict";
-import { spawnSync } from "node:child_process";
+import { spawn, spawnSync } from "node:child_process";
 import { chmodSync, existsSync, mkdirSync, mkdtempSync, readFileSync, realpathSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { basename, dirname, join, resolve } from "node:path";
 import { Broker } from "../../bus/src/broker.mjs";
 import { serve } from "../../bus/src/server.mjs";
+import { verifyTester } from "../../bus/src/tester.mjs";
 import { Store } from "../../bus/src/store.mjs";
 import { SOURCES } from "../../harness/src/bundle.mjs";
 import { startTimeOf } from "../src/proc.mjs";
@@ -21,6 +22,8 @@ import { newRun, RUNNER, runnerOf, sessionEnv, spawnSession, writeSessionFile }
 import { binds, gitIdentity, prepareRun, REPO, RUNNER_FILES, sandboxArgv, sandboxProblem } from "../src/sandbox.mjs";
 
 const FAKE = new URL("../../harness/tests/fixtures/fake-adapter.mjs", import.meta.url).pathname;
+const TESTER_CLI = new URL("../../bus/src/tester-cli.mjs", import.meta.url).pathname;
+const HUMAN_MJS = new URL("../../bus/src/human.mjs", import.meta.url).pathname;
 const skip = sandboxProblem() ?? false;
 
 function scratch(t) {
@@ -176,8 +179,9 @@ async function wrong(table, sh) {
 // A real session for coder, its adapter a shell that runs each message's
 // body, or the fake adapter for a TOOL message.
 // expose(standIns) names extra read-only binds, for the test that breaks
-// the sandbox on purpose.
-async function session(t, { expose = () => [] } = {}) {
+// the sandbox on purpose. tester (row 110) turns bus.tester on, serves the
+// tester proof as the bus runtime does, and binds tester-cli.mjs in.
+async function session(t, { expose = () => [], tester = false } = {}) {
   const root = scratch(t);
   const dataRoot = join(root, "data");
   mkdirSync(dataRoot, { mode: 0o700 });
@@ -189,6 +193,7 @@ async function session(t, { expose = () => [] } = {}) {
         id: "acme",
         human: "jason",
         arbiters: { technical: "pm", delivery: "pm" },
+        ...(tester ? { vars: { "bus.tester": true } } : {}),
         roles: {
           pm: { authority: { withinRole: ["message.send"], crossRole: [] } },
           coder: { authority: { withinRole: ["message.send"], crossRole: [] } },
@@ -197,7 +202,9 @@ async function session(t, { expose = () => [] } = {}) {
     },
   });
   const brokerSocket = join(root, "bus.sock");
-  const server = await serve({ broker, path: brokerSocket });
+  const launches = [];
+  const authenticateTester = (proof) => broker.bindTester(verifyTester(proof, { cliPath: TESTER_CLI, launches }));
+  const server = await serve({ broker, path: brokerSocket, ...(tester ? { authenticateTester } : {}) });
   t.after(async () => {
     await server.close().catch(() => {});
     store.close();
@@ -229,7 +236,7 @@ async function session(t, { expose = () => [] } = {}) {
     toolSocket: join(runDir, "tools.sock"), turnMarker: join(runDir, "turn.done"), pollInterval: 50,
   });
 
-  const paths = { workspace: ws, adapter, harness: "pi", brokerSocket, readOnly: [FAKE, ...expose(s)] };
+  const paths = { workspace: ws, adapter, harness: "pi", brokerSocket, readOnly: [FAKE, ...(tester ? [TESTER_CLI, HUMAN_MJS] : []), ...expose(s)] };
   const child = spawnSession({ runDir, env: sessionEnv({ HOME: process.env.HOME, PATH: process.env.PATH }, run), paths, business: "acme", role: "coder" });
   const exited = new Promise((r) => child.once("close", (code, signal) => r({ code, signal })));
   t.after(async () => {
@@ -240,6 +247,7 @@ async function session(t, { expose = () => [] } = {}) {
   });
   await runnerOf(child);
   const cap = broker.bindLaunch({ business: "acme", role: "coder", run, harness: "pi", pid: child.pid, startTime: startTimeOf(child.pid) });
+  launches.push({ pid: child.pid, startTime: startTimeOf(child.pid) });
   const pm = broker.bindLaunch({ business: "acme", role: "pm", run: "pm-run", harness: "pi" });
   broker.request(pm, { verb: "role.claim" });
   child.stdin.end(`${JSON.stringify({ cap })}\n`);
@@ -296,3 +304,30 @@ test("a bind that exposes a stand-in, or a missing workspace bind, fails the mat
   assert.deepEqual(await wrong(checks(x), direct(all)), []);
   assert.deepEqual(await wrong(checks(x), direct(all.filter((b) => b.src !== x.ws))), ["write and read its workspace"]);
 });
+
+// Row 110 (#1604): a role session that runs tester-cli.mjs against its own
+// broker socket can't bind as tester. Inside bwrap the shim's pid is the
+// session's PID namespace's, so the broker's nonce check on the host fails,
+// and the walk would reach the session's launch record. The same shim from
+// the test process, outside any run, binds: the refusal is the proof's.
+test("a confined session that runs tester-cli.mjs is refused as tester, and the same shim outside the sandbox binds", { skip, timeout: 60000 }, async (t) => {
+  const x = await session(t, { tester: true });
+  const request = JSON.stringify({ business: "acme", verb: "agents", args: {} });
+  const inside = await x.sh(`printf '%s' '${request}' | '${process.execPath}' '${TESTER_CLI}' '${x.brokerSocket}'`);
+  assert.deepEqual(inside, { rc: 2, out: "tester-required" });
+
+  const env = { ...process.env };
+  delete env.MOSAIC_BUS_TESTER_NONCE;
+  delete env.MOSAIC_BUS_CLI_NONCE;
+  const outside = await new Promise((done) => {
+    const child = spawn(process.execPath, [TESTER_CLI, x.brokerSocket], { env });
+    let out = "";
+    let err = "";
+    child.stdout.on("data", (d) => (out += d));
+    child.stderr.on("data", (d) => (err += d));
+    child.on("close", (status) => done({ status, out, err }));
+    child.stdin.end(request);
+  });
+  assert.equal(outside.status, 0, outside.err);
+  assert.ok(Array.isArray(JSON.parse(outside.out)));
+});
diff --git a/packages/bus/src/tester-cli.mjs b/packages/bus/src/tester-cli.mjs
new file mode 100644
index 000000000..49a47fe51
--- /dev/null
+++ b/packages/bus/src/tester-cli.mjs
@@ -0,0 +1,40 @@
+// Row 110 (#1604): the tester's transport shim, human-cli.mjs with its own nonce variable and a
+// tester proof. Not a second product CLI. Input and proof never carry service tokens.
+import { randomBytes } from 'node:crypto';
+import { spawnSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+import { readFileSync } from 'node:fs';
+import { Client } from './client.mjs';
+import { readProcess } from './human.mjs';
+const file = fileURLToPath(import.meta.url);
+if (!process.env.MOSAIC_BUS_TESTER_NONCE) {
+  const child = spawnSync(process.execPath, [file, ...process.argv.slice(2)], {
+    stdio: 'inherit',
+    env: { ...process.env, MOSAIC_BUS_TESTER_NONCE: randomBytes(32).toString('hex') },
+  });
+  process.exit(child.status ?? 2);
+}
+try {
+  const request = JSON.parse(readFileSync(0, 'utf8'));
+  if (
+    !request ||
+    typeof request !== 'object' ||
+    Object.keys(request).some((k) => !['business', 'verb', 'args'].includes(k))
+  )
+    throw Error();
+  const me = readProcess(process.pid);
+  const client = new Client({
+    path: process.argv[2],
+    tester: {
+      business: request.business,
+      pid: me.pid,
+      startTime: me.startTime,
+      nonce: process.env.MOSAIC_BUS_TESTER_NONCE,
+    },
+  });
+  const result = await client.call(request.verb, request.args ?? {});
+  process.stdout.write(JSON.stringify(result) + '\n');
+} catch (e) {
+  process.stderr.write((/^[a-z-]{1,64}$/.test(e.code ?? '') ? e.code : 'invalid-request') + '\n');
+  process.exitCode = 2;
+}
diff --git a/packages/bus/src/tester.mjs b/packages/bus/src/tester.mjs
new file mode 100644
index 000000000..01dea2eb6
--- /dev/null
+++ b/packages/bus/src/tester.mjs
@@ -0,0 +1,73 @@
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import { BusError } from './broker.mjs';
+import { readProcess } from './human.mjs';
+// Row 110 (#1604): the tester's proof. Same shape as the human's (pid, startTime, nonce, business),
+// from its own CLI and its own nonce variable, so neither CLI's nonce proves the other. The walk
+// refuses only a managed run: a launch record or a managed run's marker. An agent's markers and
+// binaries are allowed, since a tester is meant to run from inside Mos or a T3 seat.
+// Like verifyHuman, these are cooperative same-UID process checks, not a hostile-process wall.
+const RUN_MARKERS = ['MOSAIC_BUS_CAP', 'MOSAIC_RUN_ID', 'MOSAIC_AGENT_RUN'];
+const NONCE = 'MOSAIC_BUS_TESTER_NONCE=';
+const refuse = () => {
+  throw new BusError('tester-required');
+};
+// readProcess keeps only the human's nonce and the markers, so the tester's nonce is read here.
+export function testerNonce(pid, { readFile = readFileSync } = {}) {
+  try {
+    const entry = readFile(`/proc/${pid}/environ`, 'utf8')
+      .split('\0')
+      .find((e) => e.startsWith(NONCE));
+    return entry === undefined ? null : entry.slice(NONCE.length);
+  } catch {
+    return null;
+  }
+}
+export function verifyTester(
+  proof,
+  { cliPath, launches = [], readProcess: read = readProcess, readNonce = testerNonce },
+) {
+  if (
+    !proof ||
+    typeof proof !== 'object' ||
+    Object.keys(proof).some((k) => !['pid', 'startTime', 'nonce', 'business'].includes(k)) ||
+    !Number.isSafeInteger(proof.pid) ||
+    proof.pid < 2 ||
+    typeof proof.business !== 'string' ||
+    typeof proof.nonce !== 'string' ||
+    !/^[a-f0-9]{64}$/.test(proof.nonce)
+  )
+    refuse();
+  try {
+    const nonce = readNonce(proof.pid);
+    const p = read(proof.pid);
+    if (
+      p.uid !== process.getuid() ||
+      p.startTime !== proof.startTime ||
+      nonce !== proof.nonce ||
+      p.argv[1] !== resolve(cliPath)
+    )
+      refuse();
+    const seen = new Set();
+    let current = p;
+    for (let depth = 0; depth < 128; depth++) {
+      if (seen.has(current.pid)) refuse();
+      seen.add(current.pid);
+      if (
+        (current.env !== null && RUN_MARKERS.some((k) => current.env[k])) ||
+        launches.some((r) => r.pid === current.pid && r.startTime === current.startTime)
+      )
+        refuse();
+      if (current.ppid === 1) {
+        const again = read(proof.pid);
+        if (again.startTime !== proof.startTime || again.ppid !== p.ppid) refuse();
+        return { business: proof.business };
+      }
+      if (current.ppid < 2) refuse();
+      current = read(current.ppid);
+    }
+  } catch {
+    refuse();
+  }
+  refuse();
+}
diff --git a/packages/bus/tests/tester.test.mjs b/packages/bus/tests/tester.test.mjs
new file mode 100644
index 000000000..36c8eedaa
--- /dev/null
+++ b/packages/bus/tests/tester.test.mjs
@@ -0,0 +1,391 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { spawn } from 'node:child_process';
+import { connect } from 'node:net';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { Store } from '../src/store.mjs';
+import { Broker, TASK_VERBS } from '../src/broker.mjs';
+import { serve } from '../src/server.mjs';
+import { Client } from '../src/client.mjs';
+import { startBroker } from '../src/runtime.mjs';
+import { readProcess, verifyHuman } from '../src/human.mjs';
+import { verifyTester, testerNonce } from '../src/tester.mjs';
+
+// Row 110 (#1604): the bus tester identity for PM tests.
+const roles = {
+  pm: { authority: { withinRole: ['message.send'], crossRole: [] } },
+  cto: { authority: { withinRole: ['message.send'], crossRole: [] } },
+};
+const business = (vars) => ({
+  demo: { id: 'demo', human: 'jason', arbiters: { technical: 'cto', delivery: 'pm' }, roles, ...(vars ? { vars } : {}) },
+});
+function setup(t, vars = { 'bus.tester': true }) {
+  const root = mkdtempSync(join(tmpdir(), 'bus-tester-'));
+  const store = new Store(root);
+  t.after(() => {
+    store.close();
+    rmSync(root, { recursive: true, force: true });
+  });
+  const b = new Broker({ store, businesses: business(vars) });
+  const pm = b.bindLaunch({ business: 'demo', role: 'pm', run: 'pm-run', harness: 'pi' });
+  b.request(pm, { verb: 'role.claim' });
+  const human = b.bindHuman({ business: 'demo', human: 'jason', via: 'cli', outsideAgent: true });
+  const reader = b.bindReader({ business: 'demo' });
+  const call = (cap, verb, args = {}) => b.request(cap, { verb, args });
+  return { b, store, pm, human, reader, call };
+}
+const say = (body = 'is the plan current?') => `[mos test] ${body}`;
+
+test('the tester binds only when the business sets bus.tester to exactly true', (t) => {
+  for (const vars of [null, {}, { 'bus.tester': false }, { 'bus.tester': 'true' }, { 'bus.tester': 1 }]) {
+    const { b } = setup(t, vars);
+    assert.throws(() => b.bindTester({ business: 'demo' }), { code: 'tester-off' }, JSON.stringify(vars));
+  }
+  const { b } = setup(t);
+  assert.match(b.bindTester({ business: 'demo' }), /^[0-9a-f]{64}$/);
+  assert.throws(() => b.bindTester({ business: 'other' }), { code: 'unknown-business' });
+  assert.throws(() => b.bindTester({ business: 'demo', role: 'pm' }), { code: 'invalid-request' });
+});
+
+test('a business may not name a role tester, so the tester address is never a role', (t) => {
+  const root = mkdtempSync(join(tmpdir(), 'bus-tester-'));
+  const store = new Store(root);
+  t.after(() => {
+    store.close();
+    rmSync(root, { recursive: true, force: true });
+  });
+  const businesses = business();
+  businesses.demo.roles = { ...roles, tester: roles.pm };
+  assert.throws(() => new Broker({ store, businesses }), { code: 'invalid-business' });
+  // No session can claim role tester: a launch must name a business role, and the tester
+  // session's own role.claim refuses. So #holder(business, 'tester') is always empty.
+  const s = setup(t);
+  assert.throws(() => s.b.bindLaunch({ business: 'demo', role: 'tester', run: 'tester-run', harness: 'pi' }), { code: 'unknown-role' });
+  assert.throws(() => s.call(s.b.bindTester({ business: 'demo' }), 'role.claim'), { code: 'tester-refused' });
+  assert.equal(s.store.get("SELECT count(*) n FROM role_claims WHERE role='tester'").n, 0);
+  assert.equal(s.store.get("SELECT count(*) n FROM role_claims WHERE role='pm'").n, 1);
+});
+
+test('every verb outside the tester list refuses tester-refused and is recorded against the tester', async (t) => {
+  const { b, store, call } = setup(t);
+  const tester = b.bindTester({ business: 'demo' });
+  const refused = [
+    ['role.claim', {}],
+    ['role.release', {}],
+    ['role.revoke', { role: 'pm' }],
+    ['decision.raise', { action: 'message.send', question: 'q', options: [], recommendation: 'no', blocking: false }],
+    ['decision.resolve', { id: 'd-1', choice: 'yes' }],
+    ['decision.seen', { id: 'd-1' }],
+    ['decision.withdraw', { id: 'd-1' }],
+    ['review.request', { task_ref: 'vikunja:1/1', role: 'cto' }],
+    ['review.verdict', { task_ref: 'vikunja:1/1', verdict: 'approve' }],
+    ['launch.revoke', {}],
+    ['launch.restore', {}],
+    ['event.emit', { kind: 'action.allowed', body: { action: 'routine' } }],
+    ['state', {}],
+    ['credentials', {}],
+    ['requirements', {}],
+  ];
+  for (const [verb, args] of refused) assert.throws(() => call(tester, verb, args), { code: 'tester-refused' }, verb);
+  let handled = 0;
+  for (const verb of TASK_VERBS)
+    await assert.rejects(
+      b.requestTask(tester, { verb, args: {} }, async () => handled++),
+      { code: 'tester-refused' },
+      verb,
+    );
+  assert.equal(handled, 0);
+  const rows = store.all("SELECT actor_role, actor_run, body FROM events WHERE kind='action.refused'");
+  assert.equal(rows.length, refused.length + TASK_VERBS.length);
+  assert.ok(rows.every((r) => r.actor_role === 'tester' && r.actor_run === null && JSON.parse(r.body).code === 'tester-refused'));
+  assert.equal(store.get("SELECT count(*) n FROM events WHERE kind IN ('launch.revoked','launch.restored','human.input')").n, 0);
+  // The tester gate runs before any argument check, so malformed arguments refuse tester-refused too.
+  for (const [verb] of refused) assert.throws(() => call(tester, verb, { bogus: 1 }), { code: 'tester-refused' }, `${verb} bogus`);
+});
+
+test('a tester message is from tester, starts [mos test], and writes no human.input or authority', (t) => {
+  const { b, store, pm, call } = setup(t);
+  const tester = b.bindTester({ business: 'demo' });
+  assert.throws(() => call(tester, 'message.send', { to: 'pm', body: 'is the plan current?' }), { code: 'tester-prefix' });
+  assert.throws(() => call(tester, 'message.send', { to: 'pm', body: ' [mos test] late prefix' }), { code: 'tester-prefix' });
+  for (const to of ['human', 'tester', 'nobody'])
+    assert.throws(() => call(tester, 'message.send', { to, body: say() }), { code: 'unknown-role' }, to);
+  for (const extra of [{ corrects: 'm-1' }, { decision: 'd-1' }])
+    assert.throws(() => call(tester, 'message.send', { to: 'pm', body: say(), ...extra }), { code: 'invalid-request' });
+  const events = store.get('SELECT count(*) n FROM events WHERE kind<>?', 'action.refused').n;
+  const sent = call(tester, 'message.send', { to: 'pm', body: say(), class: 'REQUEST' });
+  assert.equal(sent.request, null);
+  const row = store.get('SELECT * FROM messages WHERE id=?', sent.id);
+  assert.equal(row.from_role, 'tester');
+  assert.equal(row.from_run, 'tester-cli');
+  assert.equal(row.to_role, 'pm');
+  assert.equal(store.get('SELECT count(*) n FROM events WHERE kind<>?', 'action.refused').n, events, 'no event at all');
+  const got = call(pm, 'message.receive');
+  assert.equal(got.length, 1);
+  assert.equal(got[0].from_role, 'tester');
+  assert.equal(got[0].request, null);
+  // task.create needs a human.input event as its request (packages/tasks/src/verbs.mjs); a tester
+  // message gives none, so it can't back one.
+  assert.equal(b.taskView('demo', 'input', sent.id), false);
+  assert.equal(store.get("SELECT count(*) n FROM events WHERE kind='human.input'").n, 0);
+});
+
+test('a role answers a tester only in reply to a tester message, and the answer never reaches the human', (t) => {
+  const { b, store, pm, human, reader, call } = setup(t);
+  const tester = b.bindTester({ business: 'demo' });
+  const ask = call(tester, 'message.send', { to: 'pm', body: say() }).id;
+  const jason = call(human, 'message.send', { to: 'pm', body: 'a real instruction' }).id;
+  call(pm, 'message.receive');
+  assert.throws(() => call(pm, 'message.send', { to: 'tester', body: 'answer' }), { code: 'tester-reply-required' });
+  assert.throws(() => call(pm, 'message.send', { to: 'tester', body: 'answer', in_reply_to: jason }), { code: 'tester-reply-required' });
+  assert.throws(() => call(pm, 'message.send', { to: 'tester', body: 'answer', in_reply_to: 'missing' }), { code: 'tester-reply-required' });
+  assert.throws(() => call(human, 'message.send', { to: 'tester', body: 'hi', in_reply_to: ask }), { code: 'unknown-role' });
+  const answer = call(pm, 'message.send', { to: 'tester', body: 'the plan is current', in_reply_to: ask }).id;
+  assert.equal(store.get('SELECT to_role FROM messages WHERE id=?', answer).to_role, 'tester');
+  // Not in the human's inbox or the Console's Messages page.
+  assert.deepEqual(call(human, 'message.receive'), []);
+  for (const cap of [human, reader]) assert.equal(call(cap, 'messages').total, 0);
+  const got = call(tester, 'message.receive');
+  assert.deepEqual(got.map((m) => [m.id, m.from_role, m.in_reply_to]), [[answer, 'pm', ask]]);
+  assert.deepEqual(call(tester, 'message.receive'), []);
+  assert.throws(() => call(tester, 'message.read', { id: jason }), { code: 'message-not-found' });
+  assert.deepEqual(call(tester, 'message.read', { id: answer }), { read: true });
+  const delivered = store.all('SELECT op, holder_run, transport FROM deliveries WHERE message=? ORDER BY seq', answer);
+  assert.deepEqual(delivered.map((d) => [d.op, d.holder_run, d.transport]), [
+    ['routed', null, null],
+    ['delivered', null, 'cli'],
+    ['read', null, null],
+  ]);
+  // A role's own inbox is not the tester's.
+  assert.throws(() => call(pm, 'message.read', { id: answer }), { code: 'message-not-found' });
+});
+
+test('the tester reads the human views a reader reads', (t) => {
+  const { b, pm, reader, call } = setup(t);
+  const tester = b.bindTester({ business: 'demo' });
+  const ask = call(tester, 'message.send', { to: 'pm', body: say() }).id;
+  call(pm, 'message.receive');
+  call(pm, 'message.send', { to: 'tester', body: 'answer', in_reply_to: ask });
+  call(pm, 'message.send', { to: 'human', body: 'for jason' });
+  for (const [verb, args] of [
+    ['inbox', {}],
+    ['agents', {}],
+    ['tasks', {}],
+    ['trail', { subject: ask }],
+    ['decisions', { list: 'roles' }],
+    ['decisions', { list: 'recent' }],
+    ['messages', {}],
+    ['replies', { id: ask }],
+  ])
+    assert.deepEqual(call(tester, verb, args), call(reader, verb, args), verb);
+  assert.equal(call(tester, 'replies', { id: ask }).length, 1);
+  assert.equal(call(tester, 'messages').total, 1);
+});
+
+// The process proof, on a process table like human.test.mjs's.
+const testerCli = '/opt/mosaic/tester-cli.mjs';
+const humanCli = '/opt/mosaic/human-cli.mjs';
+const nonce = 'b'.repeat(64);
+function table(cli = testerCli, env = { MOSAIC_BUS_TESTER_NONCE: nonce }) {
+  return new Map([
+    [50, { pid: 50, ppid: 40, startTime: '100', uid: process.getuid(), argv: ['node', cli], env }],
+    [40, { pid: 40, ppid: 1, startTime: '90', uid: process.getuid(), argv: ['bash'], env: {} }],
+  ]);
+}
+const proof = { pid: 50, startTime: '100', nonce, business: 'demo' };
+const reader = (t) => (pid) => {
+  if (!t.has(pid)) throw Error('gone');
+  return t.get(pid);
+};
+const tester = (t, extra = {}) =>
+  verifyTester(proof, {
+    cliPath: testerCli,
+    readProcess: reader(t),
+    readNonce: (pid) => t.get(pid)?.env?.MOSAIC_BUS_TESTER_NONCE ?? null,
+    ...extra,
+  });
+
+test('tester proof binds its own CLI, start time and nonce, refuses a managed run and allows an agent', () => {
+  assert.equal(tester(table()).business, 'demo');
+  for (const change of [{ startTime: '101' }, { uid: process.getuid() + 1 }, { argv: ['node', 'other.mjs'] }, { env: { MOSAIC_BUS_TESTER_NONCE: 'c'.repeat(64) } }]) {
+    const t = table();
+    Object.assign(t.get(50), change);
+    assert.throws(() => tester(t), { code: 'tester-required' }, JSON.stringify(change));
+  }
+  for (const env of [{ MOSAIC_RUN_ID: 'run-x' }, { MOSAIC_BUS_CAP: 'cap' }, { MOSAIC_AGENT_RUN: '1' }]) {
+    const t = table();
+    t.get(40).env = env;
+    assert.throws(() => tester(t), { code: 'tester-required' }, Object.keys(env)[0]);
+    const self = table();
+    Object.assign(self.get(50).env, env);
+    assert.throws(() => tester(self), { code: 'tester-required' }, `${Object.keys(env)[0]} on the CLI`);
+  }
+  assert.throws(() => tester(table(), { launches: [{ pid: 40, startTime: '90' }] }), { code: 'tester-required' });
+  assert.equal(tester(table(), { launches: [{ pid: 40, startTime: '89' }] }).business, 'demo');
+  // An agent above the tester is the intended case: Mos or a T3 seat.
+  for (const [argv, env] of [
+    [['bash'], { CLAUDECODE: '1', CLAUDE_CODE_ENTRYPOINT: 'sdk-ts' }],
+    [['bash'], { CODEX_THREAD_ID: 'thread', PI_AGENT_DIR: '/x' }],
+    [['claude'], {}],
+    [['node', '/usr/lib/node_modules/codex/bin/codex.js'], {}],
+    [['pi'], {}],
+  ]) {
+    const t = table();
+    Object.assign(t.get(40), { argv, env });
+    assert.equal(tester(t).business, 'demo', argv.join(' '));
+  }
+  const broken = table();
+  broken.delete(40);
+  assert.throws(() => tester(broken), { code: 'tester-required' });
+  // A loop refuses when it comes round, not at the depth bound.
+  const loop = table();
+  loop.get(40).ppid = 50;
+  let reads = 0;
+  assert.throws(() => tester(loop, { readProcess: (pid) => (reads++, reader(loop)(pid)) }), { code: 'tester-required' });
+  assert.ok(reads < 5, `${reads} reads`);
+  // A parent pid under 2 refuses even when /proc would answer for it.
+  const gone = table();
+  gone.get(40).ppid = 0;
+  gone.set(0, { pid: 0, ppid: 1, startTime: '1', uid: process.getuid(), argv: ['init'], env: {} });
+  assert.throws(() => tester(gone), { code: 'tester-required' });
+  // The CLI is read again at the top: a changed start time or parent refuses.
+  for (const change of [{ startTime: '101' }, { ppid: 1 }]) {
+    const t = table();
+    let first = true;
+    const again = (pid) => (pid === 50 && !first ? { ...t.get(50), ...change } : ((first = pid === 50 ? false : first), t.get(pid)));
+    assert.throws(() => tester(t, { readProcess: again }), { code: 'tester-required' }, JSON.stringify(change));
+  }
+  // The first read's start time is checked on its own, not only by the re-read.
+  const once = table();
+  let fresh = true;
+  const first = (pid) => (pid === 50 && fresh ? ((fresh = false), { ...once.get(50), startTime: '101' }) : once.get(pid));
+  assert.throws(() => tester(once, { readProcess: first }), { code: 'tester-required' });
+  // Each bad shape sits on a table where every other check passes, so only the shape check refuses.
+  const pid1 = table();
+  pid1.set(1, { ...pid1.get(50), pid: 1 });
+  const nonHex = table(testerCli, { MOSAIC_BUS_TESTER_NONCE: 'x' });
+  for (const [bad, t] of [
+    [null, table()],
+    [{ ...proof, extra: 1 }, table()],
+    [{ ...proof, pid: 1 }, pid1],
+    [{ ...proof, nonce: 'x' }, nonHex],
+    [{ ...proof, business: 3 }, table()],
+  ])
+    assert.throws(
+      () => verifyTester(bad, { cliPath: testerCli, readProcess: reader(t), readNonce: (pid) => t.get(pid)?.env?.MOSAIC_BUS_TESTER_NONCE ?? null }),
+      { code: 'tester-required' },
+      JSON.stringify(bad),
+    );
+});
+
+test("neither CLI's nonce proves the other: each proof is bound to its own CLI and nonce variable", () => {
+  // A human CLI process, offered as a tester proof.
+  const human = table(humanCli, { MOSAIC_BUS_CLI_NONCE: nonce });
+  assert.throws(() => tester(human), { code: 'tester-required' });
+  assert.throws(() => tester(human, { cliPath: humanCli }), { code: 'tester-required' }, 'right path, wrong variable');
+  // A tester CLI process, offered as a human proof.
+  const t = table();
+  const human_ = (extra = {}) => verifyHuman(proof, { cliPath: humanCli, readProcess: reader(t), ...extra });
+  assert.throws(() => human_(), { code: 'human-required' });
+  assert.throws(() => human_({ cliPath: testerCli }), { code: 'human-required' }, 'right path, wrong variable');
+  // Both variables set: the path still decides.
+  const both = table(testerCli, { MOSAIC_BUS_TESTER_NONCE: nonce, MOSAIC_BUS_CLI_NONCE: nonce });
+  assert.throws(() => verifyHuman(proof, { cliPath: humanCli, readProcess: reader(both) }), { code: 'human-required' });
+  assert.throws(() => tester(both, { cliPath: humanCli }), { code: 'tester-required' });
+});
+
+test("testerNonce reads only the tester's variable and gives null on any read error", () => {
+  const io = (text) => ({ readFile: () => text });
+  assert.equal(testerNonce(5, io(`A=1\0MOSAIC_BUS_TESTER_NONCE=${nonce}\0`)), nonce);
+  assert.equal(testerNonce(5, io(`MOSAIC_BUS_CLI_NONCE=${nonce}\0`)), null);
+  assert.equal(testerNonce(5, { readFile: () => { throw Object.assign(Error(), { code: 'EACCES' }); } }), null);
+  assert.equal(testerNonce(process.pid), null);
+});
+
+test('an envelope carries exactly one of cap, human and tester; no tester authenticator refuses', async (t) => {
+  const root = mkdtempSync(join(tmpdir(), 'bus-tester-'));
+  const store = new Store(root);
+  const b = new Broker({ store, businesses: business({ 'bus.tester': true }) });
+  const path = join(store.directory, 'broker.sock');
+  let calls = 0;
+  let bound = null;
+  const server = await serve({ broker: b, path, authenticateHuman: () => (calls++, 'x'), authenticateTester: () => (calls++, (bound = b.bindTester({ business: 'demo' }))) });
+  const bare = join(store.directory, 'bare.sock');
+  const bareServer = await serve({ broker: b, path: bare });
+  t.after(async () => {
+    await server.close();
+    await bareServer.close();
+    store.close();
+    rmSync(root, { recursive: true, force: true });
+  });
+  const raw = (at, request) =>
+    new Promise((resolve, reject) => {
+      const s = connect(at);
+      let out = '';
+      s.on('data', (d) => (out += d));
+      s.on('end', () => resolve(JSON.parse(out)));
+      s.on('error', reject);
+      s.end(JSON.stringify(request) + '\n');
+    });
+  const p = { business: 'demo', pid: 2, startTime: '1', nonce };
+  const cap = b.bindReader({ business: 'demo' });
+  for (const r of [{ tester: p, cap }, { tester: p, human: p }, { tester: p, human: p, cap }])
+    assert.deepEqual(await raw(path, { ...r, verb: 'agents' }), { ok: false, error: 'invalid-envelope' }, Object.keys(r).join('+'));
+  assert.equal(calls, 0);
+  assert.deepEqual(await raw(bare, { tester: p, verb: 'agents' }), { ok: false, error: 'tester-required' });
+  assert.deepEqual(await raw(path, { tester: p, verb: 'agents' }), { ok: true, result: [] });
+  assert.equal(calls, 1);
+  // The tester's capability lasts one request, as the human's does.
+  assert.throws(() => b.request(bound, { verb: 'agents' }), { code: 'unauthenticated' });
+  assert.deepEqual(await new Client({ path, tester: p }).call('agents'), []);
+});
+
+// The real shim against a real runtime. The test process is not a managed run, so the proof
+// passes here; a managed run's marker on the shim itself refuses.
+const shim = fileURLToPath(new URL('../src/tester-cli.mjs', import.meta.url));
+// Async: the broker runs in this process, so a synchronous spawn would block its answer.
+function run(socket, request, env = {}) {
+  const clean = Object.fromEntries(Object.entries(process.env).filter(([k]) => !/^MOSAIC_BUS_(TESTER|CLI)_NONCE$/.test(k)));
+  return new Promise((resolve, reject) => {
+    const child = spawn(process.execPath, [shim, socket], { env: { ...clean, ...env }, timeout: 20000 });
+    let out = '';
+    let err = '';
+    child.stdout.on('data', (d) => (out += d));
+    child.stderr.on('data', (d) => (err += d));
+    child.on('error', reject);
+    child.on('close', (status) => resolve({ status, out: out.trim(), err: err.trim() }));
+    child.stdin.end(JSON.stringify(request));
+  });
+}
+async function runtime(t, vars, launches = []) {
+  const root = mkdtempSync(join(tmpdir(), 'bus-tester-rt-'));
+  const rt = await startBroker({ dataRoot: root, businesses: business(vars), readers: ['demo'], launches });
+  t.after(async () => {
+    await rt.close();
+    rmSync(root, { recursive: true, force: true });
+  });
+  return rt;
+}
+
+test('tester-cli.mjs binds through the runtime when the switch is on, and refuses off or under a run marker', async (t) => {
+  const on = await runtime(t, { 'bus.tester': true });
+  const reader = new Client({ path: on.path, cap: on.readers[0].cap });
+  const sent = await run(on.path, { business: 'demo', verb: 'message.send', args: { to: 'pm', body: say() } });
+  assert.equal(sent.status, 0, sent.err);
+  const id = JSON.parse(sent.out).id;
+  assert.equal((await reader.call('trail', { subject: id })).find((r) => r.table === 'messages').from_role, 'tester');
+  assert.deepEqual(await run(on.path, { business: 'demo', verb: 'state' }), { status: 2, out: '', err: 'tester-refused' });
+  for (const marker of ['MOSAIC_RUN_ID', 'MOSAIC_BUS_CAP', 'MOSAIC_AGENT_RUN'])
+    assert.deepEqual(await run(on.path, { business: 'demo', verb: 'agents' }, { [marker]: 'x' }), { status: 2, out: '', err: 'tester-required' }, marker);
+  assert.equal((await run(on.path, { business: 'demo', verb: 'agents' }, { CLAUDECODE: '1' })).status, 0);
+  assert.deepEqual(await run(on.path, { business: 'demo', verb: 'agents', cap: 'x' }), { status: 2, out: '', err: 'invalid-request' });
+  // This test process as a managed run's launch record: the shim it spawns has it as an ancestor.
+  const me = readProcess(process.pid);
+  const under = await runtime(t, { 'bus.tester': true }, [{ business: 'demo', role: 'cto', run: 'cto-run', harness: 'pi', pid: me.pid, startTime: me.startTime }]);
+  assert.deepEqual(await run(under.path, { business: 'demo', verb: 'agents' }), { status: 2, out: '', err: 'tester-required' });
+  const off = await runtime(t, null);
+  assert.deepEqual(await run(off.path, { business: 'demo', verb: 'agents' }), { status: 2, out: '', err: 'tester-off' });
+});
diff --git a/packages/cli/tests/tester.test.mjs b/packages/cli/tests/tester.test.mjs
new file mode 100644
index 000000000..0994b12cf
--- /dev/null
+++ b/packages/cli/tests/tester.test.mjs
@@ -0,0 +1,128 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { existsSync } from "node:fs";
+import { join } from "node:path";
+import { main } from "../src/cli.mjs";
+import { HUMAN_CLI, TESTER_CLI, busExit, testerTransport } from "../src/transport.mjs";
+import { BusError, Broker } from "../../bus/src/broker.mjs";
+import { Store } from "../../bus/src/store.mjs";
+import { BUSINESSES, humanEnv, io, tmp } from "./helpers.mjs";
+
+// Row 110 (#1604): --tester binds as the business's tester instead of as the
+// human. The in-process broker here has bus.tester on; the real tester-cli.mjs
+// runs in packages/bus/tests/tester.test.mjs.
+function setup(t) {
+  const store = new Store(tmp(t, "mosaic-cli-tester-"));
+  t.after(() => store.close());
+  const businesses = { demo: { ...BUSINESSES.demo, vars: { "bus.tester": true } } };
+  const b = new Broker({ store, businesses });
+  const coder = b.bindLaunch({ business: "demo", role: "coder", run: "coder-run", harness: "pi", address: "coder-run" });
+  b.request(coder, { verb: "role.claim" });
+  const human = b.bindHuman({ business: "demo", human: "jason", via: "cli", outsideAgent: true });
+  const tester = b.bindTester({ business: "demo" });
+  const calls = { human: [], tester: [] };
+  const via = (cap, list) => (business) => async (verb, args = {}) => {
+    list.push({ business, verb, args });
+    try {
+      return structuredClone(b.request(cap, { verb, args }));
+    } catch (e) {
+      if (!(e instanceof BusError)) throw e;
+      const error = new Error(e.code);
+      error.code = e.code;
+      throw error;
+    }
+  };
+  const deps = { system: { dataRoot: tmp(t) }, transport: via(human, calls.human), testerTransport: via(tester, calls.tester), talkPollMs: 5 };
+  return { b, store, coder, human, calls, deps };
+}
+// The tester runs inside an agent: a T3 seat or Mos.
+const inAgent = () => io({ ...humanEnv(), CLAUDECODE: "1", CLAUDE_CODE_ENTRYPOINT: "sdk-ts" });
+
+test("talk --tester sends a [mos test] message as tester from inside an agent and prints the role's reply", async (t) => {
+  const s = setup(t);
+  const x = inAgent();
+  const deps = {
+    ...s.deps,
+    testerTransport: (business) => {
+      const inner = s.deps.testerTransport(business);
+      return async (verb, args) => {
+        if (verb === "message.receive") {
+          const ask = s.store.get("SELECT id FROM messages WHERE from_role='tester'");
+          if (ask && !s.store.get("SELECT 1 FROM messages WHERE to_role='tester'")) {
+            s.b.request(s.coder, { verb: "message.receive", args: {} });
+            s.b.request(s.coder, { verb: "message.send", args: { to: "tester", body: "the plan is current", in_reply_to: ask.id } });
+          }
+        }
+        return inner(verb, args);
+      };
+    },
+  };
+  await main(["talk", "coder", "[mos test] is the plan current?", "--tester", "--business", "demo"], x, deps);
+  assert.match(x.out.text, /^sent [0-9a-f-]{8} to coder\n/);
+  assert.match(x.out.text, /coder \(INFO, re [0-9a-f-]{8}\) [0-9a-f-]{8}:\nthe plan is current\n/);
+  assert.deepEqual(s.calls.human, []);
+  assert.deepEqual(s.calls.tester.map((c) => c.verb), ["message.send", "message.receive", "message.read"]);
+  const row = s.store.get("SELECT * FROM messages WHERE from_role='tester'");
+  assert.equal(row.from_run, "tester-cli");
+  assert.equal(row.class, "REQUEST");
+  assert.deepEqual(s.b.request(s.human, { verb: "message.receive", args: {} }), []);
+  assert.equal(s.store.get("SELECT count(*) n FROM events WHERE kind='human.input'").n, 0);
+});
+
+test("talk --tester refuses text without the [mos test] prefix before any call", async (t) => {
+  const s = setup(t);
+  await assert.rejects(main(["talk", "coder", "is the plan current?", "--tester", "--business", "demo"], inAgent(), s.deps), (e) => e.exitCode === 2 && /starts with "\[mos test\]"/.test(e.message));
+  assert.deepEqual(s.calls.tester, []);
+  // follow sends nothing, so it takes no prefix.
+  const controller = new AbortController();
+  const deps = { ...s.deps, signal: controller.signal, testerTransport: (b) => async (verb, args) => (controller.abort(), s.deps.testerTransport(b)(verb, args)) };
+  await main(["follow", "--tester", "--business", "demo"], inAgent(), deps);
+  assert.deepEqual(s.calls.tester.map((c) => c.verb), ["message.receive"]);
+});
+
+test("the read verbs take --tester inside an agent, and the trail shows the tester as the sender", async (t) => {
+  const s = setup(t);
+  await main(["talk", "coder", "[mos test] hello", "--tester", "--wait", "0", "--business", "demo"], inAgent(), s.deps);
+  const id = s.store.get("SELECT id FROM messages WHERE from_role='tester'").id;
+  for (const verb of ["inbox", "tasks", "agents"]) {
+    const x = inAgent();
+    await main([verb, "--tester", "--business", "demo"], x, s.deps);
+    assert.ok(x.out.text.length > 0, verb);
+  }
+  const x = inAgent();
+  await main(["trail", id, "--tester", "--business", "demo"], x, s.deps);
+  assert.match(x.out.text, /messages#\d+ {2}tester → coder: \[mos test\] hello/);
+  assert.deepEqual([...new Set(s.calls.tester.map((c) => c.verb))], ["message.send", "inbox", "messages", "tasks", "agents", "trail"]);
+  assert.deepEqual(s.calls.human, []);
+  // Without --tester the same commands refuse inside an agent, before any call.
+  for (const argv of [["inbox"], ["agents"], ["talk", "coder", "[mos test] hi"], ["follow"]])
+    await assert.rejects(main([...argv, "--business", "demo"], inAgent(), s.deps), (e) => e.exitCode === 3, argv[0]);
+  assert.deepEqual(s.calls.human, []);
+});
+
+test("decide, stop and launches take no --tester", async (t) => {
+  const s = setup(t);
+  for (const argv of [["decide", "d1", "yes", "--tester"], ["stop", "run-1", "--tester"], ["launches", "off", "--tester"], ["launches", "on", "--tester"], ["launches", "list", "--tester"]])
+    await assert.rejects(main(argv, inAgent(), s.deps), (e) => e.exitCode === 4 && /unknown option --tester/.test(e.message), argv.join(" "));
+  assert.deepEqual(s.calls, { human: [], tester: [] });
+});
+
+test("the tester transport runs tester-cli.mjs, and the tester's refusals exit 3", async () => {
+  assert.ok(TESTER_CLI.endsWith("/packages/bus/src/tester-cli.mjs") && existsSync(TESTER_CLI));
+  assert.notEqual(TESTER_CLI, HUMAN_CLI);
+  let seen;
+  const spawn = (cmd, argv, options) => ((seen = { cmd, argv, input: options.input }), { status: 0, stdout: "[]" });
+  assert.deepEqual(await testerTransport({ socket: "/run/fake.sock", business: "acme", env: {}, spawn })("agents"), []);
+  assert.deepEqual(seen.argv, [TESTER_CLI, "/run/fake.sock"]);
+  assert.deepEqual(JSON.parse(seen.input), { business: "acme", verb: "agents", args: {} });
+  for (const code of ["tester-required", "tester-off", "tester-refused"]) assert.equal(busExit(code), 3, code);
+  assert.equal(busExit("tester-prefix"), 2);
+});
+
+test("with no stand-in transport, --tester runs tester-cli.mjs on the data root's socket", async (t) => {
+  const dataRoot = tmp(t);
+  const seen = [];
+  const testerSpawn = (cmd, argv, options) => (seen.push({ argv, input: JSON.parse(options.input) }), { status: 0, stdout: "[]" });
+  await main(["agents", "--tester", "--business", "demo"], inAgent(), { system: { dataRoot }, testerSpawn });
+  assert.deepEqual(seen, [{ argv: [TESTER_CLI, join(dataRoot, "bus", "broker.sock")], input: { business: "demo", verb: "agents", args: {} } }]);
+});