diff --git a/docs/TOOLS.md b/docs/TOOLS.md
index fc38cefab..13366b63a 100644
--- a/docs/TOOLS.md
+++ b/docs/TOOLS.md
@@ -351,6 +351,11 @@ check is expected to refuse this restored mixed setup; #225 remains open.
 Later rollback repeats steps 2-6 with the prior shared copy's full id, each
 live step again approved by Mos. Nothing prunes copies or removes mosaic-old.
 
+After a switch, the human commands and `--tester` work only through `mosaic`
+on PATH; the checkout's `scripts/mosaic` exits 3 with `human-required` or
+`tester-required`, and queue writes stay on it ([packages/cli/README.md, One
+pinned copy](../packages/cli/README.md#one-pinned-copy-row-85-1579)).
+
 ## Console service (`scripts/webui-service.sh`)
 
 ```bash
diff --git a/packages/cli/README.md b/packages/cli/README.md
index fb4532c84..1757ef1b6 100644
--- a/packages/cli/README.md
+++ b/packages/cli/README.md
@@ -86,7 +86,9 @@ mosaic launches list [--json]
   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
+  (`tester-off`), each exit 3. Like the human commands, `--tester` works
+  only from the tree the bus runs from ("One pinned copy" below).
+  `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).
@@ -494,6 +496,15 @@ Each live switch/unit change/stop/start requires Mos's go; agents build
 and test fixtures only. Restarting the bus ends its sessions, so no PM
 turn may be in flight. Queue writes stay on the canonical scripts/mosaic.
 
+The human commands and `--tester` run only from the tree the bus runs from
+(row 130, #1625). The broker checks the path of the calling human-cli.mjs or
+tester-cli.mjs against its own. On a host with a pinned copy that tree is
+the copy, and `mosaic` on PATH is the wrapper that runs it. The checkout's
+`scripts/mosaic` exits 3 with `human-required` or `tester-required` and
+prints one more line: "the bus accepts these commands only from the tree it
+runs from; on a pinned host run `mosaic` on PATH". Queue writes still go
+through the checkout's `scripts/mosaic`.
+
 ## Notifier
 
 The notifier is a child of the host. Each poll (every 30 s) it reads the
diff --git a/packages/cli/src/cli.mjs b/packages/cli/src/cli.mjs
index a547e36c7..a95eabaab 100644
--- a/packages/cli/src/cli.mjs
+++ b/packages/cli/src/cli.mjs
@@ -388,12 +388,27 @@ export async function main(argv, io = { env: process.env, stdin: process.stdin,
   throw usage();
 }
 
-if (process.argv[1] === fileURLToPath(import.meta.url)) {
+// The broker's human and tester proofs accept only the human-cli.mjs and
+// tester-cli.mjs of the tree the bus runs from. Since row 85 that is a
+// pinned copy, so the checkout's own scripts/mosaic is refused with these
+// codes (row 130). The message stays the bare code: app.mjs reads it.
+export const OTHER_TREE = "the bus accepts these commands only from the tree it runs from; on a pinned host run `mosaic` on PATH";
+const OTHER_TREE_CODES = new Set(["human-required", "tester-required"]);
+
+// main, with a CliError printed to stderr. Returns the exit code.
+export async function run(argv, io = { env: process.env, stdin: process.stdin, stdout: process.stdout, stderr: process.stderr }, deps = {}) {
   try {
-    await main(process.argv.slice(2));
+    await main(argv, io, deps);
+    return 0;
   } catch (error) {
     if (!(error instanceof CliError)) throw error;
-    process.stderr.write(`mosaic: ${error.message}\n`);
-    process.exitCode = error.exitCode;
+    io.stderr.write(`mosaic: ${error.message}\n`);
+    if (OTHER_TREE_CODES.has(error.code)) io.stderr.write(`mosaic: ${OTHER_TREE}\n`);
+    return error.exitCode;
   }
 }
+
+if (process.argv[1] === fileURLToPath(import.meta.url)) {
+  const code = await run(process.argv.slice(2));
+  if (code !== 0) process.exitCode = code;
+}
diff --git a/packages/cli/tests/other-tree.test.mjs b/packages/cli/tests/other-tree.test.mjs
new file mode 100644
index 000000000..d00d0a9c1
--- /dev/null
+++ b/packages/cli/tests/other-tree.test.mjs
@@ -0,0 +1,44 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { OTHER_TREE, run } from "../src/cli.mjs";
+import { humanTransport } from "../src/transport.mjs";
+import { humanEnv, io, tmp } from "./helpers.mjs";
+
+// Row 130 (#1625): the broker accepts the human and tester proofs only from
+// the tree the bus runs from, so a refusal with human-required or
+// tester-required gets one more stderr line naming the command that works.
+// The spawn stands in for human-cli.mjs and tester-cli.mjs: it exits 1 with
+// the code on stderr, and the real transport parses it.
+const refusing = (code) => () => ({ status: 1, stdout: "", stderr: `${code}\n` });
+const HINT = `mosaic: ${OTHER_TREE}\n`;
+
+test("a human command refused with human-required prints the other-tree line and exits 3", async (t) => {
+  const x = io();
+  const transport = (business) => humanTransport({ socket: "/nonexistent/bus.sock", business, env: {}, spawn: refusing("human-required") });
+  const code = await run(["inbox", "--business", "demo"], x, { system: { dataRoot: tmp(t) }, transport });
+  assert.equal(code, 3);
+  assert.equal(x.err.text, `mosaic: human-required\n${HINT}`);
+  assert.equal(x.out.text, "");
+});
+
+test("a --tester command refused with tester-required prints the other-tree line and exits 3", async (t) => {
+  const x = io({ ...humanEnv(), CLAUDECODE: "1" });
+  const code = await run(["agents", "--tester", "--business", "demo"], x, { system: { dataRoot: tmp(t) }, testerSpawn: refusing("tester-required") });
+  assert.equal(code, 3);
+  assert.equal(x.err.text, `mosaic: tester-required\n${HINT}`);
+});
+
+test("other exit-3 refusals print no other-tree line", async (t) => {
+  const off = io({ ...humanEnv(), CLAUDECODE: "1" });
+  assert.equal(await run(["agents", "--tester", "--business", "demo"], off, { system: { dataRoot: tmp(t) }, testerSpawn: refusing("tester-off") }), 3);
+  assert.equal(off.err.text, "mosaic: tester-off\n");
+
+  const agent = io({ ...humanEnv(), CLAUDECODE: "1" });
+  assert.equal(await run(["inbox", "--business", "demo"], agent, { system: { dataRoot: tmp(t) } }), 3);
+  assert.match(agent.err.text, /^mosaic: refused: this runs only from a human shell/);
+  assert.doesNotMatch(agent.err.text, /tree it runs from/);
+});
+
+test("the line names no path", () => {
+  assert.doesNotMatch(OTHER_TREE, /\//);
+});