docs(test): name the real reason the suite could reach ~/.codeman

#356 stopped a bare suite run from overwriting the production
`remote-hosts.json` by pointing `CODEMAN_DATA_DIR` at a throwaway dir, and it
gated every case-tree delete on the temp HOME. Both changes are right; the
explanation written next to them is not. It says `os.homedir()` reads
/etc/passwd rather than `$HOME` on Linux, which would mean the temp HOME in
test/setup.ts never worked. It does: libuv checks the env var before the passwd
entry (measured: `HOME=/tmp/x node -e 'console.log(os.homedir())'` prints
/tmp/x), and CLAUDE.md's testing section relies on exactly that.

What bypasses the temp HOME is `CODEMAN_DATA_DIR` itself. `getDataDir()` reads
it as an absolute override before it looks at `homedir()`, so one inherited from
the shell (a second instance, a beta run) sends the whole suite at the real data
dir. That is the case setup.ts now closes, and #371 names the same variable from
the other direction.

The comments in setup.ts, the `safeRmHomeTree` helper, the voice-routes and
case-clone tests now say that, and the containment gate is described as what it
is: defense in depth. CLAUDE.md's testing paragraph gets the same note so the
next reader does not chase a homedir() bug that does not exist.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qg6bcATm1pNNY4kQWGwzgu

test/mocks/test-helpers.ts

@@ -42,13 +42,14 @@ export function createDeferred<T = void>(): {
  * Delete a directory tree, but ONLY when it lives inside the test HOME.
  *
  * SAFETY (2026-08-29): `test/setup.ts` redirects `process.env.HOME` to a
- * throwaway dir, but code that resolves paths via `os.homedir()` does NOT
- * follow that redirect on every Linux build/Node version — some read
- * /etc/passwd instead of $HOME. A test that `rmSync(CASES_DIR, recursive)` can
- * therefore delete the PRODUCTION `~/codeman-cases` (or any home-anchored
- * tree) on those platforms. This gate refuses to delete anything not under the
- * (redirected) `process.env.HOME`. Lexical `resolve()` is used because the leaf
- * often does not exist and `realpathSync` would throw.
+ * throwaway dir and `os.homedir()` follows it, so a `rmSync(CASES_DIR,
+ * recursive)` normally lands inside the fixture. This gate is defense in depth
+ * for the day that stops being true (a test that runs outside setup.ts, an
+ * env override that anchors a path elsewhere): it refuses to delete anything
+ * not under the redirected `process.env.HOME`, so the failure mode is a
+ * leftover temp dir rather than a deleted PRODUCTION `~/codeman-cases`.
+ * Lexical `resolve()` is used because the leaf often does not exist and
+ * `realpathSync` would throw.
  */
 export function safeRmHomeTree(path: string): void {
   const home = process.env.HOME;
@@ -63,8 +64,7 @@ export function safeRmHomeTree(path: string): void {
 /**
  * True when `path` resolves strictly inside `process.env.HOME` (or to it).
  * Same rationale as `safeRmHomeTree`; use for guarded non-recursive deletes
- * (single files like `linked-cases.json`) so they never touch prod state on
- * platforms where `os.homedir()` ignores `$HOME`.
+ * (single files like `linked-cases.json`) so they can never touch prod state.
  */
 export function isUnderTestHome(path: string): boolean {
   const home = process.env.HOME;

test/routes/case-clone-routes.test.ts

@@ -9,10 +9,10 @@
  * working tree in the case directory, that scaffolding does not overwrite the
  * repository's own files, and that a rejected URL never reaches git.
  *
- * `test/setup.ts` points HOME at a per-file temp dir, but CASES_DIR is
- * `join(homedir(), 'codeman-cases')` and `os.homedir()` ignores the HOME
- * override on some platforms/Node builds — so cleanup below goes through
- * `safeRmHomeTree`, which refuses to delete anything outside the temp HOME.
+ * `test/setup.ts` points HOME at a per-file temp dir, so CASES_DIR
+ * (`join(homedir(), 'codeman-cases')`) resolves inside the fixture; cleanup
+ * below still goes through `safeRmHomeTree`, which refuses to delete anything
+ * outside the temp HOME, so a wrong anchor can never reach the real tree.
  *
  * Port: N/A (app.inject).
  */

test/routes/voice-routes.test.ts

@@ -25,9 +25,10 @@ import { registerVoiceRoutes, _resetVoiceStreamCountForTesting } from '../../src
 import { MAX_CONCURRENT_STREAMS } from '../../src/config/voice.js';
 
 // SAFETY (2026-08-29): anchor on the REDIRECTED test HOME (process.env.HOME,
-// which test/setup.ts points at a throwaway dir) instead of os.homedir().
-// On some Linux builds os.homedir() reads /etc/passwd and would resolve to the
-// REAL home, clobbering the user's ~/.claude/.credentials.json.
+// which test/setup.ts points at a throwaway dir). `os.homedir()` follows it too,
+// but this file writes and deletes `~/.claude/.credentials.json`, the one file
+// where a wrong anchor would sign the developer out of their own CLI, so it
+// fails loudly if setup.ts did not run rather than trusting any fallback.
 function testHome(): string {
   if (!process.env.HOME) throw new Error('process.env.HOME unset — test/setup.ts must run first');
   return process.env.HOME;

test/setup.ts

@@ -34,14 +34,15 @@ process.env.HOME = testHome;
 process.env.USERPROFILE = testHome;
 process.env.VITEST = 'true';
 
-// SAFETY: `getDataDir()` resolves via `homedir()` → `~/.codeman<INSTANCE_SUFFIX>`.
-// Overriding HOME above is NOT enough: on Linux `os.homedir()` reads /etc/passwd,
-// not $HOME, so without this a route test that writes `remote-hosts.json` (or
-// any state file) into `getDataDir()` silently clobbers the PRODUCTION
-// `~/.codeman` tree (found 2026-08-29: `session-routes-workspace-hooks.test.ts`
-// overwrote prod `remote-hosts.json` with an `h1/box/10.0.0.5` fixture during a
-// bare full-suite run, wiping every user-defined remote host and emptying the
-// launch case dropdown). Point every test at a throwaway data dir instead.
+// SAFETY: `getDataDir()` is `process.env.CODEMAN_DATA_DIR || join(homedir(), '.codeman<suffix>')`.
+// The temp HOME above already redirects the second half (`os.homedir()` follows
+// `$HOME`; libuv checks the env var before the passwd entry), but the first half
+// is an ABSOLUTE override: a `CODEMAN_DATA_DIR` inherited from the shell (a
+// second instance, a beta run) bypasses the temp HOME entirely, and a bare suite
+// run then reads and writes the REAL data dir (found 2026-08-29:
+// `session-routes-workspace-hooks.test.ts` overwrote the production
+// `remote-hosts.json` with an `h1/box/10.0.0.5` fixture, wiping every user-defined
+// remote host and emptying the launch case dropdown). Point it at a throwaway dir.
 process.env.CODEMAN_DATA_DIR = testDataDir;
 
 delete process.env.CODEMAN_PASSWORD;