fix(test): remove all 8 delayed process.exit teardown bombs — the tier-1 gate can finally fail

bun test runs every file in ONE process, so a 500ms setTimeout(process.exit(0))
armed in afterAll fired mid-way through a LATER file and killed the entire
suite with exit 0 and no summary — only ~16 of 434 files ran, and every
downstream failure was invisible (observed live throughout this wave's
enumeration). Changes, all guarded by fault injection:

- Replace every delayed-exit teardown with a time-boxed close of the file's
  own browser (8 files across browse/ and design/); stub the daemon
  /shutdown timer instead of letting its unconditional process.exit tear
  the runner down.
- test/no-suicide-exit.test.ts: static tripwire — no *.test.ts may schedule
  a delayed process.exit again.
- test/exit-propagation.test.ts + fixtures: fault injection with REAL bun
  output proves the truncation shape (exit 0, no summary) and that
  scripts/test-free-shards.ts now detects it: a shard exiting 0 WITHOUT
  bun's final summary line is treated as FAILED (exit code alone is not
  evidence of completion).
- handoff: the three headed-mode integration tests are darwin-skipped with
  a pointer to the known macOS headed-launch breakage (#2242/#2554); they
  keep running on Linux CI. Un-skip in the browse-daemon wave.
- feedback-roundtrip: repair the handler call sites unmasked by the fix —
  handlers take (command, args, session, bm); passing the manager where a
  session belongs broke all six tests.
- user-slug-fallback: HOME isolation makes endpoint_hash deterministic.

Fixes #2421, #2435.

Contributed by @sneakygriff (PR #2172) with repairs from @time-attack
(PR #2230 feedback-roundtrip hunks); supersedes PR #2252 by @whd4 (same
defect, credited).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

design/test/daemon.test.ts

@@ -361,16 +361,27 @@ describe("daemon /shutdown", () => {
     await fetchHandler(
       req("POST", `/boards/${board.id}/api/feedback`, { regenerated: false }),
     );
-    // Now non-done count is 0 — handler should return shuttingDown:true.
-    // We DON'T let the real gracefulShutdown timer fire (it calls process.exit
-    // after 50ms which would tear down the test runner); instead we just
-    // observe the immediate response.
-    const r = await fetchHandler(req("POST", "/shutdown"));
-    expect(r.status).toBe(200);
-    const body = (await r.json()) as any;
-    expect(body.shuttingDown).toBe(true);
-    // Reset state for subsequent tests; the shutdown timer will be a no-op
-    // because the next resetForTest flips shuttingDown back to false.
+    // The handler arms setTimeout(gracefulShutdown, 50), and gracefulShutdown
+    // arms setTimeout(process.exit, 50). bun test runs ALL files in one
+    // process, so letting that exit fire would kill the whole suite ~100ms
+    // later (exit 0, no summary — see test/no-suicide-exit.test.ts). Stub
+    // process.exit, wait past both timers so they fire harmlessly while
+    // stubbed, then restore. (resetForTest does NOT defuse the timers: the
+    // exit callback is unconditional.)
+    const origExit = process.exit;
+    (process as any).exit = (() => undefined) as any;
+    try {
+      const r = await fetchHandler(req("POST", "/shutdown"));
+      expect(r.status).toBe(200);
+      const body = (await r.json()) as any;
+      expect(body.shuttingDown).toBe(true);
+      // Let both 50ms timers (gracefulShutdown, then its process.exit) fire
+      // against the stub before restoring the real process.exit.
+      await new Promise((resolve) => setTimeout(resolve, 200));
+    } finally {
+      (process as any).exit = origExit;
+    }
+    // Reset state for subsequent tests (gracefulShutdown set shuttingDown).
     resetDaemon();
   });
 });