"tries at /signin close the API door" passes every time on a loaded check machine #4406

Replaces #4402. Both runs on #4402 ended at the clone (an infrastructure fault, not the work), so nobody has tried the work yet. The sentinel saw test/signin-password-doors.test.ts ("the doors count in one window: tries at /signin close the API door", around line 93) fail on 3 pulls in one hour.

Done:

• [ ] The pull names the cause of the load sensitivity, with evidence. Suspects: the sign-in window's clock rolls between the TRIES /signin posts and the API attempt; full-cost argon2 makes the test outlast its timeout; the /signin posts are not counted (the fetch sends no Origin, or its response is not awaited) before the API try.
• [ ] Fix that cause in the test setup (an injected clock, a low hash cost under test, or awaiting each response) without weakening what the test proves: after TRIES wrong passwords at /signin, POST /api/v1/sessions with the right password is a 429.
• [ ] Each /signin try is asserted to be a refusal (not a 403 from the origin check), so the test cannot pass for the wrong reason.
• [ ] for i in $(seq 20); do bun test test/signin-password-doors.test.ts || break; done passes 20 of 20, and once more beside a parallel bun test. Put the numbers in the pull.
• [ ] Change production code only if the cause is a real race in counting tries, and add a test that pins the fix.

Files: test/signin-password-doors.test.ts, perhaps src/core/users.ts or the sign-in throttle. Builder: sentinel or torque.

Parked by the crew: the run ended without a pull: clone failed: fatal: unable to parse commit 1446f69e8ea54fbdf88845347be4133484fd163e warning: Clone succeeded, but checkout failed. You can inspect what was checked out with 'git status' and retry with 'git restore

Parked by the crew: the run ended without a pull: clone failed: fatal: unable to parse commit 1446f69e8ea54fbdf88845347be4133484fd163e warning: Clone succeeded, but checkout failed. You can inspect what was checked out with 'git status' and retry with 'git restore

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the run ended without a pull: clone failed: fatal: unable to parse commit 1446f69e8ea54fbdf88845347be4133484fd163e warning: Clone succeeded, but checkout failed. You can inspect what was checked out with 'git status' and retry with 'git restore
2. the run ended without a pull: clone failed: fatal: unable to parse commit 1446f69e8ea54fbdf88845347be4133484fd163e warning: Clone succeeded, but checkout failed. You can inspect what was checked out with 'git status' and retry with 'git restore

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Deferred behind the Later gate (#595). This issue and #4402 before it have now parked four times, every time at the clone (fatal: unable to parse commit 1446f69e), and no builder has reached the work. 1446f69e is a sound commit on main and clones cleanly in the planner's checkout, so the fault is in the builders' clone or mirror, not in this issue. Writing another replacement would park the same way. It waits until a person repairs the crew's clone; then take it off the gate as written.

Steward (a person): this run failed to check out ("unable to parse commit 1446f69e") during the 0.7.231 rollout, 13:50-13:58Z - an infrastructure fault, not this work. Strike reset; run again.