fix(3726): replace racy 600ms subprocess poll with deterministic test (#3745)

* test(3726): replace racy spawn-poll with deterministic sentinel assertions

The original bug-1974 test asserted STATE.md content against a
2000ms wall-clock deadline while the hook's fire-and-forget
spawn().unref() subprocess raced to write it — causing intermittent
CI failures under Docker contention (#3726).

Fix: assert the synchronously-written warnData.criticalRecorded
sentinel (readable the moment spawnSync runHook() returns), and
invoke `gsd-tools state record-session` synchronously via spawnSync
to verify the persistence seam. Adds a counter-test for WARNING-only
fires (5 tests total). No production code changed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(3726): repair Windows state add-blocker concurrent-write race

acquireStateLock silently returned a false-success lockPath on any non-EEXIST
openSync error (the old guard was `if (err.code !== 'EEXIST') return lockPath`).
On Windows-24 CI, the releaseStateLock unlink briefly leaves the file in a
transitional state so the next O_CREAT|O_EXCL call from a racing process gets
EPERM or EBUSY instead of EEXIST. The old guard treated this as "lock not yet
created, you own it" and let the second process proceed with its own
read-modify-write while the first still held the actual lock — causing one
blocker to be silently overwritten.

Fix mirrors commits ab24d80b and 47983914 already on main: replace the
silent-bypass guard with an explicit ACQUIRE_LOCK_RETRY_ERRNOS allowlist
(EPERM, EBUSY, EAGAIN, EINTR, EINVAL, EIO, ENOENT, ESTALE) that retries on
transient filesystem conditions, and throw on all other non-EEXIST codes rather
than returning a false-success lockPath. The same retry set is applied to
withPlanningLock in planning-workspace.cjs (shared root cause, same fix).
Local test run: 10/10 pass (locking-bugs-1909-1916-1925-1927.test.cjs).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>