test(raft-apply-decoupling): idempotent and ordered re-application of apply seam (task 2.4)

Add test_apply_reapply_idempotency.c (3 tests, no production changes):
triple-reapplication of an identical job submit with hook-count and
pointer-identity assertions across every call, the NOOP_DUPLICATE
guard branch (untested by task 2.2), and the task's named scenario --
real SUBMIT then real FINISH then a stale out-of-order START, all
through the real apply_committed_entry() dispatch -- confirming the
job stays terminal with no spurious notification.

Closes out task-group 2 (shared apply seam for committed entries).

.kiro/specs/raft-apply-decoupling/tasks.md

@@ -38,7 +38,7 @@
   - _Requirements: 9.1, 9.2, 9.3, 9.4_
   - _Depends: 1.4_
 
-- [ ] 2. Shared apply seam for committed entries
+- [x] 2. Shared apply seam for committed entries
 - [x] 2.1 (P) Extract the guarded state-transition logic used by fact handling into a form usable outside the receipt-time call site
   - Keep the existing monotonic-rank checks (reject backward transitions, no-op duplicate terminal transitions) intact and unchanged in behavior
   - Decouple the transition logic from firing its own hook inline, so hook-firing can be relocated by a later task without touching this logic again
@@ -61,7 +61,7 @@
   - _Requirements: 3.1, 3.2_
   - _Depends: 2.2_
 
-- [ ] 2.4 Unit test idempotent and ordered re-application of the dispatch function
+- [x] 2.4 Unit test idempotent and ordered re-application of the dispatch function
   - Cover applying the same committed entry twice is a no-op with respect to observable state
   - Cover that a duplicate or out-of-order fact entry does not regress a job's lifecycle state
   - Observable: a test applies a FINISH entry followed by a stale, previously-unapplied START entry for the same job and confirms the job remains in its terminal state
@@ -193,6 +193,7 @@
 - **1.2**: implemented `commit_resolve()` + wired it into all 6 commit.c-internal paths that can advance `committed_lsn`/`writable_lsn` (the COMMITTED/majority-ack outcome). Chose `VTASK_LIVE_BLOCK` for dispatch (never admission-gated, unlike `VTASK_REQ_BLOCK` which can fast-reject — unacceptable for "exactly-once, never unresolved"). **Reviewer caught a real task-graph gap, not a defect in 1.2 itself**: converting `COMMIT_MODE_WAIT` away from a blocking wait also removes the *only* mechanism that ever detected a commit timing out (the caller's own `pthread_cond_timedwait` deadline) — nothing yet arms an equivalent timeout for async-registered continuations, and nothing yet wires demotion/log-truncation detection to call `commit_resolve(FAILED, ...)`. Without this, a pending async command during quorum loss would hang forever instead of failing — worse than today's behavior. Split out as new tasks **1.3** (timeout arming) and **1.4** (demotion/truncation wiring), inserted before the renumbered **1.5** (was 1.3, concurrency test — now exercises the real detection paths from 1.3/1.4 instead of calling `commit_resolve()` directly). Task 3.2 now also depends on 1.3/1.4, since its own "failure/timeout outcome replies" observable is meaningless without them.
 - **1.3**: added a dedicated per-commit-engine sweep thread (not the shared `delaymgr` — would violate boundary + delaymgr's 200ms poll granularity vs. `DEFAULT_SYNC_TIMEOUT_MS`=500ms would add timing jitter). Race rule: majority-satisfied always wins over an already-expired deadline when both are true under the same lock hold. **Round 1 REJECTED**: `commit_sweep_once()` computed the next-deadline snapshot under `ce->lock`, unlocked to dispatch, then slept on the *stale* snapshot — a `commit_submit_async()` registration/broadcast landing during that unlocked dispatch window was lost (no thread parked on the condvar to receive it), so the sweep thread could sleep on an absent/late deadline indefinitely (worst case: unbounded delay in a low-traffic quorum-loss scenario, violating the "identical failure timing" no-regression bar). **Fixed** by holding `ce->lock` continuously across scan→wait decisions (releasing only for the unlocked dispatch step) and always re-scanning under the lock immediately before ever calling `cond_wait`/`cond_timedwait` — the standard recheck-then-wait idiom. Round 2 reviewer independently reproduced the round-1 bug shape to confirm the fix actually closes it, not just narrows it. **Precedent for 1.4**: any future code that needs to interrupt the sweep thread's wait (e.g., a demotion/truncation handler resolving a pending LSN out-of-band) must go through the same lock+broadcast discipline `commit_submit_async()` uses, or it risks the identical lost-wakeup class of bug.
 - **1.4**: added `commit_resolve_pending_above(ce, lsn_floor, rc)` (snapshot-then-`commit_resolve()`-per-entry, no parallel bookkeeping). Truncation: a single new `on_truncate`/`truncate_cb_ctx` callback slot on `persist_t` (same inversion-of-control shape as the existing `on_durable_advance` hook) fires from `persist_truncate_wal_above` after releasing `p->lock`, only when a truncation actually removed entries — this ONE wrapper covers all three real truncation call sites (`raft_cb_become_leader`'s post-election truncate, the library's `on_truncate_from` conflict-reconcile, `ha_demotion_convergence_fn`'s post-demotion truncate), verified by the reviewer reading all three. Demotion: `raft_cb_become_follower` calls `commit_resolve_pending_above(&c->commit, 0, -XCE_ERR_STANDBY)` (lsn_floor=0 → fails everything — a demoted node can never authoritatively confirm anything pending; verified against the CP posture). **Known residual, non-blocking**: a fourth internal truncation path (`persist.c` inside `persist_wal_write_replicated`'s tip-conflict-repair branch, STANDBY replicated-apply only) calls `truncate_wal_above_locked()` directly, bypassing the new wrapper — safe today only because demotion resolves ALL pending continuations before role flips to STANDBY (so nothing can still be registered by the time that path runs), but this is an *implicit* ordering invariant, not an asserted one. Flag for whoever next touches the STANDBY replicated-apply path: add a defensive comment/assertion there, or route it through the wrapper too, before relying on it further. Also: bug-1407 was believed closed at this point (70/70 across 3 runs) — **see 1.5's note below, this was a false reading, not a real fix**.
+- **2.4**: pure test-only close-out of task-group 2 — new `test_apply_reapply_idempotency.c` (3 tests), no production changes, approved first round. Covers three distinct cases beyond 2.2's existing coverage: (1) triple-reapplication of an identical WAL_JOB_SUBMIT through `apply_committed_entry()` with hook-fire-count AND pointer-identity assertions across all 3 calls (not just final state); (2) the `JOB_TRANSITION_NOOP_DUPLICATE` guard branch (state == current state) — a genuinely untested path, distinct from 2.2's forward-once and backward-rejected cases; (3) the task's named scenario, driven entirely through the real dispatch seam (not seeded/shortcut): real SUBMIT → real FINISH → stale out-of-order START (lower LSN, arriving after), asserting the job stays in its FINISH/terminal state and no third hook fires for the rejected START. Test assertions key on hook-fire COUNT and job STATE, never a specific `HOOK_DETAIL_*` value — so these tests stay valid even if 2.2's documented generic-hook-routing deviation is later corrected. **Task-group 2 (shared apply seam) is now complete**: 2.1 (guard cores extracted) → 2.2 (dispatch function built, generic job-state-family routing is a confirmed permanent deviation from design.md, tracked) → 2.3 (replay wired to the seam, duplicate-notification-on-restart hazard confirmed inert today but must be re-verified before 4.1/6.1/6.2/6.3) → 2.4 (idempotency proven through the real dispatch path). Next: task-group 3 (command apply-after-commit ordering), which is the first consumer of both this seam and task-group 1's commit-engine continuation API.
 - **2.3**: rewired `replay_wal()` (persist.c) to call `apply_committed_entry()` (task 2.2's seam) instead of `apply_wal_entry()` for restart replay's per-entry apply. `apply_wal_entry`/`apply_committed_entry` are siblings, not wrapper/wrappee — `apply_wal_entry` is NOT retired, it remains ha.c's live standby catch-up/replicated-apply dispatch (untouched, different call sites, out of this task's boundary). **Confirmed hazard, investigated to resolution by the reviewer (not left open)**: `replay_wal(p, p->checkpoint_lsn, ...)` replays the FULL WAL range since the last snapshot on every restart (`last_applied_lsn` is deliberately not persisted — recomputed at replay time per design.md), not just a narrow crash-gap tail. Since `apply_committed_entry` fires `AFTER_EVENT` hooks (unlike the old `apply_wal_entry`, which never did), this means every restart re-fires notification hooks for entries already applied+notified in a prior process life — a duplicate-notification hazard in principle. **Independently traced and confirmed inert today** for both existing hook consumers: scheduler hooks aren't registered until `on_scheduler_join()` (sched.c), which happens post-boot via network JOIN handshake, strictly after `persist_recover()` runs; apiserver hooks ARE registered before `persist_recover()` (`apiserver_init()` in `cluster_init_phase2()`), but every apiserver hook body gates its actual network notify on `apiservers[i].ep != NULL`, and the apiserver-join table starts empty each process life — a no-op except via a narrow reconnect race. **MUST be re-verified before tasks 4.1/6.1/6.2/6.3** make this path unambiguously live and broad (e.g. if a future task registers apiserver connections earlier, or scheduler hooks get registered pre-replay) — at that point this either needs a replay-mode flag suppressing hook-firing, or an explicit accepted-idempotent-duplicate-notification decision recorded in design.md. A loud in-line comment cross-referencing this note now sits at the `apply_committed_entry()` call site in `replay_wal()` (persist.c). Also confirmed: job-state facts now replay through 2.1's guarded `apply_job_update_transition()` instead of the previously-unguarded `restore_job_state()` — intentional (Req 3/7 online-replay divergence fix), verified no existing test depended on the old unguarded semantics. `apply_committed_entry`'s missing oversized-payload guard (vs. `apply_wal_entry`'s `MAX_WAL_PAYLOAD_BYTES`/`-EMSGSIZE` check) confirmed inert — `persist_wal_write_replicated()` already rejects oversized payloads at write time, before anything reaches disk.
 - **2.2**: implemented `apply_committed_entry(persist_t*, uint32_t wal_type, uint64_t lsn, const void* payload, uint32_t len)` in persist.c/persist.h, matching design.md's signature. Routes `WAL_JOB_SUBMIT` through `restore_job()` (idempotent on duplicate jobid — no-op, Req 7.1), `WAL_QUEUE_CTRL`/`WAL_WORKER_CTRL` through their existing restore primitives, and fires each type's post-mutation hook exactly once, after mutation. **Confirmed permanent, non-cosmetic deviation from design.md's Apply Seam wording**: ALL nine job-state fact WAL types (`WAL_JOB_{START,FINISH,FAIL,STOP,RESUME,UPDATE,RUSAGE,CKPT,PREASON}`) route through the single guard-only `apply_job_update_transition()` core from 2.1 — NOT the type-specific `apply_job_{start,finish,fail}_transition` cores — and fire one generic `HOOK_DETAIL_JOB_UPDATE` hook, not the type-specific `HOOK_DETAIL_JOB_START`/`_EXIT`/`_FAIL`. Root cause, independently verified by two review rounds: the on-disk wire format for every one of these types (`wal_jobstate_t {jobid, state}`) genuinely only carries the resulting state, not the richer `job_pidinfo_t`/`xce_jobfinish_t`/`job_failinfo_t` payload the type-specific cores/hooks require — this is a pre-existing wire-format reality (`apply_wal_entry` already collapsed these the same way before this task), not a shortcut invented here. **design.md's Apply Seam section and Fact Ingestion → Event Contract section currently describe per-type hook dispatch that this wire format cannot support as written** — this is a real, standing design/reality conflict, not yet reconciled in design.md itself. No task in the current plan (2.3, 4.1, 4.2, 6.1, 6.2, 6.3) enriches the wire format to close this gap — confirmed by reading all of them; task 4.1 is exclusively about removing receipt-time mutation/hook-firing, not payload enrichment. **Explicit blocking-style call-out for whoever implements 4.1/6.2/6.3**: wiring this dispatch function into a live fact-apply path will permanently change every worker-reported job start/finish/fail notification to a generic UPDATE detail instead of the type-specific one, unless the wire format is enriched first or design.md is corrected to formally accept this substitution — verify this is still the accepted behavior before wiring it live, don't assume it'll be fixed by then. Took 3 review rounds to land: round 1 rejected two doc-comment defects (a citation blaming the wrong crash site, and a dangling pointer to task 4.1 as the fix location); round 2's fix corrected the crash site (real one is `sched.c`'s `sched_job_start_fun`/`_exit_fun`/`_fail_fun`, which unconditionally dereference `info->jobid` before any NULL check) but fabricated a nonexistent function name (`encode_JobPIDInfo_ptr`) as supporting evidence; round 3 replaced it with a narrower, fully source-verified claim (apiserver.c's equivalent functions store the raw pointer into a notify union without dereferencing it at that call site — real, checked line-by-line). **Lesson**: when a reviewer catches a citation error, the safest fix is the narrowest claim you can personally verify by reading the actual code, not a broader-sounding replacement — round 2's attempt to explain "why the alternative is fine" reached for an unverified downstream mechanism and got caught fabricating it.
 - **2.1**: split `mark_job_start`/`mark_job_finish`/`mark_job_fail`/`mark_job_update` (job.c) into four hook-free cores (`apply_job_{start,finish,fail,update}_transition`, new `job_transition_result_t` enum in cluster.h) containing only the monotonic-rank guard + mutation, verified an unmodified lift line-by-line against pre-extraction code. Wrappers peek the same guard predicate to decide hook-firing, then delegate to the core — no unlock/relock gap between peek and delegated call, so no new race from the double-evaluation. `mark_job_fail`'s pre-existing lack of a guard is preserved, not added or removed. New `test_apply_seam.c` (8 tests) calls the cores directly, bypassing `on_job_*` receipt handlers entirely — this is the form task 2.2 (dispatch function) and task 6.1 (apply pump) will call into. **Non-blocking follow-up flagged by reviewer**: the new doc-comments on `apply_job_fail_transition`/`apply_job_update_transition` overclaim a universal "caller holds RTTI_LOCK_WRITE" precondition — `job_ctrl` (job.c:396, pre-existing, untouched) calls `mark_job_update`/`mark_job_fail` under only RTTI_LOCK_READ. No new race (extraction added no unlock/relock), but whoever writes task 2.2/6.1 should not trust that comment's blanket claim — verify the actual lock held at each call site instead.