docs: promote raft-apply-decoupling spec family from /kiro-discovery

Adds the Raft Apply-Ordering & Hook Decoupling roadmap phase: canonical
pre-hooks -> raft commit -> apply -> notify ordering, with the raft protocol
step lifted out of the notification hook fan-out (root of the bug-795/828/
851/1060 divergence family). Decision: apply-after-commit via a single
shared apply_committed_entry() seam reused by online apply and restart
replay.

- raft-drive-async: full spec docs (brief/requirements/research/design)
  committed alongside its already-tracked tasks.md; async-drive prerequisite
  for the apply-decoupling work, sequenced to start first (threatens
  failover liveness today).
- raft-apply-decoupling: new spec (brief + facts-in-raft.md) covering the
  apply seam and the facts (WAL_MODE_RETAIN) apply-timing question (open
  decision D1).
- job-array-single-wal-record: promoted from backlog to a tracked spec,
  sequenced after raft-apply-decoupling.
- ha-consistency-invariants: add criterion 2.9 (Facts-Apply invariant),
  documenting the current on-receipt fact-reaction deviation this family
  will reconcile.
- raft-commit-safety / raft-log-replication: reconcile spec.json phase to
  "implemented" (both were mislabeled tasks-generated despite full 18/18
  and 24/24 task completion + raft_sim GO).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SDWVNQLKxqTVHh42cH7rV3

.kiro/steering/roadmap.md

@@ -20,6 +20,33 @@ XCE is in the persistence + HA transformation (branch `persistent_ha`). Governin
 
 > **ha-term-safety** (requirements + design generated 2026-06-21; `.kiro/specs/ha-term-safety/`) is the XCE-side INTEGRATION + REGRESSION umbrella for this family: it wires the controller WAL / commit-barrier into the new raft callbacks (thin adapter — protocol delegated to the library), owns the **config-change marker** (R7 — config changes as `(term,lsn)` log markers; bytes via the existing out-of-band config-push transport, hash-verified against the marker), and holds the live **bug-851 chaotic-failover regression**. Its protocol invariants R1–R6 are realized by the library specs above (not re-implemented in the controller). **Scope: R1–R7 only.** The former R8 (config-upgrade full-snapshot consistency, bug-857) was **descoped 2026-06-21 to the independent `config-upgrade-snapshot` spec** (below), because it requires entity-bearing snapshots that do not exist yet. Next: `/kiro-spec-tasks ha-term-safety`.
 
+## Raft Apply-Ordering & Hook Decoupling — NEW 2026-06-24 (`/kiro-discovery`)
+
+**Goal:** make the controller follow canonical Raft ordering — *pre-hooks → raft commit → apply → notify* — with the raft protocol step lifted OUT of the notification hook fan-out. Today `persist_job_hook_fun` (an `AFTER_EVENT` hook) performs the WAL append + synchronous majority-commit barrier inline, and `create_job()` mutates in-memory state BEFORE that commit (`job.c:558` before `job.c:593`; `persist.c:2532`/`persist.c:2198`/`ha.c:3080`). A failed/timed-out commit does not cleanly revert the optimistic mutation — the structural root of the bug-795/828/851/1060 divergence family. Decision (user, 2026-06-24): **apply-after-commit (canonical)** — a single shared `apply_committed_entry()` seam mutates the state machine only after commit, reused by restart replay so online-apply and replay-apply are identical. Hooks demote to notification-only. Decompose via Path E (2 new specs + touchpoints).
+
+### Async-drive prerequisites (surfaced 2026-06-25 by blocking audit; thread-role contract now in `ha-async-io.md`)
+
+The protocol **drive** is NOT fully event-driven. Root cause: `peer_ctrl_msg_handler` runs inline on iomgr instead of dispatching to the vtask pool, and delaymgr (the heartbeat driver) was the documented blocking sink. Corrected thread-role contract is now steering (`ha-async-io.md`, 2026-06-25; SUPERSEDES "delaymgr for blocking ops = Permitted"). Two separable prerequisites (full evidence: `.kiro/specs/raft-apply-decoupling/facts-in-raft.md` § Keystone + "Two distinct prerequisites" + P2 offload mechanism):
+
+- **P1 — commit-barrier async** (the *commit* drive). Convert `repl_wait_majority_ack()` from blocking `pthread_cond_timedwait` (commit.c:359) to event-driven `resolve(lsn,outcome)` on the existing commit engine. Dissolves apply-self-deadlock (B), enables reply continuations (C), removes vtask-pool exhaustion. **Owned within `raft-apply-decoupling` as its keystone** (sequenced before its Phase A).
+- **P2 — drive hardening** (the *transport/timer* drive). Now its own spec **`raft-drive-async`** (brief: `.kiro/specs/raft-drive-async/brief.md`) — promoted because it threatens liveness independently. See the Specs list below.
+
+### Specs (dependency order — Raft Drive & Apply Async family)
+
+- [ ] **raft-drive-async** *(START FIRST — threatens failover liveness TODAY)* — bring the code into compliance with the corrected `ha-async-io.md` thread-role contract: dispatch `peer_ctrl_msg_handler` to the vtask pool (root-cause fix); snapshot send + config-push off iomgr → admission-capped slow lane (per-peer dedup + WAL coordination); delaymgr peer connect → bounded non-blocking + offloaded (reuse `xce_probe_config_tag` pattern); add a general non-IO vtask-submit path + admission reservation (extend `COMMIT_WAIT_RESERVED`). Verify with a **partition** (unreachable-not-killed) soak: heartbeats to survivors continue, no spurious election. Likely root of the bug-851 chaotic-failover family. Dependencies: none hard (builds on existing commit engine + vtask + the steering contract); `election-iomgr-refactor` is completed upstream (provides `delay_task_ms`/`on_connected`/non-blocking vote fan-out) — STANDALONE per 2026-06-25 scope-check (ADJACENT-SAME-AREA: it fixed startup blocking, this fixes runtime drive blocking). Brief + requirements + research + **design + tasks done**; phase=tasks-generated (tasks `approved: false`). **`/kiro-validate-design` GO 2026-06-25** — three review findings folded into design+tasks: (1) **deadlock-freedom + LivenessAdmission** — the documented invariant reversal (ack/`commit_on_ack` moves off iomgr to the vtask pool, `commit.c:16`) co-locates commit-barrier wakers+waiters; review found `COMMIT_WAIT_RESERVED` is **insufficient** because it counts only commit-waits while peer_ctrl also puts vote-grant fsync + config-ack waits on the pool (invisible to it). Fix: generalize the reservation to a **pool-level task-class admission in vtaskmgr** (`VTASK_LIVENESS`/`LIVE_BLOCK`/`REQ_BLOCK`; liveness never gated; `COMMIT_WAIT_RESERVED` folded in) — new **Phase-1 task 1.6** (dormant infra), hard prerequisite of 3.1; task 3.4 is the admission gate. Transient until `raft-apply-decoupling` P1 makes the barrier async; (2) **WAL-trim cursor-bound guard** added to task 3.2 (bug-1147, see Hardening below — moving checkpoint/trim onto a concurrent lane worsens the existing latent trim-vs-cursor race); (3) **in-process partition primitive** in `xce_test` as the portable primary for R7 (firewall DROP secondary) so the soak actually runs unprivileged. **Next: approve tasks (`/kiro-spec-tasks raft-drive-async`) → `/kiro-impl`; ship Phase 1 (bounded connect) first.**
+- [ ] raft-apply-decoupling — decouple the raft protocol step from the hook fan-out (item #1); canonical pre-hooks → commit → apply → notify ordering (item #2); single `apply_committed_entry()` seam shared by online commit + restart replay; post-restart validation that committed log was correctly applied to materialized state (item #4); requirement + regression tests (item #5). **Contains P1 (commit-barrier async) as its keystone.** Commands (WAL_MODE_WAIT) apply-after-commit; **facts (WAL_MODE_RETAIN) routed through commit-then-apply too** — D1 RESOLVED (block-but-durable under quorum loss); formalized as `ha-consistency-invariants` criterion 2.9. Dependencies: **raft-drive-async (HARD — reuses its slow-lane + admission infra; drive must be async first)**, raft-log-replication + raft-commit-safety (DONE/implemented), worker-rejoin-resync (HARD for the facts-recovery half — see below); coordinate with ha-term-safety. Briefs: `.kiro/specs/raft-apply-decoupling/brief.md` + `facts-in-raft.md`.
+- [ ] worker-rejoin-resync — **elevated to HARD prereq for the facts half of raft-apply-decoupling 2026-06-25** (was backlog "designated backstop"). Worker re-reports running/finished job state on rejoin so facts lost in a failover window are recovered; re-reports flow through commit-then-apply idempotently (criterion 2.9). Today workers send only `hostattrs` on join (bug-396). Already on the backlog below; pulled forward into this family. Dependencies: ha-consistency-invariants (commit barrier + idempotency guards).
+- [ ] job-array-single-wal-record — **PROMOTED from backlog 2026-06-24.** Persist/replicate/push a job-array submission as ONE Raft record (base spec + index range/count + per-index overrides) committed atomically through a single barrier; expand on apply (online + replay) and on the scheduler side; preserve per-element identity/addressing; idempotent re-apply (item #3). Dependencies: raft-apply-decoupling (HARD — builds on the shared apply seam), ha-commit-engine, ha-commit-barrier-rollout, ha-consistency-invariants. Brief: `.kiro/specs/job-array-single-wal-record/brief.md`.
+
+### Existing Spec Updates (Raft Apply-Ordering phase)
+
+- [ ] raft-sim-conformance — add apply-after-commit regression assertions (item #5): no apply on a failed/uncommitted entry; online-apply ≡ replay-apply for the same committed log; ordering invariant pre-hooks → commit → apply → notify. Revisit with `/kiro-spec-requirements raft-sim-conformance` once raft-apply-decoupling requirements land.
+- [ ] ha-term-safety — coordinate: raft-apply-decoupling restructures the same controller submit→commit path this umbrella wires. Sequence the apply-decoupling edits against ha-term-safety's adapter work (disjoint-but-adjacent regions) to avoid conflicting refactors.
+
+### Direct Implementation Candidates (Raft Apply-Ordering phase)
+
+- [ ] xce_test waldump/walcompare/snapdump inspectors (already a Hardening item below) double as the offline evidence for the item #4 restart-validation requirement — wire their nonzero-exit-on-divergence into the decoupling spec's E2E rather than as a separate spec.
+
 ## Specs (dependency order)
 
 > `[x]` = spec generated (requirements/design/tasks approved, ready for implementation). Implementation tracked via each spec's tasks.md; implement in roadmap order (cross-spec review 2026-06-11: four specs touch ha_dispatch_gate / raft_cb_become_follower in disjoint-but-adjacent regions).
@@ -37,16 +64,17 @@ XCE is in the persistence + HA transformation (branch `persistent_ha`). Governin
 - [ ] worker-rejoin-resync — **planned long ago, no effort yet (recorded 2026-06-10).** When a worker rejoins after disconnect or controller failover, it shall re-report its running/finished job states so the controller recovers facts whose notifications were lost. Evidence of the gap (ha-consistency-invariants research deep-dive §A): `xce_join_req` carries only `hostattrs_t` (src/lib/request.c:1154-1181) — no job state; worker notify is fire-and-forget with zero redelivery (bug-396), so any job start/finish/fail sent during a disconnect or failover window is permanently lost today. Scope sketch: extend the join/hello exchange (or a post-join message) with a running+recent job-state report; controller reconciles against its job table through the commit barrier (entries go through majority commit like any state change); requires the `mark_job_*` idempotency guards (shared need with ha-consistency-invariants' pending-facts queue). Complements — does not replace — the primary-side pending-facts queue: the queue covers quorum-loss windows while connected; resync covers disconnect/failover windows. **Elevated 2026-06-11**: designated as the official backstop in ha-consistency-invariants Req 2.8 / boundary context — facts the controller received are retained-and-retried until committed; facts that never arrived (or died with the controller) are recovered only by this resync. Dependencies: ha-consistency-invariants (commit barrier + idempotency guards). Extends: worker-join-refactor (implemented — covers attribute/endpoint update on rejoin only).
 - [ ] admin-config-tool — drives `OP_upgradeConfig` (prerequisite for config-upgrade Phase 2). Encode ClusterConfig YAML/JSON → Cap'n Proto binary, SHA-256 over the bytes, connect to primary (SSL, same CA), send `OP_upgradeConfig`, display reply (version tag, acked count, errors), poll `OP_probe` after restart. Suggested CLI: `xce-config push --controller <host:port> --config cluster.yaml`. MUST validate that user configs don't use the reserved name `"lost_and_found"` for any queue/host (defence-in-depth: controller enforces at runtime via `load_primary_config()` FATAL, tool prevents at authoring time; migration: pre-existing clusters must rename before upgrade — see config-replication-design.md §6.5/§7.1). _(From FUTURE_WORK.md §1 + §8, 2026-05-12.)_
 - [ ] lightweight rejoin re-attach (failover optimization) — **recorded 2026-06-16; deferred (YAGNI).** Today, on controller failover a reconnecting daemon does a full re-join and apiserver/scheduler receive **full** state (e.g. the whole job list), not a delta; for a large cluster this is sizable but rare. Decision (libxce-failover design review): accept full-state rejoin — it is simple, correct, and still cheaper than a full-history replace with no snapshot (cf. IBM LSF). Future optimization: a session-token "re-attach" hello that lets the new primary skip re-pushing already-replicated state, or a delta-only state transfer keyed on the consumer's last-known committed LSN. Delta reconciliation is non-trivial (the primary must know what each consumer already holds). Promote only if failover-rejoin latency/bandwidth is **measured** as a problem at scale. Dependencies: libxce-failover (rejoin hook), component-failover-adoption (daemon rejoin content), worker-rejoin-resync (worker job state).
-- [ ] job-array-single-wal-record — **recorded 2026-06-16.** Enhance controller & scheduler so a job-array submission persists, replicates, and pushes to the scheduler as a **single WAL record** rather than one record per array element. Today a job array fans out to N per-job state changes, so a 10k-element array means 10k WAL appends + 10k replicated commits + 10k scheduler pushes — amplifying commit-engine load, replication bandwidth, and failover replay time linearly in array size. Scope sketch: (a) controller writes one WAL entry describing the array (base spec + index range/count + per-index overrides) committed atomically through the commit barrier; (b) replication carries the single record so standbys reconstruct the whole array from one committed LSN; (c) scheduler receives the array as one push and expands locally. Must preserve per-element identity/state addressing after expansion (status, cancel, completion still operate per task id). Dependencies: ha-commit-engine + ha-commit-barrier-rollout (single atomic commit), ha-consistency-invariants (replicated scheduling state). Spec advised before implementation; promote via `/kiro-spec-init "job-array-single-wal-record"` when ready.
+- [→] job-array-single-wal-record — **PROMOTED to a spec 2026-06-24** (`/kiro-discovery`; brief at `.kiro/specs/job-array-single-wal-record/brief.md`; now tracked under the *Raft Apply-Ordering & Hook Decoupling* phase above, sequenced after raft-apply-decoupling). Original note retained for provenance: Enhance controller & scheduler so a job-array submission persists, replicates, and pushes to the scheduler as a **single WAL record** rather than one record per array element. Today a job array fans out to N per-job state changes, so a 10k-element array means 10k WAL appends + 10k replicated commits + 10k scheduler pushes — amplifying commit-engine load, replication bandwidth, and failover replay time linearly in array size. Scope sketch: (a) controller writes one WAL entry describing the array (base spec + index range/count + per-index overrides) committed atomically through the commit barrier; (b) replication carries the single record so standbys reconstruct the whole array from one committed LSN; (c) scheduler receives the array as one push and expands locally. Must preserve per-element identity/state addressing after expansion (status, cancel, completion still operate per task id). Dependencies: ha-commit-engine + ha-commit-barrier-rollout (single atomic commit), ha-consistency-invariants (replicated scheduling state). Spec advised before implementation; promote via `/kiro-spec-init "job-array-single-wal-record"` when ready.
 - [x] ~~WAL group-commit batching~~ — **recorded 2026-06-17 as deferred; ABSORBED INTO ha-commit-durability 2026-06-18 (design-review reversal).** The `/kiro-validate-design` review surfaced that the highest-volume WAL traffic is `WAL_MODE_RETAIN` facts (job start/finish/fail/rusage) — not array-collapsible and not covered by `job-array-single-wal-record` — so a pure per-entry synchronous design would penalize the dominant write path. Decision (with user): **do group-commit now** — repurpose `fsync_worker` from a timer into a demand-driven flusher (batch one `fdatasync` across pending appends, advance `durable_lsn`, wake commit-eval) as part of ha-commit-durability rather than deferring. No longer a separate backlog item.
 - [ ] primary step-down-on-quorum-loss — optional CP follow-on noted in ha-consistency-invariants brief (writes already blocked on quorum loss; step-down is an availability/clarity optimization).
 - [ ] read consistency / leader leases — Raft §8 read-only optimization; status queries may currently observe stale or provisional state (documented deviation in ha-consistency-invariants).
-- [ ] entity-bearing snapshots ("Task 11" format) — snapshot files are currently a 16-byte LSN sentinel (persist.c:435-437); real entity serialization unblocks snapshot-based state transfer and faster recovery. **Cheaper than it looks (verified 2026-06-11)**: the dual-zarray COW machinery it needs is already built and unit-tested but dormant — `xzarray_freeze`/`xzarray_thaw` in the vtable (zarray.c:695-757, O(1) freeze, thaw with `should_retain` GC filter, test_zarray_cow.c) with zero production callers (kvmgr.c:297 `vfreeze = NULL /* wired in P0-2 */`). Note: single-generation COW — the snapshot consumer owns freeze/thaw; do not add second concurrent consumers. Slot-level only (snapshots array structure, not object contents — serialize item state under per-object locks during the freeze window). Once landed, also strengthens ha-consistency-invariants §C eviction option (iii) and faster rebuild-on-demotion. **Downstream (recorded 2026-06-21): `config-upgrade-snapshot` HARD-depends on this** — it needs an entity-bearing snapshot to deliver an identical materialized post-upgrade state to every member (bug-857).
+- [ ] entity-bearing snapshots ("Task 11" format) — snapshot files are currently a 16-byte LSN sentinel (persist.c:435-437); real entity serialization unblocks snapshot-based state transfer and faster recovery. **Cheaper than it looks (verified 2026-06-11)**: the dual-zarray COW machinery it needs is already built and unit-tested but dormant — `xzarray_freeze`/`xzarray_thaw` in the vtable (zarray.c:695-757, O(1) freeze, thaw with `should_retain` GC filter, test_zarray_cow.c) with zero production callers (kvmgr.c:297 `vfreeze = NULL /* wired in P0-2 */`). Note: single-generation COW — the snapshot consumer owns freeze/thaw; do not add second concurrent consumers. Slot-level only (snapshots array structure, not object contents — serialize item state under per-object locks during the freeze window). Once landed, also strengthens ha-consistency-invariants §C eviction option (iii) and faster rebuild-on-demotion. **Downstream (recorded 2026-06-21): `config-upgrade-snapshot` HARD-depends on this** — it needs an entity-bearing snapshot to deliver an identical materialized post-upgrade state to every member (bug-857). **This is also strategy B for catch-up of a far-behind / empty-rejoin standby (cursor=0) — recorded 2026-06-25:** WAL streaming alone cannot serve a standby whose needed range was trimmed (bug-795/828/1147), and a new node always starts empty, so safe aggressive WAL trimming + new-node join *requires* InstallSnapshot (snapshot-at-boundary + tail WAL). Until this lands, trim must stay cursor-bounded (strategy-A stopgap, see Hardening) and the system cannot safely admit a standby that has fallen below the trim floor. Scope to add when promoted: the standby-side snapshot-install / apply path (request snapshot when its cursor is below the leader's earliest retained LSN, install, resume from snapshot tail).
 
 ## Hardening / Direct-Implementation Items
 
 Smaller items that likely don't warrant a full spec; pick up opportunistically or bundle into adjacent spec work.
 
+- [ ] **WAL-trim cursor-bound guard (bug-1147; surfaced 2026-06-25 by raft-drive-async design review)** — `trim_wal_segments` (`persist.c:1374`) bounds deletion ONLY by the open segment (`if (seg_start_lsn < active_seg_lsn) unlink()`) — it consults **no** standby `acked_lsn`, **no** `committed_lsn`, **no** in-flight snapshot boundary. With no working snapshot backfill (`write_snapshot` emits a 16-byte sentinel only), a standby lagging by more than ~one open segment hits a log range that exists nowhere → permanent committed-prefix gap (the bug-795/828 family). This is **strategy-A retention discipline that should exist regardless**. Stopgap fix: compute `floor = min(all standby acked_lsn, in-flight snapshot boundaries)` under `p->lock` and refuse to delete at/above `floor`. **Folded into `raft-drive-async` task 3.2** (which moves checkpoint/trim onto a concurrent lane, worsening the race) — but stands alone if that slips. Does NOT fix empty/far-behind join (cursor=0); that needs `entity-bearing snapshots` (strategy B, backlog). Related: bug-795, bug-828, bug-1060.
 - [ ] OP_heartbeat peers cross-validation — include a hash of the local `--peers` string in heartbeat requests; log ERROR on mismatch between candidates. Detects misconfigured nodes at election time instead of silently risking dual-primary split-brain. _(FUTURE_WORK.md §3.)_
 - [ ] validate_host() real authorization — currently a stub returning success for all peers; MUST be implemented before `CONF_ENABLE_UPGRADE_CONFIG=1`. Minimum: verify peer X.509 CN against a configured allowlist (`--admin-cn` flag or `admin_cn_list` config), reject non-allowlisted `OP_upgradeConfig` with clear error, WARN-log rejected attempts with CN+IP. Future: IP allowlist, role-based access, admin-specific CA. _(FUTURE_WORK.md §6; security-critical.)_
 - [ ] OP_replConfig access control hardening — currently serves the full config blob to any CA-signed SSL peer (trusted-LAN model). Consider: verify requester is a known `--peers` controller, rate-limit per peer, `minimum_role` check (controllers only). _(FUTURE_WORK.md §7.)_