decompose wave 5 — contract suite: audit-first split of the verification backlog (engines' columns already discharge most rows; map in review-wave-5's appendix), seven mechanism-grouped suite-row tasks (queue depth, scheduler, tx commit-atomicity, streams, locks, wakes, opts/backoff equivalence), two engine-side hardening tasks (sqlite commit-error arm, pg F-1 defense-in-depth), and the review-wave-5 gate that flips the engine specs to stable

docs/plans/implementation.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-10-09 (pg-fix-tx-wake landed — the second HIGH fix, retiring F-1's engine arm; wave 5's remaining gate is the fix batch's review gate)
+last_updated: 2026-10-10 (wave-4 fix batch landed and gate-verified — review-wave-4-fixes passed; wave 5 decomposed)
 ---
 
 # alkstore — Implementation plan
@@ -36,7 +36,7 @@ parallel).
 | [2](#wave-2--sqlite-substrate-fork) | honker-core fork into `alkstore-sqlite/src/substrate/`: port, deltas, provenance, test floor | wave 1 (workspace scaffold only) | implemented + reviewed (2026-10-08) |
 | [3](#wave-3--sqlite-engine) | SQLite engine: connection architecture, re-derived queue ops on contract v1, scheduler/outbox, tx seam, SQLite backlog column | waves 1 + 2 | implemented + reviewed (2026-10-08) |
 | 4 | [Postgres engine](#wave-4--postgres-engine): schema bootstrap, pool/open, listener/forwarder, all mechanisms, tx seam, pg backlog column | wave 1 | implemented + reviewed (2026-10-08) |
-| 5 | Contract suite: the cross-engine equivalence properties (core-contract.md §Verification backlog), version-stamped per ADR-017 | waves 3 + 4 | not yet decomposed |
+| 5 | [Contract suite](#wave-5--contract-suite): the cross-engine equivalence properties (core-contract.md §Verification backlog), version-stamped per ADR-017 | waves 3 + 4 | decomposed (2026-10-10) |
 | 6 | Release readiness: crate docs, deployment matrix final pass, README (written last, honestly), publish prep; mem-engine and fuzzing decisions | wave 5 | not yet decomposed |
 
 ## Wave 1 — Foundations
@@ -181,6 +181,69 @@ natural realization — the mechanism name *is* the wake channel
 streams), legal by construction under the shared namespace — with
 the reserved reconnect-wake channel staying the only reserved string.
 
+## Wave 5 — Contract suite
+
+Filling the scaffolded suite (`alkstore-contract-suite`) with the
+remaining verification-backlog rows and running the compatibility
+gate. Waves 3 and 4 each landed a nine/ten-row backlog column; the
+wave-5 decomposition started from an audit of what those columns
+already discharge versus what the backlog still lacks.
+
+**Already discharged by the engines' columns** (the wave-5 review
+gate verifies each claim by reading the pinning row, not by trusting
+the audit): name validation (the exemplar, incl. `schedule()`'s
+queue-argument validation), the numeric-domain rows (extents +
+durations), `encode_payload` typed failure + round-trip, the
+`PayloadTooLarge` occurrence asymmetry (both engine-scoped arms),
+drop-=-rollback no-ghosts, in-tx read-your-own-writes (which also
+discharges the `save_offset_tx` exactly-once backlog row across
+itself and the drop-rollback row), receiver close/save arms + monotone
+composition (both columns), and — pinned engine-side rather than as
+suite rows, per the sqlite-engine-integration task's scoping call —
+plain-path SQLite open and the watcher-cadence knob
+(`open_tests.rs`; SQLite-scoped backlog rows).
+
+**Wave 5's task set** (the gaps):
+
+- Queue depth: the job-handle validity predicate, the ADR-010 depth
+  properties (reclaim-eats-attempt, dead-letter moves, the
+  no-stranded-rows sweep), and M-1's retention-failure pin
+  (`suite-queue-depth-rows`).
+- Scheduler: boundary fires, bounded catch-up, leadership discipline —
+  with a documented extension of the suite's determinism posture to
+  admit runner-driving rows (`suite-scheduler-rows`).
+- Tx seam: `outbox_enqueue_tx` and `publish_with_key_tx`
+  commit-atomicity, plus N-5's `with_tx` panic-disposition probe —
+  the panic path pinned against real engines for the first time
+  (`suite-tx-commit-atomicity-rows`).
+- Streams: the cross-engine ordering-equivalence row and the full
+  `trim_to` semantics row (`suite-stream-rows`).
+- Locks: TTL/expiry re-acquisition and the concurrent-`try_lock`
+  loser posture — the SQLite busy-path is the open question the row
+  exists to answer (`suite-lock-rows`).
+- Wakes: the pinned `WakeReceiver` shapes, tolerance-bounded
+  (`suite-wake-rows`).
+- Arithmetic equivalence: the backoff-curve row and the two
+  wall-clock-adjacent opts-resolution legs the existing row deferred
+  to this wave (`suite-opts-backoff-rows`).
+- Engine-side hardening riding the window: the wave-3 review's
+  deferred SQLite commit-error-arm coverage (`sqlite-commit-error-arm`)
+  and F-1's defense-in-depth candidates — explicitly not load-bearing
+  since `pg-fix-tx-wake` retired the flake's root cause
+  (`pg-suite-infra-hardening`).
+- The review gate (`review-wave-5`): the backlog discharge audit,
+  stamp verification, green-on-both-engines, the parked-disposition
+  audit — and the gate that flips `engine-sqlite.md` /
+  `engine-postgres.md` to `stable`.
+
+Judgment calls the decomposition parked in task Notes (the review
+gate audits each): where the M-1 retention-failure pin, the
+beyond-64-cap skip-forward leg, and the backoff 1-hour-cap leg land
+when the public surface cannot express them (engine-side is the
+expected answer, recorded per case); whether the scheduler rows
+demand the pg fire-wake parity the wave-4 fix-batch gate recorded;
+and what the SQLite lock busy-path actually returns under contention.
+
 ## Decided points
 
 - **Contract-suite layout — option (a)**: a small internal
@@ -261,6 +324,12 @@ decomposes. Specific gates:
   `tasks/review-wave-4.md`) and making `tx_publishes_compose_with_the_handle`
   deterministic (20 consecutive solo runs green); the remaining fixes
   ride the wave-4 fix-batch decomposition below.
+- **Wave 5 decomposition** (2026-10-10) — audit-first: the engines'
+  backlog columns already discharge most of the §Verification backlog
+  (map recorded in `tasks/review-wave-5.md`'s appendix for the gate to
+  verify); the wave fills the gaps with seven suite-row tasks grouped
+  by mechanism, two engine-side hardening tasks, and the gate. See the
+  Wave 5 section.
 - **Wave 4 decomposition** (2026-10-08) — shaped as wave 3's
   structural twin; wave-3 outcomes absorbed (constructors exist;
   arithmetic re-owned per engine; per-engine `@every` parser;