ADR-024 — the mem engine adopted as the family's third engine (wave 6; release readiness renumbered to wave 7)

Row-first gate: consumer-inventory.md gains an engine-tier section — the mem-engine need recorded operator-authority, dated 2026-10-10 (wasm32 sandboxing across the alk protocol family + downstream ffi/napi/python-adapter economics; rusqlite/tokio-postgres structurally out on wasm, so mem is the only triad member the sandbox can carry).

ADR-024 (decisions/024-mem-engine.md) pins the decision set: (1) separate `alkstore-mem` crate — discharges and amends ADR-001 §4 (superseded in part: full contract-v1 engine, not an "implementation convenience"; annotation on ADR-001 §4 + Status, class-1 window still open); (2) honest-ephemeral posture — no durability, single-process, ephemeral by design, never fleet-valid (ADR-010 §3's shared-pool predicate fails structurally), riding ADR-016's carriers unchanged (identity + docs + matrix); (3) full contract v1 tier with the asymmetry classification — `PayloadTooLarge` never produced (SQLite arm), no reconnection concept (reconnect-wake/watcher rows absent from mem's per-engine column), receiver close at engine drop, wake coalescing N/A; (4) `MemStore::new()` engine-native constructor — the one documented exception to the open-prose, core-contract.md Store concept amended; shared-instance (two opens → one engine) rejected with the ADR-016 §4-style re-entry gate (consumer-inventory row), register stays closed; (5) wasm32 — compile-clean for wasm32-unknown-unknown plus the suite's mem column green on host under a current-thread runtime flavor are wave-6 acceptance items; on-target suite execution scoped out with a named collapse condition (wasm-bindgen-test adapter crate) — a scope decision, not a pending-client hedge; (6) mem is not a core dev-dependency — core's doc examples stay mock-based, ADR-001 §4's doctest posture declines.

engine-mem.md (draft): the in-process mapping — guarded per-mechanism state (no pool, no schema bootstrap, no forwarder, no spawn_blocking seam), the tx overlay (staged *_tx effects merged atomically at commit; read-your-own-writes easy, drop-=-rollback trivial; wake-at-commit structural — the seam pg needed pg-fix-tx-wake for, mem pins from birth via the existing tx-commit-atomicity rows), ADR-012 §2 third owner of the curve/opts/@every arithmetic (three-way equivalence, ADR-022's StoreFactory reused verbatim — born pinned).

deployment.md: host-semantics row (single-process, ephemeral, never fleet-valid, wasm32-clean), mem connection-budget subsection (none — nothing to budget), durability-knobs row (the honest row is the absence), toolchain row (wasm32 subset + current-thread-clean, acceptance-cited). README/overview: engine-mem.md row, ADR-024 row, family table entry (alkstore-mem, no driver deps), current-state updated to the implementation phase with engine specs' stable statuses reflected.

implementation.md: wave table gains wave 6 (mem engine, depends waves 1 + 5) and renumbers release readiness to wave 7 (fuzzing decision — the one remaining decided-at-implementation deferral — rides wave 7); wave-6 section records the born-pinned posture, acceptance items, the one suite-harness pre-task (past_stamp_sleep blocking sleep → async sleep, review 003's properties.rs:1683 note), and the window riders (review 003 Finding 1: the pg transient-fault seam, MEDIUM, rides wave 6; Findings 2–3 follow their park into wave 7's pre-release); wave-6 review gate defined; Decided points updated (mem discharged, fuzzing renumbered); stale wave-6 references swept across review docs and the landed tasks' notes (release-readiness items renumbered or annotated).

Docs-only change; verified by cross-reference audit (all ADR/OQ/anchor references resolve, residual wave-6 mentions are correct under the new numbering or carry dated annotations).

docs/research/consumer-inventory.md

@@ -1,10 +1,10 @@
 ---
 status: draft
-last_updated: 2026-10-05 (streams corrected to documented/in-scope —
-operator-authority record: type-filtered event watching from multiple
-places, e.g. repo-change subscriptions in a git app. alkcall row added
-2026-10-05 as ecosystem-shape evidence for streams (no per-key-ordering
-need named anywhere); rate-limits + result-storage remain the
+last_updated: 2026-10-10 (mem-engine engine-tier row added —
+operator-authority record: wasm32 sandboxing + downstream
+ffi/napi/python-adapter economics; the record the ADR-024 scope
+decision cites per the row-first gate. Earlier: 2026-10-05 streams
+correction and alkcall row; rate-limits + result-storage remain the
 keep-with-flag rows.)
 ---
 
@@ -203,6 +203,31 @@ cut-at-implementation.** Adjacent-tooling shape (a queue job's outcome
 queryable by id), useful to queues+scheduler consumers but named by
 none of them yet.
 
+## Engine-tier inventory
+
+This section answers the engine-tier question (which backing engines
+exist) under this document's discipline. The two shipped engines
+(SQLite, Postgres) were Phase 0 decisions with consumer evidence
+throughout; the mem engine entered as ADR-001 §4's implementation-time
+deferral, so its need gets a row here *before* any scope decision
+assumed it — the row-first gate, engine-shaped. (Rows above grade
+*features*; this row grades *which engine tier a consumer needs*.)
+
+| Consumer | Evidence | Need | Confidence |
+|---|---|---|---|
+| wasm-sandboxed consumers (family-wide) | operator-authority record, 2026-10-10 | an engine that runs in-process on `wasm32-unknown-unknown`: the alk protocol crates (alkcall, alktty, alktunnels, alksocks) are wasm-compatible at the protocol level by design and sandboxing is the family's deployment direction; of the engine triad, only the in-memory engine can ride along (rusqlite and tokio-postgres are structurally out on wasm) | **operator-authority** (the REQ-2 recording convention; expected where the wanter is an *application above* the paused crates) |
+| downstream adapter crates (ffi/napi/python) | operator-authority record, 2026-10-10 | a zero-configuration engine for adapter crates and first-running examples: wasm compatibility downstream makes ffi/napi/python adapters far cheaper to build (no per-platform registration/build matrix the operator cannot run — no mac/windows hosts); the engine an adapter always needs is one that just works in-process | **operator-authority** (same record) |
+
+Verdict: **in scope as a third engine — full contract v1**
+([ADR-024](../architecture/decisions/024-mem-engine.md), 2026-10-10):
+separate `alkstore-mem` crate, no durability, single-process,
+ephemeral by design, never fleet-valid. The tier is *full contract
+v1*, not a reduced test-only profile: a reduced engine never gets
+born-pinned by the contract suite, and the wasm/adapter motivation is
+consumer-shaped, not test-shaped. *(Upgrade path to `documented`:
+whichever consumer document first names the mem engine's need grows
+the row, per this document's conventions.)*
+
 ## What this inventory changes
 
 - **OQ-ST-01** stops being "blocked on a consumer-driven inventory