Wave-6 decomposition (mem engine): eleven tasks per the pg-wave rhythm — foundations (crate scaffold, MemStore::new isolation, guarded state core, wake routing, wasm32 gate from birth), seam-tx (the load-bearing tx overlay: eleven staged _tx methods, commit-merge + wake-at-commit — pg-fix-tx-wake's discipline structural from the start, drop = discard trivial, with_tx panic posture), mechanisms mutually parallel (notify-listen close-at-engine-drop/no-replay/never-coalesced; queues = ADR-010 machine driver-free with the equal-jitter curve and opts resolution as ADR-012 §2's third owner; streams log+offsets+trim; locks TTL registry, no busy-path analog), scheduler-outbox (tick/catch-up-64/leadership through the __alkstore_scheduler lock, engine-uniform per ADR-009 §4; outbox over queues with the 60/5/5 seam stamp), integration (suite third StoreFactory column green on host under a current-thread flavor, wasm32 acceptance items, engine-mem.md to implementation-complete), and the review-wave-6 gate (born-pinned audit: conformance read, discharge-map wiring, wasm items, three-way equivalence green, class-1 window discipline). Window riders: suite-harness-current-thread — the wave's one suite-side pre-task, past_stamp_sleep's blocking sleep goes async per review 003's properties.rs:1683 posture note, enabling the current-thread flavor; pg-fix-scheduler-tick-seam — review 003 Finding 1, the cfg(test) transient-fault seam driving the real tick_with_retries through retry-then-success and exhaustion arms (the last uncovered wave-4 hardening arm, sqlite-commit-error-arm pattern). Task hygiene: pg-fix-open-path frontmatter fixed (unquoted 'max_size: 0' colon-space inside the name scalar broke YAML parsing — taskgraph validate had been red one-error since the wave-4 fix-batch decomposition; also restores review-wave-4-fixes' dependency resolution). implementation.md: wave-6 table row → decomposed, task-set listing with the parallelism note (rider + pre-task independent of the mem chain; rider closes before the gate), wave-6 decomposition bullet in the review-rounds record. Docs-only change; verified taskgraph validate (60 tasks, no cycles), cargo fmt --check, cross-reference read

tasks/mem-engine-foundations.md

@@ -0,0 +1,92 @@
+---
+id: mem-engine-foundations
+name: Mem engine — crate scaffold, `MemStore::new()`, guarded state core, wake routing
+status: pending
+depends_on: []
+scope: moderate
+risk: medium
+impact: component
+level: implementation
+tags: [wave-6, mem-engine]
+---
+
+## Description
+
+The mem engine's foundations (wave 6 — [ADR-024](../architecture/decisions/024-mem-engine.md)):
+a new workspace member `alkstore-mem` and the state core every later
+task builds on.
+
+- **Crate + manifest**: workspace member per
+  [ADR-024](../architecture/decisions/024-mem-engine.md) §1 —
+  dependencies are `alkstore` (versioned path pin per
+  [ADR-017](../architecture/decisions/017-contract-versioning.md) §4.1,
+  matching the other engines' manifests) plus tokio restricted to the
+  **wasm-supported subset (sync + time only)**. No driver
+  dependencies. `thiserror` via core; no other crates.io surface.
+- **Constructor**: `MemStore::new()` — engine-native, no connection
+  string, no file path (the one documented exception to the
+  core-contract open prose, amended by
+  [ADR-024](../architecture/decisions/024-mem-engine.md) §4). Each
+  `new()` yields a fully isolated instance sharing nothing (the suite
+  factory's isolation contract); teardown is drop. No `PgOpts`-equivalent
+  opts struct exists — nothing to configure (if a knob surfaces during
+  the wave, `MemOpts` with `..Default::default()` follows the family
+  opts pattern; not assumed now).
+- **Guarded per-mechanism state core**: the store instance is the
+  state — per-mechanism structures (queues+jobs, dead letters,
+  streams+offsets, locks, schedules) behind the family's locking
+  discipline (parking_lot short-held internal locks per AGENTS
+  convention 3; tokio primitives for cross-await coordination).
+  Layout is module-per-file under `src/`, mirroring the other
+  engines. Subsequent mechanism tasks own their tables' shapes; this
+  task owns the shared scaffolding: the guarded-state container idiom,
+  name validation at entry (same `InvalidName`/`ReservedName` rules as
+  every other engine — reserved prefix `__alkstore_`, the one
+  reserved string `__alkstore_listener_reconnected__` unused here but
+  still rejected), and the wake-routing substrate (in-process channels;
+  a mechanism registers its commit-ordered wake source, receivers
+  attach per channel).
+- **Wake substrate shape**: no batching boundary exists — wakes
+  deliver at the commit boundary directly to each open receiver,
+  per-subscriber FIFO by commit order (engine-mem.md §Architecture;
+  coalescing not applicable). The routing core lives here; the
+  `listen()`/`WakeReceiver` surface lives in `mem-engine-notify-listen`.
+- **Clock posture**: every timestamp (unix-seconds stamps, visibility
+  deadlines, TTLs, scheduler boundaries) reads the process clock —
+  there is no server clock to defer to. Keep the clock behind one
+  internal accessor so tests can observe timestamps deterministically
+  the same way the SQL engines' row shapes do.
+
+The `Store` trait impl itself is ADR-007-shaped and lands in
+`mem-engine-seam-tx` (the tx overlay is the load-bearing half);
+this task lands everything up to the trait boundary.
+
+## Acceptance Criteria
+
+- [ ] `alkstore-mem` is a workspace member compiling clean; manifest
+      dependency surface is core + tokio (sync + time) only
+- [ ] `MemStore::new()` constructs; two instances share nothing
+      (pinned by a unit test)
+- [ ] The guarded state core, validation rules, wake-routing
+      substrate, and clock accessor exist with unit pins
+- [ ] `cargo check --target wasm32-unknown-unknown -p alkstore-mem`
+      clean from this task onward (tokio subset discipline enforced
+      here, not retro-fitted)
+- [ ] Workspace gates green (`cargo build`, `cargo test`, clippy
+      `-D warnings`, fmt)
+
+## References
+
+- docs/architecture/decisions/024-mem-engine.md §1/§4
+- docs/architecture/engine-mem.md §Identity and posture, §Architecture
+- docs/architecture/core-contract.md §Naming / reserved namespace
+- tasks/pg-engine-schema.md (the wave-4 rhythm this wave mirrors — its
+  "foundations first" slot)
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion