mem engine: pin notify/listen burst floor and close-at-drop arms (mem-engine-notify-listen)

tasks/mem-engine-notify-listen.md

@@ -1,7 +1,7 @@
 ---
 id: mem-engine-notify-listen
 name: Mem engine — notify/listen surface (`WakeReceiver`, close-at-engine-drop)
-status: pending
+status: completed
 depends_on: [mem-engine-seam-tx]
 scope: narrow
 risk: medium
@@ -66,8 +66,71 @@ terminal `None`, commit-boundary delivery timing through
 
 ## Notes
 
-> To be filled by implementation agent
+> Filled by implementation agent, 2026-10-10.
+
+1. **The implementation already landed in the seam task** —
+   `mem-engine-seam-tx` Note 1 records that the mem engine's full
+   `Store` surface (including `notify`/`listen`/`notify_tx` and the
+   `MemWakeReceiver` bridge in `alkstore-mem/src/notify.rs`, the
+   `WakeBus` substrate in `wakes.rs`, and the tx overlay's staged
+   notify) is all-or-nothing per trait impl, so this task found its
+   mechanism *implemented*. Its work was the remaining engine-side
+   unit pins its description enumerates, against that foundation.
+2. **Coverage reconciliation at pickup** — already pinned by the seam
+   task: channel-scoped delivery with the field carried + foreign-
+   channel silence (`structurally` silent on mem — the vacuous-column
+   analog of the suite row's scoping observable), never-coalesced
+   (per-notify) counts, attach-after-commit no-replay, entry
+   validation on both paths (empty/blank/reserved-prefix/the reserved
+   reconnect string rejected on `notify` and `listen`),
+   `PayloadTooLarge` never at 2 MiB (ADR-016 §5 non-occurrence), the
+   three recv forms' pinned arms (idle `Ok(None)`, timeout `Ok(None)`,
+   post-drop `try_recv → Err(Closed)` + `recv → None`),
+   receiver-drop-detaches, and the `notify_tx` commit-atomicity legs
+   (silence pre-merge → one wake post-merge, per-notify, rollback
+   no-ghosts, `with_tx` panics) in `tx.rs`. The FIFO-by-commit-order
+   property is pinned at the substrate with the commit watermark
+   (`wakes.rs`: `per_subscriber_fifo_by_commit_order`).
+3. **What this task added** — the two unpinned shapes from the
+   description's list: (a) the **burst floor** — a 5-notify burst
+   delivers ≥1 wake through `recv` (the suite row's tolerance shape)
+   and drains exactly 5 through `try_recv` (mem's per-notify column,
+   the exact-count coalescing pin); (b) the dedicated **close-at-drop
+   pin** — engine drop closes *every* open receiver across channels
+   (terminal `None` on both, whole-engine not per-channel), the
+   closed state stable across all three recv shapes with
+   `recv_timeout`/`try_recv` carrying `Err(Closed)` (distinguishable
+   from idle) and no reconnect-wake ever following (no reconnection
+   concept; the reserved string stays rejected as a consumer name —
+   pinned in the seam task's validation test).
+4. **No production code changed** — the seam task's realization was
+   verified correct as-found; this task is tests + surface review
+   only (`notify.rs` tests module, +2 tests).
 
 ## Summary
 
-> To be filled on completion
+> Filled on completion, 2026-10-10.
+
+Completed the mem engine's notify/listen task against the seam task's
+foundation: reconciled the description's pin list against
+`alkstore-mem/src/notify.rs`'s existing suite (13 pre-existing
+mechanism tests across `notify.rs` + the substrate pins in `wakes.rs`
++ the tx-atomicity legs in `tx.rs`), found everything but the burst
+floor and the multi-receiver close-at-drop shape already pinned, and
+added those two: `burst_delivers_at_least_one_wake_and_never_coalesces`
+(floor ≥1 through `recv`, exact per-notify count through `try_recv`)
+and `engine_drop_closes_every_open_receiver_on_the_terminal_arms`
+(terminal `None` on every open receiver across channels, closed state
+stable across `recv`/`try_recv`/`recv_timeout`, `Err(Closed)`
+distinguishable from idle, no reconnect-wake). Acceptance criteria:
+trait-complete surface + entry validation + core payload encoding ✓
+(seam task, validation test), commit-ordered channel-scoped no-replay
+never-coalesced delivery ✓ (subsurface watermark test + store-level
+pins), engine-drop close ✓ (now dedicated-pinned), `notify_tx`
+post-merge-only delivery ✓ (seam task's `tx.rs` tests, criterion's
+"pinned with the seam task's commit-atomicity tests" satisfied
+as-written). Verified: `cargo test -p alkstore-mem` 91/91 (89 + 2
+new), workspace `cargo test` green (core 25, suite-harness 3,
+mem 91, pg 124+25+9, SQLite 191+25), `cargo clippy --all-targets --
+-D warnings` clean, `cargo fmt --check` clean,
+`cargo check --target wasm32-unknown-unknown -p alkstore-mem` clean.