mem engine queues — the wave-6 mechanism task lands: coverage reconciliation against the seam task's foundation, with the six unpinned engine-side pins (mem-engine-queues)

The queue mechanism (ADR-010 state machine over the in-memory job
table, mem's third-owner equal-jitter curve + opts resolution)
already landed implemented with the seam task's whole-engine scope
(mem-engine-seam-tx Note 1); this task's work, per the disposition the
notify/listen twin recorded, was reconciling the description's pin
list against the existing suite and adding the missing engine-side
unit pins — no production code changed, the realization verified
correct as-found.

Already pinned by the seam task (reconciled, recorded in Notes):
lifecycle + stamps + resolved get_job values, claim ordering, extent
clamps at entry, worker-id validation, the uniform validity predicate,
late-heartbeat refusal + absolute-reset renewal, reclaim-eats-attempt
+ loser-ack-refuses, the pinned dead-letter default strings, dead-row
get_job visibility, both-states sweep + retention + scoping, the tx
stamp shapes, and the resolution legs + base-5 curve range/cap/spread.

Added (6): the in-process claim-race atomicity pin (8 concurrent
workers over 4 rows — every row handed exactly once through the
guarded section, the description's claim-vs-claim bullet); the
claim-vs-expiry boundary determinism pin (at now == deadline: the d <
now reclaim predicate and the d >= now holder-op predicate are
coherent — no reclaim, heartbeat/ack still valid; one second past:
reclaimable with its attempt consumed; lapsed ids silently uncounted
by ack_batch); the engine-side mirror of the suite's
backoff_curve_equivalence row — base 2 s at [1,2]/[2,4]/[4,8] driven
end-to-end through claim -> retry(None) -> get_job's run_at with the
Some(5)-verbatim and Some(0)-ready-now override legs, exact under the
frozen clock — both through the handle and pinned at backoff_delay_s
itself (the cap leg stays in resolution.rs's base-5 pins per
suite-opts-backoff-rows' recorded disposition); the D-12 pre-claim
sweep pin (a lapsed row with its budget spent claims nothing and
dead-letters with the exhaust string at the next claim, never
strands); and unconditional cancel across both states (the holder's
post-cancel ack refusing — the not-an-interrupt honesty). One
test-authoring note recorded: heartbeat's absolute reset moves the
deadline, so boundary legs stage on fresh rows to keep each
observation exact.

Task file: status completed, Notes (the seam-carried disposition +
reconciliation inventory + the six adds + the heartbeat-observation
note) + Summary filled. Verified: cargo test -p alkstore-mem 97/97
(91 + 6 new; new tests green solo x3), workspace cargo test green
(core 25, suite-harness 3, mem 97, pg 124+25+9, SQLite 191+25),
clippy --all-targets -D warnings clean, cargo fmt --check clean,
cargo check --target wasm32-unknown-unknown -p alkstore-mem clean

alkstore-mem/src/resolution.rs

@@ -218,6 +218,22 @@ mod tests {
         assert_eq!(resolve_enqueue_opts(now, &none).expires_at, None);
     }
 
+    #[test]
+    fn backoff_base_two_lands_in_the_suite_rows_exact_bounds() {
+        // The `backoff_curve_equivalence` suite row's identical ranges
+        // (base 2 s: [1,2], [2,4], [4,8]) — the engine-side numeric pin
+        // of the equivalence the row asserts across engines.
+        for (attempts, lower, upper) in [(1i64, 1i64, 2i64), (2, 2, 4), (3, 4, 8)] {
+            for id in [1i64, 2, 42, 999_999] {
+                let delay = backoff_delay_s(2, attempts, id);
+                assert!(
+                    (lower..=upper).contains(&delay),
+                    "base 2 attempt {attempts} id {id}: delay {delay} outside [{lower}, {upper}]"
+                );
+            }
+        }
+    }
+
     #[test]
     fn backoff_lands_in_the_pinned_equal_jitter_range() {
         for attempts in [1i64, 2, 3, 5, 30] {