docs: POC #2 findings verified + folded — OQ-ST-03 closed (per-engine drivers)

Review pass in this repo: contract suite re-verified (11/11 pass under
--test-threads=1 against the harness server; default parallel runs
interfere across tests via the shared db/channels engine_for_test
harness — each test spawns its own listener on poc:q/s/n and truncates
shared tables, so parallel tests receive each other's notifications and
race truncates). Recorded as a harness caveat in the findings with the
Phase 1 note (per-test namespaces), NOT as a contract failure — every
test passes in isolation. Findings invocation note + artifacts section
updated; phase-0 frontmatter carries the verification qualifier.
OQ-ST-03 closure text already folded by the POC session stands.

docs/research/phase-0.md

@@ -5,7 +5,11 @@ per-engine drivers, rusqlite+honker-core for SQLite / tokio-postgres+
 deadpool-postgres for Postgres, findings in poc-pg-posture-findings.md;
 OQ-ST-04 now has measured ground on both engines, wake contract
 numbers + tx-seam shapes + listener-recovery semantics recorded from
-POC #2; OQ-ST-05/06 carry both POCs' per-subsystem votes)
+POC #2; OQ-ST-05/06 carry both POCs' per-subsystem votes. Findings
+review-pass verified 2026-10-04: contract suite runs green sequentially
+(`--test-threads=1`); parallel invocation fails by cross-test
+interference (shared db/channels harness) — recorded in the findings,
+not a contract failure.)
 ---
 
 # alkstore — Phase 0 (Exploration)
@@ -480,13 +484,38 @@ inherited watcher is tighter than a re-derived one (p50 1.40 vs 2.15
 ms, max 29 vs 172 ms, with battle-tested failure handling), and the
 `.so` runtime dependency is packaging cost A doesn't pay for no
 compensating advantage. The transactional contract holds identically
-on both (it is SQLite's property, not the posture's). New
-constraints recorded for the engine crate regardless:
+on both (it is SQLite's property, not the posture's). Constraints
+recorded for the engine crate regardless:
 honker-core=0.5.0 pins rusqlite ^0.40.1 whose rustc requirement
 (≥1.99) is a deployment note, and mixed rusqlite+sqlx binaries
 currently need a vendored one-line libsqlite3-sys patch — OQ-ST-02's
 per-engine-crate split is what keeps the engine binary single-driver.
 
+**Postgres half resolved by POC #2 (2026-10-04; findings:
+`poc-pg-posture-findings.md`): tokio-postgres + deadpool-postgres.**
+All three gate conditions held: the transactional property is native
+(in-tx NOTIFY delivers only at commit; rollback drops job row +
+business row + notification), exactly-once claim via `FOR UPDATE SKIP
+LOCKED`, and the LISTEN wake layer is push (p50 1.1 ms, 300/300;
+claim latency 3–6 ms vs poll-only 32–50 ms — 5–16×, the push channel
+pgboss-rs lacks, measured). Structural findings the contract must
+absorb: pooled connections cannot carry LISTEN (deadpool#360 — pinned
+as our own test; the dedicated listener connection is a per-process
+budget line outside the pool), and the `*_tx` seam differs from
+SQLite's exactly where expected (pg's client is Send+Sync — the tx
+handle is held directly across awaits; SQLite's is a bridged
+writer-slot lease — same seam shape, different bridging). Listener
+substrate vote: hand-rolled ~90-line forwarder (immediate reconnect,
+quoting control, no dependency posture) over `postgres-notify` 0.3.8
+(lazy reconnect, connect_script skipped at initial connect,
+unquoted-identifier LISTEN — derive-not-adopt; fallback if upstream
+improves). The sqlx `PgListener` fallback retired unfired.
+
+**OQ-ST-03 resolution: per-engine drivers — rusqlite + honker-core
+(SQLite engine), tokio-postgres + deadpool-postgres (Postgres
+engine), under OQ-ST-02's per-engine-crate split.** Resolved
+(2026-10-04), POC-backed on both halves.
+
 **Resolved (2026-10-04, both halves): per-engine drivers —
 rusqlite + honker-core for the SQLite engine; tokio-postgres +
 deadpool-postgres for the Postgres engine.** The Postgres half is

docs/research/poc-pg-posture-findings.md

@@ -352,10 +352,23 @@ Reading (shape, not absolute — different machines/databases):
   ~19–25 ms B2-era figure and validates the pooling discipline's
   value (~2.4 ms amortized vs 23 ms fresh).
 
-## Property tests (the contract suite) — all green
+## Property tests (the contract suite) — all green, sequentially
 
 `tests/contract.rs` — 11 tests, pg twin of POC #1's suite, all shared
-assertions reused:
+assertions reused. **Invocation note (verified 2026-10-04 in this
+repo's review pass): the suite passes under `cargo test --test contract
+-- --test-threads=1` in one process; default parallel execution fails
+6–8 tests by cross-test interference, not by contract failure — each
+test builds its own engine + listener over the same database and
+channels (`poc:q/s/n`) and truncates the shared tables, so parallel
+tests receive each other's notifications and race each other's
+truncates ("delivered before commit", "jobs lost", incomplete
+state re-reads). Every test passes in isolation; the harness lacks
+per-test channel/table namespaces, which a Phase 1 test harness must
+have as a first-class feature (the same shared-server parallel-suite
+shape alkblobs' `--all-features` gates solve with engine-scoped
+namespaces). Recorded as a harness caveat — none of the failure modes
+are contract failures.**
 
 | Property | Result |
 |---|---|
@@ -467,7 +480,9 @@ retired — no condition requiring it fired.**
 
 - POC crate: `/workspace/alkstore-pg-posture-poc` (self-contained,
   published-deps-only).
-- Tests: `cargo test` → `tests/contract.rs` (11 tests).
+- Tests: `cargo test` → `tests/contract.rs` (11 tests; sequential
+  invocation: all pass; parallel default invocation interferes across
+  tests via the shared db/channels — see the invocation note above).
 - Probe binary: `cargo run --release -- seam|watch|burst|claim|pollvlisten|pool|pnlisten|smoke`
   per the binary's help (wake command prints the notify-latency table;
   pollvlisten the consumption-posture table).