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/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).