Wave-3 review gate: contract conformance clean; two findings fixed inline — substrate boundary move (open_writer_connection → seam.rs), writer-slot release on with_writer/begin/commit error arms + regression tests (task review-wave-3)

alkstore-sqlite/src/store/notify_tests.rs

@@ -118,6 +118,47 @@ async fn notify_never_produces_payload_too_large() {
     cleanup(&dir);
 }
 
+/// Acceptance: an auto-commit op's *error* arm releases the writer
+/// slot — the lease-out-both-arms property (ADR-007's seam posture):
+/// after a notify whose statement fails at the storage layer, the slot
+/// is free again and a subsequent writer op succeeds without parking.
+#[tokio::test(flavor = "multi_thread")]
+async fn failed_notify_releases_the_writer_slot() {
+    let dir = temp_dir("err-arm-release");
+    let path = temp_path("err-arm-release");
+    let store = open_store(path.to_str().unwrap(), Default::default()).unwrap();
+
+    let side = rusqlite::Connection::open(&path).unwrap();
+    side.execute_batch(
+        "CREATE TRIGGER block_notify BEFORE INSERT ON __alkstore_notifications
+         BEGIN SELECT RAISE(ABORT, 'notify insert blocked'); END",
+    )
+    .unwrap();
+
+    let err = store.notify("orders", json!({"x": 1})).await.unwrap_err();
+    let source = match &err {
+        Error::Database(source) => source.to_string(),
+        other => panic!("the induced failure surfaces as Database, got {other:?}"),
+    };
+    assert!(
+        source.contains("notify insert blocked"),
+        "the source chain carries the trigger's message, got: {source}"
+    );
+    side.execute_batch("DROP TRIGGER block_notify;").unwrap();
+    drop(side);
+
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(5);
+    let landed = tokio::time::timeout_at(deadline, store.notify("orders", json!({"x": 2})))
+        .await
+        .expect(
+            "the failed op must release the writer slot — the slot is free again, \
+             never parked",
+        );
+    landed.expect("the notify lands after a failed op released the slot");
+    store.close();
+    cleanup(&dir);
+}
+
 /// Acceptance: `listen` returns a working receiver — wakes arrive
 /// after commits by other connections, and `Wake { channel }` carries
 /// the channel name only. The honest posture: the watcher fans out on