test: observe assignment lock waits with a two-connection pool

Reuse the lock holder connection for inspection, bound the fixture to two connections, and propagate early transaction failures.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/__tests__/human-directed-work.test.ts

@@ -18,7 +18,7 @@ const support = await getEmbeddedPostgresTestSupport();
   let db: ReturnType<typeof createDb>;
   beforeAll(async () => {
     database = await startEmbeddedPostgresTestDatabase("paperclip-human-work-");
-    db = createDb(database.connectionString);
+    db = createDb(database.connectionString, { maxConnections: 2 });
   }, 30_000);
   afterAll(async () => { await database?.cleanup(); }, 60_000);
 
@@ -121,14 +121,19 @@ const support = await getEmbeddedPostgresTestSupport();
     const f = await seed(); const issue = await task(f);
     let release!: () => void;
     let locked!: () => void;
+    let observeLock!: (pid: number) => Promise<boolean>;
     const held = new Promise<void>((resolve) => { release = resolve; });
     const ready = new Promise<void>((resolve) => { locked = resolve; });
     const commentWrite = db.transaction(async (tx) => {
       await issueService(db).addComment(issue.id, "Please proceed", { userId: "owner" }, { humanDirectedByUserId: "owner" }, tx);
+      observeLock = async (pid) => {
+        const [state] = await tx.execute(sql`select cardinality(pg_blocking_pids(${pid}::int)) > 0 as blocked`);
+        return state.blocked === true;
+      };
       locked();
       await held;
     });
-    await ready;
+    await Promise.race([ready, commentWrite]);
     let started!: (pid: number) => void;
     const waiter = new Promise<number>((resolve) => { started = resolve; });
     const reassignment = db.transaction(async (tx) => {
@@ -137,13 +142,13 @@ const support = await getEmbeddedPostgresTestSupport();
       await tx.update(issues).set({ assigneeAgentId: f.other.id }).where(eq(issues.id, issue.id));
     });
     try {
-      const pid = await waiter;
+      const pid = await Promise.race([waiter, reassignment.then(() => { throw new Error("Reassignment ended before publishing its backend"); })]);
       const deadline = Date.now() + 5_000;
       let blocked = false;
       // Observe an actual PostgreSQL lock wait, not merely two queued promises.
       while (Date.now() < deadline) {
-        const [state] = await db.execute(sql`select cardinality(pg_blocking_pids(${pid}::int)) > 0 as blocked`);
-        if (state.blocked === true) { blocked = true; break; }
+        // Reuse the lock holder's connection; a third pool slot is unnecessary.
+        if (await observeLock(pid)) { blocked = true; break; }
         await new Promise((resolve) => setTimeout(resolve, 10));
       }
       expect(blocked).toBe(true);