test(companion): cover waitForIdle pre-aborted signal

docs/plans/state.json

@@ -1001,6 +1001,17 @@
       ],
       "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
     },
+    "companion-runtime-wait-for-idle-preaborted-signal-coverage": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added regression coverage for `waitForIdle()` with pre-aborted signals to ensure immediate, deterministic cancellation behavior when pending work exists.",
+      "files_modified": [
+        "src/companion/runtimeClient.test.ts",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
+    },
     "browser-tools-activation-clarity": {
       "status": "completed",
       "date": "2026-02-17",

src/companion/runtimeClient.test.ts

@@ -790,6 +790,22 @@ describe('CompanionRuntimeClient', () => {
     await pendingWait;
   });
 
+  it('waitForIdle rejects immediately when signal is already aborted', async () => {
+    const client = new CompanionRuntimeClient({
+      url: 'ws://127.0.0.1:1',
+    });
+    const pendingWait = client.waitForEvent('agent.stream', { timeoutMs: 10_000 }).catch(() => undefined);
+    const controller = new AbortController();
+    controller.abort();
+
+    await expect(
+      client.waitForIdle({ timeoutMs: 10_000, signal: controller.signal }),
+    ).rejects.toThrow('Aborted while waiting for runtime idle state');
+
+    client.clearEventSubscriptions();
+    await pendingWait;
+  });
+
   it('connects and performs node registration + capability discovery', async () => {
     if (!LISTEN_ALLOWED) {
       return;