fix: harden activity event handling

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/main/runTurnPending.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+  markRunTurnPendingErrored,
+  shouldHandleRunTurnEvent,
+  type RunTurnPendingCommand,
+} from '@main/sidecar/runTurnPending';
+
+describe('run turn pending helpers', () => {
+  test('marks a run-turn pending command as errored and rejects it once', () => {
+    const rejected: Error[] = [];
+    const pending: RunTurnPendingCommand = {
+      kind: 'run-turn',
+      resolve: () => undefined,
+      reject: (error) => rejected.push(error),
+      onDelta: () => undefined,
+      onActivity: () => undefined,
+      errored: false,
+    };
+
+    const first = markRunTurnPendingErrored(pending, 'boom');
+    const second = markRunTurnPendingErrored(pending, new Error('later'));
+
+    expect(first).toBeInstanceOf(Error);
+    expect(first.message).toBe('boom');
+    expect(second.message).toBe('later');
+    expect(pending.errored).toBe(true);
+    expect(rejected).toHaveLength(1);
+    expect(rejected[0].message).toBe('boom');
+  });
+
+  test('stops handling turn events after the pending command has errored', () => {
+    const pending: RunTurnPendingCommand = {
+      kind: 'run-turn',
+      resolve: () => undefined,
+      reject: () => undefined,
+      onDelta: () => undefined,
+      onActivity: () => undefined,
+      errored: false,
+    };
+
+    expect(shouldHandleRunTurnEvent(pending)).toBe(true);
+
+    markRunTurnPendingErrored(pending, new Error('boom'));
+
+    expect(shouldHandleRunTurnEvent(pending)).toBe(false);
+  });
+});