Complete only into a running task (contract round 35)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: mchwang

runner/store.ts

@@ -665,8 +665,10 @@ export class Store {
       const contextCurrent = sameContext(decode<InvocationContext>(row.context), this.#contextOf(key));
       let outcome = classifySettlement({ ...settlement, firstReason, contextCurrent });
       if (outcome.state === 'completed' && row.state !== 'running') throw new GuardRefusal('Only a running attempt can complete.');
-      if (outcome.state === 'completed' && (this.#closed(task.status) || task.cancel_requested !== null))
-        outcome = { state: 'cancelled', reason: 'The task was closed before the result was saved.', timeLimit: false };
+      // The task must still be running; a task never leaves running while an attempt is active, so this is a second safeguard.
+      if (outcome.state === 'completed' && (task.status !== 'running' || task.cancel_requested !== null))
+        outcome = { state: 'cancelled', reason: this.#closed(task.status) || task.cancel_requested !== null
+          ? 'The task was closed before the result was saved.' : 'The task left the running state before the result was saved.', timeLimit: false };
       let result: string | null = null;
       if (outcome.state === 'completed') {
         result = encode(settlement.result ?? null);

test/runner-lifecycle-store.test.ts

@@ -179,6 +179,13 @@ describe('attempt transitions', () => {
     const next = admit(store); store.markRunning(identity, next.id);
     expect(settle(store, next.id, { result: 'x'.repeat(1024 * 1024 + 1) })).toMatchObject({ state: 'failed', reason: 'The result exceeds 1 MiB.' });
   });
+  it('freezes the task status while an attempt is active, and never completes into a non-running task', () => {
+    const { store, path } = queued(); const attempt = admit(store); store.markRunning(identity, attempt.id);
+    expect(() => store.transitionTask(identity, store.getTask(identity).stateVersion, 'needs amendment')).toThrow(/still active/);
+    const db = new DatabaseSync(path); db.exec(`UPDATE tasks SET status='needs amendment'`); db.close();
+    expect(settle(store, attempt.id, { result: 'late' })).toMatchObject({ state: 'cancelled', reason: 'The task left the running state before the result was saved.' });
+    expect(store.getTask(identity).status).toBe('needs amendment');
+  });
   it('refuses a late settlement from an old attempt after a retry, without touching the retry', () => {
     const { store } = queued(); const old = admit(store);
     store.recordFirstReason(identity, old.id, 'cancelled'); settle(store, old.id);