Skip the session read for a request cancelled before it starts

A request whose caller had already left still read the session, and if
that read failed nobody handled the error. Check the abort first, and
let untilAborted absorb a read it no longer waits for.

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

Author: Programcode

apps/mobile/src/lib/ai-request.ts

@@ -45,7 +45,11 @@ export function abortError(): Error {
 
 /** Settles with the read, or rejects as soon as the signal aborts. The read itself cannot be cancelled, only no longer waited for. */
 export function untilAborted<T>(read: Promise<T>, signal: AbortSignal): Promise<T> {
-  if (signal.aborted) return Promise.reject(abortError());
+  if (signal.aborted) {
+    // Nobody waits for the read any more, so its own failure must not go unhandled.
+    read.catch(() => {});
+    return Promise.reject(abortError());
+  }
   return new Promise<T>((resolve, reject) => {
     const onAbort = () => reject(abortError());
     signal.addEventListener('abort', onAbort, { once: true });
@@ -107,6 +111,7 @@ export async function postFunction<T>(
   signal?.addEventListener('abort', abortForCaller);
   if (signal?.aborted) controller.abort();
   try {
+    if (controller.signal.aborted) throw abortError();
     const token = await untilAborted(accessToken(), controller.signal);
     const json = JSON.stringify(body);
     if (utf8Length(json) > MAX_REQUEST_BODY_BYTES) throw new AIError('tooLarge', 'Request is too large');

apps/mobile/src/lib/crossfire.test.ts

@@ -3,13 +3,15 @@ import { afterEach, describe, expect, it, vi } from 'vitest';
 const fetchMock = vi.hoisted(() => vi.fn());
 
 // The session read never settles, as when a token refresh stalls.
-vi.mock('./supabase', () => ({ supabase: { auth: { getSession: () => new Promise<never>(() => {}) } } }));
+const getSession = vi.hoisted(() => vi.fn(() => new Promise<never>(() => {})));
+vi.mock('./supabase', () => ({ supabase: { auth: { getSession } } }));
 vi.mock('expo/fetch', () => ({ fetch: fetchMock }));
 
 import { AIError, postFunction, untilAborted } from './ai-request';
 import { withTurnDeadline } from './crossfire';
 
 afterEach(() => {
+  vi.clearAllMocks();
   vi.useRealTimers();
 });
 
@@ -45,4 +47,11 @@ describe('postFunction', () => {
     expect((error as AIError).kind).toBe('timeout');
     expect(fetchMock).not.toHaveBeenCalled();
   });
+
+  it('never reads the session for a request cancelled before it starts', async () => {
+    const leaving = new AbortController();
+    leaving.abort();
+    await expect(postFunction('ai', {}, leaving.signal, async () => 'answer')).rejects.toMatchObject({ name: 'AbortError' });
+    expect(getSession).not.toHaveBeenCalled();
+  });
 });