fix(api): retry transient session reads safely

api-core-retry.test.mjs

@@ -0,0 +1,86 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { fetchWithTransientRetry } from './src/api/core.ts';
+
+async function withMockFetch(mock, run) {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = mock;
+  try {
+    await run();
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+}
+
+test('idempotent requests retry transient network failures', async () => {
+  let calls = 0;
+  await withMockFetch(
+    async () => {
+      calls += 1;
+      if (calls < 3) throw new TypeError('fetch failed');
+      return new Response('{}', { status: 200 });
+    },
+    async () => {
+      const response = await fetchWithTransientRetry('/api/sessions', undefined, 1_000, [0, 0]);
+      assert.equal(response.status, 200);
+    },
+  );
+  assert.equal(calls, 3);
+});
+
+test('idempotent requests retry transient gateway responses', async () => {
+  let calls = 0;
+  await withMockFetch(
+    async () => {
+      calls += 1;
+      return calls === 1
+        ? new Response('temporary', { status: 503 })
+        : new Response('{}', { status: 200 });
+    },
+    async () => {
+      const response = await fetchWithTransientRetry('/api/sessions', undefined, 1_000, [0]);
+      assert.equal(response.status, 200);
+    },
+  );
+  assert.equal(calls, 2);
+});
+
+test('non-idempotent requests are never retried', async () => {
+  let calls = 0;
+  await withMockFetch(
+    async () => {
+      calls += 1;
+      throw new TypeError('fetch failed');
+    },
+    async () => {
+      await assert.rejects(
+        fetchWithTransientRetry(
+          '/api/agent/start',
+          { method: 'POST', body: '{}' },
+          1_000,
+          [0, 0],
+        ),
+        /fetch failed/,
+      );
+    },
+  );
+  assert.equal(calls, 1);
+});
+
+test('aborted requests are never retried', async () => {
+  let calls = 0;
+  await withMockFetch(
+    async () => {
+      calls += 1;
+      throw new DOMException('Aborted', 'AbortError');
+    },
+    async () => {
+      await assert.rejects(
+        fetchWithTransientRetry('/api/sessions', undefined, 1_000, [0, 0]),
+        (error) => error instanceof DOMException && error.name === 'AbortError',
+      );
+    },
+  );
+  assert.equal(calls, 1);
+});

src/api/client.ts

@@ -1443,7 +1443,9 @@ export async function listSessions(options?: {
   if (options?.offset != null) params.set('offset', String(options.offset));
   if (options?.query?.trim()) params.set('query', options.query.trim());
   const qs = params.size ? `?${params.toString()}` : '';
-  const result = await apiFetch<SessionListResponse>(`/sessions${qs}`);
+  const result = await apiFetch<SessionListResponse>(`/sessions${qs}`, undefined, {
+    retryOnTransientFailure: true,
+  });
   return { items: result.sessions ?? [], page: result.page ?? {} };
 }
 
@@ -1452,7 +1454,9 @@ function sessionPath(sessionId: string, suffix = '') {
 }
 
 export async function getSession(sessionId: string): Promise<Session> {
-  return apiFetch<Session>(sessionPath(sessionId));
+  return apiFetch<Session>(sessionPath(sessionId), undefined, {
+    retryOnTransientFailure: true,
+  });
 }
 
 export async function deleteChatSession(sessionId: string): Promise<void> {
@@ -1474,7 +1478,9 @@ export async function loadSessionDetail(
   if (history?.before != null) params.set('history_before', String(history.before));
   if (history?.limit != null) params.set('history_limit', String(history.limit));
   const qs = params.size ? `?${params.toString()}` : '';
-  const detail = await apiFetch<Session>(`${sessionPath(sessionId)}${qs}`);
+  const detail = await apiFetch<Session>(`${sessionPath(sessionId)}${qs}`, undefined, {
+    retryOnTransientFailure: true,
+  });
   const messages = normalizeConversationMessages(
     (detail.conversation ?? []).filter((m) => m.metadata?.userVisible),
   );

src/api/core.ts

@@ -2,6 +2,8 @@ import type { InsufficientBalanceDetails, SessionEvent } from '../types';
 
 export const API = '/api';
 const DEFAULT_API_TIMEOUT_MS = 20_000;
+const DEFAULT_TRANSIENT_RETRY_DELAYS_MS = [500, 1_000] as const;
+const RETRYABLE_RESPONSE_STATUSES = new Set([502, 503, 504]);
 
 export class ApiError extends Error {
   readonly status: number;
@@ -123,7 +125,7 @@ export async function fetchWithTimeout(
 ): Promise<Response> {
   const controller = new AbortController();
   const upstreamSignal = init?.signal;
-  const timeout = window.setTimeout(() => controller.abort(), timeoutMs);
+  const timeout = globalThis.setTimeout(() => controller.abort(), timeoutMs);
 
   const abortFromUpstream = () => controller.abort();
   if (upstreamSignal) {
@@ -137,11 +139,68 @@ export async function fetchWithTimeout(
       signal: controller.signal,
     });
   } finally {
-    window.clearTimeout(timeout);
+    globalThis.clearTimeout(timeout);
     upstreamSignal?.removeEventListener('abort', abortFromUpstream);
   }
 }
 
+function isIdempotentRequest(init?: RequestInit) {
+  const method = String(init?.method ?? 'GET').toUpperCase();
+  return method === 'GET' || method === 'HEAD' || method === 'OPTIONS';
+}
+
+function isRetryableNetworkError(err: unknown) {
+  if (err instanceof DOMException && err.name === 'AbortError') return false;
+  const message = err instanceof Error ? err.message : String(err ?? '');
+  return /failed to fetch|networkerror|fetch failed|econn|enotfound|network/i.test(message);
+}
+
+async function waitForTransientRetry(delayMs: number, signal?: AbortSignal) {
+  if (signal?.aborted) throw new DOMException('Aborted', 'AbortError');
+  await new Promise<void>((resolve, reject) => {
+    const finish = () => {
+      signal?.removeEventListener('abort', abort);
+      resolve();
+    };
+    const abort = () => {
+      globalThis.clearTimeout(timeout);
+      reject(new DOMException('Aborted', 'AbortError'));
+    };
+    const timeout = globalThis.setTimeout(finish, delayMs);
+    signal?.addEventListener('abort', abort, { once: true });
+  });
+}
+
+export async function fetchWithTransientRetry(
+  input: RequestInfo | URL,
+  init: RequestInit | undefined,
+  timeoutMs: number,
+  retryDelaysMs: readonly number[] = DEFAULT_TRANSIENT_RETRY_DELAYS_MS,
+): Promise<Response> {
+  if (!isIdempotentRequest(init) || retryDelaysMs.length === 0) {
+    return fetchWithTimeout(input, init, timeoutMs);
+  }
+
+  let attempt = 0;
+  while (true) {
+    try {
+      const response = await fetchWithTimeout(input, init, timeoutMs);
+      if (
+        !RETRYABLE_RESPONSE_STATUSES.has(response.status)
+        || attempt >= retryDelaysMs.length
+      ) {
+        return response;
+      }
+      await response.body?.cancel().catch(() => undefined);
+    } catch (err) {
+      if (!isRetryableNetworkError(err) || attempt >= retryDelaysMs.length) throw err;
+    }
+
+    await waitForTransientRetry(retryDelaysMs[attempt], init?.signal ?? undefined);
+    attempt += 1;
+  }
+}
+
 export async function portalFetch<T>(path: string, init?: RequestInit): Promise<T> {
   let res: Response;
   try {
@@ -206,21 +265,21 @@ export function sanitizeSessionEvent(event: SessionEvent): SessionEvent {
 export async function apiFetch<T>(
   path: string,
   init?: RequestInit,
-  options?: { timeoutMs?: number },
+  options?: { timeoutMs?: number; retryOnTransientFailure?: boolean },
 ): Promise<T> {
   let res: Response;
   try {
-    res = await fetchWithTimeout(
-      `${API}${path}`,
-      {
-        ...init,
-        headers: {
-          'Content-Type': 'application/json',
-          ...init?.headers,
-        },
+    const requestInit = {
+      ...init,
+      headers: {
+        'Content-Type': 'application/json',
+        ...init?.headers,
       },
-      options?.timeoutMs,
-    );
+    };
+    const timeoutMs = options?.timeoutMs ?? DEFAULT_API_TIMEOUT_MS;
+    res = options?.retryOnTransientFailure
+      ? await fetchWithTransientRetry(`${API}${path}`, requestInit, timeoutMs)
+      : await fetchWithTimeout(`${API}${path}`, requestInit, timeoutMs);
   } catch (err) {
     throw new ApiError(0, formatNetworkError(err));
   }