diff --git a/api-core-retry.test.mjs b/api-core-retry.test.mjs
new file mode 100644
index 0000000..e4f807b
--- /dev/null
+++ b/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);
+});
diff --git a/package.json b/package.json
index d034cca..38e9329 100644
--- a/package.json
+++ b/package.json
@@ -74,7 +74,7 @@
     "ci:page-data-dev-loop-smoke": "node scripts/ci-page-data-dev-loop-smoke.mjs",
     "migrate:agent-code-run-config": "node scripts/migrate-agent-code-run-config-from-env.mjs",
     "test:scenario:john4-diet": "node scripts/run-scenario-test.mjs --scenario john4-children-hobby-diet-update",
-    "test": "node --test auth.test.mjs asr-proxy.test.mjs billing.test.mjs billing-token-state.test.mjs billing-recharge.test.mjs wechat-pay.test.mjs wechat-oauth.test.mjs wechat-mp.test.mjs wechat-media.test.mjs wechat/image-generation-policy.test.mjs wechat/verify/generated-thumbnail.test.mjs schedule-intent.test.mjs schedule-reminder-worker.test.mjs capabilities.test.mjs policies.test.mjs server/portal-api-auth-middleware.test.mjs server/portal-config-routes.test.mjs server/portal-plaza-discovery-routes.test.mjs server/portal-runtime-routes.test.mjs server/portal-gateway-services-bootstrap.test.mjs chat-skills.test.mjs chat-intent-router.test.mjs chat-finish-sync.test.mjs chat-agent-run-gate.test.mjs conversation-display.test.mjs user-publish.test.mjs user-memory-profile.test.mjs skills-registry.test.mjs skill-runtime-policy.test.mjs excel-analyst.test.mjs agent-run-gateway.test.mjs agent-run-routes.test.mjs session-broker.test.mjs sse-event-taxonomy.test.mjs goosed-proxy-boundary.test.mjs agent-run-stream.test.mjs mindspace-h5-html-finish-guard.test.mjs admin-routes.test.mjs services/orchestrator/admin-config.test.mjs services/orchestrator/contracts.test.mjs services/orchestrator/checkpoint.test.mjs services/orchestrator/runtime.test.mjs services/orchestrator/app.test.mjs services/orchestrator/server.test.mjs services/orchestrator/shadow-dispatcher.test.mjs services/orchestrator/shadow-observer.test.mjs services/orchestrator/observability.test.mjs services/orchestrator/executor-gateway.test.mjs services/orchestrator/executor-job-store.test.mjs image-make-admin-config.test.mjs asset-gateway.test.mjs image-make-client.test.mjs mindspace-image-generation.test.mjs mindspace-image-generation-routes.test.mjs mindspace-image-review.test.mjs mindspace-run-public-html-scope.test.mjs direct-chat-service.test.mjs tool-gateway.test.mjs mindspace.test.mjs mindspace-scan.test.mjs mindspace-assets.test.mjs mindspace-local-runtime-services.test.mjs mindspace-local-server-adapter.test.mjs mindspace-public-asset-token.test.mjs mindspace-remote-server-adapter.test.mjs mindspace-server-adapter.test.mjs mindspace-pages.test.mjs mindspace-page-sync-service.test.mjs public-site-bases.test.mjs mindspace-html-download-links.test.mjs mindspace-page-purge.test.mjs mindspace-public-delivery.test.mjs mindspace-public-page-context.test.mjs mindspace-published-page-csp.test.mjs mindspace-published-script-localize.test.mjs agent-run-deliverable-check.test.mjs mindspace-public-route.test.mjs mindspace-publications.test.mjs mindspace-public-links.test.mjs mindspace-chat-save.test.mjs mindspace-chat-docx-package.test.mjs mindspace-public-finish-sync.test.mjs mindspace-chat-context.test.mjs mindspace-canonical-url.test.mjs mindspace-conversation-package.test.mjs mindspace-conversation-package-backfill.test.mjs mindspace-conversation-package-public-html.test.mjs mindspace-conversation-package-verify.test.mjs mindspace-conversation-package-registry.test.mjs mindspace-conversation-package-routes.test.mjs mindspace-conversation-package-store.test.mjs mindspace-conversation-schema.test.mjs mindspace-runtime-config.test.mjs mindspace-config.test.mjs mindspace-analytics.test.mjs mindspace-rybbit.test.mjs mindspace-service.test.mjs mindspace-storage-adapter.test.mjs mindspace-content-scan.test.mjs mindspace-html-localize.test.mjs mindspace-visual-editor.test.mjs mindspace-cleanup.test.mjs mindspace-thumbnails.test.mjs mindspace-workspace-thumbnails.test.mjs mindspace-workspace-sync.test.mjs mindspace-asset-preview.test.mjs mindspace-agent-jobs.test.mjs mindspace-agent-runner.test.mjs mindspace-sandbox-mcp.test.mjs mindspace-userdata-postgres.test.mjs postgres-user-data-space-service.test.mjs user-data-space-service.test.mjs page-data-routes.test.mjs page-access-policy.test.mjs page-access-visitor.test.mjs page-data-public-service.test.mjs page-data-integration.test.mjs page-data-log-store.test.mjs page-data-ops.test.mjs page-data-session-store.test.mjs page-data-browser-client.test.mjs page-data-policy-index.test.mjs message-stream.test.mjs mindspace-service/mindspace-rpc-server.test.mjs plaza-posts.test.mjs plaza-interactions.test.mjs plaza-algorithm.test.mjs plaza-seo.test.mjs plaza-ops.test.mjs user-auth.test.mjs llm-providers.test.mjs admin-guard.test.mjs user-feedback.test.mjs memory-v2.test.mjs memory-v2-admin-config.test.mjs memory-v2-lifecycle.test.mjs memory-v2-adapter-scaffold.test.mjs memory-v2-backend-contract.test.mjs memory-v2-health.test.mjs memory-v2-runtime.test.mjs memory-v2-plugin-backends.test.mjs memory-v2-pgvector.test.mjs memory-v2-pgvector-schema.test.mjs memory-v2-pgvector-backfill.test.mjs memory-v2-pgvector-smoke.test.mjs memory-v2-qdrant.test.mjs memory-v2-weaviate.test.mjs memory-v2-mem0.test.mjs memory-v2-letta.test.mjs memory-v2-external-adapters.test.mjs scripts/embed-memory-v2-local-hash.test.mjs scripts/check-memory-v2-app-canary.test.mjs scripts/check-memory-v2-config-gaps.test.mjs scripts/check-memory-v2-contracts.test.mjs scripts/check-memory-v2-health.test.mjs scripts/check-memory-v2-session-flow.test.mjs scripts/check-memory-v2-stack.test.mjs scripts/setup-memory-v2-pgvector-schema.test.mjs scripts/backfill-memory-v2-pgvector.test.mjs scripts/scaffold-memory-v2-backend.test.mjs scripts/smoke-memory-v2-pgvector.test.mjs scripts/smoke-memory-v2-qdrant.test.mjs scripts/smoke-memory-v2-external.test.mjs scripts/mock-memory-v2-services.test.mjs",
+    "test": "node --test api-core-retry.test.mjs auth.test.mjs asr-proxy.test.mjs billing.test.mjs billing-token-state.test.mjs billing-recharge.test.mjs wechat-pay.test.mjs wechat-oauth.test.mjs wechat-mp.test.mjs wechat-media.test.mjs wechat/image-generation-policy.test.mjs wechat/verify/generated-thumbnail.test.mjs schedule-intent.test.mjs schedule-reminder-worker.test.mjs capabilities.test.mjs policies.test.mjs server/portal-api-auth-middleware.test.mjs server/portal-config-routes.test.mjs server/portal-plaza-discovery-routes.test.mjs server/portal-runtime-routes.test.mjs server/portal-gateway-services-bootstrap.test.mjs chat-skills.test.mjs chat-intent-router.test.mjs chat-finish-sync.test.mjs chat-agent-run-gate.test.mjs conversation-display.test.mjs user-publish.test.mjs user-memory-profile.test.mjs skills-registry.test.mjs skill-runtime-policy.test.mjs excel-analyst.test.mjs agent-run-gateway.test.mjs agent-run-routes.test.mjs session-broker.test.mjs sse-event-taxonomy.test.mjs goosed-proxy-boundary.test.mjs agent-run-stream.test.mjs mindspace-h5-html-finish-guard.test.mjs admin-routes.test.mjs services/orchestrator/admin-config.test.mjs services/orchestrator/contracts.test.mjs services/orchestrator/checkpoint.test.mjs services/orchestrator/runtime.test.mjs services/orchestrator/app.test.mjs services/orchestrator/server.test.mjs services/orchestrator/shadow-dispatcher.test.mjs services/orchestrator/shadow-observer.test.mjs services/orchestrator/observability.test.mjs services/orchestrator/executor-gateway.test.mjs services/orchestrator/executor-job-store.test.mjs image-make-admin-config.test.mjs asset-gateway.test.mjs image-make-client.test.mjs mindspace-image-generation.test.mjs mindspace-image-generation-routes.test.mjs mindspace-image-review.test.mjs mindspace-run-public-html-scope.test.mjs direct-chat-service.test.mjs tool-gateway.test.mjs mindspace.test.mjs mindspace-scan.test.mjs mindspace-assets.test.mjs mindspace-local-runtime-services.test.mjs mindspace-local-server-adapter.test.mjs mindspace-public-asset-token.test.mjs mindspace-remote-server-adapter.test.mjs mindspace-server-adapter.test.mjs mindspace-pages.test.mjs mindspace-page-sync-service.test.mjs public-site-bases.test.mjs mindspace-html-download-links.test.mjs mindspace-page-purge.test.mjs mindspace-public-delivery.test.mjs mindspace-public-page-context.test.mjs mindspace-published-page-csp.test.mjs mindspace-published-script-localize.test.mjs agent-run-deliverable-check.test.mjs mindspace-public-route.test.mjs mindspace-publications.test.mjs mindspace-public-links.test.mjs mindspace-chat-save.test.mjs mindspace-chat-docx-package.test.mjs mindspace-public-finish-sync.test.mjs mindspace-chat-context.test.mjs mindspace-canonical-url.test.mjs mindspace-conversation-package.test.mjs mindspace-conversation-package-backfill.test.mjs mindspace-conversation-package-public-html.test.mjs mindspace-conversation-package-verify.test.mjs mindspace-conversation-package-registry.test.mjs mindspace-conversation-package-routes.test.mjs mindspace-conversation-package-store.test.mjs mindspace-conversation-schema.test.mjs mindspace-runtime-config.test.mjs mindspace-config.test.mjs mindspace-analytics.test.mjs mindspace-rybbit.test.mjs mindspace-service.test.mjs mindspace-storage-adapter.test.mjs mindspace-content-scan.test.mjs mindspace-html-localize.test.mjs mindspace-visual-editor.test.mjs mindspace-cleanup.test.mjs mindspace-thumbnails.test.mjs mindspace-workspace-thumbnails.test.mjs mindspace-workspace-sync.test.mjs mindspace-asset-preview.test.mjs mindspace-agent-jobs.test.mjs mindspace-agent-runner.test.mjs mindspace-sandbox-mcp.test.mjs mindspace-userdata-postgres.test.mjs postgres-user-data-space-service.test.mjs user-data-space-service.test.mjs page-data-routes.test.mjs page-access-policy.test.mjs page-access-visitor.test.mjs page-data-public-service.test.mjs page-data-integration.test.mjs page-data-log-store.test.mjs page-data-ops.test.mjs page-data-session-store.test.mjs page-data-browser-client.test.mjs page-data-policy-index.test.mjs message-stream.test.mjs mindspace-service/mindspace-rpc-server.test.mjs plaza-posts.test.mjs plaza-interactions.test.mjs plaza-algorithm.test.mjs plaza-seo.test.mjs plaza-ops.test.mjs user-auth.test.mjs llm-providers.test.mjs admin-guard.test.mjs user-feedback.test.mjs memory-v2.test.mjs memory-v2-admin-config.test.mjs memory-v2-lifecycle.test.mjs memory-v2-adapter-scaffold.test.mjs memory-v2-backend-contract.test.mjs memory-v2-health.test.mjs memory-v2-runtime.test.mjs memory-v2-plugin-backends.test.mjs memory-v2-pgvector.test.mjs memory-v2-pgvector-schema.test.mjs memory-v2-pgvector-backfill.test.mjs memory-v2-pgvector-smoke.test.mjs memory-v2-qdrant.test.mjs memory-v2-weaviate.test.mjs memory-v2-mem0.test.mjs memory-v2-letta.test.mjs memory-v2-external-adapters.test.mjs scripts/embed-memory-v2-local-hash.test.mjs scripts/check-memory-v2-app-canary.test.mjs scripts/check-memory-v2-config-gaps.test.mjs scripts/check-memory-v2-contracts.test.mjs scripts/check-memory-v2-health.test.mjs scripts/check-memory-v2-session-flow.test.mjs scripts/check-memory-v2-stack.test.mjs scripts/setup-memory-v2-pgvector-schema.test.mjs scripts/backfill-memory-v2-pgvector.test.mjs scripts/scaffold-memory-v2-backend.test.mjs scripts/smoke-memory-v2-pgvector.test.mjs scripts/smoke-memory-v2-qdrant.test.mjs scripts/smoke-memory-v2-external.test.mjs scripts/mock-memory-v2-services.test.mjs",
     "test:episodic-memory": "node --test episodic-memory.test.mjs direct-chat-service.test.mjs chat-intent-router.test.mjs",
     "test:deep-search": "node --test deep-search.test.mjs mindsearch.test.mjs",
     "test:image-review": "node --test mindspace-image-review.test.mjs mindspace-image-generation.test.mjs",
diff --git a/src/api/client.ts b/src/api/client.ts
index 91d15df..43957f4 100644
--- a/src/api/client.ts
+++ b/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),
   );
diff --git a/src/api/core.ts b/src/api/core.ts
index de3fdf2..022c5ea 100644
--- a/src/api/core.ts
+++ b/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));
   }