diff --git a/CHANGELOG.md b/CHANGELOG.md
index 13dd783b7..224f73d2a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -108,6 +108,7 @@
 - Control UI: avoid Slack config ReferenceError by reading slack config snapshots. Thanks @sreekaransrinath for PR #249.
 - Auth: rotate across multiple OAuth profiles with cooldown tracking and email-based profile IDs. Thanks @mukhtharcm for PR #269.
 - Auth: fix multi-account OAuth rotation so round-robin alternates instead of pinning to lastGood. Thanks @mukhtharcm for PR #281.
+- Auth: lock auth profile usage updates and fail fast on 429s during rotation. Thanks @mukhtharcm for PR #342.
 - Configure: stop auto-writing `auth.order` for newly added auth profiles (round-robin default unless explicitly pinned).
 - Telegram: honor routing.groupChat.mentionPatterns for group mention gating. Thanks Kevin Kern (@regenrek) for PR #242.
 - Telegram: gate groups via `telegram.groups` allowlist (align with WhatsApp/iMessage). Thanks @kitze for PR #241.
diff --git a/src/agents/auth-profiles.ts b/src/agents/auth-profiles.ts
index 07b8f44ba..8b746707a 100644
--- a/src/agents/auth-profiles.ts
+++ b/src/agents/auth-profiles.ts
@@ -16,6 +16,16 @@ import { resolveClawdbotAgentDir } from "./agent-paths.js";
 const AUTH_STORE_VERSION = 1;
 const AUTH_PROFILE_FILENAME = "auth-profiles.json";
 const LEGACY_AUTH_FILENAME = "auth.json";
+const AUTH_STORE_LOCK_OPTIONS = {
+  retries: {
+    retries: 10,
+    factor: 2,
+    minTimeout: 100,
+    maxTimeout: 10_000,
+    randomize: true,
+  },
+  stale: 30_000,
+} as const;
 
 export type ApiKeyCredential = {
   type: "api_key";
@@ -87,6 +97,49 @@ function ensureAuthStoreFile(pathname: string) {
   saveJsonFile(pathname, payload);
 }
 
+function syncAuthProfileStore(
+  target: AuthProfileStore,
+  source: AuthProfileStore,
+): void {
+  target.version = source.version;
+  target.profiles = source.profiles;
+  target.lastGood = source.lastGood;
+  target.usageStats = source.usageStats;
+}
+
+function updateAuthProfileStoreWithLock(params: {
+  agentDir?: string;
+  updater: (store: AuthProfileStore) => boolean;
+}): AuthProfileStore | null {
+  const authPath = resolveAuthStorePath(params.agentDir);
+  ensureAuthStoreFile(authPath);
+
+  let release: (() => void) | undefined;
+  try {
+    release = lockfile.lockSync(authPath, AUTH_STORE_LOCK_OPTIONS);
+    const store = ensureAuthProfileStore(params.agentDir);
+    const shouldSave = params.updater(store);
+    if (shouldSave) {
+      saveAuthProfileStore(store, params.agentDir);
+    }
+    return store;
+  } catch {
+    return null;
+  } finally {
+    if (release) {
+      try {
+        release();
+      } catch {
+        try {
+          lockfile.unlockSync(authPath);
+        } catch {
+          // ignore unlock errors
+        }
+      }
+    }
+  }
+}
+
 function buildOAuthApiKey(
   provider: OAuthProvider,
   credentials: OAuthCredentials,
@@ -112,14 +165,7 @@ async function refreshOAuthTokenWithLock(params: {
   let release: (() => Promise<void>) | undefined;
   try {
     release = await lockfile.lock(authPath, {
-      retries: {
-        retries: 10,
-        factor: 2,
-        minTimeout: 100,
-        maxTimeout: 10_000,
-        randomize: true,
-      },
-      stale: 30_000,
+      ...AUTH_STORE_LOCK_OPTIONS,
     });
 
     const store = ensureAuthProfileStore(params.agentDir);
@@ -355,26 +401,42 @@ export function isProfileInCooldown(
 
 /**
  * Mark a profile as successfully used. Resets error count and updates lastUsed.
- * Re-reads the store from disk to avoid overwriting concurrent updates.
+ * Uses store lock to avoid overwriting concurrent usage updates.
  */
 export function markAuthProfileUsed(params: {
   store: AuthProfileStore;
   profileId: string;
   agentDir?: string;
 }): void {
-  const { profileId, agentDir } = params;
-  // Re-read from disk to get fresh usageStats from other sessions
-  const freshStore = ensureAuthProfileStore(agentDir);
-  if (!freshStore.profiles[profileId]) return;
+  const { store, profileId, agentDir } = params;
+  const updated = updateAuthProfileStoreWithLock({
+    agentDir,
+    updater: (freshStore) => {
+      if (!freshStore.profiles[profileId]) return false;
+      freshStore.usageStats = freshStore.usageStats ?? {};
+      freshStore.usageStats[profileId] = {
+        ...freshStore.usageStats[profileId],
+        lastUsed: Date.now(),
+        errorCount: 0,
+        cooldownUntil: undefined,
+      };
+      return true;
+    },
+  });
+  if (updated) {
+    syncAuthProfileStore(store, updated);
+    return;
+  }
+  if (!store.profiles[profileId]) return;
 
-  freshStore.usageStats = freshStore.usageStats ?? {};
-  freshStore.usageStats[profileId] = {
-    ...freshStore.usageStats[profileId],
+  store.usageStats = store.usageStats ?? {};
+  store.usageStats[profileId] = {
+    ...store.usageStats[profileId],
     lastUsed: Date.now(),
     errorCount: 0,
     cooldownUntil: undefined,
   };
-  saveAuthProfileStore(freshStore, agentDir);
+  saveAuthProfileStore(store, agentDir);
 }
 
 export function calculateAuthProfileCooldownMs(errorCount: number): number {
@@ -388,53 +450,90 @@ export function calculateAuthProfileCooldownMs(errorCount: number): number {
 /**
  * Mark a profile as failed/rate-limited. Applies exponential backoff cooldown.
  * Cooldown times: 1min, 5min, 25min, max 1 hour.
- * Re-reads the store from disk to avoid overwriting concurrent updates.
+ * Uses store lock to avoid overwriting concurrent usage updates.
  */
 export function markAuthProfileCooldown(params: {
   store: AuthProfileStore;
   profileId: string;
   agentDir?: string;
 }): void {
-  const { profileId, agentDir } = params;
-  // Re-read from disk to get fresh usageStats from other sessions
-  const freshStore = ensureAuthProfileStore(agentDir);
-  if (!freshStore.profiles[profileId]) return;
+  const { store, profileId, agentDir } = params;
+  const updated = updateAuthProfileStoreWithLock({
+    agentDir,
+    updater: (freshStore) => {
+      if (!freshStore.profiles[profileId]) return false;
 
-  freshStore.usageStats = freshStore.usageStats ?? {};
-  const existing = freshStore.usageStats[profileId] ?? {};
+      freshStore.usageStats = freshStore.usageStats ?? {};
+      const existing = freshStore.usageStats[profileId] ?? {};
+      const errorCount = (existing.errorCount ?? 0) + 1;
+
+      // Exponential backoff: 1min, 5min, 25min, capped at 1h
+      const backoffMs = calculateAuthProfileCooldownMs(errorCount);
+
+      freshStore.usageStats[profileId] = {
+        ...existing,
+        errorCount,
+        cooldownUntil: Date.now() + backoffMs,
+      };
+      return true;
+    },
+  });
+  if (updated) {
+    syncAuthProfileStore(store, updated);
+    return;
+  }
+  if (!store.profiles[profileId]) return;
+
+  store.usageStats = store.usageStats ?? {};
+  const existing = store.usageStats[profileId] ?? {};
   const errorCount = (existing.errorCount ?? 0) + 1;
 
   // Exponential backoff: 1min, 5min, 25min, capped at 1h
   const backoffMs = calculateAuthProfileCooldownMs(errorCount);
 
-  freshStore.usageStats[profileId] = {
+  store.usageStats[profileId] = {
     ...existing,
     errorCount,
     cooldownUntil: Date.now() + backoffMs,
   };
-  saveAuthProfileStore(freshStore, agentDir);
+  saveAuthProfileStore(store, agentDir);
 }
 
 /**
  * Clear cooldown for a profile (e.g., manual reset).
- * Re-reads the store from disk to avoid overwriting concurrent updates.
+ * Uses store lock to avoid overwriting concurrent usage updates.
  */
 export function clearAuthProfileCooldown(params: {
   store: AuthProfileStore;
   profileId: string;
   agentDir?: string;
 }): void {
-  const { profileId, agentDir } = params;
-  // Re-read from disk to get fresh usageStats from other sessions
-  const freshStore = ensureAuthProfileStore(agentDir);
-  if (!freshStore.usageStats?.[profileId]) return;
+  const { store, profileId, agentDir } = params;
+  const updated = updateAuthProfileStoreWithLock({
+    agentDir,
+    updater: (freshStore) => {
+      if (!freshStore.usageStats?.[profileId]) return false;
 
-  freshStore.usageStats[profileId] = {
-    ...freshStore.usageStats[profileId],
+      freshStore.usageStats[profileId] = {
+        ...freshStore.usageStats[profileId],
+        errorCount: 0,
+        cooldownUntil: undefined,
+      };
+      return true;
+    },
+  });
+  if (updated) {
+    syncAuthProfileStore(store, updated);
+    return;
+  }
+  if (!store.usageStats?.[profileId]) return;
+
+  store.usageStats[profileId] = {
+    ...store.usageStats[profileId],
     errorCount: 0,
     cooldownUntil: undefined,
   };
-  saveAuthProfileStore(freshStore, agentDir);
+  saveAuthProfileStore(store, agentDir);
 }
 
 export function resolveAuthProfileOrder(params: {
@@ -600,13 +699,24 @@ export function markAuthProfileGood(params: {
   profileId: string;
   agentDir?: string;
 }): void {
-  const { provider, profileId, agentDir } = params;
-  // Re-read from disk to avoid overwriting concurrent updates
-  const freshStore = ensureAuthProfileStore(agentDir);
-  const profile = freshStore.profiles[profileId];
+  const { store, provider, profileId, agentDir } = params;
+  const updated = updateAuthProfileStoreWithLock({
+    agentDir,
+    updater: (freshStore) => {
+      const profile = freshStore.profiles[profileId];
+      if (!profile || profile.provider !== provider) return false;
+      freshStore.lastGood = { ...freshStore.lastGood, [provider]: profileId };
+      return true;
+    },
+  });
+  if (updated) {
+    syncAuthProfileStore(store, updated);
+    return;
+  }
+  const profile = store.profiles[profileId];
   if (!profile || profile.provider !== provider) return;
-  freshStore.lastGood = { ...freshStore.lastGood, [provider]: profileId };
-  saveAuthProfileStore(freshStore, agentDir);
+  store.lastGood = { ...store.lastGood, [provider]: profileId };
+  saveAuthProfileStore(store, agentDir);
 }
 
 export function resolveAuthStorePathForDisplay(): string {
diff --git a/src/agents/pi-embedded-runner.ts b/src/agents/pi-embedded-runner.ts
index 3339a6031..af60309b1 100644
--- a/src/agents/pi-embedded-runner.ts
+++ b/src/agents/pi-embedded-runner.ts
@@ -133,6 +133,17 @@ type EmbeddedRunWaiter = {
 };
 const EMBEDDED_RUN_WAITERS = new Map<string, Set<EmbeddedRunWaiter>>();
 
+const isAbortError = (err: unknown): boolean => {
+  if (!err || typeof err !== "object") return false;
+  const name = "name" in err ? String(err.name) : "";
+  if (name === "AbortError") return true;
+  const message =
+    "message" in err && typeof err.message === "string"
+      ? err.message.toLowerCase()
+      : "";
+  return message.includes("aborted");
+};
+
 type EmbeddedSandboxInfo = {
   enabled: boolean;
   workspaceDir?: string;
@@ -913,7 +924,11 @@ export async function runEmbeddedPiAgent(params: {
               await waitForCompactionRetry();
             } catch (err) {
               // Capture AbortError from waitForCompactionRetry to enable fallback/rotation
-              if (!promptError) promptError = err;
+              if (isAbortError(err)) {
+                if (!promptError) promptError = err;
+              } else {
+                throw err;
+              }
             }
             messagesSnapshot = session.messages.slice();
             sessionIdUsed = session.sessionId;