diff --git a/packages/core/src/orchestrator/orchestrator-agent.ts b/packages/core/src/orchestrator/orchestrator-agent.ts
index f43ffe0454..d5eb9397b3 100644
--- a/packages/core/src/orchestrator/orchestrator-agent.ts
+++ b/packages/core/src/orchestrator/orchestrator-agent.ts
@@ -954,8 +954,19 @@ async function handleStreamMode(
       if (!commandDetected && platform.sendStructuredEvent) {
         await platform.sendStructuredEvent(conversationId, msg);
       }
-    } else if (msg.type === 'result' && msg.sessionId) {
-      newSessionId = msg.sessionId;
+    } else if (msg.type === 'result') {
+      if (msg.sessionId) {
+        newSessionId = msg.sessionId;
+      }
+      if (msg.isError) {
+        getLog().warn({ conversationId, errorSubtype: msg.errorSubtype }, 'ai_result_error');
+        const syntheticError = new Error(msg.errorSubtype ?? 'AI result error');
+        await platform.sendMessage(conversationId, classifyAndFormatError(syntheticError));
+        if (newSessionId) {
+          await tryPersistSessionId(session.id, newSessionId);
+        }
+        return;
+      }
       if (!commandDetected && platform.sendStructuredEvent) {
         await platform.sendStructuredEvent(conversationId, msg);
       }
@@ -1066,8 +1077,19 @@ async function handleBatchMode(
         allChunks.push({ type: 'tool', content: toolMessage });
         getLog().debug({ toolName: msg.toolName }, 'tool_call');
       }
-    } else if (msg.type === 'result' && msg.sessionId) {
-      newSessionId = msg.sessionId;
+    } else if (msg.type === 'result') {
+      if (msg.sessionId) {
+        newSessionId = msg.sessionId;
+      }
+      if (msg.isError) {
+        getLog().warn({ conversationId, errorSubtype: msg.errorSubtype }, 'ai_result_error');
+        const syntheticError = new Error(msg.errorSubtype ?? 'AI result error');
+        await platform.sendMessage(conversationId, classifyAndFormatError(syntheticError));
+        if (newSessionId) {
+          await tryPersistSessionId(session.id, newSessionId);
+        }
+        return;
+      }
     }
 
     if (!commandDetected && allChunks.length > MAX_BATCH_TOTAL_CHUNKS) {
diff --git a/packages/core/src/utils/error-formatter.test.ts b/packages/core/src/utils/error-formatter.test.ts
index 0e3bfe01c8..c9c82c867b 100644
--- a/packages/core/src/utils/error-formatter.test.ts
+++ b/packages/core/src/utils/error-formatter.test.ts
@@ -19,25 +19,97 @@ describe('classifyAndFormatError', () => {
     });
   });
 
-  describe('authentication errors', () => {
+  describe('Claude OAuth refresh-token errors', () => {
+    test('detects "refresh token" in message', () => {
+      const result = classifyAndFormatError(new Error('Your refresh token was already used'));
+      expect(result).toContain('Claude authentication expired');
+      expect(result).toContain('/login');
+    });
+
+    test('detects "could not be refreshed" in message', () => {
+      const result = classifyAndFormatError(new Error('Your access token could not be refreshed'));
+      expect(result).toContain('Claude authentication expired');
+    });
+
+    test('detects "log out and sign in" in message', () => {
+      const result = classifyAndFormatError(new Error('Please log out and sign in again'));
+      expect(result).toContain('Claude authentication expired');
+    });
+
+    test('detects "OAuth token has expired" in message', () => {
+      const result = classifyAndFormatError(
+        new Error('API Error: 401 OAuth token has expired. Please run /login')
+      );
+      expect(result).toContain('Claude authentication expired');
+      expect(result).toContain('claude logout && claude login');
+    });
+
+    test('detects "sign-in has expired" in message', () => {
+      const result = classifyAndFormatError(
+        new Error('Unable to start session: sign-in has expired')
+      );
+      expect(result).toContain('Claude authentication expired');
+    });
+
+    test('handles full Claude OAuth error with refresh token race condition', () => {
+      const result = classifyAndFormatError(
+        new Error(
+          'Claude Code auth error: Your access token could not be refreshed because your refresh token was already used. Please log out and sign in again.'
+        )
+      );
+      expect(result).toContain('Claude authentication expired');
+    });
+  });
+
+  describe('Claude general auth errors', () => {
+    test('detects "Claude Code auth error:" prefix for non-OAuth errors', () => {
+      const result = classifyAndFormatError(new Error('Claude Code auth error: 403 forbidden'));
+      expect(result).toContain('Claude authentication error');
+      expect(result).toContain('/login');
+    });
+  });
+
+  describe('Codex auth errors', () => {
+    test('detects Codex 401 retry exhaustion', () => {
+      const result = classifyAndFormatError(
+        new Error('Codex query failed: exceeded retry limit, last status: 401 Unauthorized')
+      );
+      expect(result).toContain('Codex authentication error');
+      expect(result).toContain('codex login');
+    });
+
+    test('detects Codex query failed with Unauthorized', () => {
+      const result = classifyAndFormatError(new Error('Codex query failed: Unauthorized'));
+      expect(result).toContain('Codex authentication error');
+      expect(result).toContain('codex login');
+    });
+  });
+
+  describe('general authentication errors', () => {
     test('detects "API key" in message', () => {
       const result = classifyAndFormatError(new Error('Invalid API key provided'));
-      expect(result).toBe('⚠️ AI service authentication error. Please check configuration.');
+      expect(result).toContain('authentication error');
+    });
+
+    test('detects "authentication_error" in message', () => {
+      const result = classifyAndFormatError(new Error('authentication_error: invalid'));
+      expect(result).toContain('authentication error');
     });
 
-    test('detects "authentication" in message', () => {
-      const result = classifyAndFormatError(new Error('authentication failed'));
-      expect(result).toBe('⚠️ AI service authentication error. Please check configuration.');
+    test('detects "authentication error" in message', () => {
+      const result = classifyAndFormatError(new Error('authentication error'));
+      expect(result).toContain('authentication error');
     });
 
     test('detects "401" in message', () => {
       const result = classifyAndFormatError(new Error('HTTP 401 Unauthorized'));
-      expect(result).toBe('⚠️ AI service authentication error. Please check configuration.');
+      expect(result).toContain('authentication error');
     });
 
-    test('detects 401 as standalone in message', () => {
-      const result = classifyAndFormatError(new Error('Status: 401'));
-      expect(result).toBe('⚠️ AI service authentication error. Please check configuration.');
+    test('does not false-positive on generic messages containing "auth"', () => {
+      // "auth" alone should NOT match — only specific patterns
+      const result = classifyAndFormatError(new Error('author name missing'));
+      expect(result).not.toContain('authentication');
     });
   });
 
@@ -232,9 +304,24 @@ describe('classifyAndFormatError', () => {
       expect(result).toBe('⚠️ AI rate limit reached. Please wait a moment and try again.');
     });
 
+    test('Claude OAuth check takes precedence over general auth check', () => {
+      // Contains both "refresh token" and "Claude Code auth error:" — OAuth branch fires first
+      const result = classifyAndFormatError(
+        new Error('Claude Code auth error: refresh token expired')
+      );
+      expect(result).toContain('Claude authentication expired');
+    });
+
+    test('Codex auth takes precedence over generic Codex error handler', () => {
+      // Contains "Codex query failed:" AND "401" — Codex auth branch fires first
+      const result = classifyAndFormatError(new Error('Codex query failed: 401 Unauthorized'));
+      expect(result).toContain('Codex authentication error');
+      expect(result).toContain('codex login');
+    });
+
     test('auth check takes precedence over short-message fallback', () => {
       const result = classifyAndFormatError(new Error('API key'));
-      expect(result).toBe('⚠️ AI service authentication error. Please check configuration.');
+      expect(result).toContain('authentication error');
     });
 
     test('Codex check is applied before generic fallback', () => {
diff --git a/packages/core/src/utils/error-formatter.ts b/packages/core/src/utils/error-formatter.ts
index 86e51f8a41..25658b5cd6 100644
--- a/packages/core/src/utils/error-formatter.ts
+++ b/packages/core/src/utils/error-formatter.ts
@@ -19,13 +19,42 @@ export function classifyAndFormatError(error: Error): string {
     return '⚠️ AI rate limit reached. Please wait a moment and try again.';
   }
 
-  // AI/SDK errors - authentication
+  // Claude-specific auth errors — OAuth token refresh failures
+  // These come from Claude Code subprocess stderr or SDK result subtypes.
+  // Recovery: `/login` in-session or `claude logout && claude login` in terminal.
+  if (
+    message.includes('refresh token') ||
+    message.includes('could not be refreshed') ||
+    message.includes('log out and sign in') ||
+    message.includes('OAuth token has expired') ||
+    message.includes('sign-in has expired')
+  ) {
+    return '⚠️ Claude authentication expired. Run `/login` inside Claude Code or `claude logout && claude login` in your terminal.';
+  }
+
+  // Claude-specific auth errors — general (subprocess crash with auth classification)
+  if (message.startsWith('Claude Code auth error:')) {
+    return '⚠️ Claude authentication error. Run `/login` inside Claude Code or check your API key configuration.';
+  }
+
+  // Codex-specific auth errors — 401 retry exhaustion
+  // Codex surfaces auth failures as "exceeded retry limit, last status: 401 Unauthorized"
+  // Recovery: `codex login` in terminal.
+  if (
+    message.includes('Codex query failed:') &&
+    (message.includes('401') || message.includes('Unauthorized'))
+  ) {
+    return '⚠️ Codex authentication error. Run `codex login` in your terminal to re-authenticate.';
+  }
+
+  // General AI/SDK authentication errors
   if (
     message.includes('API key') ||
-    message.includes('authentication') ||
+    message.includes('authentication_error') ||
+    message.includes('authentication error') ||
     message.includes('401')
   ) {
-    return '⚠️ AI service authentication error. Please check configuration.';
+    return '⚠️ AI service authentication error. Please check your API key or credentials.';
   }
 
   // Network errors - timeout