diff --git a/packages/cli/src/serve/routes/session-turn-failure.test.ts b/packages/cli/src/serve/routes/session-turn-failure.test.ts
new file mode 100644
index 00000000000..73441cdefee
--- /dev/null
+++ b/packages/cli/src/serve/routes/session-turn-failure.test.ts
@@ -0,0 +1,94 @@
+/**
+ * @license
+ * Copyright 2026 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, expect, it } from 'vitest';
+import { describePromptTurnFailure } from './session.js';
+
+describe('describePromptTurnFailure', () => {
+  it('keeps Error name and message', () => {
+    const err = new Error('agent channel closed mid-request');
+    err.name = 'BridgeChannelClosedError';
+    expect(describePromptTurnFailure(err)).toBe(
+      '[BridgeChannelClosedError] agent channel closed mid-request',
+    );
+  });
+
+  it('extracts data details from Error rejections carrying JSON-RPC data', () => {
+    const err = Object.assign(new Error('Internal error'), {
+      name: 'RequestError',
+      data: { details: 'session not found' },
+    });
+    expect(describePromptTurnFailure(err)).toBe(
+      '[RequestError] session not found',
+    );
+  });
+
+  it('keeps the Error name prefix over a code prefix', () => {
+    const err = Object.assign(new Error('write EPIPE'), { code: 'EPIPE' });
+    expect(describePromptTurnFailure(err)).toBe('[Error] write EPIPE');
+  });
+
+  it('extracts message and code from a bare JSON-RPC error object', () => {
+    expect(
+      describePromptTurnFailure({ code: -32603, message: 'Internal error' }),
+    ).toBe('[code -32603] Internal error');
+  });
+
+  it('prefers JSON-RPC data details over the generic message', () => {
+    expect(
+      describePromptTurnFailure({
+        code: -32603,
+        message: 'Internal error',
+        data: { details: 'model provider rejected the request' },
+      }),
+    ).toBe('[code -32603] model provider rejected the request');
+  });
+
+  it('prefers nested provider error text shipped as parsed data', () => {
+    expect(
+      describePromptTurnFailure({
+        code: -32603,
+        message: 'Internal error',
+        data: { error: { message: 'upstream 429 rate limited' } },
+      }),
+    ).toBe('[code -32603] upstream 429 rate limited');
+  });
+
+  it('reads a plain object message property without a code', () => {
+    expect(describePromptTurnFailure({ message: 'something broke' })).toBe(
+      'something broke',
+    );
+  });
+
+  it('never degrades structured rejections to [object Object]', () => {
+    const candidates: unknown[] = [
+      { code: -32000, message: 'boom' },
+      { code: 'EPIPE', message: 'write failed' },
+      { data: 'provider closed the stream' },
+      { message: 'partial' },
+      { code: -32603 },
+      {},
+      { message: '' },
+    ];
+    for (const candidate of candidates) {
+      const rendered = describePromptTurnFailure(candidate);
+      expect(rendered).not.toBe('');
+      expect(rendered).not.toContain('[object Object]');
+    }
+  });
+
+  it('renders circular rejections without degrading', () => {
+    const err: Record<string, unknown> = { code: -32603 };
+    err['self'] = err;
+    const rendered = describePromptTurnFailure(err);
+    expect(rendered).toContain('[code -32603]');
+    expect(rendered).not.toContain('[object Object]');
+  });
+
+  it('stringifies primitive rejections', () => {
+    expect(describePromptTurnFailure('socket hang up')).toBe('socket hang up');
+  });
+});
diff --git a/packages/cli/src/serve/routes/session.ts b/packages/cli/src/serve/routes/session.ts
index e36dc8d956b..cfff0e5c0b5 100644
--- a/packages/cli/src/serve/routes/session.ts
+++ b/packages/cli/src/serve/routes/session.ts
@@ -7,6 +7,7 @@
 import * as crypto from 'node:crypto';
 import * as fs from 'node:fs';
 import * as path from 'node:path';
+import { inspect } from 'node:util';
 import {
   APPROVAL_MODES,
   BTW_MAX_INPUT_LENGTH,
@@ -46,7 +47,11 @@ import {
   type BridgeBranchedSession,
 } from '@qwen-code/acp-bridge/bridgeTypes';
 import type { BridgeEvent } from '@qwen-code/acp-bridge/eventBus';
-import { parseSessionSource } from '@qwen-code/acp-bridge';
+import {
+  extractErrorCode,
+  extractErrorMessage,
+  parseSessionSource,
+} from '@qwen-code/acp-bridge';
 import {
   isReservedLiveSessionSource,
   isReservedStandaloneSessionSource,
@@ -450,6 +455,31 @@ function sendSessionOrganizationError(res: Response, err: unknown): boolean {
   return true;
 }
 
+/**
+ * Renders a prompt-turn rejection for the daemon log. Non-Error rejections
+ * (bare JSON-RPC error objects forwarded by the bridge) must not degrade to
+ * `[object Object]` — that hid the failure cause in production incidents
+ * (#10710), so extract the structured message/code instead.
+ */
+export function describePromptTurnFailure(err: unknown): string {
+  const detail = extractErrorMessage(err);
+  if (err instanceof Error) {
+    return `[${err.name}] ${detail}`;
+  }
+  const code = extractErrorCode(err);
+  // `extractErrorMessage` terminates in `String(err)`, which renders a plain
+  // object as `[object Object]`. Fall back to `inspect` for those: unlike
+  // `JSON.stringify` it never throws, so circular and non-serializable
+  // rejections stay readable instead of degrading again.
+  const rendered =
+    typeof err === 'object' &&
+    err !== null &&
+    (detail === '' || detail === String(err))
+      ? inspect(err, { depth: 2, breakLength: Infinity })
+      : detail;
+  return code === undefined ? rendered : `[code ${code}] ${rendered}`;
+}
+
 function parseTranscriptLimitQuery(
   rawLimit: unknown,
   res: Response,
@@ -5397,9 +5427,8 @@ export function registerSessionRoutes(
             },
             (err) => {
               if (daemonLog) {
-                const errName = err instanceof Error ? err.name : undefined;
                 daemonLog.warn(
-                  `prompt turn failed: ${errName ? `[${errName}] ` : ''}${err instanceof Error ? err.message : String(err)}`,
+                  `prompt turn failed: ${describePromptTurnFailure(err)}`,
                   { sessionId, promptId, clientId },
                 );
               }