fix: 修复额度耗尽错误展示

问题：Token balance exhausted 被作为原始助手气泡展示，且额度确认可能跨会话复用。

修复：区分绝对余额与滚动额度，绑定当前会话失败 key，并补充真实消息结构与双会话回归测试。

tests/unit/opencode-error-kind.test.ts

@@ -1,5 +1,8 @@
 import { describe, expect, it } from 'vitest';
-import { getOpencodeErrorKind } from '../../shared/opencode-error-kind';
+import {
+  getOpencodeErrorKind,
+  isOpencodeTokenBalanceExhausted,
+} from '../../shared/opencode-error-kind';
 
 describe('getOpencodeErrorKind', () => {
   it('classifies a generic Works Square gateway authorization failure as invalid authentication', () => {
@@ -14,4 +17,20 @@ describe('getOpencodeErrorKind', () => {
   ])('classifies explicit quota evidence as exhausted: %s', (message) => {
     expect(getOpencodeErrorKind(message)).toBe('quota_exhausted');
   });
+
+  it.each([
+    'token_balance_exhausted',
+    'Token balance exhausted (request id: req-1)',
+    'works_square_gateway_authorize_failed: balance exhausted',
+  ])('identifies authoritative token-balance exhaustion: %s', (message) => {
+    expect(isOpencodeTokenBalanceExhausted(message)).toBe(true);
+  });
+
+  it.each([
+    'Token quota exhausted for rolling 5-hour window',
+    'user quota is not enough',
+    'works_square_gateway_authorize_failed',
+  ])('does not mistake other failures for token-balance exhaustion: %s', (message) => {
+    expect(isOpencodeTokenBalanceExhausted(message)).toBe(false);
+  });
 });