fix: let direct models continue after tool execution failures

Return ordinary tool exceptions as paired error results so the model can decide how to recover. Preserve cancellation, existing recovery guidance, and failed tool activities without adding automatic retries or retry limits.

Validate all three text protocols with real process execution and cover bounded errors and cancellation. Focused tests: 161 passed, 1 skipped; typecheck and lint passed. Full suite: 6230 passed, 87 skipped, 1 Obsidian temporary-directory assertion failed.

Release note: Direct-model conversations can continue after a tool fails, allowing the model to use the reported error to choose its next step.

docs/features/unified-execution/progress.md

@@ -259,3 +259,8 @@ SSH 专家保留父请求已解析的 OpenCode 或 Continue 选择，通过现
 `deai-writing` 扫描九份文档，阻断项为 0。复核项主要为未验证状态、数据保留条件和字段枚举；结合技术文档语境保留这些限定，不将迁移计划改写为已完成事实。
 
 `git diff --check -- docs/features/unified-execution docs/features/assistant-workbar/README.md` 通过已跟踪改动的空白检查。新建文档另经内容与链接核对；该命令不会把未跟踪文件当作已验证差异。文档检查不替代运行时验收，后者按用户故事与技术设计执行。
+
+## 2026-10-05 直连模型工具错误回传
+
+普通工具执行失败不再直接终止直连模型循环，错误结果继续交给模型处理，取消行为保留。
+实现、三协议回归及全量测试边界见[直连模型修复记录](../direct-model-agent/progress.md#2026-10-05-工具执行异常回传)。