```

feat(learning): 添加技能学习候选者合成锁定机制

添加了 DraftSynthesisInProgress 和 DraftHasNoChanges 异常来处理并发场景，
确保同一技能学习候选者的合成过程不会重复执行。实现了 claim_learning_candidate_for_synthesis
方法来原子性地锁定候选者进行合成。

fix(web): 为技能草案创建端点添加适当的HTTP状态码

当草案没有变化或正在合成时，现在正确返回409状态码而不是内部错误。

feat(skills): 实现技能修订内容比较以检测无变化情况

添加了 _is_noop_revision 方法来比较基础技能和提议的修订，
如果内容没有实际变化则抛出 NoDraftChanges 异常。

refactor(process): 修复任务证据记录后根运行状态更新逻辑

将任务证据记录事件后的状态从 waiting 更改为 done，并设置 finished_at 时间戳。

feat(tools): 防止在同一运行中重复执行外部写入操作

为邮件发送、日历创建等外部写入工具添加去重机制，避免重复的外部操作。

test: 添加技能学习和工具执行的单元测试

增加测试用例验证并发草案合成、重复外部写入抑制和无变化修订检测等功能。
```

app-instance/backend/beaver/tools/runtime/executor.py

@@ -11,6 +11,7 @@
 
 from __future__ import annotations
 
+import hashlib
 import json
 from typing import TYPE_CHECKING, Any
 
@@ -44,7 +45,45 @@ class ToolExecutor:
                 tool_name=tool_name,
                 error="tool_not_found",
             )
-        return await tool.invoke(arguments or {}, context or ToolContext())
+        normalized_arguments = dict(arguments or {})
+        tool_context = context or ToolContext()
+        write_key = _external_write_key(tool_name, normalized_arguments)
+        if write_key is None:
+            return await tool.invoke(normalized_arguments, tool_context)
+
+        external_writes = _external_write_state(tool_context)
+        previous = external_writes.get(write_key)
+        if previous is not None:
+            previous_content = str(previous.get("content") or "").strip()
+            detail = f" Previous result: {previous_content}" if previous_content else ""
+            return ToolResult(
+                success=True,
+                content=(
+                    f"Duplicate external write suppressed for {tool_name}. "
+                    "A matching write was already attempted in this run."
+                    f"{detail}"
+                ),
+                tool_name=tool_name,
+                error="duplicate_external_write_suppressed",
+                raw_output={"duplicate": True, "previous": previous},
+            )
+
+        external_writes[write_key] = {
+            "tool_name": tool_name,
+            "arguments": normalized_arguments,
+            "status": "attempted",
+            "content": "",
+            "error": None,
+        }
+        result = await tool.invoke(normalized_arguments, tool_context)
+        external_writes[write_key] = {
+            "tool_name": tool_name,
+            "arguments": normalized_arguments,
+            "status": "done" if result.success else "error",
+            "content": result.content,
+            "error": result.error,
+        }
+        return result
 
     async def execute_tool_call(
         self,
@@ -115,3 +154,42 @@ class ToolExecutor:
         if tool_call.get("name"):
             return str(tool_call["name"])
         return "unknown"
+
+
+_EXTERNAL_WRITE_TOOL_TERMS = (
+    "mail_send_email",
+    "mail_reply_to_message",
+    "mail_forward_message",
+    "mail_move_message",
+    "calendar_create_event",
+    "calendar_update_event",
+)
+
+
+def _external_write_state(context: ToolContext) -> dict[str, dict[str, Any]]:
+    state = context.metadata.setdefault("external_write_attempts", {})
+    if not isinstance(state, dict):
+        state = {}
+        context.metadata["external_write_attempts"] = state
+    return state
+
+
+def _external_write_key(tool_name: str, arguments: dict[str, Any]) -> str | None:
+    lowered = tool_name.lower()
+    if not any(term in lowered for term in _EXTERNAL_WRITE_TOOL_TERMS):
+        return None
+    payload = json.dumps(_normalize_for_key(arguments), ensure_ascii=False, sort_keys=True, separators=(",", ":"))
+    digest = hashlib.sha256(payload.encode("utf-8")).hexdigest()
+    return f"{lowered}:{digest}"
+
+
+def _normalize_for_key(value: Any) -> Any:
+    if isinstance(value, dict):
+        return {str(key): _normalize_for_key(value[key]) for key in sorted(value, key=str)}
+    if isinstance(value, list):
+        return [_normalize_for_key(item) for item in value]
+    if isinstance(value, tuple):
+        return [_normalize_for_key(item) for item in value]
+    if isinstance(value, (str, int, float, bool)) or value is None:
+        return value
+    return str(value)