feat: Step 2-4 Task/Mail/Toolchain handlers + PromptSections + BaseTaskHandler

- base_task_handler.py: 基类统一4步流程(crash→verify→mark→notify)
- task_handler.py: 5 PromptSections + 三信号验证 + review流程
- mail_handler.py: 3 PromptSections + inform/request区分 + 基类统一流程
- toolchain_handler.py: 3 PromptSections + 模板引擎渲染 + Mail API通知
- 背靠背设计-编码一致性检查通过(4严重已修/6轻微保留)

src/daemon/mail_handler.py

@@ -0,0 +1,206 @@
+"""mail_handler.py — Mail 任务 handler。
+
+处理 Agent 间通信（飞鸽传书），含 inform 和 request 两种类型。
+"""
+from __future__ import annotations
+
+import json
+import logging
+from pathlib import Path
+from typing import Dict, List, Optional
+
+from src.daemon.base_task_handler import BaseTaskHandler, VerifyResult
+from src.daemon.prompt_composer import PromptComposer, PromptContext
+from src.blackboard.db import get_connection
+
+logger = logging.getLogger("moziplus-v2.handler.mail")
+
+class MailHandler(BaseTaskHandler):
+    """Mail 任务 handler。"""
+
+    task_type = "mail"
+    virtual_project = "_mail"
+
+    def target_success_status(self) -> str:
+        return "done"
+
+    def pre_spawn(self, task_id: str, db_path: Path) -> bool:
+        """auto_working：pending → working"""
+        return self._auto_mark_working(task_id, db_path)
+
+    def build_prompt(self, context: PromptContext) -> str:
+        """通过 PromptComposer 拼装 3 个 section。"""
+        composer = PromptComposer()
+        composer.add_many(self.get_sections())
+        return composer.compose(context)
+
+    def get_sections(self) -> List:
+        return [MailContextSection(), MailApiSection(), MailConstraintsSection()]
+
+    def verify_completion(self, task_id: str, db_path: Path) -> VerifyResult:
+        """Mail 完成验证：区分 inform/request。
+
+        - inform: 始终通过（通知已阅即 done，不需要检查产出）
+        - request: 检查是否已回复
+        """
+        performative = self._parse_performative(task_id, db_path)
+
+        if performative == "inform":
+            return VerifyResult(True, "inform_auto", f"performative={performative}")
+
+        # request: 检查是否已回复
+        has_reply = self._check_reply(task_id, db_path)
+        if has_reply:
+            return VerifyResult(True, "has_reply", f"performative={performative}")
+        return VerifyResult(False, "no_reply", f"performative={performative}")
+
+    # post_complete 由基类 BaseTaskHandler 统一处理（crash→verify→mark→notify）
+    # inform: verify 始终通过 → 基类 mark done ✅
+    # request 有回复: verify 通过 → 基类 mark done ✅
+    # request 无回复: verify 失败 → 基类调 on_failure ✅
+
+    def on_failure(self, task_id: str, agent_id: str,
+                   db_path: Path, verify: VerifyResult) -> None:
+        """request 验证失败 → 标 failed + 通知发件人"""
+        self._mark_task_status(db_path, task_id, "failed")
+        logger.info("Mail %s: request verify failed (%s), marked failed",
+                     task_id, verify.reason)
+
+        # 通知发件人
+        try:
+            from src.daemon.mail_notify import notify_mail_failed
+            notify_mail_failed(db_path, task_id, "no_reply_found")
+        except Exception as e:
+            logger.warning("Mail %s: failed to send notification: %s", task_id, e)
+
+    # === 内部方法 ===
+
+    def _parse_performative(self, task_id: str, db_path: Path) -> str:
+        """解析 mail 类型（inform/request）"""
+        try:
+            conn = get_connection(db_path)
+            try:
+                row = conn.execute(
+                    "SELECT must_haves FROM tasks WHERE id=?", (task_id,)
+                ).fetchone()
+                if row and row["must_haves"]:
+                    meta = json.loads(row["must_haves"])
+                    return meta.get("performative", meta.get("type", "request"))
+            finally:
+                conn.close()
+        except Exception:
+            pass
+        return "request"
+
+    def _check_reply(self, task_id: str, db_path: Path) -> bool:
+        """检查是否已回复（从 dispatcher._mail_check_reply 迁移）"""
+        try:
+            conn = get_connection(db_path)
+            try:
+                row = conn.execute(
+                    "SELECT COUNT(*) as cnt FROM comments "
+                    "WHERE task_id=? AND author != 'daemon' "
+                    "AND comment_type != 'system'",
+                    (task_id,)
+                ).fetchone()
+                count = row["cnt"] if row else 0
+                return count > 0
+            finally:
+                conn.close()
+        except Exception as e:
+            logger.error("Mail %s: check reply error: %s", task_id, e)
+            return False
+
+    def check_completion(self, task_id: str, db_path: Path) -> bool:
+        """ticker 级别的完成检查：检查是否已回复"""
+        return self._check_reply(task_id, db_path)
+
+
+# ===================================================================
+# Mail PromptSections
+# ===================================================================
+
+class MailContextSection:
+    """邮件上下文段 — 发件人/收件人/主题/内容，区分 inform/request。"""
+
+    name: str = "mail_context"
+    priority: int = 10
+
+    def render(self, context: PromptContext) -> str:
+        if context.mail_type == "inform":
+            return self._render_inform(context)
+        return self._render_request(context)
+
+    def should_include(self, context: PromptContext) -> bool:  # noqa: ARG002
+        return True
+
+    @staticmethod
+    def _render_inform(context: PromptContext) -> str:
+        return (
+            f"你收到一封飞鸽传书(纯通知)。\n\n"
+            f"发件者: {context.from_agent}\n"
+            f"主题: {context.title}\n"
+            f"内容: {context.description}\n\n"
+            f"已阅即可。如需回复,用 in_reply_to 回复发件者(不需要填 to)。\n"
+            f"⚠️ 不要执行任何状态转换命令。"
+        )
+
+    @staticmethod
+    def _render_request(context: PromptContext) -> str:
+        return (
+            f"你收到一封飞鸽传书,需要你处理并回复。\n\n"
+            f"发件者: {context.from_agent}\n"
+            f"主题: {context.title}\n"
+            f"内容: {context.description}\n\n"
+            f"### 如何回复发件者\n\n"
+            f'curl -s -X POST http://localhost:8083/api/mail \\\n'
+            f"  -H 'Content-Type: application/json' \\\n"
+            f'  -d \'{{"from": "{context.agent_id}", '
+            f'"in_reply_to": "{context.task_id}", '
+            f'"title": "回复: {context.title}", '
+            f'"text": "你的回复内容"}}\'\n\n'
+            f"⚠️ 不需要填 \"to\",系统自动回复给发件者。"
+        )
+
+
+class MailApiSection:
+    """Mail API 操作指令段。"""
+
+    name: str = "mail_api"
+    priority: int = 40
+
+    def render(self, context: PromptContext) -> str:
+        return (
+            f"### 如何给其他人发新邮件\n\n"
+            f'curl -s -X POST http://localhost:8083/api/mail \\\n'
+            f"  -H 'Content-Type: application/json' \\\n"
+            f'  -d \'{{"from": "{context.agent_id}", '
+            f'"to": "对方agent-id", '
+            f'"title": "标题", '
+            f'"text": "正文", '
+            f'"type": "inform"}}\'\n\n'
+            f"⚠️ to 必须是有效的 agent id\n"
+            f"⚠️ 纯通知用 type=inform,需要对方回复不填 type(默认 request)"
+        )
+
+    def should_include(self, context: PromptContext) -> bool:
+        return context.mail_type == "request"
+
+
+class MailConstraintsSection:
+    """Mail 硬约束段。"""
+
+    name: str = "mail_constraints"
+    priority: int = 50
+
+    def render(self, context: PromptContext) -> str:  # noqa: ARG002
+        return (
+            "## 硬约束\n\n"
+            "1. ⚠️ 不要执行任何状态转换命令(标 working/done/review/failed 等),系统会自动处理。\n"
+            "2. ⚠️ 不能给自己发邮件\n"
+            "3. ⚠️ 发邮件时 to 必须是有效的 agent id\n"
+            "4. ⚠️ 纯通知用 type=inform,需要对方回复不填 type(默认 request)"
+        )
+
+    def should_include(self, context: PromptContext) -> bool:  # noqa: ARG002
+        return True