feat(agent): unified cross-platform shell execution contract (cmd/bash)

Windows runs 'cmd.exe /d /s /c <command>' as a string command line; Linux uses ['/bin/bash', '-lc', command]. Removes implicit shell=True behavior and aligns the agent system prompt per platform.

core/agent/tools.py

@@ -32,6 +32,7 @@ from typing import Any, Callable, Dict, List, Optional
 
 from .types import (AgentMessage, AgentTool, AgentToolResult, AbortSignal,
                     ToolCall, new_id)
+from ..platform_shell import kill_process_tree, popen_flags, shell_command  # P1-02
 
 try:
     from core.debug_log import debug_log as _dbg_log  # 🆕 计时观察日志（线程安全/静默）
@@ -448,8 +449,8 @@ def tool_bash(tool_call_id: str, args: Dict[str, Any], signal: AbortSignal,
         return AgentToolResult.text("command 不能为空", is_error=True)
     timeout = min(float(args.get("timeout", 120)), 600)
     cwd = ctx.get("cwd") or os.getcwd()
-    # 对照 pi bash 工具：命令始终经 shell 解释（支持管道/别名/内置命令）
-    use_shell = ctx.get("shell", True)
+    # P1-02：显式 shell 契约（Windows cmd.exe /d /c；Linux /bin/bash -lc），
+    # 不再依赖 shell=True 的平台默认值；ctx 的 "shell" 键已废弃（bash 工具即 shell 工具）
     on_timer = ctx.get("on_timer")
     t0 = time.time()
     # 🆕 计时观察①：计时器启动时刻 + 模型实际传的 timeout 值
@@ -466,19 +467,9 @@ def tool_bash(tool_call_id: str, args: Dict[str, Any], signal: AbortSignal,
             pass
 
     def _kill_tree(proc):
-        """杀整个进程树：Windows 上默认 kill 只杀 cmd 壳，孤儿子进程继续
-        持管道 → 假超时（设定10s 实际20s）。taskkill /T 整树杀。"""
-        try:
-            if os.name == "nt":
-                subprocess.run(["taskkill", "/F", "/T", "/PID", str(proc.pid)],
-                               capture_output=True, timeout=10)
-            else:
-                proc.kill()
-        except Exception:
-            try:
-                proc.kill()
-            except Exception:
-                pass
+        """杀整个进程树：Windows taskkill /F /T；Linux 独立进程组
+        SIGTERM → 宽限 → SIGKILL（见 core.platform_shell.kill_process_tree）。"""
+        kill_process_tree(proc)
 
     # 🐛 修复：text=True 不带 encoding 时按系统码页（中文 Windows=GBK）解码，
     # 子进程输出 UTF-8（python/git/中文 echo）→ _readerthread UnicodeDecodeError。
@@ -486,10 +477,11 @@ def tool_bash(tool_call_id: str, args: Dict[str, Any], signal: AbortSignal,
     _env = dict(os.environ, PYTHONIOENCODING="utf-8")
     try:
         proc = subprocess.Popen(
-            command, shell=use_shell,
+            shell_command(command),  # P1-02：显式 shell 命令
             stdout=subprocess.PIPE, stderr=subprocess.PIPE,
             text=True, encoding="utf-8", errors="replace",
             cwd=cwd, env=_env,
+            **popen_flags(),  # P1-02：Linux 独立进程组（start_new_session）
         )
     except Exception as e:
         return AgentToolResult.text(f"执行失败: {e}", is_error=True)