fix(chv): execd 单元 KillMode=process（构建 #6 驱动实证）

缺 KillMode 时 systemd 默认 control-group，kill -9 execd 主进程
后重启会 SIGTERM 整个 cgroup，sleep 任务同 pid 存活的要求被破、
新 execd 认领时 pid 已死记 unknown，驱动 kill 相断言失败。
KillMode=process 只信号主进程，任务在重启后同 pid 存活认领；
stop 仍干净停 daemon 本身。回归测试
BuildWiringTest.test_build_sh_execd_unit_keeps_tasks_on_restart。

chv-guest/build.sh

@@ -325,7 +325,14 @@ VC_ARGS=(-a "$OUT/disk.raw"
   --run-command 'printf "[Unit]\nDescription=CHV cell broker (Muse P2)\nAfter=network.target\n\n[Service]\nType=simple\nExecStart=/usr/bin/python3 /usr/local/bin/chv-broker\nRestart=on-failure\nRestartSec=2\n\n[Install]\nWantedBy=multi-user.target\n" > /etc/systemd/system/chv-broker.service'
   --run-command 'printf "[Unit]\nDescription=CHV browser sub-agent (Muse P2)\nAfter=network.target\n\n[Service]\nType=simple\nUser=chv-browser\nGroup=chv-browser\nExecStart=/usr/bin/python3 /usr/local/bin/chv-browser\nRestart=on-failure\nRestartSec=2\n\n[Install]\nWantedBy=multi-user.target\n" > /etc/systemd/system/chv-browser.service'
   --run-command 'printf "[Unit]\nDescription=CHV guest runtime daemon (stage 2: heartbeat/resources/snapshot)\nAfter=network.target\n\n[Service]\nType=simple\nExecStart=/usr/bin/python3 /usr/local/bin/chv-daemon\nRestart=always\nRestartSec=2\n\n[Install]\nWantedBy=multi-user.target\n" > /etc/systemd/system/chv-daemon.service'
-  --run-command 'printf "[Unit]\nDescription=CHV guest exec daemon (stage 2: shell/files/codex hosting)\nAfter=network.target\n\n[Service]\nType=simple\nExecStart=/usr/bin/python3 /usr/local/bin/chv-execd\nRestart=always\nRestartSec=2\n\n[Install]\nWantedBy=multi-user.target\n" > /etc/systemd/system/chv-execd.service'
+  # 构建 #6 驱动实证（2026-11-08）：execd 单元缺 KillMode 时默认
+  # control-group，kill -9 主进程后 systemd 重启会 SIGTERM 整个
+  # cgroup，sleep 任务（同 pid 应存活）被连带杀死，新 execd 认领
+  # 时 pid 已死、记 unknown，驱动 kill 相断言失败。KillMode=process
+  # 只信号主进程，任务在 execd 重启后同 pid 存活、按登记认领；
+  # systemctl stop 仍干净停掉 daemon 本身，任务以孤儿存活、下次
+  # 启动再按 pid 认领（登记落盘 /run/chv/execd-tasks.json）。
+  --run-command 'printf "[Unit]\nDescription=CHV guest exec daemon (stage 2: shell/files/codex hosting)\nAfter=network.target\n\n[Service]\nType=simple\nExecStart=/usr/bin/python3 /usr/local/bin/chv-execd\nRestart=always\nRestartSec=2\nKillMode=process\n\n[Install]\nWantedBy=multi-user.target\n" > /etc/systemd/system/chv-execd.service'
   --run-command 'printf "[Unit]\nDescription=CHV Gitea sync daemon (stage 2: resident pull/push loop)\nAfter=network.target\n\n[Service]\nType=simple\nUser=chv\nGroup=chv\nRuntimeDirectory=chv-syncd\nRuntimeDirectoryMode=0755\nExecStart=/usr/bin/python3 /usr/local/bin/chv-syncd\nRestart=always\nRestartSec=2\n\n[Install]\nWantedBy=multi-user.target\n" > /etc/systemd/system/chv-syncd.service'
   --run-command 'printf "d /run/chv 0755 root root -\nd /run/chv/shots 0755 chv-browser chv-browser -\nd /run/chv/tasks 0755 root root -\n" > /etc/tmpfiles.d/chv.conf && systemctl enable chv-broker chv-browser chv-daemon chv-execd chv-syncd || true')
 # P1 交接（Muse P1 的 vsock_notify.py）：文件在仓库里存在时拷入

cloud/tests/test_chv_opt_stage2.py

@@ -451,6 +451,25 @@ class BuildWiringTest(unittest.TestCase):
             'stat -c %a /etc/systemd/network/79-chv-cell.network',
             text)
 
+    def test_build_sh_execd_unit_keeps_tasks_on_restart(self):
+        # 构建 #6 驱动实证：缺 KillMode 时 systemd 重启会杀整个
+        # cgroup，sleep 任务同 pid 存活的要求被破。execd 单元须
+        # KillMode=process；daemon/syncd 无长活子进程，不动。
+        with open(_repo("chv-guest", "build.sh")) as fh:
+            text = fh.read()
+        execd = next(
+            line for line in text.splitlines()
+            if "chv-execd.service" in line
+            and "Description=CHV guest exec daemon" in line)
+        self.assertIn("KillMode=process", execd)
+        self.assertEqual(execd.count("KillMode=process"), 1)
+        for svc in ("chv-daemon", "chv-syncd"):
+            block = next(
+                line for line in text.splitlines()
+                if "%s.service" % svc in line
+                and "Description=" in line)
+            self.assertNotIn("KillMode", block)
+
     def test_lockfile_and_buildinfo_declare_services(self):
         spec = importlib.util.spec_from_file_location(
             "stage2_buildinfo",