修看门狗日志编码：*>> 在 PS5.1 默认写 UTF-16LE，污染同一个日志文件

现场（2026-10-12 注册计划任务后实测）：runner-stdout.log 尾部按 UTF-8 读出来
是 "t i m e =   2 0 2 6 - 1 0 - 1 2 ..."，即每个字节后面跟一个 NUL。

根因正是我自己刚写进文档的那条坑：PS 5.1 的 *>> 重定向由 Out-File 实现，而
Out-File 的默认编码是 UTF-16LE。同一个文件里 Log() 用 Add-Content -Encoding
ascii 写 ASCII 行、daemon 输出却以 UTF-16LE 追加，于是"一个文件两种编码"，
排障时按 UTF-8 读就是乱码——等于把唯一的 runner 现场日志弄成不可读。

- daemon 输出改到独立文件 runner-daemon.log，显式 Out-File -Encoding utf8
  （不用 ascii：提交标题与作业输出可能含非 ASCII，ascii 会打成问号）
- 看门狗自身日志改名 runner-watchdog.log，与 daemon 输出彻底分离
- 模板与生成物均校验通过：parseErrors=0、nonASCII=0
- 旧 runner-stdout.log 保留作历史，不再写入

scripts/ci_runner_bootstrap.ps1

@@ -338,7 +338,8 @@ $runnerDir   = '__RUNNER_DIR__'
 $runnerExe   = Join-Path $runnerDir 'gitea-runner.exe'
 $runnerCfg   = Join-Path $runnerDir 'config.yaml'
 $logDir      = Join-Path $runnerDir 'log'
-$log         = Join-Path $logDir 'runner-stdout.log'
+$log         = Join-Path $logDir 'runner-watchdog.log'
+$daemonLog   = Join-Path $logDir 'runner-daemon.log'
 $probeUrl    = '__GITEA_URL__/api/v1/version'
 $maxWaitSec  = 1800
 
@@ -371,7 +372,15 @@ while ($true) {
     }
 
     Log 'starting daemon'
-    & $runnerExe daemon --config $runnerCfg *>> $log
+    # MEASURED TRAP (2026-10-12, hit by this very script): in PowerShell 5.1 the
+    # *>> redirection is implemented with Out-File, whose DEFAULT ENCODING IS
+    # UTF-16LE. Appending that into a file whose other lines come from
+    # Add-Content -Encoding ascii leaves ONE FILE WITH TWO ENCODINGS, and the
+    # daemon lines read back as "t i m e = 2 0 2 6 ..." (a NUL after every byte).
+    # Never rely on a redirection's default encoding -- state it explicitly.
+    # utf8 (not ascii) because job/commit text can legitimately be non-ASCII.
+    & $runnerExe daemon --config $runnerCfg 2>&1 |
+        Out-File -FilePath $daemonLog -Append -Encoding utf8
     Log ("daemon exited, exit code {0}; restarting in 10s" -f $LASTEXITCODE)
     Start-Sleep -Seconds 10
 }
@@ -415,7 +424,8 @@ if ($StartNow) {
         Warn "Gitea is not answering at $GiteaUrl right now -- the watchdog will keep waiting"
     }
     Start-ScheduledTask -TaskName $TaskName
-    Ok "task started; watch: Get-Content '$(Join-Path $RunnerDir 'log\runner-stdout.log')' -Tail 20"
+    Ok "task started; daemon log: Get-Content '$(Join-Path $RunnerDir 'log\runner-daemon.log')' -Tail 20"
+    Ok "watchdog log: Get-Content '$(Join-Path $RunnerDir 'log\runner-watchdog.log')' -Tail 20"
     Info 'verify on the web UI: repo -> Settings -> Actions -> Runners -> win-stm32-ci should turn Idle'
 }