diff --git a/scripts/test_public_runtime_watchdog_provenance.py b/scripts/test_public_runtime_watchdog_provenance.py
index fb98ad6..86dee61 100644
--- a/scripts/test_public_runtime_watchdog_provenance.py
+++ b/scripts/test_public_runtime_watchdog_provenance.py
@@ -182,6 +182,61 @@ $local = [pscustomobject]@{
 if (-not (Test-VoiceApiReady -Health $local)) { throw 'exact local API was rejected' }
 $local.limits.uvicorn_ws_max_queue = 5
 if (Test-VoiceApiReady -Health $local) { throw 'wrong websocket queue was accepted' }
+''',
+                encoding="utf-8-sig",
+            )
+            completed = subprocess.run(
+                [
+                    powershell,
+                    "-NoLogo",
+                    "-NoProfile",
+                    "-NonInteractive",
+                    "-ExecutionPolicy",
+                    "Bypass",
+                    "-File",
+                    str(harness),
+                ],
+                capture_output=True,
+                text=True,
+                encoding="utf-8",
+                errors="replace",
+                timeout=30,
+                check=False,
+            )
+            self.assertEqual(
+                completed.returncode,
+                0,
+                msg=f"stdout={completed.stdout}\nstderr={completed.stderr}",
+            )
+
+    def test_failed_native_sidecar_probe_returns_unhealthy_under_powershell_51(self) -> None:
+        powershell = shutil.which("powershell.exe")
+        python = shutil.which("python.exe")
+        if powershell is None or python is None:
+            self.skipTest("Windows PowerShell 5.1 and Python are required")
+
+        watchdog_contract = WATCHDOG_SOURCE[
+            WATCHDOG_SOURCE.index("function Test-VoiceSidecarStack") :
+            WATCHDOG_SOURCE.index("function Test-CloudflaredProcess")
+        ].strip()
+
+        with tempfile.TemporaryDirectory() as temporary_directory:
+            harness = Path(temporary_directory) / "voice-sidecar-failure-contract.ps1"
+            python_escaped = python.replace("'", "''")
+            probe_escaped = str(VOICE_PROBE).replace("'", "''")
+            harness.write_text(
+                "$ErrorActionPreference = 'Stop'\n"
+                + f"$Python = '{python_escaped}'\n"
+                + f"$voiceSidecarProbe = '{probe_escaped}'\n"
+                + "$WhisperPort = 1\n"
+                + "$MeloTtsPort = 2\n"
+                + watchdog_contract
+                + r'''
+$result = Test-VoiceSidecarStack
+if ($result.Ok) { throw 'unreachable sidecars were accepted' }
+if ($result.Detail -ne 'exact readiness probe failed') {
+  throw "unexpected detail: $($result.Detail)"
+}
 ''',
                 encoding="utf-8-sig",
             )
diff --git a/scripts/watch-public-runtime.ps1 b/scripts/watch-public-runtime.ps1
index 48e2a70..6513125 100644
--- a/scripts/watch-public-runtime.ps1
+++ b/scripts/watch-public-runtime.ps1
@@ -242,8 +242,17 @@ function Test-VoiceSidecarStack {
     "--tts-language", "KR",
     "--timeout-seconds", "5"
   )
-  $output = @(& $Python @probeArgs 2>$null)
-  $probeExit = $LASTEXITCODE
+  # Windows PowerShell 5.1은 native stderr를 ErrorRecord로 승격한다. 스크립트
+  # 전역의 Stop 정책을 그대로 두면 sidecar 장애를 복구 신호로 반환하기 전에
+  # NativeCommandError로 종료하므로, 이 단일 probe 경계에서만 Continue로 낮춘다.
+  $previousErrorActionPreference = $ErrorActionPreference
+  try {
+    $ErrorActionPreference = "Continue"
+    $output = @(& $Python @probeArgs 2>$null)
+    $probeExit = $LASTEXITCODE
+  } finally {
+    $ErrorActionPreference = $previousErrorActionPreference
+  }
   return [pscustomobject]@{
     Name = "voice-sidecars"
     Ok = $probeExit -eq 0