fix(media): require successful tool version probes

backend/services/ffmpeg_utils.py

@@ -174,12 +174,12 @@ def _binary_runs(path: str) -> bool:
     if cached is not None:
         return cached
     try:
-        subprocess.run(
+        result = subprocess.run(
             [path, "-version"],
             stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
             timeout=10, check=False,
         )
-        ok = True
+        ok = result.returncode == 0
     except (OSError, subprocess.TimeoutExpired, subprocess.SubprocessError) as e:
         logger.warning(
             "Rejecting non-runnable ffmpeg/ffprobe candidate %s: %s",

tests/backend/services/test_ffmpeg_utils.py

@@ -188,3 +188,23 @@ def test_windows_tool_candidates_derive_from_environment(monkeypatch):
     assert any(p.startswith("E:\\Program Files") for p in got)  # env-derived Program Files
     assert "C:\\ffmpeg\\bin\\ffprobe.exe" in got            # conventional fallbacks kept
     assert "D:\\ffmpeg\\bin\\ffprobe.exe" in got
+
+
+def test_binary_probe_rejects_nonzero_exit(monkeypatch):
+    import sys
+    from services import ffmpeg_utils
+    monkeypatch.setattr(ffmpeg_utils, "_BINARY_OK", {})
+    # Python is portable and executable, but rejects FFmpeg's -version flag.
+    assert not ffmpeg_utils._binary_runs(sys.executable)
+
+
+def test_sibling_probe_rejects_nonzero_exit(monkeypatch, tmp_path):
+    import subprocess
+    from services import ffmpeg_utils
+    ffprobe = tmp_path / "ffprobe"
+    ffprobe.touch()
+    monkeypatch.setattr(ffmpeg_utils, "_BINARY_OK", {})
+    monkeypatch.setattr(ffmpeg_utils, "resolve_ffprobe", lambda: None)
+    monkeypatch.setattr(ffmpeg_utils, "find_ffmpeg", lambda: str(tmp_path / "ffmpeg"))
+    monkeypatch.setattr(ffmpeg_utils.subprocess, "run", lambda *a, **kw: subprocess.CompletedProcess(a, 1))
+    assert ffmpeg_utils.find_ffprobe() is None