fix: address 2 new review comments and CI mypy failures on PR #20

Two new review comments arrived after the previous round. This commit
addresses both plus the CI mypy failure they exposed.

CodeRabbit Major (comment #36) — race in _ensure_jobs initialization:
- plexmuxy_gui/api.py: pywebview runs exposed js_api methods on separate
  threads, so the lazy first-access path in _ensure_jobs could create
  duplicate JobStore/JobQueue instances over the same state store. Added a
  threading.Lock (_jobs_lock) to __init__ and wrapped the lazy
  initialization so concurrent callers cannot double-initialize.

CodeRabbit Minor (comment #37) — gate _embed_ass_subtitles on format:
- plexmuxy/muxer.py: scanner.py forwards configured subtitle_extensions
  unchanged and the default config includes .ssa, so non-ASS inputs can
  reach _embed_ass_subtitles. Added _ASS_SUBTITLE_SUFFIXES = {'.ass',
  '.ssa'} and skip tracks whose suffix is not ASS/SSA compatible, leaving
  them for normal muxing instead of passing them to embed_fonts_into_ass.

CI mypy failure (exposed by the earlier os.startfile change):
- plexmuxy_gui/api.py: os.startfile is Windows-only and absent from the
  Linux CI type stubs. Kept the direct os.startfile(path) call inside the
  sys.platform == 'win32' guard with '# type: ignore[attr-defined]'.
  Verified with 'mypy --platform linux' (Success) since the ignore is
  required and consumed on the Linux CI where os.startfile does not exist
  in the stubs.

All 341 non-integration tests pass; ruff and mypy (Linux platform) report
no issues.

Author: Masterain98

plexmuxy/muxer.py

@@ -86,6 +86,12 @@ def _embed_ass_subtitles(
         if not track.path or not track.path.exists():
             produced.append(None)
             continue
+        if track.path.suffix.lower() not in _ASS_SUBTITLE_SUFFIXES:
+            # Only ASS/SSA formats support the embedded [Fonts] section; skip
+            # incompatible subtitle tracks (e.g. .srt, .sub, .smi) so they are
+            # left untouched for normal muxing.
+            produced.append(None)
+            continue
         suffix = f".embedded.{index}.ass" if multi else ".embedded.ass"
         out = parent / f"{stem}{suffix}"
         try:
@@ -147,6 +153,11 @@ def execute_prepared_mux_plan(
     ".ttf", ".otf", ".ttc", ".otc", ".woff", ".woff2",
 })
 
+# Subtitle formats that share the ASS/SSA ``[Fonts]`` section syntax and can
+# receive embedded fonts. Other formats (e.g. .srt, .sub) are not compatible
+# with embed_fonts_into_ass and must be skipped during ASS embedding.
+_ASS_SUBTITLE_SUFFIXES = frozenset({".ass", ".ssa"})
+
 
 def _execute_runtime_plan(
     original_plan: MuxPlan,

plexmuxy_gui/api.py

@@ -190,6 +190,7 @@ def __init__(
         self._state_path = state_path
         self._job_store: JobStore | None = None
         self._job_queue: JobQueue | None = None
+        self._jobs_lock = threading.Lock()
         self._preview = AudioPreviewManager(preview_root)
         self._active_plan_ids: dict[Path, str] = {}
         self._last_diagnostics_path: Path | None = None
@@ -1107,11 +1108,15 @@ def run() -> dict[str, Any]:
         return self.guarded(run)
 
     def _ensure_jobs(self) -> tuple[JobStore, JobQueue]:
-        if self._job_store is None:
-            self._job_store = JobStore(self._state_path or platform_state_path())
-        if self._job_queue is None:
-            self._job_queue = JobQueue(self._job_store, terminal_callback=self._notify_job_terminal)
-        return self._job_store, self._job_queue
+        # pywebview exposed methods run on separate threads, so the lazy
+        # first-access path must be guarded to avoid creating duplicate
+        # JobStore/JobQueue instances over the same state store.
+        with self._jobs_lock:
+            if self._job_store is None:
+                self._job_store = JobStore(self._state_path or platform_state_path())
+            if self._job_queue is None:
+                self._job_queue = JobQueue(self._job_store, terminal_callback=self._notify_job_terminal)
+            return self._job_store, self._job_queue
 
     def _request_context(self, payload: dict[str, Any]):
         if not isinstance(payload, dict):
@@ -1376,8 +1381,11 @@ def requires_delete_confirmation(config) -> bool:
 
 
 def open_path(path: Path) -> None:
-    if os.name == "nt":
-        os.startfile(path)
+    if sys.platform == "win32":
+        # os.startfile is a Windows-only API; the guard above ensures this
+        # branch only executes on Windows. The ignore is required because the
+        # Linux CI type stubs have no os.startfile attribute.
+        os.startfile(path)  # type: ignore[attr-defined]
         return
     if sys.platform == "darwin":
         subprocess.Popen(["open", str(path)])