Codebase review fixes: stability, performance, quality improvements

Stability: Add outer try/except/finally with _running=False cleanup to all 6
processing loop methods (live, color_strip, effect, audio, composite, mapped).
Add exponential backoff on consecutive capture errors in live_stream. Move
audio stream.stop() outside lock scope.

Performance: Replace per-pixel Python loop with np.array().tobytes() in
ddp_client. Vectorize pixelate filter with cv2.resize down+up. Vectorize
gradient rendering with np.searchsorted.

Frontend: Add lockBody/unlockBody re-entrancy counter. Add {once:true} to
fetchWithAuth abort listener. Null ws.onclose before ws.close() in LED preview.

Backend: Remove auth token prefix from log messages. Add atomic_write_json
helper (tempfile + os.replace) and update all 10 stores. Add name uniqueness
checks to all update methods. Fix DELETE status codes to 204 in audio_sources
and value_sources. Fix get_source() silent bug in color_strip_sources.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/utils/__init__.py

@@ -1,7 +1,8 @@
 """Utility functions and helpers."""
 
+from .file_ops import atomic_write_json
 from .logger import setup_logging, get_logger
 from .monitor_names import get_monitor_names, get_monitor_name, get_monitor_refresh_rates
 from .timer import high_resolution_timer
 
-__all__ = ["setup_logging", "get_logger", "get_monitor_names", "get_monitor_name", "get_monitor_refresh_rates", "high_resolution_timer"]
+__all__ = ["atomic_write_json", "setup_logging", "get_logger", "get_monitor_names", "get_monitor_name", "get_monitor_refresh_rates", "high_resolution_timer"]

server/src/wled_controller/utils/file_ops.py

@@ -0,0 +1,34 @@
+"""Atomic file write utilities."""
+
+import json
+import os
+import tempfile
+from pathlib import Path
+
+
+def atomic_write_json(file_path: Path, data: dict, indent: int = 2) -> None:
+    """Write JSON data to file atomically via temp file + rename.
+
+    Prevents data corruption if the process crashes or loses power
+    mid-write. The rename operation is atomic on most filesystems.
+    """
+    file_path = Path(file_path)
+    file_path.parent.mkdir(parents=True, exist_ok=True)
+
+    # Write to a temp file in the same directory (same filesystem for atomic rename)
+    fd, tmp_path = tempfile.mkstemp(
+        dir=file_path.parent,
+        prefix=f".{file_path.stem}_",
+        suffix=".tmp",
+    )
+    try:
+        with os.fdopen(fd, "w", encoding="utf-8") as f:
+            json.dump(data, f, indent=indent, ensure_ascii=False)
+        os.replace(tmp_path, file_path)
+    except BaseException:
+        # Clean up temp file on any error
+        try:
+            os.unlink(tmp_path)
+        except OSError:
+            pass
+        raise