fix(display): Vegas resumes after live priority, and six smaller runtime fixes (#644)

- Vegas: a live-priority pause was only lifted from inside run_frame(),
  which returns before that check while paused, so the ticker never came
  back until a restart. run_iteration() now resumes it (the controller
  only calls it when nothing preempts Vegas); start()/stop() clear the
  pause state. Iteration length is timed with the monotonic clock.
- Dim schedule: a per-day disabled day now updates the minute-gate cache,
  so brightness no longer flips back to dim within each minute.
- On-demand: a second request no longer overwrites the rotation resume
  index with the first request's mode.
- Render pipeline: reset() drops the prepared group and deferred queue,
  and a prefetch in flight across a reset discards its result.
- Sync: stop() removes the status file (and the controller's cleanup now
  calls it), standalone removes a stale one at startup, and writes use a
  unique mkstemp temp file.
- render_gate.swap_releases_gil() delegates to frame_timing.
- Stale docstrings/comments corrected.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/display_controller.py

@@ -284,7 +284,10 @@ class DisplayController:
             if os.path.isabs(plugins_dir_name):
                 plugins_dir = plugins_dir_name
             else:
-                # If relative, resolve relative to the project root (LEDMatrix directory)
+                # If relative, resolve against the current working directory.
+                # That is the project root only because ledmatrix.service
+                # sets WorkingDirectory to it; run from anywhere else, a
+                # relative path resolves against wherever that is.
                 project_root = os.getcwd()
                 plugins_dir = os.path.join(project_root, plugins_dir_name)
             
@@ -801,7 +804,15 @@ class DisplayController:
         if use_per_day:
             day_config = days_config[current_day]
             if not day_config.get('enabled', True):
+                # Past the minute gate, so the cache must say the same thing:
+                # returning here without it left the previous minute's dim
+                # value to be served for the rest of this one, and the
+                # brightness flipped between dim and normal every minute.
+                if self._was_dimmed:
+                    logger.info(f"Dim schedule deactivated: brightness restored to {normal_brightness}%")
                 self.is_dimmed = False
+                self._was_dimmed = False
+                self._cached_target_brightness = normal_brightness  # persist for minute-gate
                 return normal_brightness
             start_time_str = day_config.get('start_time', '20:00')
             end_time_str = day_config.get('end_time', '07:00')
@@ -1710,10 +1721,16 @@ class DisplayController:
         pinned = bool(request.get('pinned', False))
         now = time.time()
 
-        if self.available_modes:
-            self.rotation_resume_index = self.current_mode_index
-        else:
-            self.rotation_resume_index = None
+        # Only a request that starts a session records where rotation was.
+        # A request made while on-demand is already showing would otherwise
+        # save the previous request's mode (current_mode_index points at it
+        # by now), and clearing would resume there instead of where the
+        # normal rotation was interrupted.
+        if not self.on_demand_active:
+            if self.available_modes:
+                self.rotation_resume_index = self.current_mode_index
+            else:
+                self.rotation_resume_index = None
 
         if resolved_mode in self.available_modes:
             self.current_mode_index = self.available_modes.index(resolved_mode)
@@ -3310,6 +3327,13 @@ class DisplayController:
                 self.vegas_coordinator.cleanup()
             except Exception as e:
                 logger.warning("Error cleaning up Vegas mode: %s", e)
+        # After Vegas, which sends through it. Stopping also withdraws the
+        # sync status file, which the web UI otherwise kept showing as live.
+        if getattr(self, 'sync_manager', None) is not None:
+            try:
+                self.sync_manager.stop()
+            except Exception as e:
+                logger.warning("Error stopping display sync: %s", e)
         # Shutdown config service if it exists
         if hasattr(self, 'config_service'):
             try: