refactor(plugins): the display publishes plugin runtime state; retire plugin_state.json (#690)

Stage 2 of the web plugin catalog, after #688.

- The display publishes a plugin runtime snapshot (plugin_runtime.py) to
  the shared cache: per plugin loaded, lifecycle state, a short redacted
  error summary, the version it loaded and when, plus published_at /
  stale_after / running. Written on change (throttled to 10 s; the
  RUNNING/ENABLED flip of an ordinary update is not a change) and once a
  minute otherwise; cleanup() publishes running: false.
- The web reads it back and restores loaded / state / error_info in
  /api/v3/plugins/installed (plus loaded_version, loaded_at and
  data.runtime). Only a live snapshot counts; stale, stopped or missing
  answers null and says which.
- data/plugin_state.json is retired: every reader and writer moved to
  config + disk (desired) or the snapshot (observed). Nothing in it was
  non-derivable, so nothing is migrated and an existing file is left
  unread. The web-side PluginStateManager (state_manager.py) is removed;
  the display's plugin_state.PluginStateManager is the only state machine.
- StateReconciliation compares config + disk with the snapshot, reporting
  enabled-but-not-loaded and older-version-loaded as no_action findings.
- Backups list installed manifests with enabled from config.json.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/display_controller.py

@@ -218,6 +218,7 @@ class DisplayController:
         # Initialize Plugin System
         plugin_time = time.time()
         self.plugin_manager = None
+        self._plugin_runtime_publisher = None
         self.plugin_modes = {}  # mode -> plugin_instance mapping for plugin-first dispatch
         self.mode_to_plugin_id: Dict[str, str] = {}
         self.plugin_display_modes: Dict[str, List[str]] = {}
@@ -322,6 +323,13 @@ class DisplayController:
                 font_manager=self.font_manager
             )
 
+            # The web UI's loaded / state / error_info for each plugin read
+            # what this publishes. Started before loading, so the loads that
+            # follow are published as they land.
+            from src.plugin_system.plugin_runtime import start_plugin_runtime_publisher
+            self._plugin_runtime_publisher = start_plugin_runtime_publisher(
+                self.cache_manager, self.plugin_manager.state_manager)
+
             # Activate the plugin health/metrics subsystem. PluginManager leaves
             # health_tracker/resource_monitor as None by default; wiring real
             # instances here turns on the circuit breaker (a repeatedly-failing
@@ -452,6 +460,12 @@ class DisplayController:
         except Exception:  # pylint: disable=broad-except
             logger.exception("Plugin system initialization failed")
             self.plugin_manager = None
+            # Its state machine no longer describes what runs; let the last
+            # snapshot go stale (readers then say unknown) rather than keep
+            # refreshing it.
+            if self._plugin_runtime_publisher is not None:
+                self._plugin_runtime_publisher.stop(publish_stopped=False)
+                self._plugin_runtime_publisher = None
 
         # The web UI's Fonts tab ("Used by") reads what this publishes.
         from src.font_usage import start_font_usage_publisher
@@ -3641,6 +3655,12 @@ class DisplayController:
                 logger.warning("Error shutting down config service: %s", e)
         if getattr(self, '_font_usage_publisher', None) is not None:
             self._font_usage_publisher.stop()
+        # Publishes "stopped", so the web UI stops reporting what was loaded.
+        if getattr(self, '_plugin_runtime_publisher', None) is not None:
+            try:
+                self._plugin_runtime_publisher.stop()
+            except Exception as e:
+                logger.warning("Error stopping the plugin runtime publisher: %s", e)
         logger.info("Cleaning up display controller...")
         if hasattr(self, 'display_manager'):
             self.display_manager.cleanup()