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>

web_interface/blueprints/api_v3/plugins.py

@@ -47,10 +47,13 @@ def get_installed_plugins():
     """Get installed plugins.
 
     Metadata comes from the plugin catalog (manifests on disk), ``enabled``
-    from config.json. ``loaded``, ``state`` and ``error_info`` are always
-    null: they would describe the display process's plugin instances, and
-    the display does not publish which plugins it has loaded. What it does
-    publish -- health, metrics, errors -- is served by /plugins/health,
+    from config.json. ``loaded``, ``state``, ``error_info``,
+    ``loaded_version`` and ``loaded_at`` come from the runtime snapshot the
+    display publishes (src/plugin_system/plugin_runtime.py), and only while
+    that snapshot is live: when the display is stopped, hung or has never
+    published, they are null and ``data.runtime.status`` says why
+    (``stale``, ``stopped``, ``unknown``) instead of passing on old truth.
+    Health, metrics and errors are served by /plugins/health,
     /plugins/metrics and /errors.
     """
     if not api_v3.plugin_catalog or not api_v3.plugin_store_manager:
@@ -65,6 +68,8 @@ def get_installed_plugins():
 
     # Load config once before the loop (not per-plugin)
     full_config = api_v3.config_manager.load_config() if api_v3.config_manager else {}
+    # One read of the display's snapshot for the whole listing.
+    runtime = _pkg._plugin_runtime_view()
 
     def _build_plugin_entry(plugin_info):
         plugin_id = plugin_info.get('id')
@@ -154,10 +159,9 @@ def get_installed_plugins():
             'icon': plugin_info.get('icon') if isinstance(plugin_info.get('icon'), str) else None,
             'enabled': enabled,
             'verified': verified,
-            # Not published by the display process; see the docstring.
-            'loaded': None,
-            'state': None,
-            'error_info': None,
+            # loaded, state, error_info, loaded_version, loaded_at: the
+            # display's snapshot, null unless it is live (see the docstring).
+            **runtime.plugin(plugin_id),
             'last_updated': last_updated,
             'last_commit': last_commit,
             'last_commit_message': last_commit_message,
@@ -175,7 +179,8 @@ def get_installed_plugins():
     plugins = [r for r in results if r is not None]
     plugins.extend(_starlark_virtual_plugins())
 
-    return jsonify({'status': 'success', 'data': {'plugins': plugins}})
+    return jsonify({'status': 'success', 'data': {'plugins': plugins,
+                                                  'runtime': runtime.describe()}})
 
 
 @api_v3.route('/plugins/toggle', methods=['POST'])
@@ -247,10 +252,6 @@ def toggle_plugin():
                 status_code=500
             )
 
-        # Update state manager if available
-        if api_v3.plugin_state_manager:
-            api_v3.plugin_state_manager.set_plugin_enabled(plugin_id, enabled)
-
         # Log operation
         if api_v3.operation_history:
             api_v3.operation_history.record_operation(