Guard lookups when adding/deleting cameras at runtime (#23994)

* Guard object processor queue handlers against unknown cameras

* Skip embeddings post processing for removed cameras

* End review segments for removed cameras

* Drop queued autotracker moves for removed cameras

* Release tracked event thumbnails when skipping a removed camera

* Add locked accessors for camera states

* Read camera states through the processor accessors

* Guard output and recording paths against cameras not yet known

* Resolve camera state once in ONVIF, notification, and transcription paths

frigate/embeddings/maintainer.py

@@ -609,6 +609,18 @@ class EmbeddingMaintainer(threading.Thread):
                 # Embed the thumbnail
                 self._embed_thumbnail(event_id, thumbnail)
 
+            # every post processor below reads config.cameras[camera], but
+            # tracked_events still has to be released or the thumbnails held
+            # for this event leak, same as the two exits above
+            if camera not in self.config.cameras:
+                logger.debug("Skipping post processing for removed camera %s", camera)
+
+                for processor in self.post_processors:
+                    if isinstance(processor, ObjectDescriptionProcessor):
+                        processor.cleanup_event(event_id)
+
+                continue
+
             # call any defined post processors
             for processor in self.post_processors:
                 if isinstance(processor, LicensePlatePostProcessor):
@@ -666,11 +678,18 @@ class EmbeddingMaintainer(threading.Thread):
         to_remove = []
 
         for id, data in self.detected_license_plates.items():
+            camera_config = self.config.cameras.get(data["camera"])
+
+            if camera_config is None:
+                # camera was removed, drop the entry rather than expiring it
+                to_remove.append(id)
+                continue
+
             last_seen = data.get("last_seen", 0)
             if not last_seen:
                 continue
 
-            if now - last_seen > self.config.cameras[data["camera"]].lpr.expire_time:
+            if now - last_seen > camera_config.lpr.expire_time:
                 to_remove.append(id)
         for id in to_remove:
             self.event_metadata_publisher.publish(