add session ID handling to worker communication protocol; allow backend to associate session IDs with subscriptions

worker.md

@@ -255,6 +255,27 @@ Backend's response to a `patchSession` message.
 }
 ```
 
+### 5.5. Set Session ID
+
+Allows the backend to instruct the worker to associate a session ID with a subscription. This is useful for linking detection events to a specific session.
+
+- **Type:** `setSessionId`
+
+**Payload:**
+
+```json
+{
+  "type": "setSessionId",
+  "payload": {
+    "subscriptionIdentifier": "display-001;cam-002",
+    "sessionId": 12345
+  }
+}
+```
+
+> **Note:**
+> - The worker should store the session ID for the given subscription and use it in subsequent detection or patch messages as appropriate.
+
 ## 6. Example Communication Log
 
 This section shows a typical sequence of messages between the backend and the worker. Patch messages are not included, as they are only used when the worker cannot keep up.