first commit

backend/services/ws_manager.py

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+import json
+import logging
+from fastapi import WebSocket
+
+logger = logging.getLogger(__name__)
+
+
+class ConnectionManager:
+    def __init__(self) -> None:
+        self._connections: set[WebSocket] = set()
+
+    async def connect(self, ws: WebSocket) -> None:
+        await ws.accept()
+        self._connections.add(ws)
+        logger.info(f"WS client connected. Total: {len(self._connections)}")
+
+    def disconnect(self, ws: WebSocket) -> None:
+        self._connections.discard(ws)
+        logger.info(f"WS client disconnected. Total: {len(self._connections)}")
+
+    async def broadcast(self, data: dict) -> None:
+        if not self._connections:
+            return
+        message = json.dumps(data, default=str)
+        dead: set[WebSocket] = set()
+        for ws in self._connections:
+            try:
+                await ws.send_text(message)
+            except Exception:
+                dead.add(ws)
+        self._connections -= dead
+
+
+# Singleton — imported by both the MQTT subscriber and the WS route
+manager = ConnectionManager()