feat(node): push USB changes and preserve sensor setup across sessions

src/k1link/fleet/events.py

@@ -0,0 +1,34 @@
+"""Bounded notifications from the registry writer to local operator streams."""
+
+import asyncio
+import threading
+
+
+class FleetEvents:
+    def __init__(self):
+        self.lock = threading.Lock()
+        self.listeners = set()
+
+    def subscribe(self):
+        loop = asyncio.get_running_loop()
+        queue = asyncio.Queue(maxsize=1)
+
+        def put_latest():
+            if not queue.full():
+                queue.put_nowait(None)
+
+        listener = (loop, put_latest)
+        with self.lock:
+            self.listeners.add(listener)
+
+        def close():
+            with self.lock:
+                self.listeners.discard(listener)
+
+        return queue, close
+
+    def notify(self):
+        with self.lock:
+            for loop, callback in self.listeners:
+                if not loop.is_closed():
+                    loop.call_soon_threadsafe(callback)

src/k1link/fleet/registry.py

@@ -27,6 +27,9 @@ class FleetRegistry:
         self.started_at = time.time()
         self.root = root
         self.lock = threading.RLock()
+        from .events import FleetEvents
+
+        self.events = FleetEvents()
         self.trust = CoreTrust(root)
         path = root / "fleet.sqlite3"
         if path.is_symlink():
@@ -58,6 +61,7 @@ class FleetRegistry:
                 "ON CONFLICT(id) DO UPDATE SET body=excluded.body",
                 (row["id"], row["node_id"], json.dumps(row)),
             )
+        self.events.notify()
 
     def find(self, identifier):
         result = self.db.execute("SELECT body FROM vehicles WHERE id=?", (identifier,)).fetchone()

src/k1link/web/fleet_api.py

@@ -2,11 +2,15 @@
 
 from __future__ import annotations
 
+import asyncio
 import ipaddress
+import json
+from contextlib import suppress
 from typing import Annotated
 from urllib.parse import urlsplit
 
 from fastapi import APIRouter, Depends, HTTPException, Request, Response
+from fastapi.responses import StreamingResponse
 from pydantic import BaseModel, ConfigDict, Field
 
 from k1link.fleet.registry import FleetRegistry
@@ -53,6 +57,31 @@ def fleet_list(response: Response, fleet: Annotated[FleetRegistry, Depends(local
     return fleet.listing()
 
 
+@router.get("/events")
+async def fleet_events(fleet: Annotated[FleetRegistry, Depends(local_operator)]):
+    async def stream():
+        queue, close = fleet.events.subscribe()
+        try:
+            while not fleet.stop.is_set():
+                # Full replacement snapshots recover missed events/reconnections.
+                # The timeout updates link expiry locally; it never queries a Node.
+                value = await asyncio.to_thread(fleet.listing)
+                yield "retry: 3000\ndata: " + json.dumps(value) + "\n\n"
+                with suppress(TimeoutError):
+                    await asyncio.wait_for(queue.get(), timeout=5)
+        finally:
+            close()
+
+    return StreamingResponse(
+        stream(),
+        media_type="text/event-stream",
+        headers={
+            "Cache-Control": "no-store",
+            "X-Accel-Buffering": "no",
+        },
+    )
+
+
 @router.post("/preview")
 def fleet_preview(
     body: PreviewRequest,