Host signals can_up, can_bus_state, can_rx_fps: the recorder's CAN interface

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

schema/signals.json

@@ -311,6 +311,28 @@
         480000
       ]
     },
+    "can_up": {
+      "unit": "",
+      "type": "boolean",
+      "source": "host",
+      "description": "The recorder's CAN interface (the PEAK, can_pcan) is present and up; false when absent or down"
+    },
+    "can_bus_state": {
+      "unit": "",
+      "type": "string",
+      "source": "host",
+      "description": "CAN controller state: ERROR-ACTIVE (normal), ERROR-WARNING, ERROR-PASSIVE, BUS-OFF, STOPPED (down), or absent with no adapter"
+    },
+    "can_rx_fps": {
+      "unit": "frames/s",
+      "type": "number",
+      "source": "host",
+      "description": "CAN frames received per second on that interface",
+      "range": [
+        0,
+        10000
+      ]
+    },
     "ups_battery_v": {
       "unit": "V",
       "type": "number",