obd-poller: OBD-II mode 01, the single CAN writer; recorder keeps its values

obd-poller asks 0x7DF for the nine obd2 signals, only while the bus is alive,
and publishes envelopes stamped with the reply's kernel time. The recorder
subscribes to yukart/vehicle/* and writes vehicle.ndjson beside the frames.
Tested against a fake ECU on vcan0.

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

docs/GUIDELINES.md

@@ -3,10 +3,13 @@ type: guidelines
 ---
 # Core services guidelines
 
-## 1. Listen-only until `obd-poller` exists
-- Nothing here opens a CAN socket for writing. The recorder only reads, and the
-  host brings `can_pcan` up listen-only.  
-- `obd-poller` will be the single writer. Until it lands, any transmit is a bug.
+## 1. One CAN writer: `obd-poller`
+- `obd-poller` is the only thing that transmits on the car's bus (project-yukart
+  decision 3): OBD-II requests, one at a time, only while the bus is visibly
+  alive. Anything else that transmits is a bug; the recorder only reads.  
+- `can_pcan` is no longer listen-only (2026-10-12), so the adapter acknowledges
+  frames like any scan tool. Going back is one line in orin-nano-env-setup's
+  `/etc/default/can-can_pcan`.
 
 ## 2. Capture never waits
 - A frame missed is gone. Producers hand frames to the writer without blocking;