replay-session.sh: a recorded session's frames through the decoder, live to displays

Frames go onto vcan_replay (the recorder never sees them); the decoder service
stands aside for the replay and comes back however it ends.

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

README.md

@@ -30,6 +30,8 @@ scripts/deploy-native.sh BIN               # build BIN on the development Orin,
                                            # Redeploy after any contracts signals.json change
 yukart-decoder --list                      # the signals it decodes, and where
 zstdcat can-*.log.zst | yukart-decoder --replay   # what it would publish for a recording
+scripts/replay-session.sh SESSION_DIR [SKIP_S]   # on the Orin: replay a session's frames through a
+                                           # decoder on vcan_replay, live to displays; never recorded
 yukart-obd-poller --elm ADDR --once        # on the Orin, service stopped: adapter, protocol,
                                            # supported PIDs and one value each
 yukart-gnss --once                         # the next fix as JSON, no broker

scripts/replay-session.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# Replay a recorded session's CAN frames through the decoder, so displays react as
+# if the car were live. Runs on the car Orin (sudo: vcan and the decoder service).
+#
+#   usage: scripts/replay-session.sh SESSION_DIR [SKIP_S]
+#     SESSION_DIR  e.g. /var/lib/yukart/recordings/000001-20261013T170050
+#     SKIP_S       seconds of the recording to skip first (default 0)
+#
+# Frames go onto a virtual interface, vcan_replay, never can_pcan: the recorder only
+# watches can_pcan, so a replay is never recorded as a drive. The decoder service is
+# stopped for the replay (one MQTT client id) and a decoder runs on vcan_replay instead;
+# however the replay ends (finished, Ctrl-C, killed), the service comes back and the
+# interface goes. Values carry the replay's own timing; nothing marks them as replayed.
+set -euo pipefail
+
+SESSION="${1:?usage: replay-session.sh SESSION_DIR [SKIP_S]}"
+SKIP="${2:-0}"
+IF=vcan_replay
+ls "$SESSION"/can-*.log* >/dev/null
+
+cleanup() {
+  [ -n "${DEC:-}" ] && kill "$DEC" 2>/dev/null || true
+  sudo ip link del "$IF" 2>/dev/null || true
+  sudo systemctl start yukart-decoder
+  echo "replay: done; yukart-decoder back on can_pcan"
+}
+trap cleanup EXIT INT TERM
+
+sudo modprobe vcan
+sudo ip link add "$IF" type vcan 2>/dev/null || true
+sudo ip link set "$IF" up
+sudo systemctl stop yukart-decoder
+/usr/local/bin/yukart-decoder --can "$IF" &
+DEC=$!
+sleep 1
+
+echo "replay: $SESSION from +${SKIP} s onto $IF"
+# candump -L lines: "(1791878450.945008) can_pcan 139#...". Skip by the first frame's time.
+zstdcat -f "$SESSION"/can-*.log* 2>/dev/null \
+  | awk -v skip="$SKIP" '{ t = substr($1, 2, length($1) - 2) + 0; if (NR == 1) t0 = t; if (t - t0 >= skip) print }' \
+  | canplayer "$IF=can_pcan"