IMU signals in the car's frame (attitude, gravity-free g, yaw rate) on yukart/imu/<signal>

The WT61's publisher owns mounting and gravity; displays get car-frame values.

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

docs/BOUNDARY.md

@@ -37,7 +37,7 @@ The two channels from decision 24 share the socket but keep different guarantees
 | `ack` | reply to a `cmd` | `id`, `ok`, `detail`, `dup` (true when answered from the cache) |
 
 With `source: bus`, `signals` is the newest envelope of every signal svc-gw has
-seen on `yukart/vehicle/+`, `yukart/host/+` and `yukart/gnss/+`. svc-gw marks one
+seen on `yukart/vehicle/+`, `yukart/host/+`, `yukart/gnss/+` and `yukart/imu/+`. svc-gw marks one
 `quality: "stale"` when it has not been refreshed for 5 s, or is known only from
 the broker's retained copy (which may predate a reboot). A signal once seen is
 never removed.

schema/signals.json

@@ -1,5 +1,5 @@
 {
-  "$comment": "Single source for signal identity. Topic name and envelope unit are both derived from these entries and are never authored separately. source=obd2 is standardised (OBD-II mode 01 over the K-line, through the ELM327): calibration references, every name prefixed obd_ (project-yukart decision 30); source=host is the Orin itself (orin-status), not the car. source=gnss is the receiver (svc-core gnss), on yukart/gnss/<signal>. source=z27ag is reverse-engineered from the car's own broadcast frames, and its 'can' block is the only place its layout is written down: id (11-bit, hex string), byte (first data byte, 0-7), length in bits (1, 8 or 16), bit (length 1 only: 0 = LSB of that byte), order (length 16: big = byte first is most significant, little = the reverse), scale and offset (value = raw * scale + offset; booleans are raw != 0). 'evidence' names the contracts report that found it.",
+  "$comment": "Single source for signal identity. Topic name and envelope unit are both derived from these entries and are never authored separately. source=obd2 is standardised (OBD-II mode 01 over the K-line, through the ELM327): calibration references, every name prefixed obd_ (project-yukart decision 30); source=host is the Orin itself (orin-status), not the car. source=gnss is the receiver (svc-core gnss), on yukart/gnss/<signal>. source=imu is the WT61 IMU, already turned into the car's frame (mounting and gravity handled by its publisher), on yukart/imu/<signal>. source=z27ag is reverse-engineered from the car's own broadcast frames, and its 'can' block is the only place its layout is written down: id (11-bit, hex string), byte (first data byte, 0-7), length in bits (1, 8 or 16), bit (length 1 only: 0 = LSB of that byte), order (length 16: big = byte first is most significant, little = the reverse), scale and offset (value = raw * scale + offset; booleans are raw != 0). 'evidence' names the contracts report that found it.",
   "signals": {
     "obd_vehicle_speed_kph": {
       "unit": "kph",
@@ -634,6 +634,56 @@
         0,
         64
       ]
+    },
+    "imu_roll_deg": {
+      "unit": "degree",
+      "type": "number",
+      "source": "imu",
+      "description": "Body roll in the car's frame: positive leaning right (right side down)",
+      "range": [
+        -180,
+        180
+      ]
+    },
+    "imu_pitch_deg": {
+      "unit": "degree",
+      "type": "number",
+      "source": "imu",
+      "description": "Body pitch in the car's frame: positive nose up",
+      "range": [
+        -90,
+        90
+      ]
+    },
+    "imu_accel_lon_g": {
+      "unit": "g",
+      "type": "number",
+      "source": "imu",
+      "description": "Longitudinal acceleration in the car's frame, gravity removed: positive forward (speeding up), negative braking",
+      "range": [
+        -4,
+        4
+      ]
+    },
+    "imu_accel_lat_g": {
+      "unit": "g",
+      "type": "number",
+      "source": "imu",
+      "description": "Lateral acceleration in the car's frame, gravity removed: positive to the right (a right turn reads positive)",
+      "range": [
+        -4,
+        4
+      ]
+    },
+    "imu_yaw_rate_dps": {
+      "unit": "degree/s",
+      "type": "number",
+      "source": "imu",
+      "description": "Yaw rate: positive turning left (counter-clockwise from above)",
+      "range": [
+        -500,
+        500
+      ]
     }
   }
 }

schema/topics.json

@@ -29,6 +29,13 @@
       "publisher": "gnss",
       "description": "The receiver's fix as single values, one topic per signal, named exactly as in signals.json (source=gnss). For displays; yukart/gnss/fix stays the composite for navigation."
     },
+    "yukart/imu/<signal>": {
+      "payload": "envelope",
+      "retained": true,
+      "rate": "10-50/s",
+      "publisher": "imu",
+      "description": "The IMU (WT61) in the car's frame: attitude, gravity-free acceleration, yaw rate; one topic per signal, named exactly as in signals.json (source=imu)."
+    },
     "yukart/host/<signal>": {
       "payload": "envelope",
       "retained": true,