Forward yukart/imu/+; mock IMU values (pull-away, braking, a weave)

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

docs/impl/plans/INITIAL.md

@@ -24,7 +24,7 @@ directly.
    `mark` forwarded to the recorder's control socket, mock state behind `--mock`.
    Protocol in contracts [`docs/BOUNDARY.md`](gitea:yukart/contracts).
    **Bus input** — in place (2026-10-12): subscribes to `yukart/vehicle/+`,
-   `yukart/host/+` and `yukart/gnss/+`, keeps the newest envelope per signal, marks stale after 5 s
+   `yukart/host/+`, `yukart/gnss/+` and `yukart/imu/+`, keeps the newest envelope per signal, marks stale after 5 s
    or when known only from a retained copy. Bus or mock, never both.
 1. Static file serving for the basemap — smallest useful thing, unblocks the map.
 2. Nav HTTP proxy to [svc-nav](gitea:yukart/svc-nav).

src/bus.rs

@@ -15,7 +15,7 @@ use std::time::{Duration, Instant};
 use rumqttc::{Client, Event, MqttOptions, Packet, QoS};
 use serde_json::{json, Map, Value};
 
-const TOPICS: [&str; 3] = ["yukart/vehicle/+", "yukart/host/+", "yukart/gnss/+"];
+const TOPICS: [&str; 4] = ["yukart/vehicle/+", "yukart/host/+", "yukart/gnss/+", "yukart/imu/+"];
 const STALE: Duration = Duration::from_secs(5);
 
 struct Entry {

src/mock.rs

@@ -52,6 +52,19 @@ impl Mock {
         } else {
             put("obd_intake_air_temp_c", json!((31.0 + (t * 0.05).sin()).round()), None);
         }
+        // IMU in the car's frame: pulling away 4 km/h/s (0.11 g), braking 6 km/h/s, and a
+        // gentle weave while cruising. Body roll follows lateral g, pitch follows longitudinal.
+        let lon = match phase {
+            p if (10.0..25.0).contains(&p) => 0.11,
+            p if (45.0..55.0).contains(&p) => -0.17,
+            _ => 0.0,
+        } + 0.01 * (t * 5.3).sin();
+        let lat = if (25.0..45.0).contains(&phase) { 0.3 * (t * 0.9).sin() } else { 0.0 } + 0.01 * (t * 4.1).sin();
+        put("imu_accel_lon_g", json!((lon * 100.0_f64).round() / 100.0), None);
+        put("imu_accel_lat_g", json!((lat * 100.0_f64).round() / 100.0), None);
+        put("imu_roll_deg", json!((lat * 30.0_f64).round() / 10.0), None);
+        put("imu_pitch_deg", json!((-lon * 20.0_f64).round() / 10.0), None);
+        put("imu_yaw_rate_dps", json!(if speed > 1.0 { ((-lat * 9.81 / (speed / 3.6)).to_degrees() * 10.0).round() / 10.0 } else { 0.0 }), None);
         // Fuel level is known but has no value: the registry has it, the car never sent it.
         put("obd_fuel_level_pct", Value::Null, None);
         s