chore(task): archive 08-12-vehicle-incident-info

.trellis/tasks/archive/2026-08/08-12-vehicle-incident-info/design.md

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+# Design: Vehicle Incident And Information Preview
+
+## Boundary
+
+This is browser-only Cesium preview state. It changes neither generated OSM data nor `package/` assets.
+Vehicle routes and models remain `_preview/` resources; refresh resets all vehicle event state.
+
+## Data Model
+
+Each object returned by `addCruiseVehicle()` gains:
+
+```js
+{
+  id: "vehicle-1",
+  modelName: "car_a01_002",
+  status: "normal" | "breakdown" | "accident",
+  incidentNote: "",
+  motion: { state },
+  markerEntity
+}
+```
+
+The current route distance remains the single motion source. The clock tick leaves it unchanged while
+status is not `normal`; returning to normal resumes from that position.
+
+## Interaction Flow
+
+1. Vehicle Cesium Entities carry a `vehicleId` property.
+2. A `ScreenSpaceEventHandler` picks a clicked entity, resolves its vehicle, synchronizes the existing
+   vehicle selector, and opens a positioned information card.
+3. The card displays vehicle number, model family, route label/length, configured speed, state, and note.
+4. Card controls set normal/breakdown/accident and persist only in the in-memory vehicle object.
+5. State changes update marker visibility, the route material, card content, and Cesium render request.
+
+## Visual Contract
+
+- Normal: no marker; original route color; motion active.
+- Breakdown: yellow wrench label above the vehicle; route retains its original color; motion frozen.
+- Accident: red warning-triangle label above the vehicle; route material becomes red; motion frozen.
+- Marker positions use the same vehicle `CallbackProperty`, so they move with the vehicle before an event
+  and remain at the incident location while stopped.
+
+## Compatibility And Risks
+
+- Picking must ignore routes, static models, and signal entities.
+- No route must retain the existing disabled cruise controls and never show a card.
+- The card must be HTML/CSS UI, not Cesium InfoBox, because the viewer deliberately disables InfoBox.
+- The feature must not alter signal runtime behavior or vehicle asset URLs.