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# Navigation service guidelines

## 1. Routing providers stay behind one interface
- Nothing outside the provider boundary may reference Valhalla types, Valhalla
  URLs, or Valhalla's response shapes.  
- A cloud provider (GCP or equivalent) must be addable without changes to the
  bridge, the published topics, or any display.  
- Local Valhalla is the default because it works with no signal; a cloud provider
  is an option, never a dependency.

## 2. Guidance is published, routes are requested
- Live guidance goes onto `yukart/nav/guidance`, retained.  
- Route requests are request/response and are served over HTTP, not MQTT.

## 3. To be added