Valhalla-compatible route endpoint (see module docs).

Valhalla route response, with an adr echo when an ADR profile was applied, a rationale block when requested (avoided[] entries carry basis: "route_divergence"; see the module docs for the method's honesty limits), and, when landmarks was requested, a landmark_instruction on each manoeuvre where a recognisable place cleared the salience bar plus a landmarks summary block reporting how many were annotated, and, when traffic was requested, a traffic object on each leg plus a top-level traffic summary carrying the route aggregate, the coverage snapshot's freshness and the method's caveats, and, when scenic was requested, a top-level scenic block with the chosen route, its stated reason, the measured features behind it, the extra minutes it costs and every candidate that was compared with why it lost, and, on a truck route on a deployment with a baked restriction grid, a top-level restriction_coverage receipt naming how many grid cells the route crosses, how they are graded for restriction-tagging density, how many fall outside the grid's own extent and what absence of a recorded restriction does not prove, and, when the route crosses a UK clean-air or low-emission zone (or avoid_zones was set), a top-level zones block naming each crossed zone, whether the declared vehicle is charged, banned or compliant there, the published daily charge with its source URL and checked date, and an estimated_charges total kept separate from every routing cost, and, when the gateway's road walk succeeded, on each manoeuvre speed_limit (in the trip's units) plus country (ISO 3166-1 alpha-2), subdivision (ISO 3166-2), ref (route numbers only, ; separated), road_class, speed_limit_unit (mph or km/h, the road's unit, never the request's), speed_limit_sign (vienna or mutcd) and speed_limit_posted ({"type":"known","value":30,"unit":"mph"}, unlimited or unknown, with "national": true for a GB national speed limit where the map records it) and driving_side (left or right, from the road's country), and, on a pedestrian wheelchair route where the deployment has a surface graph (or the request set surface_quality), a top-level surface_quality block saying whether the route was computed on the surface-quality graph (applied, with the region, the exact rule, the data timestamp and a caveat) or why not (reason: outside_coverage, opted_out, surface_graph_unavailable or not_configured), and, on a wheelchair route, a grade cap or grade_report: true, a top-level grade block with the maximum grade and total ascent and descent sampled every 10 m from the elevation model, the use_hills preference sent and whether a requested cap was enforced