Wire the map-core codec into route-data.ts so the Yjs session doc stores
the computed route compactly, without changing the routing-host
compute-once-and-share model.
- Codec: add encodeElevations/decodeElevations (delta+varint) so geometry
= encoded [lon,lat] polyline + elevation channel; precision bumped to
1e6 (~0.11 m) to preserve the router's 6-decimal output.
- writeComputedRoute: geometry stored once (encoded polyline + elevations,
no redundant geojson), road metadata run-length encoded.
- Dual-format reads: getCoordinates / readRoadMetadata / new readGeojson
transparently handle the new encoding AND legacy JSON docs (+ oldest
geojson-only) — no migration, no flag day; legacy docs re-encode on the
next recompute. use-elevation-data reads readGeojson (assembled for new
docs).
- Spec correction: a lossy compact codec can't be byte-identical to legacy
(generateGpx emits raw precision), so "GPX byte-compatible" is corrected
to "coordinates preserved within the router's ~0.1 m precision".
Tests: legacy-format read, size assertion (>4x smaller / round-trips),
elevation round-trip. map-core + planner typecheck/lint clean; full
pnpm test 11/11.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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