trails/openspec/changes/planner-route-encoding/tasks.md
Ullrich Schäfer c33a413395
feat(planner): store computed route compact-encoded (groups 2–4)
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>
2026-07-15 17:07:28 +02:00

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## 1. Codec primitives
- [x] 1.1 Add a framework-free codec in `@trails-cool/map-core` (e.g. `route-codec.ts`): `encodePolyline(coords: [lon,lat][]) -> string` / `decodePolyline(str) -> [lon,lat][]` using fixed-precision (1e5) delta + zig-zag varint + base64, with a version tag
- [x] 1.2 Add `encodeRuns(values: string[]) -> string` / `decodeRuns(str, length?) -> string[]` run-length codec for the road-metadata channels
- [x] 1.3 Unit tests: polyline round-trip within ~1 m over random + real fixtures; empty/single-point; RLE round-trip incl. all-same, all-distinct, and a realistic run pattern
## 2. Write path (new encoding)
- [x] 2.1 In `route-data.ts` `writeComputedRoute`: store geometry once as `encodePolyline(coordinates)` (drop the separate `geojson` write); write each `ROAD_METADATA_KEYS` channel via `encodeRuns`; keep `segmentBoundaries` + profile
- [x] 2.2 Add a `readGeojson(routeData)` helper that assembles the GeoJSON LineString from decoded coordinates (so callers that needed `geojson` no longer read a stored copy)
## 3. Read path (dual-format, backward compatible)
- [x] 3.1 In `route-data.ts` read helpers (`readComputedRoute`, `readRoadMetadata`, coordinate accessors): detect format per key (encoding version tag/sentinel → new decoder; else `JSON.parse` legacy) and return the same decoded shapes as today
- [x] 3.2 Point every reader (SessionView map render, elevation profile, GPX export, save-to-journal, road-type/surface coloring) at the helpers; confirm none reads a raw `routeData.get("geojson"|"coordinates"|<metadata>)` directly
- [x] 3.3 Tests: a legacy-format `routeData` decodes correctly through the helpers; a new-format one decodes correctly; both yield identical reader-facing data
## 4. Verification
- [x] 4.1 GPX-export golden test: export the same route via legacy and new encoding → byte-identical output
- [x] 4.2 Size assertion on a realistic route fixture (e.g. the ~77 km / multi-waypoint case): new-encoded `Y.encodeStateAsUpdate` size is ≥~4× smaller than legacy and a small fraction of `MAX_DOC_BYTES`
- [x] 4.3 Confirm routing-host election / BRouter usage unchanged (no client recompute); `pnpm --filter @trails-cool/planner --filter @trails-cool/map-core typecheck && lint && test`, full `pnpm test`
- [x] 4.4 Encode/decode + legacy-read + size covered by unit tests (route-codec, route-data); render/colors/export paths read through the same helpers and compile; live browser sanity rides the e2e suite (autonomous run)