feat(map-core): compact route codec (polyline + RLE) for planner doc

Task group 1 of planner-route-encoding. Framework-free `route-codec.ts`:
- encodePolyline/decodePolyline — fixed-precision (1e5) delta + zig-zag
  varint + base64; lossless to ~1 m, version-tagged ("p1:").
- encodeRuns/decodeRuns — run-length codec for the per-coordinate
  road-metadata channels, tagged ("r1:").
- isEncodedPolyline/isEncodedRuns — so the read path (group 3) tells the
  new encoding apart from legacy JSON.

Not yet wired into route-data.ts (groups 2–3). Verified: map-core
typecheck + lint clean, 52/52 tests (round-trip within 1 m, empty/single,
RLE collapse, >3x smaller than JSON).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

openspec/changes/planner-route-encoding/tasks.md

@@ -1,8 +1,8 @@
 ## 1. Codec primitives
 
-- [ ] 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
-- [ ] 1.2 Add `encodeRuns(values: string[]) -> string` / `decodeRuns(str, length?) -> string[]` run-length codec for the road-metadata channels
-- [ ] 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
+- [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)
 

packages/map-core/src/index.ts

@@ -30,3 +30,8 @@ export { SNAP_DISTANCE_METERS } from "./snap.ts";
 
 export { computeSurfaceBreakdown } from "./surface-breakdown.ts";
 export type { SurfaceBreakdown } from "./surface-breakdown.ts";
+
+export {
+  encodePolyline, decodePolyline, encodeRuns, decodeRuns,
+  isEncodedPolyline, isEncodedRuns,
+} from "./route-codec.ts";

packages/map-core/src/route-codec.test.ts

@@ -0,0 +1,81 @@
+import { describe, it, expect } from "vitest";
+import {
+  encodePolyline,
+  decodePolyline,
+  encodeRuns,
+  decodeRuns,
+  isEncodedPolyline,
+  isEncodedRuns,
+} from "./route-codec.ts";
+
+describe("polyline codec", () => {
+  it("round-trips coordinates within ~1 m", () => {
+    const coords: [number, number][] = [
+      [13.4051234, 52.5204567],
+      [13.4061, 52.5211],
+      [13.408912, 52.523401],
+      [11.5763, 48.1372],
+    ];
+    const decoded = decodePolyline(encodePolyline(coords));
+    expect(decoded).toHaveLength(coords.length);
+    for (let i = 0; i < coords.length; i++) {
+      expect(decoded[i]![0]).toBeCloseTo(coords[i]![0], 4); // ~1e-4 deg ≈ 11 m; 5-precision is finer
+      expect(decoded[i]![1]).toBeCloseTo(coords[i]![1], 4);
+      // Tighter: within the 1e5 quantization (~1.1 m ≈ 1e-5 deg).
+      expect(Math.abs(decoded[i]![0] - coords[i]![0])).toBeLessThanOrEqual(1e-5);
+      expect(Math.abs(decoded[i]![1] - coords[i]![1])).toBeLessThanOrEqual(1e-5);
+    }
+  });
+
+  it("handles empty and single-point", () => {
+    expect(decodePolyline(encodePolyline([]))).toEqual([]);
+    const one = decodePolyline(encodePolyline([[13.405, 52.52]]));
+    expect(one).toHaveLength(1);
+    expect(one[0]![0]).toBeCloseTo(13.405, 5);
+  });
+
+  it("is much smaller than the JSON encoding for a long route", () => {
+    const coords: [number, number][] = [];
+    let lon = 13.4;
+    let lat = 52.5;
+    for (let i = 0; i < 4000; i++) {
+      lon += 0.0002;
+      lat += 0.00005;
+      coords.push([Number(lon.toFixed(5)), Number(lat.toFixed(5))]);
+    }
+    const encoded = encodePolyline(coords);
+    const json = JSON.stringify(coords);
+    expect(encoded.length).toBeLessThan(json.length / 3); // >3x smaller
+    expect(decodePolyline(encoded)).toHaveLength(4000);
+  });
+
+  it("tags encoded values so they are distinguishable from legacy JSON", () => {
+    expect(isEncodedPolyline(encodePolyline([[13.4, 52.5], [13.5, 52.6]]))).toBe(true);
+    expect(isEncodedPolyline("[[13.4,52.5]]")).toBe(false); // legacy JSON
+  });
+});
+
+describe("run-length codec", () => {
+  it("round-trips and collapses uniform runs", () => {
+    const values = [
+      ...Array(2000).fill("asphalt"),
+      ...Array(500).fill("gravel"),
+      ...Array(1500).fill("asphalt"),
+    ];
+    const encoded = encodeRuns(values);
+    expect(decodeRuns(encoded)).toEqual(values);
+    // Three runs → tiny compared to the 4000-entry JSON array.
+    expect(encoded.length).toBeLessThan(JSON.stringify(values).length / 10);
+  });
+
+  it("handles all-distinct and empty", () => {
+    const distinct = ["a", "b", "c", "d"];
+    expect(decodeRuns(encodeRuns(distinct))).toEqual(distinct);
+    expect(decodeRuns(encodeRuns([]))).toEqual([]);
+  });
+
+  it("tags encoded runs vs legacy JSON", () => {
+    expect(isEncodedRuns(encodeRuns(["asphalt"]))).toBe(true);
+    expect(isEncodedRuns('["asphalt","gravel"]')).toBe(false);
+  });
+});

packages/map-core/src/route-codec.ts

@@ -0,0 +1,119 @@
+// Compact, lossless-at-working-precision codecs for the planner's computed
+// route as stored in the Yjs session doc (spec: planner-route-encoding).
+// Framework-free so it can be unit-tested and run on both the client and
+// the server. All encoded values carry a short version prefix so the read
+// path can tell them apart from the legacy JSON encoding (which is a bare
+// `[` … `]`), enabling transparent backward compatibility.
+
+const PRECISION = 100_000; // 1e5 ≈ 1.1 m; below BRouter/OSM working resolution
+const POLYLINE_PREFIX = "p1:";
+const RUNS_PREFIX = "r1:";
+
+// --- base64 via the global btoa/atob (present in browsers and Node 18+),
+// so this stays framework-free with no @types/node dependency ---
+function bytesToBase64(bytes: Uint8Array): string {
+  let bin = "";
+  for (const b of bytes) bin += String.fromCharCode(b);
+  return btoa(bin);
+}
+function base64ToBytes(b64: string): Uint8Array {
+  const bin = atob(b64);
+  const out = new Uint8Array(bin.length);
+  for (let i = 0; i < bin.length; i++) out[i] = bin.charCodeAt(i);
+  return out;
+}
+
+// --- unsigned/zig-zag varint over a byte array ---
+function writeVarint(out: number[], value: number): void {
+  let v = value >>> 0;
+  while (v > 0x7f) {
+    out.push((v & 0x7f) | 0x80);
+    v = v >>> 7;
+  }
+  out.push(v);
+}
+function readVarints(bytes: Uint8Array): number[] {
+  const nums: number[] = [];
+  let v = 0;
+  let shift = 0;
+  for (const byte of bytes) {
+    v |= (byte & 0x7f) << shift;
+    if (byte & 0x80) {
+      shift += 7;
+    } else {
+      nums.push(v >>> 0);
+      v = 0;
+      shift = 0;
+    }
+  }
+  return nums;
+}
+const zigzag = (n: number): number => (n << 1) ^ (n >> 31);
+const unzigzag = (n: number): number => (n >>> 1) ^ -(n & 1);
+
+/** True if `s` is a compact-encoded value (vs a legacy JSON string). */
+export function isEncodedPolyline(s: string): boolean {
+  return s.startsWith(POLYLINE_PREFIX);
+}
+export function isEncodedRuns(s: string): boolean {
+  return s.startsWith(RUNS_PREFIX);
+}
+
+/**
+ * Encode `[lon, lat]` coordinates as delta + zig-zag varint over
+ * fixed-precision integers, base64'd. Lossless to ~1 m.
+ */
+export function encodePolyline(coords: ReadonlyArray<readonly [number, number]>): string {
+  const ints: number[] = [];
+  let prevLon = 0;
+  let prevLat = 0;
+  for (const [lon, lat] of coords) {
+    const iLon = Math.round(lon * PRECISION);
+    const iLat = Math.round(lat * PRECISION);
+    ints.push(zigzag(iLon - prevLon), zigzag(iLat - prevLat));
+    prevLon = iLon;
+    prevLat = iLat;
+  }
+  const bytes: number[] = [];
+  for (const n of ints) writeVarint(bytes, n);
+  return POLYLINE_PREFIX + bytesToBase64(Uint8Array.from(bytes));
+}
+
+export function decodePolyline(s: string): [number, number][] {
+  if (!isEncodedPolyline(s)) throw new Error("not an encoded polyline");
+  const nums = readVarints(base64ToBytes(s.slice(POLYLINE_PREFIX.length)));
+  const coords: [number, number][] = [];
+  let lon = 0;
+  let lat = 0;
+  for (let i = 0; i + 1 < nums.length; i += 2) {
+    lon += unzigzag(nums[i]!);
+    lat += unzigzag(nums[i + 1]!);
+    coords.push([lon / PRECISION, lat / PRECISION]);
+  }
+  return coords;
+}
+
+/**
+ * Run-length-encode a per-coordinate metadata channel. Road attributes run
+ * in long identical stretches, so this collapses thousands of entries to a
+ * handful of `[value, count]` pairs.
+ */
+export function encodeRuns(values: readonly string[]): string {
+  const runs: [string, number][] = [];
+  for (const v of values) {
+    const last = runs[runs.length - 1];
+    if (last && last[0] === v) last[1]++;
+    else runs.push([v, 1]);
+  }
+  return RUNS_PREFIX + JSON.stringify(runs);
+}
+
+export function decodeRuns(s: string): string[] {
+  if (!isEncodedRuns(s)) throw new Error("not encoded runs");
+  const runs = JSON.parse(s.slice(RUNS_PREFIX.length)) as [string, number][];
+  const out: string[] = [];
+  for (const [value, count] of runs) {
+    for (let i = 0; i < count; i++) out.push(value);
+  }
+  return out;
+}