Extract shared extractWaypoints into @trails-cool/gpx

Both new.tsx and api.sessions.ts had duplicated track-segment
waypoint extraction logic. Moved to packages/gpx as
extractWaypoints(gpxData) — uses <wpt> elements when present,
falls back to start of each track segment + end of last.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/gpx/src/index.ts

@@ -1,3 +1,4 @@
 export { parseGpxAsync } from "./parse.ts";
 export { generateGpx } from "./generate.ts";
+export { extractWaypoints } from "./waypoints.ts";
 export type { GpxData, TrackPoint, ElevationProfile } from "./types.ts";

packages/gpx/src/waypoints.ts

@@ -0,0 +1,33 @@
+import type { GpxData } from "./types.ts";
+
+/**
+ * Extract waypoints from parsed GPX data.
+ * Uses explicit <wpt> elements if present, otherwise extracts the start
+ * of each track segment + end of the last segment.
+ */
+export function extractWaypoints(gpxData: GpxData): Array<{ lat: number; lon: number; name?: string }> {
+  if (gpxData.waypoints.length > 0) return gpxData.waypoints;
+  if (gpxData.tracks.length === 0) return [];
+
+  const result: Array<{ lat: number; lon: number }> = [];
+  for (const seg of gpxData.tracks) {
+    if (seg.length === 0) continue;
+    const first = seg[0]!;
+    const prev = result[result.length - 1];
+    if (!prev || prev.lat !== first.lat || prev.lon !== first.lon) {
+      result.push({ lat: first.lat, lon: first.lon });
+    }
+  }
+
+  // Add end of last segment
+  const lastSeg = gpxData.tracks[gpxData.tracks.length - 1]!;
+  if (lastSeg.length > 0) {
+    const last = lastSeg[lastSeg.length - 1]!;
+    const prev = result[result.length - 1];
+    if (!prev || prev.lat !== last.lat || prev.lon !== last.lon) {
+      result.push({ lat: last.lat, lon: last.lon });
+    }
+  }
+
+  return result;
+}