trails/openspec/changes/archive/2026-06-12-journal-elevation-profile/tasks.md

1. Series helper

• 1.1 elevationSeries(tracks, maxPoints=400) in @trails-cool/gpx → { d, e, lat, lng }[], downsampled (keeps first/last), empty when <2 points carry elevation; unit-tested.
• 1.2 Expose the series from the route + activity detail loaders (one parse; activity reuses the moving-time parse). Highest/lowest are computed in the chart; ascent/descent stay in the stat row.

2. Chart component

• 2.1 Presentational ElevationProfile SVG area chart (vertical gradient fill) with a highest/lowest summary + a hover readout (distance · elevation).
• 2.2 Renders nothing when the series has <2 points.

3. Active-distance interaction

• 3.1 Lift a shared activeIndex | null (+ centerOn) above the detail page's map + chart.
• 3.2 Chart hover → onActive(index); map draws a CircleMarker at that sample's lat/lng.
• 3.3 Map route hover → HoverTracker finds the nearest sample → onHoverIndex; chart draws a crosshair + dot.
• 3.4 Chart pointer-down → onSeek bumps centerOn; map panTos that point (read-only, no data change).

4. Wire-in & i18n

• 4.1 Mounted in routes.$id.tsx and activities.$id.tsx (props forwarded through ClientMap).
• 4.2 Add journal.elevation.{highest,lowest} to en + de.

5. Tests & checks

• 5.1 Unit: elevationSeries (cumulative distance, flatten segments, downsample first/last, no-elevation → empty).
• 5.2 Component (jsdom): chart renders for a series + highest/lowest summary; nothing for a too-short series; marker on active; onSeek on pointer-down.
• 5.3 E2E: create an activity from an elevation GPX, assert the profile chart + summary render (e2e/elevation-profile.test.ts, registered in playwright.config.ts). Passes locally.
• 5.4 typecheck + lint + unit (gpx 67, journal 315) green; new e2e passes locally. Full pnpm test:e2e runs in CI.