Expand multi-day-routes spec to include Journal integration

The spec was Planner-only — day structure would be lost when saving to the
Journal. Added GPX roundtrip (D9), Journal storage (D10), route detail day
breakdown (D11), and shared computeDays in @trails-cool/gpx (D12).

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

openspec/changes/multi-day-routes/tasks.md

@@ -1,8 +1,8 @@
 ## 1. Data Model & Computation
 
 - [ ] 1.1 Add `overnight` property support to Yjs waypoint Y.Maps: helper functions `setOvernight(yjs, index, value)` and `isOvernight(yMap)` in a new `apps/planner/app/lib/overnight.ts`
-- [ ] 1.2 Create `apps/planner/app/lib/compute-days.ts` with `computeDays()` pure function: takes waypoints array + `EnrichedRoute`, returns `DayStage[]` (day number, waypoint range, coord range, distance, ascent, descent, estimated time)
-- [ ] 1.3 Create `useDays()` hook in `apps/planner/app/lib/use-days.ts`: observes Yjs waypoints + routeData, calls `computeDays()`, returns reactive `DayStage[]`
+- [ ] 1.2 Create `computeDays()` pure function in `packages/gpx/src/compute-days.ts`: takes `Waypoint[]` + `TrackPoint[][]`, returns `DayStage[]` (day number, waypoint range, distance, ascent, descent). Export from package index.
+- [ ] 1.3 Create `useDays()` hook in `apps/planner/app/lib/use-days.ts`: maps Yjs waypoints + EnrichedRoute into `computeDays()` input, returns reactive `DayStage[]`
 
 ## 2. Sidebar Day Breakdown
 
@@ -22,19 +22,30 @@
 - [ ] 4.1 Add day divider rendering to `ElevationChart`: dashed vertical lines at overnight waypoint distances with "Day N" labels at top
 - [ ] 4.2 Show per-day distance ranges on x-axis labels (e.g. "120 km" at each day boundary)
 
-## 5. GPX Export
+## 5. GPX Roundtrip
 
 - [ ] 5.1 Extend `generateGpx` in `@trails-cool/gpx` to emit `<type>overnight</type>` for waypoints with `isDayBreak: true`
-- [ ] 5.2 Add multi-track export option: split track into one `<trk>` per day, each named "Day N: Start - End"
+- [ ] 5.2 Extend `parseGpx` in `@trails-cool/gpx` to recognize `<type>overnight</type>` and set `isDayBreak: true` on parsed waypoints
+- [ ] 5.3 Add multi-track export option: split track into one `<trk>` per day, each named "Day N: Start - End"
 
-## 6. i18n
+## 6. Journal Integration
 
-- [ ] 6.1 Add translation keys for en + de: day labels ("Day 1", "Tag 1"), overnight toggle ("Mark as overnight stop" / "Als Ubernachtung markieren"), per-day stats, route summary
+- [ ] 6.1 Update `updateRoute` in `apps/journal/app/lib/routes.server.ts` to extract `dayBreaks` indices from parsed GPX waypoints and write to `dayBreaks` column
+- [ ] 6.2 Expose `dayBreaks` and per-day stats in route detail loader (`routes.$id.tsx`)
+- [ ] 6.3 Add day breakdown section to route detail page: per-day distance, ascent, descent, start/end names — shown only when dayBreaks is non-empty
+- [ ] 6.4 Color route map segments per day (alternating colors) on the route detail map when dayBreaks exist
 
-## 7. Testing
+## 7. i18n
 
-- [ ] 7.1 Unit tests for `computeDays()`: single day (no overnight), two days, three days, empty route, single waypoint, overnight on first/last waypoint edge cases
-- [ ] 7.2 Unit tests for `overnight.ts` helpers: set/clear/check overnight on Y.Map
-- [ ] 7.3 Unit tests for GPX export with overnight waypoints: verify `<type>overnight</type>` output, multi-track splitting
-- [ ] 7.4 E2E test: add waypoints, toggle overnight on one, verify sidebar shows day breakdown with correct stats
-- [ ] 7.5 E2E test: export GPX with day breaks, verify downloaded file contains overnight metadata
+- [ ] 7.1 Add Planner translation keys for en + de: day labels ("Day 1", "Tag 1"), overnight toggle ("Mark as overnight stop" / "Als Übernachtung markieren"), per-day stats, route summary
+- [ ] 7.2 Add Journal translation keys for en + de: day breakdown header, per-day stats labels
+
+## 8. Testing
+
+- [ ] 8.1 Unit tests for `computeDays()`: single day (no overnight), two days, three days, empty route, single waypoint, overnight on first/last waypoint edge cases
+- [ ] 8.2 Unit tests for `overnight.ts` helpers: set/clear/check overnight on Y.Map
+- [ ] 8.3 Unit tests for GPX roundtrip: generate with `isDayBreak`, parse back, verify `isDayBreak` preserved
+- [ ] 8.4 Unit tests for `dayBreaks` extraction in route update logic
+- [ ] 8.5 E2E test: add waypoints, toggle overnight on one, verify sidebar shows day breakdown with correct stats
+- [ ] 8.6 E2E test: export GPX with day breaks, verify downloaded file contains overnight metadata
+- [ ] 8.7 E2E test: save multi-day route to Journal, verify day breakdown displays on route detail page