docs(01-01): complete SortOrderProvider and Trip day derivation plan

Tasks completed: 2/2
- Create SortOrderProvider utility
- Add day derivation methods to Trip

SUMMARY: .planning/phases/01-semantic-position-model/01-01-SUMMARY.md

.planning/phases/01-semantic-position-model/01-01-SUMMARY.md

@@ -0,0 +1,95 @@
+---
+phase: 01-semantic-position-model
+plan: 01
+subsystem: domain
+tags: [swift, sortOrder, calendar, trip, itinerary]
+
+# Dependency graph
+requires: []
+provides:
+  - SortOrderProvider utility with 6 static methods for sortOrder calculation
+  - Trip.dayNumber(for:) and Trip.date(forDay:) for semantic day derivation
+affects:
+  - 01-02-PLAN (tests depend on these utilities)
+  - Phase 2 constraint validation (will use sortOrder utilities)
+  - Phase 3 visual flattening (will sort by sortOrder)
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "SortOrderProvider enum with static methods for sortOrder calculation"
+    - "Double-based sortOrder with midpoint insertion (~52 insertions before precision loss)"
+    - "1-indexed day numbering relative to trip.startDate"
+
+key-files:
+  created:
+    - SportsTime/Core/Models/Domain/SortOrderProvider.swift
+  modified:
+    - SportsTime/Core/Models/Domain/Trip.swift
+
+key-decisions:
+  - "Games get sortOrder from 100 + minutes since midnight (range 100-1540)"
+  - "Midpoint insertion via (above + below) / 2.0"
+  - "Normalization threshold at 1e-10 gap between adjacent items"
+  - "Day 1 = trip.startDate, games belong to their start date"
+
+patterns-established:
+  - "SortOrderProvider.initialSortOrder(forGameTime:) for deriving sortOrder from game time"
+  - "SortOrderProvider.sortOrderBetween(_:_:) for insertion between items"
+  - "Trip.dayNumber(for:) and Trip.date(forDay:) for semantic day calculation"
+
+# Metrics
+duration: 3min
+completed: 2026-01-18
+---
+
+# Phase 1 Plan 1: SortOrder Utilities Summary
+
+**SortOrderProvider enum with 6 static methods for sortOrder calculation plus Trip.dayNumber/date(forDay:) for semantic day derivation**
+
+## Performance
+
+- **Duration:** 3 min
+- **Started:** 2026-01-18T19:49:28Z
+- **Completed:** 2026-01-18T19:52:00Z
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- Created SortOrderProvider utility with all sortOrder calculation methods
+- Added day derivation methods to Trip for semantic (day, sortOrder) positioning
+- Both files compile successfully with no warnings
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Create SortOrderProvider utility** - `9915ad3` (feat)
+2. **Task 2: Add day derivation methods to Trip** - `6d43edf` (feat)
+
+## Files Created/Modified
+- `SportsTime/Core/Models/Domain/SortOrderProvider.swift` - Enum with 6 static methods: initialSortOrder(forGameTime:), sortOrderBetween(_:_:), sortOrderBefore(_:), sortOrderAfter(_:), needsNormalization(_:), normalize(_:)
+- `SportsTime/Core/Models/Domain/Trip.swift` - Added extension with dayNumber(for:) and date(forDay:) instance methods
+
+## Decisions Made
+None - followed plan as specified. Research document provided complete implementation guidance.
+
+## Deviations from Plan
+None - plan executed exactly as written.
+
+## Issues Encountered
+None.
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- SortOrderProvider and Trip day derivation methods ready for use
+- Plan 01-02 can now create tests verifying semantic position persistence
+- All 6 SortOrderProvider methods are static and publicly accessible
+- Trip extension methods are instance methods callable on any Trip value
+
+---
+*Phase: 01-semantic-position-model*
+*Completed: 2026-01-18*