docs: initialize project

Interactive drag-and-drop itinerary editor with semantic positioning

.planning/PROJECT.md

@@ -0,0 +1,75 @@
+# Itinerary Editor
+
+## What This Is
+
+An interactive drag-and-drop itinerary editor for the SportsTime iOS app. Users can rearrange travel segments and custom items within their trip itinerary while respecting game schedules and city-based travel constraints. Built as a UITableView bridged into SwiftUI to enable precise drag-and-drop with insertion line feedback.
+
+## Core Value
+
+Drag-and-drop that operates on semantic positions (day + sortOrder), not row indices — so user intent is preserved across data reloads.
+
+## Requirements
+
+### Validated
+
+- ✓ Trip itineraries display with day headers and games — existing (`TripDetailView`)
+- ✓ Conflict detection for same-day games in different cities — existing
+- ✓ SwiftUI + SwiftData architecture — existing
+
+### Active
+
+- [ ] Semantic position model using `(day: Int, sortOrder: Double)` for all movable items
+- [ ] Custom items can be placed anywhere within any day (including between games)
+- [ ] Travel segments respect city constraints (after from-city games, before to-city games)
+- [ ] Travel segments respect day range constraints (within valid travel window)
+- [ ] Invalid drops are rejected with snap-back behavior
+- [ ] Insertion lines show precise drop targets during drag
+- [ ] External drops (from outside the table) work with same semantic rules
+- [ ] Position persists correctly across data reloads
+- [ ] No visual jumpiness or dead zones during drag operations
+
+### Out of Scope
+
+- Reordering games — games are fixed by schedule
+- Reordering day headers — structural, one per day
+- Zone-based drop highlighting — using insertion lines instead
+- Multi-day travel segments — travel belongs to exactly one day
+
+## Context
+
+**Existing codebase:** SportsTime iOS app with Clean MVVM architecture. `TripDetailView` already displays itineraries with conflict detection. The new editor replaces the display-only view with an interactive one.
+
+**Technical environment:**
+- iOS 26+, Swift 6 concurrency
+- SwiftUI drives data, UITableView handles drag-and-drop
+- SwiftData for persistence
+- Frequent reloads from data changes; visual-only state is not acceptable
+
+**What went wrong in previous attempts:**
+- Row-based snapping instead of semantic (day, sortOrder)
+- Treating travel as structural ("travelBefore") instead of positional
+- Losing sortOrder for travel during flattening
+- Hard-coded flatten order (header → games → customs) that ignored sortOrder
+- Drag logic and reload logic fighting each other
+
+## Constraints
+
+- **Architecture**: SwiftUI wrapper must drive data; UIKit table handles drag/drop mechanics
+- **Persistence**: All positions must be semantic (day, sortOrder) — no ephemeral visual state
+- **Reload tolerance**: Reloads must not undo valid user actions; position must survive reload
+- **iOS version**: iOS 26+ (per existing app target)
+
+## Key Decisions
+
+| Decision | Rationale | Outcome |
+|----------|-----------|---------|
+| UITableView over SwiftUI List | SwiftUI drag-and-drop lacks insertion line precision and external drop support | — Pending |
+| (day, sortOrder) position model | Row indices break on reload; semantic position is reload-stable | — Pending |
+| Insertion lines (not zones) | User wants precise feedback on exact drop location | — Pending |
+| Custom items interleave with games | Maximum flexibility for user — can add notes between games | — Pending |
+| Travel position-constrained within day | After from-city games, before to-city games on same day | — Pending |
+| Invalid drops rejected (snap back) | Cleaner than auto-clamping; user knows exactly what happened | — Pending |
+| Items always belong to a day | No liminal "between days" state; visual gap is end of previous day | — Pending |
+
+---
+*Last updated: 2026-01-18 after initialization*