docs(03): capture phase context

Phase 03: visual-flattening
- Implementation decisions documented
- Phase boundary established

.planning/phases/03-visual-flattening/03-CONTEXT.md

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+# Phase 3: Visual Flattening - Context
+
+**Gathered:** 2026-01-18
+**Status:** Ready for planning
+
+<domain>
+## Phase Boundary
+
+Transform semantic items (games, travel, custom) into display rows, sorted deterministically by sortOrder within each day. This phase provides the row-to-semantic translation needed for Phase 4 drag interaction.
+
+</domain>
+
+<decisions>
+## Implementation Decisions
+
+### Sort boundaries
+- sortOrder = 0 is the first game position; negatives appear before games, positives appear after/between
+- Purely sequential sorting within a day — no time-of-day grouping (morning/afternoon/evening)
+- No visual indicator at the boundary between pre-game items and games
+- Items just flow in sortOrder order; games are distinguished by their visual style
+
+### Section structure
+- Day headers display day number + date (e.g., "Day 1 - Jan 15" or "Day 1 (Wed, Jan 15)")
+- Headers scroll with content — not sticky
+- Empty days show the day header with no rows beneath (don't skip empty days)
+
+### Item differentiation
+- **Games:** Sport-colored accent (left border or icon matching sport: MLB=red, NBA=orange, NHL=blue)
+- **Travel segments:** Subtle/muted style — gray text, smaller row, less prominent than games
+- **Custom items:** Note icon + text indicating user-added item
+- **Drag affordance:** Drag handle icon (three-line grip) on draggable items
+
+### Edge case handling
+- Ties shouldn't occur — system always assigns unique sortOrder when positioning items
+- No special visual treatment for items at first/last position in a day
+- Days with only games can still receive drops (between games, subject to Phase 2 constraints)
+- Flattening is a pure function — stateless, same input always produces same output
+
+### Claude's Discretion
+- Whether to use UITableView sections or inline day headers (based on drag-drop requirements)
+- Whether travel/custom items can use sortOrder in the 100-1540 range (based on Phase 2 constraint logic)
+- Exact styling details (spacing, typography, border thickness)
+- Tiebreaker for identical sortOrder (by item type priority: games > travel > custom) if it ever occurs despite unique assignment
+
+</decisions>
+
+<specifics>
+## Specific Ideas
+
+- "New items added to specific positions should get unique sortOrder values" — the system should proactively avoid ties rather than handling them after the fact
+- Sport colors should match existing SportsTime app patterns for consistency
+
+</specifics>
+
+<deferred>
+## Deferred Ideas
+
+None — discussion stayed within phase scope
+
+</deferred>
+
+---
+
+*Phase: 03-visual-flattening*
+*Context gathered: 2026-01-18*