docs(04-01): complete modern drag-drop delegates plan

Tasks completed: 3/3
- Task 1: Migrate to modern UITableViewDragDelegate/UITableViewDropDelegate
- Task 2: Implement lift animation with scale, shadow, and tilt
- Task 3: Add haptic feedback for grab and drop

All tasks completed in single commit due to code interdependency.

SUMMARY: .planning/phases/04-drag-interaction/04-01-SUMMARY.md

.planning/STATE.md

@@ -4,21 +4,21 @@
 
 **Core Value:** Drag-and-drop that operates on semantic positions (day + sortOrder), not row indices - so user intent is preserved across data reloads.
 
-**Current Focus:** Phase 2 Complete - Ready for Phase 3 (Visual Flattening)
+**Current Focus:** Phase 4 Plan 1 Complete - Modern drag-drop delegates with lift animation and haptics
 
 ## Current Position
 
-**Phase:** 2 of 4 (Constraint Validation) - COMPLETE
-**Plan:** 2 of 2 complete
-**Status:** Phase complete
-**Last activity:** 2026-01-18 - Completed 02-02-PLAN.md
+**Phase:** 4 of 4 (Drag Interaction)
+**Plan:** 1 of 2 complete
+**Status:** In progress
+**Last activity:** 2026-01-18 - Completed 04-01-PLAN.md
 
 ```
-Progress: [####------] 50%
+Progress: [########--] 87.5%
 Phase 1:  [##########] 100% (2/2 plans) COMPLETE
 Phase 2:  [##########] 100% (2/2 plans) COMPLETE
-Phase 3:  [----------] Not Started
-Phase 4:  [----------] Not Started
+Phase 3:  [##########] 100% (2/2 plans) COMPLETE
+Phase 4:  [#####-----] 50% (1/2 plans)
 ```
 
 ## Performance Metrics
@@ -26,9 +26,9 @@ Phase 4:  [----------] Not Started
 | Metric | Value |
 |--------|-------|
 | Total Requirements | 23 |
-| Completed | 12 |
-| Current Phase | 2 (complete) |
-| Plans Executed | 4 |
+| Completed | 20 |
+| Current Phase | 4 (in progress) |
+| Plans Executed | 7 |
 
 ## Accumulated Context
 
@@ -47,6 +47,14 @@ Phase 4:  [----------] Not Started
 | LocalItineraryItem conversion for testing | Avoids #Predicate macro issues with local captures | 01-02 |
 | Edge case tests cover all boundaries | Day 0, beyond trip, exact sortOrder, negative/large values | 02-02 |
 | Success criteria verification tests | Tests named 'success_*' directly verify ROADMAP criteria | 02-02 |
+| Day headers not positioned items | Always first in each day, not part of sortOrder-based ordering | 03-01 |
+| Flattener is pure function | No instance state, no side effects for easy testing and determinism | 03-01 |
+| gamesByDay dictionary for flattener | Built in reloadData() to pass to flattener | 03-01 |
+| success_* test naming convention | Maps tests directly to ROADMAP success criteria | 03-02 |
+| Modern drag delegates for custom previews | UITableViewDragDelegate/UITableViewDropDelegate enable lift animation | 04-01 |
+| DragContext for session state | Store drag state in session.localContext for access across delegates | 04-01 |
+| Lift animation: 1.025x scale, 2-deg tilt | iOS Reminders-style quick/snappy lift per CONTEXT.md | 04-01 |
+| Dual haptic generators (light/medium) | Prepare both at drag start for reduced latency | 04-01 |
 
 ### Learned
 
@@ -58,12 +66,21 @@ Phase 4:  [----------] Not Started
 - 50 midpoint insertions maintain distinct sortOrder values before precision loss
 - ItineraryConstraints provides isValidPosition(), validDayRange(), barrierGames() for drag validation
 - Travel sortOrder constraints: must be AFTER (not equal to) departure game sortOrder
+- ItineraryFlattener.flatten() is the single source of truth for display ordering
+- 13 tests now verify deterministic flattening behavior
+- Modern drag delegates require holistic implementation (can't separate lift/haptics from delegates)
+- CATransform3D with m34 perspective creates convincing 3D lift effect
+- Snapshot-based animation avoids modifying actual cell during drag
 
 ### TODOs
 
 - [x] Create tests for semantic position persistence (Plan 01-02) - COMPLETE
 - [x] Migrate constraint tests to Swift Testing (Plan 02-01) - COMPLETE
 - [x] Add edge case tests and API documentation (Plan 02-02) - COMPLETE
+- [x] Create ItineraryFlattener utility (Plan 03-01) - COMPLETE
+- [x] Add flattening tests (Plan 03-02) - COMPLETE
+- [x] Migrate to modern drag-drop delegates (Plan 04-01) - COMPLETE
+- [ ] Add insertion line and invalid zone feedback (Plan 04-02) - NEXT
 
 ### Blockers
 
@@ -71,24 +88,29 @@ None currently.
 
 ## Session Continuity
 
-**Last Session:** 2026-01-18T21:13:45Z
-**Stopped at:** Completed 02-02-PLAN.md (Phase 2 complete)
-**Resume file:** .planning/phases/03-visual-flattening/03-01-PLAN.md
+**Last Session:** 2026-01-18T22:44:26Z
+**Stopped at:** Completed 04-01-PLAN.md
+**Resume file:** None
 
 ### Context for Next Session
 
-Phase 2 complete with 22 constraint tests covering:
-- CONS-01: Games cannot move (2 tests)
-- CONS-02: Travel day range constraints (3 tests)
-- CONS-03: Travel sortOrder constraints (5 tests)
-- CONS-04: Custom item flexibility (2 tests)
-- Edge cases: 8 tests
-- Success criteria: 3 tests
-- Barrier games: 1 test
+Phase 4 Plan 1 complete:
+- Migrated to UITableViewDragDelegate/UITableViewDropDelegate
+- Implemented lift animation with scale (1.025x), shadow, and tilt (2 degrees)
+- Added dual haptic feedback (light grab, medium drop)
+- Created DragContext class for drag session state
 
-API documentation ready for Phase 4 at CONSTRAINT-API.md.
+Requirements completed in 04-01:
+- DRAG-01: Lift animation on grab (shadow + slight scale)
+- DRAG-06: Haptic feedback on grab (light) and drop (medium)
+- DRAG-08: Slight tilt during drag (2-3 degrees)
 
-Ready to start Phase 3: Visual Flattening (sortOrder-based flattening, deterministic ordering).
+Ready for 04-02: Themed insertion line, invalid zone feedback, snap-back animation
+- DRAG-02: Insertion line showing drop target
+- DRAG-03: Items shuffle during drag
+- DRAG-04: Magnetic snap on drop
+- DRAG-05: Invalid drops with snap-back
+- DRAG-07: Auto-scroll at viewport edge
 
 ---
 *State initialized: 2026-01-18*