docs(03-03): complete UDP simulator and FastAPI integration plan

- Create 03-03-SUMMARY.md: simulator, e2e tests, lifespan integration
- Update STATE.md: advance plan, 100% progress, record decisions
- Update ROADMAP.md: phase 03 marked Complete (3/3 plans)
- Mark UDP-04 requirement complete in REQUIREMENTS.md

.planning/phases/03-communication-protocol/03-03-SUMMARY.md

@@ -0,0 +1,75 @@
+---
+phase: 03-communication-protocol
+plan: "03"
+subsystem: protocol
+tags: [udp, simulator, e2e-testing, fastapi, tdd]
+dependency_graph:
+  requires: ["03-01", "03-02"]
+  provides: ["UDP simulator with packet logging", "UDPSender in FastAPI lifespan", "end-to-end protocol tests"]
+  affects: ["lightsync/main.py", "lightsync/protocol/simulator.py", "tests/test_e2e_protocol.py"]
+tech_stack:
+  added: ["asyncio.DatagramProtocol for UDP simulation"]
+  patterns: ["TDD RED-GREEN", "asyncio.run() in tests (no pytest-asyncio)", "dataclass for structured packet logs"]
+key_files:
+  created:
+    - lightsync/protocol/simulator.py
+    - tests/test_e2e_protocol.py
+  modified:
+    - lightsync/main.py
+decisions:
+  - "asyncio.run() test pattern chosen over pytest-asyncio — not installed, plan explicitly provided this fallback"
+  - "SimulatorProtocol uses port=0 in tests — OS assigns free port, read back via get_extra_info('sockname')[1]"
+  - "UDPSender stopped before registry.save() in shutdown — orderly teardown, no sends after socket close"
+metrics:
+  duration: "2 min"
+  completed_date: "2026-04-06"
+  tasks_completed: 2
+  files_created: 2
+  files_modified: 1
+---
+
+# Phase 03 Plan 03: UDP Simulator and FastAPI Integration Summary
+
+**One-liner:** Async UDP simulator parses all 4 WLED packet types (DRGB/DRGBW/DNRGB/ANIM_CMD) with structured packet logging; UDPSender integrated into FastAPI lifespan; 7 end-to-end tests prove full animation-to-wire pipeline.
+
+## What Was Built
+
+### Task 1: UDP Simulator with Packet Logging (TDD)
+
+`lightsync/protocol/simulator.py` — a `SimulatorProtocol(asyncio.DatagramProtocol)` that:
+- Parses DRGB (0x02): extracts `led_count = (len(data)-2) // 3`
+- Parses DRGBW (0x03): extracts `led_count = (len(data)-2) // 4`
+- Parses DNRGB (0x04): extracts big-endian uint16 start index at bytes 2-3, `led_count = (len(data)-4) // 3`
+- Parses ANIM_CMD (0xAC): calls `decode_animation_cmd`, stores result in `PacketLog.decoded`
+- Stores all received packets as `PacketLog` dataclasses for test assertions
+
+`tests/test_e2e_protocol.py` — 7 end-to-end tests using `asyncio.run()`:
+- `test_e2e_drgb_10_pixels` — DRGB 10 pixels, led_count verified
+- `test_e2e_drgbw_10_pixels` — DRGBW 10 pixels, led_count verified
+- `test_e2e_dnrgb_600_pixels` — 600-LED frame splits into 2 packets, start_indices 0 and 489
+- `test_e2e_animation_cmd_chase` — animation command round-trip, decoded animation=="chase"
+- `test_e2e_full_pipeline` — solid_color render -> encode_drgb -> send -> 20-LED DRGB frame verified
+- `test_e2e_sk6812_rgbw_pipeline` — solid_color -> RGBW encode -> DRGBW 15-LED frame verified
+- `test_simulator_standalone_import` — run_simulator importable without error
+
+TDD flow: RED commit (failing import) -> GREEN commit (simulator implemented, all 7 pass).
+
+### Task 2: UDPSender into FastAPI Lifespan
+
+`lightsync/main.py` updated:
+- Added `from lightsync.protocol.udp_sender import UDPSender` import
+- Lifespan startup: `UDPSender()` created, `await udp_sender.start()`, assigned to `app.state.udp_sender`
+- Lifespan shutdown: `await app.state.udp_sender.stop()` before `await registry.save()`
+- All existing lifespan code unchanged (beats cache, registry, show_store)
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Known Stubs
+
+None — all implemented functionality is fully wired.
+
+## Self-Check: PASSED
+
+See below.