feat(sequence): complete v2 migration with DAG-based routing

Phase 4 complete: V1 system removed, v2 fully operational.

Architecture Changes:
- Explicit Node system with typed buffers (u8x4_norm, f32x4, depth24)
- DAG effect routing with multi-input/multi-output support
- Python compiler (seq_compiler_v2.py) with topological sort and ping-pong optimization
- Compile-time node aliasing for framebuffer reuse

V1 Removal (~4KB):
- Deleted effect.h/cc base classes (1.4KB)
- Deleted 19 v1 effect pairs: heptagon, particles, passthrough, gaussian_blur,
  solarize, scene1, chroma_aberration, vignette, hybrid_3d, flash_cube,
  theme_modulation, fade, flash, circle_mask, rotating_cube, sdf_test,
  distort, moving_ellipse, particle_spray (2.7KB)

V2 Effects Ported:
- PassthroughEffectV2, PlaceholderEffectV2
- GaussianBlurEffectV2 (multi-pass with temp nodes)
- HeptagonEffectV2 (scene effect with dummy texture)
- ParticlesEffectV2 (compute + render, format fixed)
- RotatingCubeEffectV2 (3D with depth node)
- Hybrid3DEffectV2 (Renderer3D integration, dummy textures for noise/sky)

Compiler Features:
- DAG validation (cycle detection, connectivity checks)
- Topological sort for execution order
- Ping-pong optimization (aliased node detection)
- Surface-based and encoder-based RenderV2Timeline generation
- init_effect_nodes() automatic generation

Fixes Applied:
- WebGPU binding layout validation (standard v2 post-process layout)
- Surface format mismatch (ctx.format for blit, RGBA8Unorm for framebuffers)
- Depth attachment compatibility (removed forced depth from gpu_create_render_pass)
- Renderer3D texture initialization (created dummy 1x1 white textures)
- ParticlesEffectV2 format (changed from ctx.format to RGBA8Unorm)
- Encoder-based RenderV2Timeline (added missing preprocess() call)

Testing:
- 34/36 tests passing (2 v1-dependent tests disabled)
- demo64k runs successfully (no crashes)
- All seek positions work (--seek 12, --seek 15 validated)

Documentation:
- Updated PROJECT_CONTEXT.md (v2 status, reference to SEQUENCE_v2.md)
- Added completion entry to COMPLETED.md

TODO (Future):
- Port CNN effects to v2
- Implement flatten mode (--flatten code generation)
- Port remaining 10+ effects
- Update HTML timeline editor for v2 (deferred)

handoff(Claude): Sequence v2 migration complete, v1 removed, system operational.
Phase 5 (editor) deferred per user preference.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/PROJECT_CONTEXT.md b/PROJECT_CONTEXT.md
index 3a7995c..f4c1f04 100644
--- a/PROJECT_CONTEXT.md
+++ b/PROJECT_CONTEXT.md
@@ -39,8 +39,8 @@
 - **Effects:** CNN post-processing: CNNEffect (v1) and CNNv2Effect operational. CNN v2: sigmoid activation, storage buffer weights (~3.2 KB), 7D static features, dynamic layers. Training stable, convergence validated.
 - **Tools:** CNN test tool operational. Texture readback utility functional. Timeline editor (web-based, beat-aligned, audio playback).
 - **Build:** Asset dependency tracking. Size measurement. Hot-reload (debug-only).
-- **Sequence v2 (In Progress):** DAG-based effect routing. Phase 1 (foundation) & Phase 2 (compiler) complete. Node system, topological sort, Python compiler operational. See `doc/SEQUENCE_v2.md`.
-- **Testing:** **35/35 passing (100%)**
+- **Sequence v2:** DAG-based effect routing with explicit node system. Python compiler with topological sort and ping-pong optimization. V1 removed, 7 effects ported (Passthrough, Placeholder, GaussianBlur, Heptagon, Particles, RotatingCube, Hybrid3D). See `doc/SEQUENCE_v2.md`.
+- **Testing:** **34/36 passing** (2 v1-dependent tests disabled pending v2 port)
 
 ---
 
@@ -58,7 +58,7 @@ See `TODO.md` for current priorities and active tasks.
 - `doc/CONTRIBUTING.md` - Development protocols
 
 **Technical Reference:**
-- Core: `ASSET_SYSTEM.md`, `SEQUENCE.md`, `TRACKER.md`, `3D.md`, `cnn_v1/docs/CNN_V1_EFFECT.md`, `cnn_v2/docs/CNN_V2.md`
+- Core: `ASSET_SYSTEM.md`, `SEQUENCE_v2.md`, `TRACKER.md`, `3D.md`, `cnn_v1/docs/CNN_V1_EFFECT.md`, `cnn_v2/docs/CNN_V2.md`
 - Formats: `SCENE_FORMAT.md`, `MASKING_SYSTEM.md`
 - Tools: `BUILD.md`, `WORKSPACE_SYSTEM.md`, `SIZE_MEASUREMENT.md`, `cnn_v1/docs/CNN_TEST_TOOL.md`, `tools/timeline_editor/README.md`