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, 2 insertions, 10 deletions

diff --git a/src/gpu/gpu.h b/src/gpu/gpu.h
index 3796517..876aa84 100644
--- a/src/gpu/gpu.h
+++ b/src/gpu/gpu.h
@@ -7,7 +7,6 @@
 #include "platform/platform.h"
 
 struct PlatformState; // Forward declaration
-class Effect;         // Forward declaration
 
 // GPU context bundling device, queue, and surface format
 struct GpuContext {
@@ -39,22 +38,15 @@ struct RenderPass {
   uint32_t instance_count;
 };
 
-class MainSequence; // Forward declaration
-
 void gpu_init(PlatformState* platform_state);
 void gpu_draw(float audio_peak, float aspect_ratio, float time, float beat_time,
               float beat_phase);
 void gpu_resize(int width, int height);
 void gpu_shutdown();
 
-const GpuContext* gpu_get_context();
-MainSequence* gpu_get_main_sequence();
+WGPUSurface gpu_get_surface();
 
-#if !defined(STRIP_ALL)
-void gpu_simulate_until(float time, float bpm = 120.0f);
-void gpu_add_custom_effect(Effect* effect, float start_time, float end_time,
-                           int priority);
-#endif
+const GpuContext* gpu_get_context();
 
 // Placeholder for GPU performance capture.
 // This define can be controlled via CMake to conditionally enable profiling