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, 7 insertions, 13 deletions

diff --git a/src/app/main.cc b/src/app/main.cc
index 406c944..75995ad 100644
--- a/src/app/main.cc
+++ b/src/app/main.cc
@@ -18,9 +18,9 @@
 #endif
 #endif
 #include "generated/assets.h" // Include generated asset header
-#include "gpu/demo_effects.h" // For GetDemoDuration()
+#include "gpu/demo_effects.h"
 #include "gpu/gpu.h"
-#include "generated/timeline_v2.h"
+#include "generated/timeline_v2.h" // For GetDemoDuration(), RenderV2Timeline()
 #include "platform/platform.h"
 #include "util/math.h"
 #include <cmath>
@@ -111,11 +111,6 @@ int main(int argc, char** argv) {
   // Initialize v2 sequences
   InitializeV2Sequences(*gpu_get_context(), width, height);
 
-  // Load timeline data (visual effects layering)
-#if !defined(DEMO_HEADLESS)
-  LoadTimeline(*gpu_get_main_sequence(), *gpu_get_context());
-#endif
-
 #if !defined(STRIP_ALL)
   // Set WAV dump backend if requested
   WavDumpBackend wav_backend;
@@ -205,8 +200,7 @@ int main(int argc, char** argv) {
       audio_render_silent((float)step);
     }
 
-    // Simulate Visuals
-    gpu_simulate_until((float)seek_time, g_tracker_score.bpm);
+    // V2: Visual simulation not needed (sequences render on-demand)
   }
 #endif /* !defined(STRIP_ALL) */
 
@@ -238,7 +232,7 @@ int main(int argc, char** argv) {
     double physical_time = 0.0;
     while (physical_time < headless_duration) {
       fill_audio_buffer(update_dt, physical_time);
-      gpu_simulate_until(g_music_time);
+      // V2: No simulation needed (sequences render on-demand)
       physical_time += update_dt;
 
       if ((int)physical_time % 5 == 0 &&
@@ -419,9 +413,9 @@ int main(int argc, char** argv) {
       last_graphics_print_time = current_physical_time;
     }
 
-    // Draw graphics using physical time and musical beat time
-    gpu_draw(visual_peak, aspect_ratio, (float)current_physical_time,
-             absolute_beat_time, beat_phase);
+    // Draw graphics using v2 timeline
+    RenderV2Timeline(gpu_get_surface(), (float)current_physical_time, width, height,
+                     absolute_beat_time, visual_peak);
     last_frame_time = current_physical_time;
 
     // Update audio systems (tracker, synth, etc.) based on audio time