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, 0 insertions, 104 deletions

diff --git a/src/effects/flash_cube_effect.cc b/src/effects/flash_cube_effect.cc
deleted file mode 100644
index c578776..0000000
--- a/src/effects/flash_cube_effect.cc
+++ /dev/null
@@ -1,104 +0,0 @@
-// This file is part of the 64k demo project.
-// It implements the FlashCubeEffect - a flashing background cube with Perlin
-// noise.
-
-#include "effects/flash_cube_effect.h"
-#include "generated/assets.h"
-#include "util/asset_manager_utils.h"
-#include <cmath>
-#include <iostream>
-
-FlashCubeEffect::FlashCubeEffect(const GpuContext& ctx) : Effect(ctx) {
-}
-
-void FlashCubeEffect::resize(int width, int height) {
-  if (width == width_ && height == height_)
-    return;
-
-  Effect::resize(width, height);
-
-  if (!initialized_)
-    return;
-
-  renderer_.resize(width_, height_);
-}
-
-void FlashCubeEffect::init(MainSequence* demo) {
-  (void)demo;
-  WGPUTextureFormat format = demo->gpu_ctx.format;
-
-  renderer_.init(ctx_.device, ctx_.queue, ctx_.format);
-  renderer_.resize(width_, height_);
-  initialized_ = true;
-
-  // Texture Manager
-  texture_manager_.init(ctx_.device, ctx_.queue);
-
-  // Load Perlin noise texture
-  TextureAsset noise_tex = GetTextureAsset(AssetId::ASSET_NOISE_TEX);
-  if (noise_tex.pixels && noise_tex.width == 256 && noise_tex.height == 256) {
-    texture_manager_.create_texture("noise", noise_tex.width, noise_tex.height,
-                                    noise_tex.pixels);
-    renderer_.set_noise_texture(texture_manager_.get_texture_view("noise"));
-  } else {
-    std::cerr << "Failed to load NOISE_TEX asset for FlashCubeEffect."
-              << std::endl;
-  }
-
-  // Create a very large background cube
-  // Scale and distance ensure it's clearly behind foreground objects
-  scene_.clear();
-  Object3D cube(ObjectType::BOX);
-  cube.position = vec3(0, 0, 0);
-  cube.scale = vec3(30.0f, 30.0f, 30.0f); // Much larger cube
-  cube.color = vec4(0.3f, 0.3f, 0.5f, 1.0f); // Dark blue base color
-  scene_.add_object(cube);
-}
-
-void FlashCubeEffect::render(WGPURenderPassEncoder pass,
-                             const CommonPostProcessUniforms& uniforms) {
-  // Detect beat changes for flash trigger (using intensity as proxy for beat
-  // hits) Intensity spikes on beats, so we can use it to trigger flashes
-  if (uniforms.audio_intensity > 0.5f &&
-      flash_intensity_ < 0.2f) { // High intensity + flash cooled down
-    flash_intensity_ = 1.0f;     // Trigger full flash
-  }
-
-  // Exponential decay of flash
-  flash_intensity_ *= 0.95f; // Slower fade for more visible effect
-
-  // Always have base brightness, add flash on top
-  float base_brightness = 0.2f;
-  float flash_boost =
-      base_brightness + flash_intensity_ * 0.8f; // 0.2 to 1.0 range
-
-  scene_.objects[0].color =
-      vec4(0.4f * flash_boost, // Reddish tint
-           0.6f * flash_boost, // More green
-           1.0f * flash_boost, // Strong blue for background feel
-           1.0f);
-
-  // Slowly rotate the cube for visual interest
-  scene_.objects[0].rotation =
-      quat::from_axis(vec3(0.3f, 1, 0.2f), uniforms.time * 0.04f);
-
-  // Position camera OUTSIDE the cube looking at it from a distance
-  // This way we see the cube as a background element
-  float cam_distance = 150.0f; // Much farther to ensure it's behind everything
-  float orbit_angle = uniforms.time * 0.1f;
-
-  camera_.set_look_at(
-      vec3(std::sin(orbit_angle) * cam_distance,
-           std::cos(orbit_angle * 0.3f) * 30.0f,
-           std::cos(orbit_angle) * cam_distance), // Camera orbits around
-      vec3(0, 0, 0),                              // Look at cube center
-      vec3(0, 1, 0));
-
-  camera_.aspect_ratio = uniforms.aspect_ratio;
-  // Extend far plane to accommodate distant camera position (150 units + cube
-  // size)
-  camera_.far_plane = 300.0f;
-
-  // Draw the cube
-  renderer_.draw(pass, scene_, camera_, uniforms.time);
-}