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, 106 deletions

diff --git a/src/effects/theme_modulation_effect.cc b/src/effects/theme_modulation_effect.cc
deleted file mode 100644
index 82bfeb8..0000000
--- a/src/effects/theme_modulation_effect.cc
+++ /dev/null
@@ -1,106 +0,0 @@
-// This file is part of the 64k demo project.
-// It implements theme modulation (bright/dark alternation).
-
-#include "effects/theme_modulation_effect.h"
-#include "gpu/post_process_helper.h"
-#include "gpu/shaders.h"
-#include <cmath>
-
-struct ThemeModulationParams {
-  float theme_brightness;
-  float _pad[3];
-};
-static_assert(sizeof(ThemeModulationParams) == 16,
-              "ThemeModulationParams must be 16 bytes for WGSL alignment");
-
-ThemeModulationEffect::ThemeModulationEffect(const GpuContext& ctx)
-    : PostProcessEffect(ctx) {
-  const char* shader_code = R"(
-    struct VertexOutput {
-      @builtin(position) position: vec4<f32>,
-      @location(0) uv: vec2<f32>,
-    };
-
-    struct CommonUniforms {
-      resolution: vec2<f32>,
-      _pad0: f32,
-      _pad1: f32,
-      aspect_ratio: f32,
-      time: f32,
-      beat: f32,
-      audio_intensity: f32,
-    };
-
-    struct ThemeModulationParams {
-      theme_brightness: f32,
-      _pad0: f32,
-      _pad1: f32,
-      _pad2: f32,
-    };
-
-    @group(0) @binding(0) var inputSampler: sampler;
-    @group(0) @binding(1) var inputTexture: texture_2d<f32>;
-    @group(0) @binding(2) var<uniform> uniforms: CommonUniforms;
-    @group(0) @binding(3) var<uniform> params: ThemeModulationParams;
-
-    @vertex
-    fn vs_main(@builtin(vertex_index) vertexIndex: u32) -> VertexOutput {
-      var output: VertexOutput;
-      // Large triangle trick for fullscreen coverage
-      var pos = array<vec2<f32>, 3>(
-        vec2<f32>(-1.0, -1.0),
-        vec2<f32>(3.0, -1.0),
-        vec2<f32>(-1.0, 3.0)
-      );
-      output.position = vec4<f32>(pos[vertexIndex], 0.0, 1.0);
-      output.uv = pos[vertexIndex] * 0.5 + 0.5;
-      return output;
-    }
-
-    @fragment
-    fn fs_main(input: VertexOutput) -> @location(0) vec4<f32> {
-      let color = textureSample(inputTexture, inputSampler, input.uv);
-      // Apply theme brightness modulation
-      return vec4<f32>(color.rgb * params.theme_brightness, color.a);
-    }
-  )";
-
-  pipeline_ =
-      create_post_process_pipeline(ctx_.device, ctx_.format, shader_code);
-
-  params_buffer_ = gpu_create_buffer(
-      ctx_.device, 16, WGPUBufferUsage_Uniform | WGPUBufferUsage_CopyDst);
-}
-
-void ThemeModulationEffect::update_bind_group(WGPUTextureView input_view) {
-  pp_update_bind_group(ctx_.device, pipeline_, &bind_group_, input_view,
-                       uniforms_.get(), params_buffer_);
-}
-
-void ThemeModulationEffect::render(WGPURenderPassEncoder pass,
-                                   const CommonPostProcessUniforms& uniforms) {
-  uniforms_.update(ctx_.queue, uniforms);
-
-  // Alternate between bright and dark every 4 seconds (2 pattern changes)
-  // Music patterns change every 2 seconds at 120 BPM
-  float cycle_time = fmodf(uniforms.time, 8.0f); // 8 second cycle (4 patterns)
-  bool is_dark_section = (cycle_time >= 4.0f);   // Dark for second half
-
-  // Smooth transition between themes using a sine wave
-  float transition =
-      (std::sin(uniforms.time * 3.14159f / 4.0f) + 1.0f) * 0.5f; // 0.0 to 1.0
-  float bright_value = 1.0f;
-  float dark_value = 0.35f;
-  float theme_brightness =
-      bright_value + (dark_value - bright_value) * transition;
-
-  // Update params buffer
-  ThemeModulationParams params = {theme_brightness, {0.0f, 0.0f, 0.0f}};
-  wgpuQueueWriteBuffer(ctx_.queue, params_buffer_.buffer, 0, &params,
-                       sizeof(params));
-
-  // Render
-  wgpuRenderPassEncoderSetPipeline(pass, pipeline_);
-  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_, 0, nullptr);
-  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
-}