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, 95 deletions

diff --git a/src/effects/flash_effect.cc b/src/effects/flash_effect.cc
deleted file mode 100644
index 00b5217..0000000
--- a/src/effects/flash_effect.cc
+++ /dev/null
@@ -1,95 +0,0 @@
-// This file is part of the 64k demo project.
-// It implements the FlashEffect - brief flash on u.beat hits.
-// Now supports parameterized color with per-frame animation.
-
-#include "effects/flash_effect.h"
-#include "gpu/post_process_helper.h"
-#include <cmath>
-
-// Backward compatibility constructor (delegates to parameterized constructor)
-FlashEffect::FlashEffect(const GpuContext& ctx)
-    : FlashEffect(ctx, FlashEffectParams{}) {
-}
-
-// Parameterized constructor
-FlashEffect::FlashEffect(const GpuContext& ctx, const FlashEffectParams& params)
-    : PostProcessEffect(ctx), params_(params) {
-  const char* shader_code = R"(
-    struct VertexOutput {
-      @builtin(position) position: vec4<f32>,
-      @location(0) uv: vec2<f32>,
-    };
-
-    struct Uniforms {
-      flash_intensity: f32,
-      audio_intensity: f32,
-      flash_color: vec3<f32>,  // Parameterized color
-      _pad: f32,
-    };
-
-    @group(0) @binding(0) var inputSampler: sampler;
-    @group(0) @binding(1) var inputTexture: texture_2d<f32>;
-    @group(0) @binding(2) var<uniform> uniforms: Uniforms;
-
-    @vertex
-    fn vs_main(@builtin(vertex_index) vertexIndex: u32) -> VertexOutput {
-      var output: VertexOutput;
-      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);
-      // Use parameterized flash color instead of hardcoded white
-      var flashed = mix(color.rgb, uniforms.flash_color, uniforms.flash_intensity);
-      return vec4<f32>(flashed, color.a);
-    }
-  )";
-
-  pipeline_ =
-      create_post_process_pipeline(ctx_.device, ctx_.format, shader_code);
-  flash_uniforms_.init(ctx_.device);
-}
-
-void FlashEffect::update_bind_group(WGPUTextureView input_view) {
-  pp_update_bind_group(ctx_.device, pipeline_, &bind_group_, input_view,
-                       flash_uniforms_.get(), {});
-}
-
-void FlashEffect::render(WGPURenderPassEncoder pass,
-                         const CommonPostProcessUniforms& uniforms) {
-  // Trigger flash based on configured threshold
-  if (uniforms.audio_intensity > params_.trigger_threshold &&
-      flash_intensity_ < 0.2f) {
-    flash_intensity_ = 0.8f; // Trigger flash
-  }
-
-  // Decay based on configured rate
-  flash_intensity_ *= params_.decay_rate;
-
-  // *** PER-FRAME PARAMETER COMPUTATION ***
-  // Animate color based on time and beat
-  const float r = params_.color[0] * (0.5f + 0.5f * sinf(uniforms.time * 0.5f));
-  const float g = params_.color[1] * (0.5f + 0.5f * cosf(uniforms.time * 0.7f));
-  const float b = params_.color[2] * (1.0f + 0.3f * uniforms.beat_phase);
-
-  // Update uniforms with computed (animated) values
-  const FlashUniforms u = {
-      .flash_intensity = flash_intensity_,
-      .intensity = uniforms.audio_intensity,
-      ._pad1 = {0.0f, 0.0f}, // Padding for vec3 alignment
-      .color = {r, g, b},    // Time-dependent, computed every frame
-      ._pad2 = 0.0f};
-  flash_uniforms_.update(ctx_.queue, u);
-
-  wgpuRenderPassEncoderSetPipeline(pass, pipeline_);
-  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_, 0, nullptr);
-  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
-}