docs: Archive historical documentation (26 files → doc/archive/)

Moved completed/historical docs to doc/archive/ for cleaner context:

Archived (26 files):
- Analysis docs: variable tempo, audio architecture, build optimization
- Handoff docs: 6 agent handoff documents
- Debug reports: shadows, peak meter, timing fixes
- Task summaries and planning docs

Kept (16 files):
- Essential: AI_RULES, HOWTO, CONTRIBUTING, CONTEXT_MAINTENANCE
- Active subsystems: 3D, ASSET_SYSTEM, TRACKER, SEQUENCE
- Current work: MASKING_SYSTEM, SPECTRAL_BRUSH_EDITOR

Updated COMPLETED.md with archive index for easy reference.

1 files changed, 0 insertions, 359 deletions

diff --git a/doc/HANDOFF_2026-02-08.md b/doc/HANDOFF_2026-02-08.md
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-# Handoff: Shader Parametrization System (February 8, 2026)
-
-## Summary
-Completed comprehensive shader parametrization system enabling dynamic per-frame parameters for visual effects via uniform buffers and .seq file syntax.
-
-## Work Completed ✅
-
-### Shader Parametrization System (Task #73 Phase 0)
-**Goal**: Enable artists to configure visual effects with parameters (color, intensity, decay rates) via .seq files without touching C++ code.
-
-**Use Cases**: Flash effect with custom colors, chromatic aberration strength control, blur radius adjustment, distortion parameters.
-
-**Implementation**:
-
-#### Phase 1: UniformHelper Template
-- Created `src/gpu/uniform_helper.h` - Generic type-safe wrapper for WebGPU uniform buffers
-- Template class handles buffer creation, updates, and lifetime management
-- Zero-overhead abstraction over `gpu_create_buffer()` and `wgpuQueueWriteBuffer()`
-
-```cpp
-template <typename T>
-class UniformBuffer {
-  void init(WGPUDevice device);
-  void update(WGPUQueue queue, const T& data);
-  GpuBuffer& get();
-};
-```
-
-#### Phase 2: FlashEffect Parameter Structs
-- Added `FlashEffectParams` (constructor-time base parameters):
-  - `color[3]` - RGB flash color (default: white)
-  - `decay_rate` - Flash fade rate per frame (default: 0.98)
-  - `trigger_threshold` - Intensity threshold to trigger flash (default: 0.7)
-
-- Added `FlashUniforms` (GPU buffer layout with WGSL alignment):
-  - `flash_intensity` (4 bytes, offset 0)
-  - `intensity` (4 bytes, offset 4)
-  - `_pad1[2]` (8 bytes, offset 8-15) - **Padding for vec3 alignment**
-  - `color[3]` (12 bytes, offset 16-27) - **Aligned to 16 bytes**
-  - `_pad2` (4 bytes, offset 28-31)
-  - Total: 32 bytes (enforced with `static_assert`)
-
-#### Phase 3: Parameterized WGSL Shader
-- Updated `flash_effect.cc` shader to use `uniforms.flash_color` instead of hardcoded white
-- Shader bindings: sampler (0), texture (1), uniforms (2)
-- Fragment shader mixes input color with parameterized flash color based on flash intensity
-
-```wgsl
-struct Uniforms {
-  flash_intensity: f32,
-  intensity: f32,
-  flash_color: vec3<f32>,  // Parameterized color
-  _pad: f32,
-};
-
-fn fs_main(input: VertexOutput) -> @location(0) vec4<f32> {
-  let color = textureSample(inputTexture, inputSampler, input.uv);
-  var flashed = mix(color.rgb, uniforms.flash_color, uniforms.flash_intensity);
-  return vec4<f32>(flashed, color.a);
-}
-```
-
-#### Phase 4: Per-Frame Parameter Computation
-- Implemented dynamic parameter animation in `FlashEffect::render()` method
-- Parameters computed each frame based on time, beat, and intensity
-- Example: Color modulated by sinusoidal functions of time and beat
-
-```cpp
-// Animate color based on time and beat
-const float r = params_.color[0] * (0.5f + 0.5f * sinf(time * 0.5f));
-const float g = params_.color[1] * (0.5f + 0.5f * cosf(time * 0.7f));
-const float b = params_.color[2] * (1.0f + 0.3f * beat);
-
-const FlashUniforms u = {
-  .flash_intensity = flash_intensity_,
-  .intensity = intensity,
-  ._pad1 = {0.0f, 0.0f},
-  .color = {r, g, b},
-  .pad2 = 0.0f
-};
-uniforms_.update(ctx_.queue, u);
-```
-
-#### Phase 5: .seq Syntax Extension
-- Extended `seq_compiler.cc` to parse `key=value` parameters after effect class name
-- Added `parse_parameters()` function to extract parameter pairs
-- Code generation creates `FlashEffectParams` struct initialization for parameterized effects
-- Backward compatibility: Effects without parameters use default constructor
-
-**Syntax Example**:
-```
-EFFECT + FlashEffect 0 1 color=1.0,0.5,0.5 decay=0.95
-```
-
-**Generated Code**:
-```cpp
-{
-  FlashEffectParams p;
-  p.color[0] = 1.0f;
-  p.color[1] = 0.5f;
-  p.color[2] = 0.5f;
-  p.decay_rate = 0.95f;
-  seq->add_effect(std::make_shared<FlashEffect>(ctx, p), 0.0f, 1.f, 0);
-}
-```
-
----
-
-### Critical Bugfix: WGSL Alignment
-**Problem**: WebGPU validation error "Buffer is bound with size 24 where the shader expects 32"
-
-**Root Cause**: WGSL alignment rules require `vec3<f32>` to be 16-byte aligned despite having 12-byte size. Initial `FlashUniforms` struct layout was:
-```cpp
-struct FlashUniforms {
-  float flash_intensity;  // 0-3
-  float intensity;        // 4-7
-  float color[3];         // 8-19 (WRONG - no padding)
-  float _pad;             // 20-23
-};  // Total: 24 bytes (WRONG)
-```
-
-**Solution**: Added explicit padding to align `color` array to 16-byte boundary:
-```cpp
-struct FlashUniforms {
-  float flash_intensity;  // 0-3
-  float intensity;        // 4-7
-  float _pad1[2];         // 8-15 (padding)
-  float color[3];         // 16-27 (aligned to 16 bytes)
-  float _pad2;            // 28-31
-};  // Total: 32 bytes (CORRECT)
-static_assert(sizeof(FlashUniforms) == 32, "FlashUniforms must be 32 bytes");
-```
-
-**Impact**: Demo now runs without validation errors, all 32/32 tests pass.
-
----
-
-## Files Modified
-
-**New Files (3)**:
-- `src/gpu/uniform_helper.h` - UniformBuffer template class
-- `src/tests/test_uniform_helper.cc` - Unit test for template compilation
-- `doc/SHADER_PARAMETRIZATION_PLAN.md` - Complete design document
-
-**Modified Files (11)**:
-- `src/gpu/effects/flash_effect.h` - Added FlashEffectParams, FlashUniforms structs, parameterized constructor
-- `src/gpu/effects/flash_effect.cc` - Implemented per-frame computation, updated shader with parameterized color
-- `src/gpu/demo_effects.h` - Removed duplicate FlashEffect definition, added include
-- `tools/seq_compiler.cc` - Added parameter parsing and code generation
-- `assets/demo.seq` - Added example with parameters
-- `src/generated/timeline.cc` - Generated code with struct initialization
-- `CMakeLists.txt` - Added test_uniform_helper target
-- `TODO.md` - Added Task #73 (extend to other effects), moved completion to summary
-- `PROJECT_CONTEXT.md` - Updated "Recently Completed" section
-- `doc/COMPLETED.md` - Added detailed completion entry
-- `doc/HANDOFF_2026-02-08.md` - This document
-
----
-
-## Commits Made
-
-**c7d1dd7** - `feat(gpu): Implement shader parametrization system`
-- Phases 1-5 implementation
-- 11 files changed (808+ / 40-)
-- UniformHelper template + FlashEffect parametrization + .seq syntax
-
-**775c0ea** - `fix(gpu): Correct FlashUniforms struct alignment for WGSL`
-- Critical alignment bugfix (24 → 32 bytes)
-- Added static_assert for future safety
-- Fixed validation error
-
----
-
-## Test Results
-
-**All 32/32 tests passing (100%)**
-
-**Test Coverage**:
-- `test_uniform_helper.cc` - Verifies UniformBuffer template compiles correctly
-- `test_demo_effects.cc` - All post-process and scene effects instantiate successfully
-- Full shader compilation tests pass with new parameterized shaders
-
-**Verification**:
-- Demo runs without WebGPU validation errors
-- Visual effects render with parameterized colors
-- .seq file parsing generates correct parameter initialization code
-- Per-frame animation produces time-dependent color modulation
-
----
-
-## Current Status
-
-**Completed:**
-- ✅ Full shader parametrization infrastructure
-- ✅ FlashEffect fully parameterized with color/decay control
-- ✅ .seq syntax extension with key=value parsing
-- ✅ Per-frame dynamic parameter computation
-- ✅ Critical WGSL alignment bug fixed
-- ✅ Documentation updated (TODO.md, PROJECT_CONTEXT.md, COMPLETED.md)
-
-**Ready for:**
-- Task #73: Extend parametrization to other effects (ChromaAberrationEffect, GaussianBlurEffect, DistortEffect, SolarizeEffect)
-- Additional parameter types (vec2, vec4, enums)
-- Parameter curve system for keyframe animation (future)
-
----
-
-## Technical Notes
-
-### WGSL Alignment Rules
-**Critical for future implementations:**
-- `vec3<f32>` has **size = 12 bytes** but **alignment = 16 bytes**
-- Always add padding before vec3 fields to align to 16-byte boundary
-- Use `static_assert(sizeof(YourStruct) == expected_size)` to catch misalignment
-- Reference: [WebGPU WGSL Spec - Alignment and Size](https://www.w3.org/TR/WGSL/#alignment-and-size)
-
-### UniformHelper Pattern
-**Reusable template for any effect parameters:**
-```cpp
-// 1. Define parameter structs
-struct YourEffectParams { /* constructor-time params */ };
-struct YourEffectUniforms { /* GPU buffer layout with padding */ };
-static_assert(sizeof(YourEffectUniforms) == expected_size);
-
-// 2. Add UniformBuffer member
-UniformBuffer<YourEffectUniforms> uniforms_;
-
-// 3. Initialize in constructor
-uniforms_.init(ctx_.device);
-
-// 4. Update in render()
-const YourEffectUniforms u = { /* compute values */ };
-uniforms_.update(ctx_.queue, u);
-
-// 5. Bind in shader
-pipeline_ = create_pipeline(...);
-bind_group_ = create_bind_group(..., uniforms_.get().buffer, ...);
-```
-
-### Backward Compatibility
-**All existing effects continue to work:**
-- Default parameter constructor delegates to parameterized constructor
-- Effects without .seq parameters use default values
-- No changes required to existing timeline code
-
----
-
-## Design Document
-
-**Complete design**: See `doc/SHADER_PARAMETRIZATION_PLAN.md`
-
-**Key Sections**:
-- Motivation and use cases
-- 5-phase implementation plan
-- WGSL alignment rules and solutions
-- Per-frame vs constructor-time parameters
-- .seq syntax specification
-- Migration path for existing effects
-- Size budget analysis (~400-500 bytes)
-- Alternative approaches considered
-
----
-
-## Size Impact
-
-**Binary Size**: +400-500 bytes net
-- UniformHelper template code: ~200 bytes
-- FlashEffectParams/Uniforms structs: ~100 bytes
-- Per-effect parameter overhead: ~50-100 bytes each
-- .seq compiler parameter parsing: ~100 bytes
-
-**Trade-off**: Acceptable size increase for significant artist workflow improvement (no C++ recompilation for parameter tweaks).
-
----
-
-## Next Steps (Recommendations)
-
-### Immediate (Task #73)
-Extend parametrization to other effects using FlashEffect as template:
-
-1. **ChromaAberrationEffect**:
-   - Parameters: `offset` (vec2), `strength` (float)
-   - Syntax: `EFFECT + ChromaAberrationEffect 0 5 offset=0.01,0.02 strength=1.5`
-
-2. **GaussianBlurEffect**:
-   - Parameters: `radius` (float), `sigma` (float)
-   - Syntax: `EFFECT + GaussianBlurEffect 2 8 radius=5.0 sigma=2.0`
-
-3. **DistortEffect** (if exists):
-   - Parameters: `amount` (float), `speed` (float), `scale` (vec2)
-
-4. **SolarizeEffect**:
-   - Parameters: `threshold` (float), `intensity` (float)
-
-### Future Enhancements
-- Parameter curve system (keyframe animation via .seq timeline)
-- vec4/mat4 parameter support (color with alpha, transformation matrices)
-- Enum parameters (blend modes, filter types)
-- Parameter validation and clamping (min/max ranges)
-
----
-
-## Context for Next Session
-
-### What Works
-- Shader parametrization infrastructure fully functional
-- FlashEffect demonstrates complete implementation pattern
-- .seq syntax parsing robust with backward compatibility
-- All tests passing, demo stable
-
-### Known Limitations
-- Only FlashEffect parametrized (other effects use hardcoded values)
-- No parameter validation or range clamping
-- No keyframe animation support (future feature)
-
-### Migration Pattern for Other Effects
-1. Copy `FlashEffectParams` / `FlashUniforms` pattern
-2. Add `UniformBuffer<YourUniforms>` member
-3. Update shader to use uniform values
-4. Implement per-frame computation in `render()`
-5. Extend `seq_compiler.cc` with effect-specific parameter parsing
-6. Test with .seq file, verify alignment with static_assert
-
----
-
-## User Feedback Summary
-
-**Session Start**: User requested shader parametrization with use cases (flash colors, aberration strength)
-
-**Key Clarifications**:
-- User confirmed parameters will be "generated in the code (manually, in effect's C++ code)"
-- User emphasized "precision: user change parameter values on a per-frame basis. time-dependent"
-- Critical feedback: Per-frame computation required, not just static constructor params
-
-**Critical Bug Report**: User provided log.txt showing GPU validation error (buffer size mismatch)
-
-**Outcome**: User satisfied, requested commit + documentation update (completed)
-
----
-
-## Handoff Checklist
-
-- [x] All tests passing (32/32)
-- [x] Working tree clean
-- [x] Documentation updated (TODO.md, PROJECT_CONTEXT.md, COMPLETED.md)
-- [x] Commits created with detailed messages (c7d1dd7, 775c0ea)
-- [x] No known regressions
-- [x] Design document complete (SHADER_PARAMETRIZATION_PLAN.md)
-- [x] Extension task noted (Task #73)
-- [x] Ready for next session
-
----
-
-**handoff(Claude):** Shader parametrization system complete. FlashEffect fully parameterized with .seq syntax. Critical alignment bug fixed. 32/32 tests passing. Ready for extension to other effects (Task #73).
-
----
-
-*Generated: February 8, 2026*
-*Claude Sonnet 4.5*