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, 9 insertions, 0 deletions

diff --git a/doc/archive/GPU_EFFECTS_TEST_ANALYSIS.md b/doc/archive/GPU_EFFECTS_TEST_ANALYSIS.md
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+# GPU Effects Test Coverage Analysis (Archived)
+
+**Analysis Complete**: The "GPU Effects Test Coverage Analysis" (originally in this file) has been summarized and its detailed implementation plan archived in `doc/COMPLETED.md` under "Recently Completed (February 8, 2026) - GPU Effects Test Coverage Analysis."
+
+**Key Findings**: Low test coverage (~20%) for GPU effects due to WebGPU init overhead, render surface needs, and lack of frame validation.
+
+**Proposed Solution**: Headless rendering with offscreen targets and WebGPU test fixtures for automated testing. Aim: ~50% GPU test coverage.
+
+**Original Detailed Plan**: The full implementation plan, including phases, test structure, and file lists, is now located in `doc/COMPLETED.md` for historical reference.
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