WASM Spore: add WebGPU acceleration for HDC operations

[Tristan-Stoltz-ERC]

Summary

The Spore WASM kernel (crates/symthaea-spore/) currently runs all HDC operations on CPU. WebGPU could accelerate bulk XOR/bind/bundle operations on 16,384-dimensional binary hypervectors.

Hot path to accelerate

1. Encode — text/numeric to 16,384D binary hypervector
2. Bind — XOR-based binding (associative memory)
3. Bundle — majority-vote bundling (set union)
4. Similarity — Hamming distance computation

These operations are embarrassingly parallel across the 16,384 dimensions and across batch inputs.

Constraints

• Current WASM binary size: 324KB (budget: 500KB)
• WebGPU adds ~50-100KB of binding overhead
• Must fall back gracefully to CPU when WebGPU is unavailable
• The wgpu crate supports WebGPU targets via wasm-bindgen

Architecture considerations

• Compute shaders for bulk XOR (bind) and popcount (similarity)
• Buffer management for hypervector pools
• Async GPU readback vs synchronous CPU fallback
• Integration with the existing Spore module system (10 modules)

References

• wgpu — Rust WebGPU implementation
• WebGPU spec — W3C standard
• Spore browser demo uses tabbed UI with cognitive subsystem visualization