WASM build uses wasi instead of freestanding due to C library dependencies

[roninjin10]

Problem

The WASM build currently uses wasm32-wasi instead of the preferred wasm32-freestanding target because the crypto module depends on C libraries that require libc.

Dependency Chain

wasm_mod → primitives_mod → crypto_mod → C libraries (bn254_wrapper.a, c-kzg-4844.a, blst.a) → libc

Current Workaround

• Using wasm32-wasi target which provides libc
• Disabled C library features in WASM build via build options:
  • use_bn254 = false
  • use_c_kzg = false
• BN254 and C-KZG precompiles are not available in WASM builds

Ideal Solution

To use wasm32-freestanding, we need to:

1. Option A: Compile C libraries to WASM

   • Build bn254_wrapper, c-kzg-4844, and blst as WASM libraries
   • May require significant porting work

2. Option B: Pure Zig implementations

   • Rewrite BN254 pairing operations in pure Zig
   • Rewrite KZG operations in pure Zig
   • Would be more maintainable but requires cryptographic expertise

3. Option C: Conditional compilation

   • Keep current approach but improve feature flags
   • Make precompiles gracefully degrade when C libraries unavailable
   • Document which features are unavailable in freestanding WASM

References

• See build.zig:523-531 for the TODO comment
• WASM build configuration starts at line 533 in build.zig

Impact

• WASM bundle size is larger due to WASI libc overhead
• Requires WASI runtime support (wasmtime, wasmer, or browser polyfills)
• Cannot run in minimal WASM environments that don't support WASI
• Some precompiles (BN254, KZG) are disabled in WASM builds