OptLevel
Optimization level of a compiled bobbin variant. Higher wins when several variants exist for the same Target. The spike's fake compiler produced a single level; the durable VariantKey address carries the level so a real optimizer (WasmOptimizer) can publish variants at distinct efforts for the same source.
The real toolchain (D4) maps each level onto a wasm-opt invocation: O2 → -O2, O3 → -O3, Oz → -Oz (size-oriented). O0 is a passthrough — no variant worth shipping — served by PassthroughWasmOptimizer. wasm-opt preserves exported functions, so the warp_alloc/warp_run ABI survives every level.