Implements the Phase A A4 NIT-1 fix from codex Phase A gate review
(verdict GO, 2 NITs flagged): the local equivalent of the Step 1b §6
+ §7.1 CI gate, runnable by developers before submitting Phase A-E
PRs. The full CI workflow remains DEFERRED in
`.github/workflows/rust-release.yml` until brew emscripten install +
EMSDK + .wasm.a → .a symlink + wasm-bindgen + wasm-opt are
automated; until then this script is the authoritative gate.
What it enforces (matches spec §6 + §7.1):
- EMSDK env var present (build-time-only emsdk libcxx headers +
wasm-aware clang)
- cargo build → wasm-bindgen → wasm-opt -Oz pipeline succeeds
- 0 env.* imports in the post-bindgen bundle (any leak = LinkError
at load time = regression)
- gzip size ≤ STEP1B_SHELL_WASM_GZIP_LIMIT_BYTES (default 1 MiB)
Verified on the C-hard.2 bundle: 613 006 bytes gzip (58% of 1 MiB
ceiling), 0 env.* imports, exit 0.
Step 1b Phase A — completes A3 (local) + A4 (codex verdict GO).
