Third failure uncovered by the restored pipeline. With checkout and the C++
build fixed, CI reached the WASM step and died on `[build-wasm] emcc not found
at emcc`: ci.yml passed `EMCC: emcc`, but the script's existence check
(`[[ ! -x "$EMCC" && ! -f "$EMCC" ]]`) only understands paths, so it looked for
a file literally named "emcc" in the working directory. This has been broken
for as long as the override existed; it was invisible because CI never got past
checkout to run it.
Resolve a bare command name through `command -v` before the check, and drop the
now-redundant EMCC override in ci.yml — setup-emsdk already puts emcc on PATH,
which is what the script's own default looks for.
Verified by invoking it the way CI does: `EMCC=emcc bash scripts/build-wasm.sh`
now builds. Incidentally confirms the new freshness gate is sound — the local
toolchain is the same pinned emcc 3.1.69, and the rebuild reproduced the
committed artifact byte-for-byte.
run-all-tests.sh ALL GREEN.
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