fix(build): resolve a bare EMCC command name in build-wasm.sh

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.

.github/workflows/ci.yml

@@ -70,10 +70,8 @@ jobs:
         run: bash scripts/parity-check.sh
 
       - name: Build WASM
-        env:
-          # The script defaults to /usr/lib/emscripten/emcc; the runner gets
-          # emcc on PATH via setup-emsdk. Override.
-          EMCC: emcc
+        # setup-emsdk puts emcc on PATH; build-wasm.sh picks it up via
+        # `command -v emcc`. No EMCC override needed.
         run: bash scripts/build-wasm.sh
 
       - name: Parity check (native vs WASM)

scripts/build-wasm.sh

@@ -18,9 +18,16 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 OUT="$ROOT/manifold/public"
 SRC="$ROOT/nisps/wasm/bindings.cpp"
 
+# EMCC may be a bare command name on PATH (emsdk installs it that way) or an
+# absolute path. Resolve the former before the existence check, which otherwise
+# looks for a file of that name in the CWD and always fails.
+if [[ "$EMCC" != */* ]]; then
+  EMCC="$(command -v "$EMCC" || echo "$EMCC")"
+fi
+
 if [[ ! -x "$EMCC" && ! -f "$EMCC" ]]; then
   echo "[build-wasm] emcc not found at $EMCC" >&2
-  echo "[build-wasm] set EMCC=/path/to/emcc and retry." >&2
+  echo "[build-wasm] set EMCC=/path/to/emcc (or put emcc on PATH) and retry." >&2
   exit 2
 fi