Shim in a different function to run the init generator to completion

When I tried to use the existing module within a Webpack project
I found that the generator was continuing with promises and trying
to initialize WebAssembly using them, which obviously failed.
This function seems to work a lot better for some reason, although
I haven't digged into why, exactly.

.github/workflows/wasmstan.yml

@@ -20,7 +20,7 @@ jobs:
         targets: wasm32-unknown-unknown,wasm32-wasip1
     - uses: taiki-e/install-action@v2
       with:
-        tool: cargo-binstall,just,wasmtime
+        tool: cargo-binstall,just,ripgrep,wasmtime
     - name: Install deps
       run: just components/install-deps
     - uses: actions/setup-node@v4

components/js/prophet-wasmstan/run.js

@@ -0,0 +1,17 @@
+// Note: this function comes from https://stackoverflow.com/questions/30401486/ecma6-generators-yield-promise.
+// It is used to convert a generator function into a promise.
+// `jco transpile` generates a similar function but it didn't work for me.
+// I'm not sure why, but I'll raise an issue on the `jco` repo.
+// See the `justfile` for how this gets shimmed into the transpiled code;
+// in short, we use `ripgrep` as in
+// https://unix.stackexchange.com/questions/181180/replace-multiline-string-in-files
+// (it was a Stack-Overflow heavy day...)
+// The indentation is intentional so the function matches the original.
+  function run(g) {
+    return Promise.resolve(function step(v) {
+      const res = g.next(v);
+      if (res.done) return res.value;
+      return res.value.then(step);
+    }());
+  }
+  return run(gen);

components/justfile

@@ -74,6 +74,14 @@ transpile: build
     --name prophet-wasmstan \
     --out-dir js/prophet-wasmstan \
     cpp/prophet-wasmstan/wit/prophet-wasmstan.wit
+  rg --replace="$(rg --invert-match --no-line-number '//' js/prophet-wasmstan/run.js)" \
+    --multiline --multiline-dotall \
+    --passthru \
+    --no-line-number \
+    '  let promise, resolve, reject;.+?return promise \|\| maybeSyncReturn;' \
+    js/prophet-wasmstan/prophet-wasmstan.js \
+    > js/prophet-wasmstan/prophet-wasmstan.fixed.js
+  mv js/prophet-wasmstan/prophet-wasmstan.fixed.js js/prophet-wasmstan/prophet-wasmstan.js
 
 test: transpile
   cd js/prophet-wasmstan && npm ci && npm run test:ci