The prebuilt files include `web/pdf_viewer.js` with some viewer APIs. Those are missing from type declarations.
"dev-sandbox",
  gulp.series(
    function scriptingDevSandbox() {
      const defines = builder.merge(DEFINES, { GENERIC: true, TESTING: true });
      return createTemporaryScriptingBundle(defines, {
        disableVersionInfo: true,
      });
    },
    function createDevSandbox() {
      console.log();
      console.log("### Building development sandbox");
      const defines = builder.merge(DEFINES, { GENERIC: true, TESTING: true });
      const sandboxDir = BUILD_DIR + "dev-sandbox/";
      rimraf.sync(sandboxDir);
      return createSandboxBundle(defines, {
        disableVersionInfo: true,
      }).pipe(gulp.dest(sandboxDir));
    }
  )
);
gulp.task(
  "server",
  gulp.parallel(
    function watchDevSandbox() {
      gulp.watch(
        [
          "src/pdf.{sandbox,sandbox.external,scripting}.js",
          "src/scripting_api/*.js",
          "src/shared/scripting_utils.js",
          "external/quickjs/*.js",