refactor(code-runtime): remove subprocess backend

packages/code-runtime/code-runtime-worker/tsdown.config.ts

@@ -1,10 +1,9 @@
 import { defineConfig } from 'tsdown'
 
 /**
- * Build the plugin, reusable runtime host, and worker as separate bundles. The
- * sibling `worker.cjs` is loaded by file and must be CommonJS for pkg's VFS
- * Worker hook. Separate builds inline shared implementation instead of
- * emitting an unlisted chunk outside the exact `files` whitelist.
+ * Build the index and worker as separate single-entry bundles. The sibling `worker.cjs` is loaded
+ * by file and must be CommonJS for pkg's VFS Worker hook. A multi-entry build emits an unlisted
+ * shared chunk omitted by the package's exact `files` whitelist; separate builds inline it.
  */
 export default defineConfig([
   {
@@ -17,16 +16,6 @@ export default defineConfig([
     dts: false,
     clean: false,
   },
-  {
-    entry: ['lib/types/runtime-host.js'],
-    outDir: 'lib',
-    format: ['esm'],
-    platform: 'node',
-    target: 'es2024',
-    fixedExtension: false,
-    dts: false,
-    clean: false,
-  },
   {
     entry: ['lib/types/worker.js'],
     outDir: 'lib',