fix: add CJS support to @netlify/runtime-utils to fix ERR_REQUIRE_ESM (#510)

@netlify/blobs is dual-format (CJS + ESM) and depends on @netlify/runtime-utils.
When the CJS build of @netlify/blobs is used (e.g., in Background Functions),
it tries to require() @netlify/runtime-utils, which was ESM-only, causing
ERR_REQUIRE_ESM errors at runtime.

This change makes @netlify/runtime-utils dual-format so it can be consumed
by both CJS and ESM contexts.

When @netlify/blobs becomes ESM-only in the future, we can remove CJS
support from @netlify/runtime-utils as well.

Fixes #437

Author: serhalp

packages/runtime-utils/package.json

@@ -6,9 +6,25 @@
   "engines": {
     "node": "^18.14.0 || >=20"
   },
-  "main": "./dist/main.js",
-  "exports": "./dist/main.js",
+  "main": "./dist/main.cjs",
+  "module": "./dist/main.js",
   "types": "./dist/main.d.ts",
+  "exports": {
+    ".": {
+      "require": {
+        "types": "./dist/main.d.cts",
+        "default": "./dist/main.cjs"
+      },
+      "import": {
+        "types": "./dist/main.d.ts",
+        "default": "./dist/main.js"
+      },
+      "default": {
+        "types": "./dist/main.d.ts",
+        "default": "./dist/main.js"
+      }
+    }
+  },
   "files": [
     "dist/**/*"
   ],

packages/runtime-utils/tsup.config.ts

@@ -7,7 +7,10 @@ export default defineConfig([
     clean: true,
     entry: ['src/main.ts'],
     outDir: 'dist',
-    format: ['esm'],
+    // We build both CJS and ESM because @netlify/blobs is dual-format and depends on this package.
+    // When @netlify/blobs becomes ESM-only, we can remove CJS here and go ESM-only too.
+    // See: https://github.com/netlify/primitives/issues/437
+    format: ['cjs', 'esm'],
     dts: true,
     splitting: false,
     watch: argv.includes('--watch'),