fix: handle CJS in SSR dev mode and fix React compat aliasing

- Add lightweight CJS shim in deno.ts load hook for dev mode: wraps
  CJS files in node_modules with module/exports/require so Vite's
  SSR module runner can evaluate them. Only ~30 lines vs the old
  960-line Babel CJS transform. Only runs in dev mode — build mode
  uses Rollup's @rollup/plugin-commonjs natively.

- Restore ssr.noExternal: true so resolve.alias (react -> preact/compat)
  is applied consistently in SSR. Without it, Node.js require() bypasses
  aliases and loads real react@19.1.1.

- Apply resolve.alias in deno.ts resolveId before @deno/loader runs,
  so aliased specifiers (react, react-dom) resolve to preact/compat
  through the Deno resolution pipeline.

- Remove environment-level noExternal (was duplicated).

Test results: 35/36 dev tests pass, 31/31 build tests pass.
The 1 failing test (remote island) is pre-existing on main.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bartlomieju

packages/plugin-vite/src/mod.ts

@@ -112,6 +112,13 @@ export function fresh(config?: FreshViteConfig): Plugin[] {
 
         return {
           define: envDefine,
+          ssr: {
+            // Bundle all deps in SSR so that resolve.alias
+            // (react -> preact/compat) is applied consistently.
+            // CJS packages are handled by the deno plugin's load
+            // hook which wraps them in an ESM-compatible shim.
+            noExternal: true,
+          },
           server: {
             watch: {
               // Ignore temp files, editor swap files, and Vite timestamp
@@ -179,13 +186,6 @@ export function fresh(config?: FreshViteConfig): Plugin[] {
               },
             },
             ssr: {
-              resolve: {
-                // Packages that depend on React compat aliases must not
-                // be externalized — Node.js require() wouldn't apply
-                // the react->preact/compat alias and would load the
-                // real React or get CJS/ESM interop issues.
-                noExternal: [/^@radix-ui/],
-              },
               build: {
                 manifest: true,
                 emitAssets: true,

packages/plugin-vite/src/plugins/deno.ts

@@ -184,6 +184,47 @@ export function deno(): Plugin {
         ? ssrLoader
         : browserLoader;
 
+      // In dev mode, non-external CJS files go through Vite's SSR
+      // module runner which evaluates them as ESM. Wrap CJS files
+      // with an ESM shim that provides module/exports/require. In
+      // build mode, Rollup's @rollup/plugin-commonjs handles CJS.
+      if (
+        isDev &&
+        !id.startsWith("\0") &&
+        id.includes("node_modules") &&
+        /\.(c?js|cjs)$/.test(id)
+      ) {
+        try {
+          const code = await Deno.readTextFile(id);
+          // Quick heuristic: if file has CJS patterns and no ESM
+          if (
+            !code.includes("export ") &&
+            !code.includes("import ") &&
+            (code.includes("module.exports") ||
+              code.includes("exports.") ||
+              code.includes("require("))
+          ) {
+            const wrapped = `
+import { createRequire as __fresh_createRequire } from "node:module";
+import { fileURLToPath as __fresh_fileURLToPath } from "node:url";
+import { dirname as __fresh_dirname } from "node:path";
+var __filename = __fresh_fileURLToPath(import.meta.url);
+var __dirname = __fresh_dirname(__filename);
+var require = __fresh_createRequire(import.meta.url);
+var module = { exports: {} };
+var exports = module.exports;
+
+${code}
+
+export default module.exports;
+`;
+            return { code: wrapped };
+          }
+        } catch {
+          // Fall through to default loading
+        }
+      }
+
       if (isDenoSpecifier(id)) {
         const { type, specifier } = parseDenoSpecifier(id);