1.4.1: nested pages dirs, CommonJS require of react in client bundles

- Page URL paths are now relative to src/pages. The old greedy
  `.*/pages/` cut mapped src/pages/admin/pages/index.tsx to /index, so
  every page under a nested `pages` directory collided with the home page
  and was never bundled. SSR also tells API routes by URL path now.
- CommonJS `require("react…")` in client bundles (for example
  use-sync-external-store/shim, pulled in by MUI) threw "Dynamic require
  of "react" is not supported" in the browser. Those requires now go
  through a small bundled ESM module that imports the external.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

dist/functions/bundler/all-pages-esbuild-context-bundler.js

@@ -128,18 +128,44 @@ export default async function allPagesESBuildContextBundler(params) {
         ], (line) => log.error(line));
     }
 }
-function forceExternalReact() {
+const ExternalRequireNamespace = "bunext-external-require";
+/**
+ * CommonJS `require("react")` (e.g. `use-sync-external-store/shim`, pulled
+ * in by MUI) for a module that is external in ESM output becomes esbuild's
+ * `__require`, which throws "Dynamic require of "react" is not supported" in
+ * the browser. Give those requires a small bundled ESM module that imports
+ * the external instead; esbuild wires `require()` to it.
+ */
+export function externalRequireShim(specifier) {
+    const spec = JSON.stringify(specifier);
+    // A namespace import never fails to link, even when the vendor module has
+    // no default export (jsx-runtime); fall back to the namespace for
+    // `require(...).default` (Babel interop).
+    return [
+        `import * as ns from ${spec};`,
+        `export * from ${spec};`,
+        `export default ns.default ?? ns;`,
+    ].join("\n");
+}
+export function forceExternalReact() {
     return {
         name: "force-external-react",
         setup(build) {
             build.onResolve({ filter: /^react(-dom)?(\/.*)?$/ }, (args) => {
                 if (args.pluginData?.externalReact)
                     return null;
+                if (args.kind === "require-call") {
+                    return { path: args.path, namespace: ExternalRequireNamespace };
+                }
                 return {
                     path: args.path,
                     external: true,
                 };
             });
+            build.onLoad({ filter: /.*/, namespace: ExternalRequireNamespace }, (args) => ({
+                contents: externalRequireShim(args.path),
+                loader: "js",
+            }));
         },
     };
 }