Date sitemap lastmod from the build pipeline; warn on skipped pages

- bunext build records when each page's client bundle hash last changed
  in .bunext/page-lastmod.json (sitemap.lastmod_file to relocate). The
  hash covers the page's whole import graph, so component edits re-date
  every page that uses them. The sitemap uses these dates as lastmod
- Add sitemap.default_lastmod
- BREAKING: use_file_lastmod now defaults to false (file mtimes are reset
  by checkouts); it is a fallback after the build record
- Warn when a page or __root.tsx is skipped because its default export
  is not at the start of a line (e.g. export { Page as default })
- Replace leaking module mocks in tests (log, grab-root-file-path) with
  spies and fixtures

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

dist/functions/bundler/grab-client-hydration-script.js

@@ -2,6 +2,8 @@ import { existsSync } from "fs";
 import grabDirNames from "../../utils/grab-dir-names";
 import grabConstants from "../../utils/grab-constants";
 import grabRootFilePath from "../server/web-pages/grab-root-file-path";
+import grabRelativePath from "../../utils/grab-relative-path";
+import { log } from "../../utils/log";
 const { ROOT_DIR } = grabDirNames();
 export default async function grabClientHydrationScript({ page_local_path, }) {
     const { ClientRootElementIDName, ClientRootComponentWindowName, ClientWindowPagePropsName, } = grabConstants();
@@ -18,12 +20,19 @@ export default async function grabClientHydrationScript({ page_local_path, }) {
             return undefined;
         }
         const root_content = await Bun.file(root_file_path).text();
-        if (!root_content.match(/^export default/m)) {
+        if (!hasBundlableDefaultExport({
+            file_path: root_file_path,
+            content: root_content,
+            is_root: true,
+        })) {
             return undefined;
         }
     }
     const page_content = await Bun.file(page_local_path).text();
-    if (!page_content.match(/^export default/m)) {
+    if (!hasBundlableDefaultExport({
+        file_path: page_local_path,
+        content: page_content,
+    })) {
         return undefined;
     }
     let txt = ``;
@@ -54,3 +63,36 @@ export default async function grabClientHydrationScript({ page_local_path, }) {
     txt += `}\n`;
     return txt;
 }
+// File path -> content hash of the last warning, so rebuilds don't repeat
+// a warning until the file changes.
+const warned_files = new Map();
+/**
+ * # Check a page or root file can be bundled
+ * Files are only bundled when `export default` starts a line. Files with
+ * no default export at all (e.g. a page still being written) are skipped
+ * silently; this warns about the confusing case where one exists
+ * elsewhere, like `import X from "x"; export default X` on one line, or
+ * `export { Page as default }`.
+ */
+function hasBundlableDefaultExport({ file_path, content, is_root, }) {
+    if (/^export default/m.test(content)) {
+        warned_files.delete(file_path);
+        return true;
+    }
+    const has_default_export = /\bexport\s+default\b/.test(content) ||
+        /\bas\s+default\b/.test(content);
+    if (!has_default_export) {
+        warned_files.delete(file_path);
+        return false;
+    }
+    const content_hash = Bun.hash(content);
+    if (warned_files.get(file_path) === content_hash)
+        return false;
+    warned_files.set(file_path, content_hash);
+    log.warn(`${grabRelativePath(file_path)} was skipped: ` +
+        `\`export default\` must be at the start of a line. ` +
+        (is_root
+            ? `No pages can be bundled until the root layout is fixed.`
+            : `This page will not be bundled.`));
+    return false;
+}