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/commands/build/index.js

@@ -4,6 +4,7 @@ import grabDirNames from "../../utils/grab-dir-names";
 import { rmSync, writeFileSync } from "fs";
 import bunextInit from "../../functions/bunext-init";
 import { v4 } from "uuid";
+import { updatePageLastmodRecord } from "../../utils/page-lastmod-record";
 const { HYDRATION_DST_DIR, BUNX_CWD_PAGES_REWRITE_DIR, BUNDLER_CTX_MAP_JSON, SSR_BUNDLER_CTX_MAP_JSON, BUNX_CWD_MODULE_CACHE_DIR, BUILD_INFO_JSON, } = grabDirNames();
 export default function () {
     return new Command("build")
@@ -39,6 +40,18 @@ export default function () {
             build_date_unix: Date.now(),
             build_date: Date(),
         };
+        if (global.BUNEXT_BUNDLER_CTX_MAP) {
+            try {
+                updatePageLastmodRecord({
+                    ctx_map: global.BUNEXT_BUNDLER_CTX_MAP,
+                    build_date: new Date(build_data.build_date_unix),
+                });
+            }
+            catch (error) {
+                // Only sitemap dates depend on this; never fail the build.
+                log.warn(`Could not update page lastmod record: ${error?.message || error}`);
+            }
+        }
         writeFileSync(BUILD_INFO_JSON, JSON.stringify(build_data, null, 4), "utf-8");
         log.success("Modules Built Successfully!");
         process.exit();