seo and geo optimizations

lib/last-modified.ts

@@ -0,0 +1,48 @@
+import { execFileSync } from 'node:child_process';
+import { statSync } from 'node:fs';
+import path from 'node:path';
+import { docsDir } from './shared';
+
+type ContentFile = { path: string; absolutePath?: string };
+
+let cached: Map<string, Date> | undefined;
+
+/** Newest commit that touched each file under content/docs. Empty when git is unavailable. */
+function commitDates(): Map<string, Date> {
+  if (cached) return cached;
+
+  const dates = new Map<string, Date>();
+  try {
+    const out = execFileSync('git', ['log', '--format=COMMIT %cI', '--name-only', '--', docsDir], {
+      encoding: 'utf8',
+    });
+    let current: Date | undefined;
+    for (const line of out.split('\n')) {
+      if (line.startsWith('COMMIT ')) {
+        const date = new Date(line.slice('COMMIT '.length));
+        current = Number.isNaN(date.getTime()) ? undefined : date;
+      } else if (line && current && !dates.has(line)) {
+        dates.set(line, current);
+      }
+    }
+  } catch {
+    // Docker builds without git fall back to file mtime.
+  }
+
+  cached = dates;
+  return dates;
+}
+
+function mtime(file: string): Date {
+  try {
+    return statSync(file).mtime;
+  } catch {
+    return new Date();
+  }
+}
+
+/** Last time this page's MDX changed: newest commit, then file mtime. */
+export function pageLastModified(page: ContentFile): Date {
+  const file = `${docsDir}/${page.path}`;
+  return commitDates().get(file) ?? mtime(page.absolutePath ?? path.join(process.cwd(), file));
+}