feat: add url shortner

lib/text-highlight.ts

@@ -249,6 +249,37 @@ export function buildHighlightUrl(selectedText: string): string {
   return url.toString();
 }
 
+/**
+ * Build a shortened, shareable URL for the current selection. POSTs the
+ * `?hl=…` URL to the BFF, which stores the mapping in Postgres (Redis-queued)
+ * and returns a short code. The destination `/share/<code>` page resolves
+ * back to the same `?hl=…` URL the existing TextHighlighter already knows
+ * how to process — no change to highlighting behavior.
+ *
+ * Falls back to the long URL on any failure so sharing never silently breaks.
+ *
+ * `buildHighlightUrl` (sync) is intentionally left in place so other callers
+ * (e.g. search-result navigation) keep working unchanged.
+ */
+export async function buildShortHighlightUrl(
+  selectedText: string,
+): Promise<string> {
+  const longUrl = buildHighlightUrl(selectedText);
+  let u: URL;
+  try {
+    u = new URL(longUrl);
+  } catch {
+    return longUrl;
+  }
+  const relativePath = u.pathname + u.search + u.hash;
+
+  const { createShortLink } = await import("@/lib/share");
+  const code = await createShortLink(relativePath);
+  if (!code) return longUrl;
+
+  return new URL(`/share/${code}`, u.origin).toString();
+}
+
 /**
  * Find and highlight text in the DOM that matches a decoded text fragment.
  * Returns true if found and highlighted.