feat: chat reactions

lib/use-chrome-visibility.ts

@@ -0,0 +1,28 @@
+"use client";
+
+/**
+ * Whether the app's own chrome should step aside for the page.
+ *
+ * A chat thread is a full-height surface with its own header and a composer
+ * pinned to the bottom: the tab bar competes with the composer for the same
+ * edge, the hamburger duplicates a back button already on screen, and the
+ * wordmark header stacks a second title bar above the thread's own.
+ *
+ * One hook so the header, the nav, the hamburger and the layout's bottom
+ * padding can never disagree — if they did, hiding one would leave a gap
+ * where it used to be. The desktop sidebar is deliberately unaffected: it is
+ * the only way out of a thread on a wide screen.
+ */
+
+import { usePathname } from "next/navigation";
+
+/**
+ * True on a thread itself (`/chats/<id>`) but NOT on the inbox or a chat's
+ * profile page: those are ordinary scrolling pages where the tab bar belongs.
+ */
+export function useHidesAppChrome(): boolean {
+  const pathname = usePathname();
+  if (!pathname?.startsWith("/chats/")) return false;
+  // "", "chats", "<id>" — anything deeper is a sub-page like /profile.
+  return pathname.split("/").filter(Boolean).length === 2;
+}