Merge MobileTabBar into nav-bar and refactor nav indicator to ResizeObserver

- Delete `components/mobile-tab-bar.tsx`; co-locate `MobileTabBar` export
  in `nav-bar.tsx` so both nav components share helpers
- Extract `isLinkActive` helper used by both desktop and mobile nav;
  fixes `/dashboard` active match when pathname is `/`
- Replace `layoutId`-based Framer Motion indicators with a
  `useActiveIndicator` hook that measures DOM rects via `ResizeObserver`,
  animating `left`/`width` directly — avoids cross-tree layout ID
  conflicts and correctly handles breakpoint visibility changes
- Add `aria-current="page"`, `aria-label="Primary"`, and
  `focus-visible` ring styles to nav links and tab bar items
- Update layout import to pull both exports from `@/components/nav-bar`

app/(pages)/layout.tsx

@@ -1,8 +1,7 @@
 import { redirect } from "next/navigation";
 import { Suspense } from "react";
 import { CommandPalette } from "@/components/command-palette";
-import { MobileTabBar } from "@/components/mobile-tab-bar";
-import { NavBar } from "@/components/nav-bar";
+import { MobileTabBar, NavBar } from "@/components/nav-bar";
 import { ProgressProvider } from "@/components/navigation-progress";
 import { UpdateToast } from "@/components/update-toast";
 import { getSession } from "@/lib/auth/session";

components/mobile-tab-bar.tsx

@@ -1,59 +0,0 @@
-"use client";
-
-import { IconCompass, IconHome, IconSettings } from "@tabler/icons-react";
-import { motion } from "motion/react";
-import Link from "next/link";
-import { usePathname } from "next/navigation";
-
-const tabs = [
-  { href: "/dashboard", label: "Home", icon: IconHome },
-  { href: "/explore", label: "Explore", icon: IconCompass },
-  { href: "/settings", label: "Settings", icon: IconSettings },
-] as const;
-
-export function MobileTabBar() {
-  const pathname = usePathname();
-
-  return (
-    <nav className="fixed right-0 bottom-0 left-0 z-50 border-border/50 border-t bg-background/90 pr-[env(safe-area-inset-right)] pl-[env(safe-area-inset-left)] backdrop-blur-xl sm:hidden">
-      <div className="flex h-14 items-stretch">
-        {tabs.map((tab) => {
-          const Icon = tab.icon;
-          const isActive =
-            tab.href === "/dashboard"
-              ? pathname === "/dashboard"
-              : pathname.startsWith(tab.href);
-          return (
-            <Link
-              key={tab.href}
-              href={tab.href}
-              className="relative flex flex-1 flex-col items-center justify-center gap-0.5"
-            >
-              <Icon
-                className={`size-5 ${isActive ? "text-primary" : "text-muted-foreground"}`}
-              />
-              <span
-                className={`font-medium text-[10px] ${isActive ? "text-primary" : "text-muted-foreground"}`}
-              >
-                {tab.label}
-              </span>
-              {isActive && (
-                <motion.div
-                  layoutId="mobile-tab-indicator"
-                  className="absolute top-0 h-0.5 w-8 rounded-full bg-primary"
-                  transition={{
-                    type: "spring",
-                    stiffness: 380,
-                    damping: 30,
-                  }}
-                />
-              )}
-            </Link>
-          );
-        })}
-      </div>
-      {/* Safe area for devices with home indicator */}
-      <div className="h-[env(safe-area-inset-bottom)]" />
-    </nav>
-  );
-}

components/nav-bar.tsx

@@ -1,10 +1,17 @@
 "use client";
 
-import { IconLogout, IconSearch, IconSettings } from "@tabler/icons-react";
+import {
+  IconCompass,
+  IconHome,
+  IconLogout,
+  IconSearch,
+  IconSettings,
+} from "@tabler/icons-react";
 import { useSetAtom } from "jotai";
 import { motion } from "motion/react";
 import Link from "next/link";
 import { usePathname, useRouter } from "next/navigation";
+import { useLayoutEffect, useRef, useState } from "react";
 import { SofaLogo } from "@/components/sofa-logo";
 import { Avatar, AvatarFallback, AvatarImage } from "@/components/ui/avatar";
 import { Badge } from "@/components/ui/badge";
@@ -20,11 +27,95 @@ import { Separator } from "@/components/ui/separator";
 import { commandPaletteOpenAtom } from "@/lib/atoms/command-palette";
 import { signOut } from "@/lib/auth/client";
 
+/** Horizontal inset (px) of the desktop indicator within each link (Tailwind `inset-x-2`). */
+const DESKTOP_INDICATOR_INSET = 8;
+/** Width (px) of the mobile indicator bar (Tailwind `w-8` = 2rem). */
+const MOBILE_INDICATOR_WIDTH = 32;
+
+const springTransition = {
+  type: "spring",
+  stiffness: 380,
+  damping: 30,
+} as const;
+
 const navLinks = [
   { href: "/dashboard", label: "Home" },
   { href: "/explore", label: "Explore" },
 ] as const;
 
+const mobileTabs = [
+  { href: "/dashboard", label: "Home", icon: IconHome },
+  { href: "/explore", label: "Explore", icon: IconCompass },
+  { href: "/settings", label: "Settings", icon: IconSettings },
+] as const;
+
+function isLinkActive(pathname: string, href: string) {
+  return (
+    pathname === href ||
+    pathname.startsWith(`${href}/`) ||
+    (href === "/dashboard" && pathname === "/")
+  );
+}
+
+function measureDesktopIndicator(itemRect: DOMRect, containerRect: DOMRect) {
+  return {
+    left: itemRect.left - containerRect.left + DESKTOP_INDICATOR_INSET,
+    width: itemRect.width - DESKTOP_INDICATOR_INSET * 2,
+  };
+}
+
+function measureMobileIndicator(itemRect: DOMRect, containerRect: DOMRect) {
+  const center = itemRect.left + itemRect.width / 2 - containerRect.left;
+  return center - MOBILE_INDICATOR_WIDTH / 2;
+}
+
+/**
+ * Tracks the active navigation item's position, recalculating on resize
+ * and visibility changes across breakpoints.
+ */
+function useActiveIndicator<T>(
+  activeIndex: number,
+  containerRef: React.RefObject<HTMLElement | null>,
+  itemRefs: React.MutableRefObject<(HTMLElement | null)[]>,
+  measure: (itemRect: DOMRect, containerRect: DOMRect) => T,
+): { value: T | null; instant: boolean } {
+  const [value, setValue] = useState<T | null>(null);
+  const instantRef = useRef(true);
+
+  useLayoutEffect(() => {
+    instantRef.current = false;
+    const update = () => {
+      if (activeIndex === -1) {
+        setValue(null);
+        return;
+      }
+      const item = itemRefs.current[activeIndex];
+      const container = containerRef.current;
+      if (item && container && container.offsetWidth > 0) {
+        setValue(
+          measure(
+            item.getBoundingClientRect(),
+            container.getBoundingClientRect(),
+          ),
+        );
+      } else {
+        setValue(null);
+      }
+    };
+    update();
+    const container = containerRef.current;
+    if (!container) return;
+    const observer = new ResizeObserver(() => {
+      instantRef.current = true;
+      update();
+    });
+    observer.observe(container);
+    return () => observer.disconnect();
+  }, [activeIndex, containerRef, itemRefs, measure]);
+
+  return { value, instant: instantRef.current };
+}
+
 export function NavBar({
   userName,
   userEmail,
@@ -42,9 +133,21 @@ export function NavBar({
 
   const initial = userName?.charAt(0).toUpperCase() ?? "?";
 
+  const activeIndex = navLinks.findIndex((link) =>
+    isLinkActive(pathname, link.href),
+  );
+  const navRef = useRef<HTMLElement>(null);
+  const linkRefs = useRef<(HTMLAnchorElement | null)[]>([]);
+  const { value: indicator, instant: desktopInstant } = useActiveIndicator(
+    activeIndex,
+    navRef,
+    linkRefs,
+    measureDesktopIndicator,
+  );
+
   return (
     <header className="sticky top-0 z-50 border-border/50 border-b bg-background/80 pt-[env(safe-area-inset-top)] backdrop-blur-xl">
-      <nav className="mx-auto flex h-14 max-w-6xl items-center justify-between gap-5 pr-[max(1rem,env(safe-area-inset-right))] pl-[max(1rem,env(safe-area-inset-left))] sm:gap-0 sm:pr-[max(1.5rem,env(safe-area-inset-right))] sm:pl-[max(1.5rem,env(safe-area-inset-left))]">
+      <div className="mx-auto flex h-14 max-w-6xl items-center justify-between gap-5 pr-[max(1rem,env(safe-area-inset-right))] pl-[max(1rem,env(safe-area-inset-left))] sm:gap-0 sm:pr-[max(1.5rem,env(safe-area-inset-right))] sm:pl-[max(1.5rem,env(safe-area-inset-left))]">
         <div className="flex items-center gap-3 sm:gap-6">
           <Link
             href="/dashboard"
@@ -52,34 +155,36 @@ export function NavBar({
           >
             <SofaLogo className="size-7" />
           </Link>
-          <div className="hidden items-center gap-1 sm:flex">
-            {navLinks.map((link) => {
-              const isActive =
-                link.href === "/dashboard"
-                  ? pathname === "/dashboard"
-                  : pathname.startsWith(link.href);
+          <nav
+            ref={navRef}
+            aria-label="Primary"
+            className="relative hidden items-center gap-1 sm:flex"
+          >
+            {navLinks.map((link, i) => {
+              const isActive = isLinkActive(pathname, link.href);
               return (
                 <Link
                   key={link.href}
+                  ref={(el) => {
+                    linkRefs.current[i] = el;
+                  }}
                   href={link.href}
-                  className="relative inline-flex items-center gap-1.5 rounded-md px-3 py-1.5 text-muted-foreground text-sm transition-colors hover:text-foreground"
+                  aria-current={isActive ? "page" : undefined}
+                  className="relative inline-flex items-center gap-1.5 rounded-md px-3 py-1.5 text-muted-foreground text-sm transition-colors hover:text-foreground focus-visible:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary/40"
                 >
                   {link.label}
-                  {isActive && (
-                    <motion.div
-                      layoutId="nav-indicator"
-                      className="absolute inset-x-2 -bottom-[11px] h-0.5 rounded-full bg-primary"
-                      transition={{
-                        type: "spring",
-                        stiffness: 380,
-                        damping: 30,
-                      }}
-                    />
-                  )}
                 </Link>
               );
             })}
-          </div>
+            {indicator && (
+              <motion.div
+                className="absolute -bottom-[11px] h-0.5 rounded-full bg-primary"
+                initial={false}
+                animate={{ left: indicator.left, width: indicator.width }}
+                transition={desktopInstant ? { duration: 0 } : springTransition}
+              />
+            )}
+          </nav>
         </div>
 
         <div className="flex flex-1 items-center justify-end gap-2 sm:flex-none sm:gap-1">
@@ -178,7 +283,67 @@ export function NavBar({
             </Avatar>
           </Link>
         </div>
-      </nav>
+      </div>
     </header>
   );
 }
+
+export function MobileTabBar() {
+  const pathname = usePathname();
+
+  const activeIndex = mobileTabs.findIndex((tab) =>
+    isLinkActive(pathname, tab.href),
+  );
+  const containerRef = useRef<HTMLDivElement>(null);
+  const tabRefs = useRef<(HTMLAnchorElement | null)[]>([]);
+  const { value: indicatorLeft, instant: mobileInstant } = useActiveIndicator(
+    activeIndex,
+    containerRef,
+    tabRefs,
+    measureMobileIndicator,
+  );
+
+  return (
+    <nav
+      aria-label="Primary"
+      className="fixed right-0 bottom-0 left-0 z-50 border-border/50 border-t bg-background/90 pr-[env(safe-area-inset-right)] pl-[env(safe-area-inset-left)] backdrop-blur-xl sm:hidden"
+    >
+      <div ref={containerRef} className="relative flex h-14 items-stretch">
+        {mobileTabs.map((tab, i) => {
+          const Icon = tab.icon;
+          const isActive = isLinkActive(pathname, tab.href);
+          return (
+            <Link
+              key={tab.href}
+              ref={(el) => {
+                tabRefs.current[i] = el;
+              }}
+              href={tab.href}
+              aria-current={isActive ? "page" : undefined}
+              className="relative flex flex-1 flex-col items-center justify-center gap-0.5 focus-visible:text-foreground focus-visible:outline-none"
+            >
+              <Icon
+                className={`size-5 ${isActive ? "text-primary" : "text-muted-foreground"}`}
+              />
+              <span
+                className={`font-medium text-[10px] ${isActive ? "text-primary" : "text-muted-foreground"}`}
+              >
+                {tab.label}
+              </span>
+            </Link>
+          );
+        })}
+        {indicatorLeft !== null && (
+          <motion.div
+            className="absolute top-0 h-0.5 w-8 rounded-full bg-primary"
+            initial={false}
+            animate={{ left: indicatorLeft }}
+            transition={mobileInstant ? { duration: 0 } : springTransition}
+          />
+        )}
+      </div>
+      {/* Safe area for devices with home indicator */}
+      <div className="h-[env(safe-area-inset-bottom)]" />
+    </nav>
+  );
+}