feat(web): mark the active phone tab with a bar that springs between tabs

The phone tab bars (resume builder, letter builder, dashboard) drop the
pill behind the active icon for a short accent bar on the tab's top
edge. Switching tabs springs it across with a little overshoot
(spring 0.4s, bounce 0.3); reduced motion moves it at once. Dashboard
tab taps swap the page without the cross-fade, like a native tab bar,
so the bar's movement isn't hidden behind the page transition.

apps/web/src/components/layout/mobile-tab-indicator.tsx

@@ -0,0 +1,18 @@
+import { m } from "motion/react";
+import { TAB_SPRING } from "@/libs/motion";
+
+/**
+ * The phone tab bar's marker: a short accent bar on the active tab's top edge. Render it inside the active tab
+ * (which must be `relative`); when another tab becomes active it springs across to it. Reduced motion moves it at
+ * once (see `followReducedMotion`).
+ */
+export function MobileTabIndicator() {
+	return (
+		<m.span
+			aria-hidden="true"
+			layoutId="mobile-tab-indicator"
+			transition={TAB_SPRING}
+			className="absolute inset-x-0 -top-px mx-auto h-0.5 w-8 rounded-full bg-accent"
+		/>
+	);
+}

apps/web/src/libs/motion.ts

@@ -20,6 +20,9 @@ export const EXIT = 0.7;
 /** --ease-out-strong. Landing page only (features/homepage/site-footer.tsx); app code uses EASE. */
 export const EASE_OUT_STRONG = [0.23, 1, 0.32, 1] as const;
 
+/** Springy, a little elastic: the mobile tab bar's marker hopping to the new tab (interruptible mid-flight). */
+export const TAB_SPRING = { type: "spring", duration: 0.4, bounce: 0.3 } as const;
+
 /** dnd-kit timing for things settling into place (sortable shuffles, drop animations): on-screen movement. */
 export const DRAG_SETTLE = { duration: D2 * 1000, easing: `cubic-bezier(${EASE_MOVE.join(", ")})` };
 

apps/web/src/routes/builder/$resumeId/-components/editor-shell.tsx

@@ -8,6 +8,7 @@ import { Icon } from "@reactive-resume/ui/components/icon";
 import { Tabs, TabsContent } from "@reactive-resume/ui/components/tabs";
 import { useBreakpoint } from "@reactive-resume/ui/hooks/use-breakpoint";
 import { cn } from "@reactive-resume/utils/style";
+import { MobileTabIndicator } from "@/components/layout/mobile-tab-indicator";
 import {
 	AssistantColumn,
 	AssistantOverlay,
@@ -285,18 +286,12 @@ function MobileBody({ mode, onModeChange }: MobileBodyProps) {
 								if (tab !== "page") onModeChange(tab);
 							}}
 							className={cn(
-								"flex min-h-[52px] flex-1 flex-col items-center justify-center gap-0.5 text-[11px]",
+								"relative flex min-h-[52px] flex-1 flex-col items-center justify-center gap-0.5 text-[11px] transition-[color,scale] duration-quick ease-enter active:scale-[0.97]",
 								active ? "font-semibold text-ink" : "text-ink-2",
 							)}
 						>
-							<span
-								className={cn(
-									"flex h-7 w-[52px] items-center justify-center rounded-full transition-colors duration-quick",
-									active && "bg-accent-soft text-accent-text",
-								)}
-							>
-								<Icon name={icon} size={24} filled={active} />
-							</span>
+							{active && <MobileTabIndicator />}
+							<Icon name={icon} size={24} filled={active} />
 							{labels[tab]}
 						</button>
 					);

apps/web/src/routes/builder/letter/-components/letter-shell.tsx

@@ -10,6 +10,7 @@ import { Tabs, TabsContent } from "@reactive-resume/ui/components/tabs";
 import { toast } from "@reactive-resume/ui/components/toast";
 import { useBreakpoint } from "@reactive-resume/ui/hooks/use-breakpoint";
 import { cn } from "@reactive-resume/utils/style";
+import { MobileTabIndicator } from "@/components/layout/mobile-tab-indicator";
 import {
 	AssistantColumn,
 	AssistantOverlay,
@@ -213,18 +214,12 @@ function MobileBody({ mode, onModeChange }: MobileBodyProps) {
 								if (tab !== "page") onModeChange(tab);
 							}}
 							className={cn(
-								"flex min-h-[52px] flex-1 flex-col items-center justify-center gap-0.5 text-[11px]",
+								"relative flex min-h-[52px] flex-1 flex-col items-center justify-center gap-0.5 text-[11px] transition-[color,scale] duration-quick ease-enter active:scale-[0.97]",
 								active ? "font-semibold text-ink" : "text-ink-2",
 							)}
 						>
-							<span
-								className={cn(
-									"flex h-7 w-[52px] items-center justify-center rounded-full transition-colors duration-quick",
-									active && "bg-accent-soft text-accent-text",
-								)}
-							>
-								<Icon name={icon} size={24} filled={active} />
-							</span>
+							{active && <MobileTabIndicator />}
+							<Icon name={icon} size={24} filled={active} />
 							{labels[tab]}
 						</button>
 					);

apps/web/src/routes/dashboard/-components/app-shell.tsx

@@ -13,6 +13,7 @@ import { Tooltip, TooltipContent, TooltipTrigger } from "@reactive-resume/ui/com
 import { useBreakpoint } from "@reactive-resume/ui/hooks/use-breakpoint";
 import { getInitials } from "@reactive-resume/utils/string";
 import { cn } from "@reactive-resume/utils/style";
+import { MobileTabIndicator } from "@/components/layout/mobile-tab-indicator";
 import { useDialogStore } from "@/dialogs/store";
 import { applicationsListQueryOptions } from "@/features/applications/queries";
 import { useCommandPaletteStore } from "@/features/command-palette/store";
@@ -289,6 +290,7 @@ function MobileTabs() {
 
 	const tab = (icon: IconName, label: string, current: boolean) => (
 		<>
+			{current && <MobileTabIndicator />}
 			<Icon name={icon} size={24} filled={current} />
 			<span className={cn("text-[11px]", current ? "font-semibold text-ink" : "text-ink-2")}>{label}</span>
 		</>
@@ -302,14 +304,16 @@ function MobileTabs() {
 			<Link
 				to="/dashboard"
 				aria-current={isCurrent("/dashboard") ? "page" : undefined}
-				className="flex min-h-[52px] flex-col items-center justify-center gap-0.5 transition-[scale] duration-quick ease-enter active:scale-[0.97]"
+				viewTransition={false}
+				className="relative flex min-h-[52px] flex-col items-center justify-center gap-0.5 transition-[scale] duration-quick ease-enter active:scale-[0.97]"
 			>
 				{tab("description", t`Documents`, isCurrent("/dashboard"))}
 			</Link>
 			<Link
 				to="/dashboard/applications"
 				aria-current={isCurrent("/dashboard/applications") ? "page" : undefined}
-				className="flex min-h-[52px] flex-col items-center justify-center gap-0.5 transition-[scale] duration-quick ease-enter active:scale-[0.97]"
+				viewTransition={false}
+				className="relative flex min-h-[52px] flex-col items-center justify-center gap-0.5 transition-[scale] duration-quick ease-enter active:scale-[0.97]"
 			>
 				{tab("work", t`Applications`, isCurrent("/dashboard/applications"))}
 			</Link>
@@ -329,7 +333,8 @@ function MobileTabs() {
 			<Link
 				to="/dashboard/settings"
 				aria-current={isCurrent("/dashboard/settings") ? "page" : undefined}
-				className="flex min-h-[52px] flex-col items-center justify-center gap-0.5 transition-[scale] duration-quick ease-enter active:scale-[0.97]"
+				viewTransition={false}
+				className="relative flex min-h-[52px] flex-col items-center justify-center gap-0.5 transition-[scale] duration-quick ease-enter active:scale-[0.97]"
 			>
 				{tab("account_circle", t`Account`, isCurrent("/dashboard/settings"))}
 			</Link>