feat(notifications): add enter/leave animations and DOM-reuse for overla

- Direction-aware slide animations (right/left/top) on enter and leave
- Cards keyed by id so re-renders reuse elements; enter animation only plays once
- Exit animates via .leaving class then removes; fallback timer guards missing animationend
- Respects prefers-reduced-motion

src/renderer/overlay-notifications.ts

@@ -16,6 +16,16 @@ const OVERLAY_NOTIFICATION_POSITION_CLASSES = [
   'position-top',
   'position-top-right',
 ] as const;
+const OVERLAY_NOTIFICATION_VARIANT_CLASSES = [
+  'info',
+  'progress',
+  'success',
+  'warning',
+  'error',
+] as const;
+// Matches the `.leaving` animation duration in style.css; the fallback timer guards
+// against `animationend` never firing (e.g. element detached or reduced-motion).
+const OVERLAY_NOTIFICATION_EXIT_FALLBACK_MS = 260;
 
 export type OverlayNotificationEntry = Required<
   Pick<OverlayNotificationPayload, 'id' | 'title' | 'persistent'>
@@ -139,6 +149,10 @@ export function createOverlayNotificationRenderer(
 ) {
   const store = createOverlayNotificationStore();
   const timers = new Map<string, number>();
+  // Live card elements keyed by notification id so re-renders reuse them: the enter
+  // animation only plays for freshly created cards instead of replaying on every render.
+  const cards = new Map<string, HTMLElement>();
+  const leaving = new Set<string>();
   let position: OverlayNotificationPosition = DEFAULT_OVERLAY_NOTIFICATION_POSITION;
 
   function clearTimer(id: string): void {
@@ -149,33 +163,65 @@ export function createOverlayNotificationRenderer(
     }
   }
 
+  function commitExit(id: string, card: HTMLElement): void {
+    if (!leaving.has(id)) return;
+    leaving.delete(id);
+    cards.delete(id);
+    card.remove();
+    if (cards.size === 0) {
+      ctx.dom.overlayNotificationStack.classList.add('hidden');
+      setInteractiveState(ctx, false);
+    }
+    options.onChanged?.();
+  }
+
+  function beginExit(id: string, card: HTMLElement): void {
+    if (leaving.has(id)) return;
+    leaving.add(id);
+    card.classList.remove('entering');
+    card.classList.add('leaving');
+    const finalize = () => {
+      window.clearTimeout(fallback);
+      commitExit(id, card);
+    };
+    const fallback = window.setTimeout(finalize, OVERLAY_NOTIFICATION_EXIT_FALLBACK_MS);
+    card.addEventListener(
+      'animationend',
+      (event) => {
+        if ((event as AnimationEvent).animationName?.startsWith('overlay-notification-leave')) {
+          finalize();
+        }
+      },
+      { once: true },
+    );
+  }
+
   function remove(id: string): void {
     clearTimer(id);
     store.remove(id);
+    const card = cards.get(id);
+    if (card) {
+      beginExit(id, card);
+    } else {
       render();
     }
+  }
 
-  function render(): void {
-    const visible = store.visible();
-    ctx.dom.overlayNotificationStack.replaceChildren();
-    ctx.dom.overlayNotificationStack.classList.toggle('hidden', visible.length === 0);
-    ctx.dom.overlayNotificationStack.classList.remove(...OVERLAY_NOTIFICATION_POSITION_CLASSES);
-    ctx.dom.overlayNotificationStack.classList.add(overlayNotificationPositionClass(position));
-
-    for (const entry of visible) {
+  function populateCard(card: HTMLElement, entry: OverlayNotificationEntry): void {
     const imageSource = normalizeImageSource(entry.image);
-      const card = document.createElement('section');
-      card.className = `overlay-notification-card ${normalizeVariant(entry.variant)}${
-        imageSource ? ' has-image' : ''
-      }`;
+    card.classList.add('overlay-notification-card');
+    for (const variant of OVERLAY_NOTIFICATION_VARIANT_CLASSES) {
+      card.classList.toggle(variant, variant === normalizeVariant(entry.variant));
+    }
+    card.classList.toggle('has-image', Boolean(imageSource));
     card.dataset.notificationId = entry.id;
     card.setAttribute('role', 'status');
 
-      const leading = imageSource ? document.createElement('img') : document.createElement('span');
-      leading.className = imageSource ? 'overlay-notification-image' : 'overlay-notification-icon';
-      leading.setAttribute('aria-hidden', 'true');
+    const leadingEl = imageSource ? document.createElement('img') : document.createElement('span');
+    leadingEl.className = imageSource ? 'overlay-notification-image' : 'overlay-notification-icon';
+    leadingEl.setAttribute('aria-hidden', 'true');
     if (imageSource) {
-        const image = leading as HTMLImageElement;
+      const image = leadingEl as HTMLImageElement;
       image.src = imageSource;
       image.alt = '';
       image.decoding = 'async';
@@ -220,11 +266,46 @@ export function createOverlayNotificationRenderer(
     closeButton.textContent = '×';
     closeButton.addEventListener('click', () => remove(entry.id));
 
-      card.append(leading, content, closeButton);
+    card.replaceChildren(leadingEl, content, closeButton);
+  }
+
+  function render(): void {
+    const visible = store.visible();
+    const visibleIds = new Set(visible.map((entry) => entry.id));
+    ctx.dom.overlayNotificationStack.classList.toggle(
+      'hidden',
+      visible.length === 0 && leaving.size === 0,
+    );
+    ctx.dom.overlayNotificationStack.classList.remove(...OVERLAY_NOTIFICATION_POSITION_CLASSES);
+    ctx.dom.overlayNotificationStack.classList.add(overlayNotificationPositionClass(position));
+
+    // Cards that vanished from the store without an explicit remove() (e.g. pruned when
+    // over the visible cap) still need to animate out.
+    for (const [id, card] of cards) {
+      if (!visibleIds.has(id)) {
+        beginExit(id, card);
+      }
+    }
+
+    for (const entry of visible) {
+      let card = cards.get(entry.id);
+      if (card && leaving.has(entry.id)) {
+        // The card was animating out but has been re-shown: cancel the exit.
+        leaving.delete(entry.id);
+        card.classList.remove('leaving');
+      }
+      if (!card) {
+        card = document.createElement('section');
+        card.classList.add('entering');
+        cards.set(entry.id, card);
+      }
+      populateCard(card, entry);
+      // Appending an element already in the stack just moves it, keeping visible order
+      // without restarting its enter animation.
       ctx.dom.overlayNotificationStack.append(card);
     }
 
-    if (visible.length === 0) {
+    if (visible.length === 0 && leaving.size === 0) {
       setInteractiveState(ctx, false);
     }
     options.onChanged?.();

src/renderer/style.css

@@ -198,7 +198,32 @@ body:focus-visible,
     0 1px 0 rgba(202, 211, 245, 0.05) inset;
   color: var(--ctp-text);
   overflow: hidden;
-  animation: overlay-notification-enter 140ms ease-out;
+}
+
+/* Direction-aware enter/exit — slide in from the stack's anchored edge, slide back out. */
+.overlay-notification-card.entering {
+  animation: overlay-notification-enter-right 240ms cubic-bezier(0.21, 1.02, 0.73, 1) both;
+}
+
+.overlay-notification-card.leaving {
+  pointer-events: none;
+  animation: overlay-notification-leave-right 190ms cubic-bezier(0.55, 0.06, 0.68, 0.19) both;
+}
+
+.overlay-notification-stack.position-top-left .overlay-notification-card.entering {
+  animation-name: overlay-notification-enter-left;
+}
+
+.overlay-notification-stack.position-top-left .overlay-notification-card.leaving {
+  animation-name: overlay-notification-leave-left;
+}
+
+.overlay-notification-stack.position-top .overlay-notification-card.entering {
+  animation-name: overlay-notification-enter-top;
+}
+
+.overlay-notification-stack.position-top .overlay-notification-card.leaving {
+  animation-name: overlay-notification-leave-top;
 }
 
 .overlay-notification-card::before {
@@ -365,15 +390,82 @@ body:focus-visible,
   color: var(--ctp-red);
 }
 
-@keyframes overlay-notification-enter {
+@keyframes overlay-notification-enter-right {
   from {
     opacity: 0;
-    transform: translateY(-6px);
+    transform: translateX(28px) scale(0.96);
   }
 
   to {
     opacity: 1;
-    transform: translateY(0);
+    transform: translateX(0) scale(1);
+  }
+}
+
+@keyframes overlay-notification-enter-left {
+  from {
+    opacity: 0;
+    transform: translateX(-28px) scale(0.96);
+  }
+
+  to {
+    opacity: 1;
+    transform: translateX(0) scale(1);
+  }
+}
+
+@keyframes overlay-notification-enter-top {
+  from {
+    opacity: 0;
+    transform: translateY(-16px) scale(0.96);
+  }
+
+  to {
+    opacity: 1;
+    transform: translateY(0) scale(1);
+  }
+}
+
+@keyframes overlay-notification-leave-right {
+  from {
+    opacity: 1;
+    transform: translateX(0) scale(1);
+  }
+
+  to {
+    opacity: 0;
+    transform: translateX(28px) scale(0.94);
+  }
+}
+
+@keyframes overlay-notification-leave-left {
+  from {
+    opacity: 1;
+    transform: translateX(0) scale(1);
+  }
+
+  to {
+    opacity: 0;
+    transform: translateX(-28px) scale(0.94);
+  }
+}
+
+@keyframes overlay-notification-leave-top {
+  from {
+    opacity: 1;
+    transform: translateY(0) scale(1);
+  }
+
+  to {
+    opacity: 0;
+    transform: translateY(-14px) scale(0.94);
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .overlay-notification-card.entering,
+  .overlay-notification-card.leaving {
+    animation-duration: 1ms;
   }
 }