From b363753dca1e631615156ad572353ca2a2391e34 Mon Sep 17 00:00:00 2001
From: Adam Malczewski <github@tradam.dev>
Date: Wed, 21 Oct 2026 20:48:53 +0900
Subject: feat(tabs): GSAP Flip animation when subagents are summoned or tabs
 close

---
 src/features/tabs/ui/TabCard.svelte     |   2 +
 src/features/tabs/ui/TabGroupBox.svelte |  19 +++-
 src/features/tabs/ui/TabList.svelte     |  22 ++++-
 src/features/tabs/ui/tab-flip.ts        | 157 ++++++++++++++++++++++++++++++++
 4 files changed, 193 insertions(+), 7 deletions(-)
 create mode 100644 src/features/tabs/ui/tab-flip.ts

(limited to 'src/features/tabs/ui')

diff --git a/src/features/tabs/ui/TabCard.svelte b/src/features/tabs/ui/TabCard.svelte
index a95f8e6..ae891c0 100644
--- a/src/features/tabs/ui/TabCard.svelte
+++ b/src/features/tabs/ui/TabCard.svelte
@@ -1,4 +1,5 @@
 <script lang="ts">
+  import { cardFlipId } from "../tab-flip";
   import type { Tab } from "../tabs";
 
   /**
@@ -115,6 +116,7 @@
   aria-selected={active}
   title={tab.title}
   data-conversation-id={tab.conversationId}
+  data-flip-id={cardFlipId(tab.conversationId)}
   data-wide={wide ? "true" : undefined}
   onclick={() => {
     if (suppressClick) {
diff --git a/src/features/tabs/ui/TabGroupBox.svelte b/src/features/tabs/ui/TabGroupBox.svelte
index f9a3ae2..5b644e0 100644
--- a/src/features/tabs/ui/TabGroupBox.svelte
+++ b/src/features/tabs/ui/TabGroupBox.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import type { Snippet } from "svelte";
   import type { TabGroupNode } from "../tab-groups";
+  import { groupFlipId } from "../tab-flip";
   import { groupBleedPx, groupTone, lastRowIsGroup } from "../tab-groups";
   import type { Tab } from "../tabs";
   import TabGroupBox from "./TabGroupBox.svelte";
@@ -17,7 +18,9 @@
    * box is tinted with one of three theme colours ROTATING by level
    * (`groupTone`), painted OPAQUE (mixed into the sidebar well colour) so a
    * nested box never blends with the box around it, plus a border in the same
-   * colour so every box edge reads at a glance.
+   * colour so every box edge reads at a glance. The tint lives on its own
+   * BACKDROP layer so the FLIP animation (`tab-flip.ts`) can fade a new
+   * group's tint in while its cards fly into place.
    */
   let {
     node,
@@ -44,8 +47,7 @@
 </script>
 
 <div
-  class="tab-group-box col-span-2 rounded-lg"
-  style:--group-tone="var(--color-{tone})"
+  class="relative col-span-2"
   style:margin-inline="-{bleed}px"
   style:padding="{bleed}px {bleed}px {padBottom}px"
   role="group"
@@ -53,8 +55,15 @@
   data-tab-group={node.tab.conversationId}
   data-level={level}
   data-tone={tone}
+  data-flip-id={groupFlipId(node.tab.conversationId)}
 >
-  <div class="grid grid-flow-row-dense grid-cols-2 gap-1.5">
+  <div
+    class="tab-group-backdrop pointer-events-none absolute inset-0 rounded-lg"
+    style:--group-tone="var(--color-{tone})"
+    data-group-backdrop
+    aria-hidden="true"
+  ></div>
+  <div class="relative grid grid-flow-row-dense grid-cols-2 gap-1.5">
     {@render card(node.tab, true, node.children.length)}
     {#each node.children as child (child.tab.conversationId)}
       {#if child.children.length > 0}
@@ -70,7 +79,7 @@
   /* Opaque tint: the tone mixed into the sidebar's `.inset-well` colour (the
      surface the tab grid sits on), so nested boxes replace — never compound
      with — the colour around them. */
-  .tab-group-box {
+  .tab-group-backdrop {
     background-color: color-mix(
       in oklab,
       var(--group-tone) 16%,
diff --git a/src/features/tabs/ui/TabList.svelte b/src/features/tabs/ui/TabList.svelte
index 06d5aa6..5bfabf6 100644
--- a/src/features/tabs/ui/TabList.svelte
+++ b/src/features/tabs/ui/TabList.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { untrack } from "svelte";
+  import { forestFlipIds } from "../tab-flip";
   import {
     buildTabGroups,
     directGroupChildren,
@@ -11,6 +13,7 @@
   import TabCard from "./TabCard.svelte";
   import TabGroupBox from "./TabGroupBox.svelte";
   import TabMenu from "./TabMenu.svelte";
+  import { createTabFlip } from "./tab-flip";
 
   let {
     tabs,
@@ -51,6 +54,20 @@
   const forest = $derived(buildTabGroups(tabs));
   const gutter = $derived(groupGutterPx(forest.maxDepth));
 
+  // FLIP: a summoned subagent / closed tab / regroup animates (GSAP Flip).
+  // Capture positions (+ ghost leaving elements) BEFORE the DOM updates, play
+  // AFTER. Keyed on `forest` only; the DOM work itself is untracked.
+  let scrollerEl = $state<HTMLDivElement | undefined>();
+  const flip = createTabFlip(() => scrollerEl);
+  $effect.pre(() => {
+    const next = forestFlipIds(forest);
+    untrack(() => flip.capture(next));
+  });
+  $effect(() => {
+    void forest;
+    untrack(() => flip.play());
+  });
+
   // Tab menu (right-click / touch-and-hold). Local UI state owned here.
   let menu = $state<{ conversationId: string; x: number; y: number } | null>(null);
   const menuTab = $derived(
@@ -95,12 +112,13 @@
        sidebar. Subagent groups span both columns; `dense` lets a later card
        fill the half-row a group would otherwise leave empty. -->
   <div
-    class="h-[40vh] overflow-y-auto py-0.5"
+    bind:this={scrollerEl}
+    class="relative h-[40vh] overflow-y-auto py-0.5"
     style:padding-inline="{gutter}px"
     data-tab-grid
     onscroll={() => (menu = null)}
   >
-    <div class="grid grid-flow-row-dense grid-cols-2 gap-1.5" role="tablist">
+    <div class="relative grid grid-flow-row-dense grid-cols-2 gap-1.5" role="tablist">
       {#each forest.roots as node (node.tab.conversationId)}
         {#if node.children.length > 0}
           <TabGroupBox {node} level={1} maxDepth={forest.maxDepth} {card} />
diff --git a/src/features/tabs/ui/tab-flip.ts b/src/features/tabs/ui/tab-flip.ts
new file mode 100644
index 0000000..9d0f0f8
--- /dev/null
+++ b/src/features/tabs/ui/tab-flip.ts
@@ -0,0 +1,157 @@
+import { gsap } from "gsap";
+import { Flip } from "gsap/Flip";
+import { isGroupFlipId, leavingFlipIds } from "../tab-flip";
+
+gsap.registerPlugin(Flip);
+
+/**
+ * GSAP Flip animation for the tab grid — the DOM EFFECT half of the tab
+ * FLIP (the pure id scheme lives in `../tab-flip.ts`).
+ *
+ * Two-phase, driven by the owning component:
+ *  - `capture(nextIds)` — BEFORE the DOM updates: record every `[data-flip-id]`
+ *    element's position (First), and spawn an inert GHOST for each element the
+ *    next render drops, so a closed tab / dissolved group box fades out in
+ *    place instead of vanishing.
+ *  - `play()` — AFTER the DOM updates: Flip every surviving element from its
+ *    recorded position to its new one (Last → Invert → Play), scale new cards
+ *    in, and fade new group boxes' backdrops in.
+ *
+ * Data-driven, not click-driven: it animates ANY change to the tab set (a
+ * summoned subagent, a close from another device, a regroup). Re-entrant —
+ * `Flip.getState` captures mid-flight positions. Disabled when the user
+ * prefers reduced motion (or the environment can't tell, e.g. jsdom).
+ */
+export interface TabFlip {
+  capture(nextIds: ReadonlySet<string>): void;
+  play(): void;
+}
+
+const DURATION = 0.4;
+const GHOST_ATTR = "data-tab-ghost";
+
+export function createTabFlip(getScroller: () => HTMLElement | undefined): TabFlip {
+  let state: ReturnType<typeof Flip.getState> | null = null;
+
+  return {
+    capture(nextIds) {
+      state = null;
+      const scroller = getScroller();
+      if (scroller === undefined || !motionAllowed()) return;
+      const els = flipElements(scroller);
+      if (els.length === 0) return;
+      state = Flip.getState(els);
+      const byId = new Map(els.map((el) => [el.dataset.flipId ?? "", el]));
+      for (const id of leavingFlipIds([...byId.keys()], nextIds)) {
+        const el = byId.get(id);
+        if (el !== undefined) spawnGhost(scroller, el, isGroupFlipId(id));
+      }
+    },
+
+    play() {
+      const captured = state;
+      state = null;
+      const scroller = getScroller();
+      if (captured === null || scroller === undefined) return;
+      Flip.from(captured, {
+        targets: flipElements(scroller),
+        duration: DURATION,
+        ease: "power3.out",
+        nested: true,
+        onEnter: (elements) => {
+          for (const el of elements) {
+            if (!(el instanceof HTMLElement)) continue;
+            if (isGroupFlipId(el.dataset.flipId ?? "")) {
+              // The box's CARDS are flipping into place — fade only its tint.
+              const backdrop = el.querySelector<HTMLElement>(":scope > [data-group-backdrop]");
+              if (backdrop !== null) {
+                gsap.fromTo(backdrop, { opacity: 0 }, { opacity: 1, duration: DURATION });
+              }
+            } else {
+              gsap.fromTo(
+                el,
+                { opacity: 0, scale: 0.6 },
+                {
+                  opacity: 1,
+                  scale: 1,
+                  duration: DURATION,
+                  delay: DURATION * 0.35, // let the grid open the gap first
+                  ease: "back.out(1.7)",
+                  clearProps: "opacity,transform",
+                },
+              );
+            }
+          }
+        },
+      });
+    },
+  };
+}
+
+function motionAllowed(): boolean {
+  return (
+    typeof window.matchMedia === "function" &&
+    !window.matchMedia("(prefers-reduced-motion: reduce)").matches
+  );
+}
+
+function flipElements(scroller: HTMLElement): HTMLElement[] {
+  return [...scroller.querySelectorAll<HTMLElement>("[data-flip-id]")];
+}
+
+/**
+ * An inert visual copy of a leaving element, absolutely positioned over its
+ * last on-screen rect, that shrinks + fades out and removes itself.
+ *
+ * Paint order matters (cards are `relative`, so everything here stacks in DOM
+ * order): a leaving CARD's ghost is appended to the scroller so it fades out
+ * ON TOP of the reflow. A leaving GROUP BOX copies only its backdrop (the
+ * tint — its cards either flip elsewhere or ghost themselves) and is inserted
+ * as the FIRST child of the box's enclosing grid: above the enclosing box's
+ * own tint, but BELOW every card, so the dissolving tint never dims the cards
+ * flying out of it.
+ */
+function spawnGhost(scroller: HTMLElement, el: HTMLElement, isGroup: boolean): void {
+  const source = isGroup ? el.querySelector<HTMLElement>(":scope > [data-group-backdrop]") : el;
+  if (source === null) return;
+  const host = isGroup ? el.parentElement : scroller;
+  if (host === null) return;
+  const r = el.getBoundingClientRect();
+  const h = host.getBoundingClientRect();
+  const ghost = source.cloneNode(!isGroup) as HTMLElement;
+  // A ghost is never a tab/group to queries, tests or assistive tech.
+  for (const node of [ghost, ...ghost.querySelectorAll<HTMLElement>("*")]) {
+    for (const attr of [
+      "data-flip-id",
+      "data-conversation-id",
+      "data-group-backdrop",
+      "role",
+      "id",
+    ]) {
+      node.removeAttribute(attr);
+    }
+  }
+  ghost.setAttribute(GHOST_ATTR, "");
+  ghost.setAttribute("aria-hidden", "true");
+  ghost.inert = true;
+  Object.assign(ghost.style, {
+    position: "absolute",
+    left: `${r.left - h.left - host.clientLeft + host.scrollLeft}px`,
+    top: `${r.top - h.top - host.clientTop + host.scrollTop}px`,
+    width: `${r.width}px`,
+    height: `${r.height}px`,
+    margin: "0",
+    transform: "none",
+    pointerEvents: "none",
+    zIndex: isGroup ? "auto" : "2",
+  });
+  if (isGroup) host.prepend(ghost);
+  else host.appendChild(ghost);
+  gsap.to(ghost, {
+    opacity: 0,
+    scale: isGroup ? 1 : 0.6,
+    duration: DURATION * 0.75,
+    ease: "power2.in",
+    onComplete: () => ghost.remove(),
+  });
+}
-- 
cgit v1.2.3