fix(desktop): restore drag previews before the release commit folds a zone

When a sash drag folds a tool zone to its rail, the store commit re-renders
only the wrappers whose style prop changed; the flex sibling the gesture
had pinned to `flex: 0 1 <px>` kept that inline preview and could not grow
into the freed space. Restore every captured style attribute before the
commit, on every release path.

apps/desktop/src/components/pane-shell/tree/renderer/tree-split-cascade-resize.test.tsx

@@ -76,6 +76,13 @@ function setWidth(element: HTMLElement, width: number) {
   Object.defineProperty(element, 'getBoundingClientRect', { configurable: true, value: () => rect(width) })
 }
 
+function setHeight(element: HTMLElement, height: number) {
+  Object.defineProperty(element, 'getBoundingClientRect', {
+    configurable: true,
+    value: () => ({ ...rect(1000), bottom: height, height })
+  })
+}
+
 function row(): SplitNode {
   const tree = $layoutTree.get()
 
@@ -180,4 +187,47 @@ describe('TreeSplit cascading expansion', () => {
     expect(row().weights[0]).toBeCloseTo(2.2)
     expect(row().children[3]).toMatchObject({ id: 'terminal-zone', minimized: true })
   })
+  it('folding a tool zone at its floor leaves no drag preview pinned on the flex sibling', () => {
+    markCollapsePane('terminal')
+    disposers.push(
+      registry.register({
+        area: 'panes',
+        data: { height: '200px', placement: 'bottom' },
+        id: 'terminal',
+        render: () => null,
+        title: 'Terminal'
+      })
+    )
+
+    const tree = split(
+      'column',
+      [group(['chat'], { id: 'chat-zone' }), group(['terminal'], { id: 'terminal-zone' })],
+      [1, 1],
+      'root-column'
+    )
+
+    $layoutTree.set(tree)
+
+    render(<TreeSplit node={tree} root />)
+
+    const container = document.querySelector<HTMLElement>('[data-tree-split="root-column"]')!
+    const [chat, terminal] = [...container.children] as HTMLElement[]
+    setHeight(container, 800)
+    setHeight(chat, 600)
+    setHeight(terminal, 200)
+    setHeight(document.querySelector<HTMLElement>('[data-tree-group="terminal-zone"]')!, 200)
+
+    const chatFlex = chat.style.flex
+    const terminalSash = document.querySelectorAll('[role="separator"]')[0]!
+    fireEvent.pointerDown(terminalSash, { button: 0, clientY: 600, pointerId: 1, pointerType: 'mouse' })
+    fireEvent.pointerMove(window, { clientY: 790, pointerId: 1, pointerType: 'mouse' })
+    fireEvent.pointerUp(window, { clientY: 790, pointerId: 1, pointerType: 'mouse' })
+
+    // The zone folds to its rail (no sliver persisted) and the chat wrapper —
+    // which the commit does not re-render — is back on React's own flex, not
+    // the `0 1 <px>` pin the gesture previewed.
+    expect(row().children[1]).toMatchObject({ id: 'terminal-zone', minimized: true })
+    expect($paneStates.get().terminal?.heightOverride).toBeUndefined()
+    expect(chat.style.flex).toBe(chatFlex)
+  })
 })

apps/desktop/src/components/pane-shell/tree/renderer/tree-split.tsx

@@ -387,10 +387,8 @@ export function TreeSplit({ node, root, rootRow }: { node: SplitNode; root?: boo
       //  - every visible flex track is pinned to `0 1 <px>`. The plan keeps
       //    the run's total px constant, so no leftover gap can open.
       //  - hidden (display:none) and minimized tracks are left untouched.
-      //  - cleanup: a real drag commits the store once, and React's re-render
-      //    rewrites the `flex` shorthand, which clears the overrides (writing
-      //    the shorthand resets the longhands). A no-movement click restores
-      //    the captured style attributes instead, since nothing re-renders.
+      //  - cleanup: release restores the captured style attributes, then a
+      //    real drag commits the store once and React re-renders from it.
       const previewPlan = (plan: ReturnType<typeof planFor>) => {
         sashTracks.forEach((track, index) => {
           if (!track.visible || track.minimized) {
@@ -458,6 +456,14 @@ export function TreeSplit({ node, root, rootRow }: { node: SplitNode; root?: boo
         done = true
         resize.finish()
 
+        // Put every wrapper's inline style back exactly as React last wrote
+        // it BEFORE the store commit. React only rewrites a wrapper whose
+        // style prop changed; a preview pinned on a track the commit leaves
+        // alone (the flex run beside a zone that folded to its rail) would
+        // otherwise survive as a stale `flex: 0 1 <px>` and stop it growing.
+        // A no-movement click has no commit, so this is also its whole cleanup.
+        restoreStyles()
+
         if (lastPlan && lastPlan.moved !== 0) {
           // Dragged a tool panel down to its collapsed header? Fold the zone
           // to its rail instead of persisting a sliver — and DON'T write the
@@ -473,10 +479,6 @@ export function TreeSplit({ node, root, rootRow }: { node: SplitNode; root?: boo
           } else {
             commitPlan(lastPlan)
           }
-        } else {
-          // Click without movement: nothing will re-render, so put the
-          // wrappers' inline styles back exactly as React last wrote them.
-          restoreStyles()
         }
 
         // Geometry vars re-enable AFTER the final store commit above, so the