perf: clean tab drag passthrough cleanup from effect

src/renderer/src/components/tab-group/TabGroupSplitLayout.test.ts

@@ -2,6 +2,7 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 const setTabGroupSplitRatioMock = vi.fn()
 const recordFeatureInteractionMock = vi.fn()
+const setDragRootNodeMock = vi.fn()
 const useAppStoreMock = vi.fn(
   (
     selector: (state: {
@@ -37,7 +38,8 @@ vi.mock('./useTabDragSplit', () => ({
     onDragMove: vi.fn(),
     onDragOver: vi.fn(),
     onDragStart: vi.fn(),
-    sensors: []
+    sensors: [],
+    setDragRootNode: setDragRootNodeMock
   })
 }))
 
@@ -47,6 +49,7 @@ describe('TabGroupSplitLayout', () => {
   beforeEach(() => {
     setTabGroupSplitRatioMock.mockClear()
     recordFeatureInteractionMock.mockClear()
+    setDragRootNodeMock.mockClear()
     useAppStoreMock.mockClear()
   })
 

src/renderer/src/components/tab-group/TabGroupSplitLayout.tsx

@@ -238,7 +238,10 @@ export default function TabGroupSplitLayout({
           state. The leftmost pane suppresses its own `border-l` via
           `touchesLeftEdge`, so the seam is always exactly 1px — previously
           both painted and stacked into a 2px bar below the drag strip. */}
-      <div className="flex flex-col flex-1 min-w-0 min-h-0 overflow-hidden border-l border-border">
+      <div
+        ref={dragSplit.setDragRootNode}
+        className="flex flex-col flex-1 min-w-0 min-h-0 overflow-hidden border-l border-border"
+      >
         <div
           className="h-[4px] shrink-0 bg-card"
           style={{ WebkitAppRegion: 'drag' } as React.CSSProperties}

src/renderer/src/components/tab-group/useTabDragSplit.ts

@@ -1,7 +1,7 @@
 /* oxlint-disable max-lines -- Why: the drag-split hook co-locates drop-zone
  * resolution, same-group reordering, and cross-group handoff so state
  * transitions stay readable in one place. */
-import { useCallback, useEffect, useRef, useState } from 'react'
+import { useCallback, useRef, useState } from 'react'
 import {
   closestCenter,
   pointerWithin,
@@ -204,6 +204,7 @@ export function useTabDragSplit({
   onDragOver: (event: DragOverEvent) => void
   onDragStart: (event: DragStartEvent) => void
   sensors: ReturnType<typeof useSensors>
+  setDragRootNode: (node: HTMLDivElement | null) => void
 } {
   const reorderUnifiedTabs = useAppStore((state) => state.reorderUnifiedTabs)
   const dropUnifiedTab = useAppStore((state) => state.dropUnifiedTab)
@@ -235,7 +236,17 @@ export function useTabDragSplit({
     releaseWebviewDragPassthroughRef.current = acquireWebviewsDragPassthrough()
   }, [releaseWebviewDragPassthrough])
 
-  useEffect(() => () => releaseWebviewDragPassthrough(), [releaseWebviewDragPassthrough])
+  const setDragRootNode = useCallback(
+    (node: HTMLDivElement | null): void => {
+      if (node) {
+        return
+      }
+      // Why: this root owns the dnd-kit gesture that temporarily puts browser
+      // webviews in pointer passthrough, so root teardown must release it.
+      releaseWebviewDragPassthrough()
+    },
+    [releaseWebviewDragPassthrough]
+  )
 
   const clearDragState = useCallback(() => {
     releaseWebviewDragPassthrough()
@@ -465,6 +476,7 @@ export function useTabDragSplit({
     onDragMove,
     onDragOver,
     onDragStart,
-    sensors
+    sensors,
+    setDragRootNode
   }
 }