fix: 面板拖动布局闪烁 — 右侧栏关闭时底部高度拖动挤压 AppFrame + 释放瞬间整体铺满再回弹

- applyDrag 仅在右侧面板打开时写入 --dsh-sidebar-width（底部高度拖动传入的是右侧栏持久化宽度，关闭时会把整个 AppFrame 左挤，直到松手才恢复）
- 布局 push effect 拆分为「仅设置」+「仅卸载移除」：React 同一提交内先执行全部 cleanup 再执行全部 setup，原 cleanup 删除 CSS 变量后，draggingRef effect 的 measureCenter 强制重算把 0px 缓存为 margin-right 过渡起点，释放时过渡重新启用 → 0→W 动画（先铺满页面再回弹）
- 回归测试：size change 提交过程中不得 removeProperty 布局变量（仅卸载时移除，issue #31 语义保留）

src/client/Sidebar.tsx

@@ -472,7 +472,13 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     // `width + detailsWidth` — derived from the measured column, keeping the
     // drag write-only (no React re-render mid-drag).
     bottomRef.current?.style.setProperty('right', `${(window.innerWidth - centerRect.right) + (width - (state?.width ?? 0))}px`)
-    document.documentElement.style.setProperty('--dsh-sidebar-width', `${width}px`)
+    // The width push exists only while the right panel is OPEN (the layout
+    // push effect writes 0 while it is collapsed). The bottom-height drag
+    // reuses this function with the right panel's PERSISTED width as `width`,
+    // so writing it unconditionally would squeeze the whole app shell left
+    // mid-drag — as if the collapsed right panel were still occupying space —
+    // until the store commit on release snaps it back.
+    document.documentElement.style.setProperty('--dsh-sidebar-width', `${state?.panelOpen === true ? width : 0}px`)
     document.documentElement.style.setProperty('--dsh-sidebar-height', `${height}px`)
     if (cornerRef.current !== null) {
       cornerRef.current.style.left = `${window.innerWidth - width - 6}px`
@@ -516,6 +522,18 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
   // crush the app shell to zero. Dragging disables the layout transition.
   // On NARROW viewports the drawer FLOATS over the app shell — no push, the
   // conversation keeps the full width behind the drawer.
+  //
+  // This effect is deliberately SET-only (no cleanup): React runs every
+  // effect cleanup before every effect setup in the same commit, so a
+  // cleanup here would remove both variables before the draggingRef effect
+  // (declared above) runs its setup and forces a layout in measureCenter
+  // (getBoundingClientRect). That forced recalc would resolve #root's
+  // margin-right to the 0px fallback, cache it as the transition start
+  // value, and measure centerRect far too wide; once the body attribute
+  // effect re-enables transitions on pointer-up, the shell would animate
+  // margin-right 0 → width — the visible "expand to the full page then
+  // bounce back" flash. Unmount release lives in the effect below
+  // (issue #31).
   useEffect(() => {
     const width = !narrow && snapshot.state?.panelOpen === true
       ? Math.min(snapshot.state.width, window.innerWidth)
@@ -525,18 +543,20 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       : 0
     document.documentElement.style.setProperty('--dsh-sidebar-width', `${width}px`)
     document.documentElement.style.setProperty('--dsh-sidebar-height', `${height}px`)
-    // Unmount must release the push (issue #31): when the boundary swaps the
-    // whole sidebar after a render crash (or the plugin fiber is disposed /
-    // HMR), the CSS variables would otherwise stay on <html> and layout.css
-    // keeps squeezing #root with a stale margin — "the sidebar cannot be
-    // hidden" until a full reload. removeProperty restores the CSS fallback
-    // (var(--dsh-sidebar-width, 0px)); React re-runs cleanup+setup in the
-    // same commit on state changes, so there is no visible flicker.
+  }, [narrow, snapshot.state?.panelOpen, snapshot.state?.width, snapshot.state?.bottomOpen, snapshot.state?.bottomHeight])
+  // Unmount must release the push (issue #31): when the boundary swaps the
+  // whole sidebar after a render crash (or the plugin fiber is disposed /
+  // HMR), the CSS variables would otherwise stay on <html> and layout.css
+  // keeps squeezing #root with a stale margin — "the sidebar cannot be
+  // hidden" until a full reload. removeProperty restores the CSS fallback
+  // (var(--dsh-sidebar-width, 0px)). Kept separate from the set effect so a
+  // dep-change re-run never removes the variables mid-commit.
+  useEffect(() => {
     return () => {
       document.documentElement.style.removeProperty('--dsh-sidebar-width')
       document.documentElement.style.removeProperty('--dsh-sidebar-height')
     }
-  }, [narrow, snapshot.state?.panelOpen, snapshot.state?.width, snapshot.state?.bottomOpen, snapshot.state?.bottomHeight])
+  }, [])
   useEffect(() => {
     if (anyDragging) document.body.setAttribute('data-dsh-sidebar-dragging', '')
     else document.body.removeAttribute('data-dsh-sidebar-dragging')

tests/sidebar-crash.spec.tsx

@@ -26,7 +26,7 @@ import { act } from 'react-dom/test-utils'
 ;(globalThis as Record<string, unknown>).IS_REACT_ACT_ENVIRONMENT = true
 
 import { Sidebar } from '../src/client/Sidebar.tsx'
-import { createSidebarStore, type SidebarStore } from '../src/client/state.ts'
+import { createSidebarStore, setBottomHeight, toggleBottomPanel, type SidebarStore } from '../src/client/state.ts'
 import { createBetterSidebarService, type BetterSidebarService } from '../src/client/service.ts'
 import { t } from '../src/client/locales.ts'
 
@@ -99,6 +99,36 @@ describe('layout-push variable cleanup', () => {
     expect(htmlStyle.getPropertyValue('--dsh-sidebar-width')).toBe('')
     expect(htmlStyle.getPropertyValue('--dsh-sidebar-height')).toBe('')
   })
+
+  it('a size change (release commit) re-applies the variables without removing them mid-commit', () => {
+    const { store, unmount } = mountSidebar()
+    const htmlStyle = document.documentElement.style
+    const width = store.getSnapshot().state!.width
+    const removeSpy = vi.spyOn(htmlStyle, 'removeProperty')
+    // Simulate a drag release: the bottom panel opens and its height commits.
+    act(() => { store.reduce(toggleBottomPanel) })
+    act(() => { store.reduce(s => setBottomHeight(s, 300)) })
+    expect(htmlStyle.getPropertyValue('--dsh-sidebar-width')).toBe(`${width}px`)
+    expect(htmlStyle.getPropertyValue('--dsh-sidebar-height')).toBe('300px')
+    // The commit must NOT have removed the variables at any point. React
+    // runs every effect cleanup before every effect setup in a commit, so a
+    // cleanup here would remove the variables before the draggingRef effect
+    // (declared above the layout push) forces a layout in measureCenter
+    // (getBoundingClientRect). That forced recalc resolves #root's
+    // margin-right to the 0px fallback, caches it as the transition start
+    // value, and measures centerRect too wide; once transitions re-enable on
+    // release, the shell animates margin-right 0 → width — the "expand to
+    // the full page then bounce back" flash.
+    const removalProps = removeSpy.mock.calls
+      .map(call => call[0] as string)
+      .filter(prop => prop === '--dsh-sidebar-width' || prop === '--dsh-sidebar-height')
+    expect(removalProps).toHaveLength(0)
+    // Only unmounting may remove them (issue #31).
+    unmount()
+    expect(removeSpy.mock.calls.some(call =>
+      call[0] === '--dsh-sidebar-width' || call[0] === '--dsh-sidebar-height')).toBe(true)
+    removeSpy.mockRestore()
+  })
 })
 
 describe('tab crash containment', () => {