fix: recalculate panel geometry on resize

src/client/Sidebar.tsx

@@ -42,7 +42,7 @@ import {
 } from './state.ts'
 import { IconPanelBottomOutline16, IconPanelRightOutline16 } from './icons.tsx'
 import { Workbench, type WorkbenchActions } from './split-pane.tsx'
-import { useNarrowViewport } from './breakpoints.ts'
+import { isNarrowWidth, useViewportSize } from './breakpoints.ts'
 import { layoutPushSize } from './layout-push.ts'
 import { parseDesktopEnv } from './desktop-env.ts'
 import { getWcoSnapshot, subscribeWco } from './wco.ts'
@@ -184,7 +184,8 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
   // — the merged display is the right sidebar alone, the bottom tabs thrown
   // into its strips. Widening never rewrites the migrated state: the tabs
   // keep living in the right tree.
-  const narrow = useNarrowViewport()
+  const viewport = useViewportSize()
+  const narrow = isNarrowWidth(viewport.width)
 
   // On-screen keyboard / visual-viewport inset (mobile, split-screen, …):
   // when the visual viewport shrinks below the layout viewport, bottom-
@@ -836,11 +837,11 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       bottomOpen: snapshot.state?.bottomOpen === true,
       width: snapshot.state?.width ?? 0,
       bottomHeight: snapshot.state?.bottomHeight ?? 0,
-      viewportWidth: window.innerWidth,
-      viewportHeight: window.innerHeight,
+      viewportWidth: viewport.width,
+      viewportHeight: viewport.height,
     })
     writeGeometry(width, height)
-  }, [narrow, snapshot.state?.panelOpen, snapshot.state?.width, snapshot.state?.bottomOpen, snapshot.state?.bottomHeight])
+  }, [narrow, snapshot.state?.panelOpen, snapshot.state?.width, snapshot.state?.bottomOpen, snapshot.state?.bottomHeight, viewport.width, viewport.height])
   // 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
@@ -955,6 +956,18 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     )
   }
 
+  const bottomPanelHeight = layoutPushSize({
+    narrow,
+    panelOpen: state.panelOpen,
+    // Keep the hidden panel's geometry ready for its slide-in transition;
+    // only the layout push itself becomes zero while it is closed.
+    bottomOpen: true,
+    width: state.width,
+    bottomHeight: state.bottomHeight,
+    viewportWidth: viewport.width,
+    viewportHeight: viewport.height,
+  }).height
+
   const onNewTab = (optionId: string): void => {
     const service = ctx.betterSidebar
     const descriptor = service?.getTab(optionId)
@@ -1205,7 +1218,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
         data-dsh-panel
         data-dsh-bottom-panel
         style={{
-          height: Math.min(state.bottomHeight, window.innerHeight),
+          height: bottomPanelHeight,
           left: centerRect.left,
           // Keep the panel above the on-screen keyboard when the visual
           // viewport shrinks (see the keyboardInset effect).

src/client/breakpoints.ts

@@ -20,6 +20,11 @@ export function isNarrowWidth(width: number): boolean {
   return width < NARROW_MAX_WIDTH
 }
 
+export interface ViewportSize {
+  width: number
+  height: number
+}
+
 /**
  * Live narrow-viewport flag for components. Reads `window.innerWidth` and
  * re-measures on resize (rAF-throttled, the repo's existing drag pattern).
@@ -27,16 +32,17 @@ export function isNarrowWidth(width: number): boolean {
  * resize listener is equally exact for a breakpoint that never changes
  * while the page is open.
  */
-export function useNarrowViewport(): boolean {
-  const [narrow, setNarrow] = useState(
-    () => typeof window !== 'undefined' && isNarrowWidth(window.innerWidth),
-  )
+export function useViewportSize(): ViewportSize {
+  const [size, setSize] = useState<ViewportSize>(() => ({
+    width: typeof window === 'undefined' ? 0 : window.innerWidth,
+    height: typeof window === 'undefined' ? 0 : window.innerHeight,
+  }))
   useEffect(() => {
     if (typeof window === 'undefined') return
     let frame: number | null = null
     const measure = (): void => {
       frame = null
-      setNarrow(isNarrowWidth(window.innerWidth))
+      setSize({ width: window.innerWidth, height: window.innerHeight })
     }
     const onResize = (): void => {
       if (frame === null) frame = requestAnimationFrame(measure)
@@ -47,5 +53,9 @@ export function useNarrowViewport(): boolean {
       if (frame !== null) cancelAnimationFrame(frame)
     }
   }, [])
-  return narrow
+  return size
+}
+
+export function useNarrowViewport(): boolean {
+  return isNarrowWidth(useViewportSize().width)
 }

tests/breakpoints-react.spec.tsx

@@ -0,0 +1,42 @@
+// @vitest-environment jsdom
+import { createRoot } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { useViewportSize } from '../src/client/breakpoints.ts'
+
+describe('useViewportSize', () => {
+  afterEach(() => {
+    document.body.replaceChildren()
+    vi.restoreAllMocks()
+  })
+
+  it('publishes height-only resizes without requiring a breakpoint change', async () => {
+    const frames: FrameRequestCallback[] = []
+    vi.stubGlobal('requestAnimationFrame', (callback: FrameRequestCallback) => {
+      frames.push(callback)
+      return frames.length
+    })
+    vi.stubGlobal('cancelAnimationFrame', vi.fn())
+    Object.defineProperty(window, 'innerWidth', { configurable: true, value: 1280 })
+    Object.defineProperty(window, 'innerHeight', { configurable: true, value: 800 })
+
+    const observed: string[] = []
+    function Probe(): null {
+      const size = useViewportSize()
+      observed.push(`${size.width}x${size.height}`)
+      return null
+    }
+
+    const host = document.createElement('div')
+    document.body.append(host)
+    const root = createRoot(host)
+    await act(async () => { root.render(<Probe />) })
+
+    Object.defineProperty(window, 'innerHeight', { configurable: true, value: 600 })
+    window.dispatchEvent(new Event('resize'))
+    await act(async () => { frames.shift()?.(0) })
+
+    expect(observed.at(-1)).toBe('1280x600')
+    await act(async () => { root.unmount() })
+  })
+})