frontend/src/components/MaterialSidebar.tsx

@@ -488,25 +488,23 @@ const MaterialSidebar: FC = () => {
 	  </div>
 	</div>
 
-	<div className="hidden md:block">
-	  <SidebarComponent sidebarKey="materials">
-	    <div className="space-y-4">
-	      <MaterialFilterButtons
-		  materialFilter={materialFilter}
-		  onChange={handleFilterChange}/>
-	      {isLoading && (
-		  <p className="text-sm text-neutral-500 dark:text-stone-400">読込中……</p>)}
-	      {isError && (
-		  <p className="text-sm text-red-600 dark:text-red-300">
-		    タグ一覧の取得に失敗しました．
-		  </p>)}
-	      {(!isLoading && !isError) && (
-		  <ul>
-		    {renderDesktopTree (visibleRootTags)}
-		  </ul>)}
-	    </div>
-	  </SidebarComponent>
-	</div>
+	<SidebarComponent sidebarKey="materials" className="hidden md:block">
+	  <div className="space-y-4">
+	    <MaterialFilterButtons
+		materialFilter={materialFilter}
+		onChange={handleFilterChange}/>
+	    {isLoading && (
+		<p className="text-sm text-neutral-500 dark:text-stone-400">読込中……</p>)}
+	    {isError && (
+		<p className="text-sm text-red-600 dark:text-red-300">
+		  タグ一覧の取得に失敗しました．
+		</p>)}
+	    {(!isLoading && !isError) && (
+		<ul>
+		  {renderDesktopTree (visibleRootTags)}
+		</ul>)}
+	  </div>
+	</SidebarComponent>
       </>)
 }
 

frontend/src/components/TagDetailSidebar.tsx

@@ -146,10 +146,13 @@ const DropSlot = ({ cat }: { cat: Category }) => {
 }
 
 
-type Props = { post: Post; sp?: boolean }
+type Props = {
+    className?: string
+    post:       Post
+    sp?:        boolean }
 
 
-const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
+const TagDetailSidebar: FC<Props> = ({ className, post, sp }) => {
   sp = Boolean (sp)
 
   const qc = useQueryClient ()
@@ -278,7 +281,7 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
   }, [baseTags])
 
   return (
-      <SidebarComponent sidebarKey="post-detail-tags">
+      <SidebarComponent sidebarKey="post-detail-tags" className={className}>
 	<TagSearch/>
 	<DndContext
 	    sensors={sensors}

frontend/src/components/layout/SidebarComponent.test.tsx

@@ -13,6 +13,16 @@ const sidebarRoot = (container: HTMLElement): Element =>
     container.querySelector ('[style*="--sidebar-width"]')!
 
 
+const sidebarTree = (props: Partial<Parameters<typeof SidebarComponent>[0]>) => (
+    <HelmetProvider>
+      <div data-sidebar-container>
+	<SidebarComponent sidebarKey="test-sidebar" {...props}>
+	  Sidebar body
+	</SidebarComponent>
+      </div>
+    </HelmetProvider>)
+
+
 const renderSidebar = (
     props: Partial<Parameters<typeof SidebarComponent>[0]> = {},
     containerWidth = 800,
@@ -24,14 +34,7 @@ const renderSidebar = (
       },
   })
 
-  const rendered = render (
-      <HelmetProvider>
-	<div data-sidebar-container>
-	  <SidebarComponent sidebarKey="test-sidebar" {...props}>
-	    Sidebar body
-	  </SidebarComponent>
-	</div>
-      </HelmetProvider>)
+  const rendered = render (sidebarTree (props))
 
   return rendered
 }
@@ -96,4 +99,26 @@ describe ('SidebarComponent', () => {
     expect (localStorage.getItem ('sidebar:test-sidebar:right:width')).toBeNull ()
     expect (localStorage.getItem ('sidebar:other-sidebar:right:width')).toBe ('480')
   })
+
+  it ('clamps current width on maxWidth changes without re-reading storage', async () => {
+    localStorage.setItem ('sidebar:test-sidebar:left:width', '420')
+
+    const { container, rerender } = renderSidebar ({ maxWidth: 420 }, 900)
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('420px')
+    })
+
+    rerender (sidebarTree ({ maxWidth: 300 }))
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('300px')
+    })
+
+    rerender (sidebarTree ({ maxWidth: 500 }))
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('300px')
+    })
+  })
 })

frontend/src/components/layout/SidebarComponent.tsx

@@ -69,6 +69,7 @@ const SidebarComponent: FC<Props> = ({
     side = 'left',
 }) => {
   const rootRef = useRef<HTMLDivElement | null> (null)
+  const maxWidthRef = useRef (maxWidth)
   const getContainerWidth = useCallback (() => {
     const containerWidth = rootRef.current
 	?.closest ('[data-sidebar-container]')
@@ -83,12 +84,14 @@ const SidebarComponent: FC<Props> = ({
 	typeof window === 'undefined' ? containerWidth : window.innerWidth
     const viewportMaxWidth = Math.floor (viewportWidth * MAX_VIEWPORT_WIDTH_RATIO)
     const maxAllowedWidth =
-	maxWidth == null
+	maxWidthRef.current == null
 	? getSidebarMaxWidth (containerWidth)
-	: Math.max (MIN_SIDEBAR_WIDTH, Math.min (viewportMaxWidth, maxWidth))
+	: Math.max (
+	    MIN_SIDEBAR_WIDTH,
+	    Math.min (viewportMaxWidth, maxWidthRef.current))
 
     return Math.min (maxAllowedWidth, Math.max (MIN_SIDEBAR_WIDTH, nextWidth))
-  }, [maxWidth])
+  }, [])
 
   const [width, setWidth] = useState (() => (
       typeof window === 'undefined'
@@ -153,6 +156,21 @@ const SidebarComponent: FC<Props> = ({
     restoreBodyStyle ()
   }, [clearLongPressTimer, restoreBodyStyle, sidebarKey])
 
+  const applyWidth = useCallback ((nextWidth: number) => {
+    if (nextWidth === widthRef.current)
+      return
+
+    widthRef.current = nextWidth
+    setWidth (nextWidth)
+  }, [])
+
+  useEffect (() => {
+    maxWidthRef.current = maxWidth
+    const containerWidth = getContainerWidth ()
+    const nextWidth = getClampedWidth (widthRef.current, containerWidth)
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth, maxWidth])
+
   const updateWidth = useCallback ((clientX: number) => {
     const state = resizeRef.current
     if (state == null)
@@ -163,9 +181,8 @@ const SidebarComponent: FC<Props> = ({
 		  ? clientX - state.startX
 		  : state.startX - clientX
     const nextWidth = getClampedWidth (state.startWidth + delta, containerWidth)
-    widthRef.current = nextWidth
-    setWidth (nextWidth)
-  }, [getClampedWidth, getContainerWidth])
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth])
 
   const handlePointerDown = (ev: PointerEvent<HTMLDivElement>) => {
     if (ev.pointerType !== 'mouse' && ev.pointerType !== 'touch')
@@ -235,10 +252,9 @@ const SidebarComponent: FC<Props> = ({
   const resetWidth = useCallback (() => {
     const containerWidth = getContainerWidth ()
     const nextWidth = getClampedWidth (DEFAULT_SIDEBAR_WIDTH, containerWidth)
-    widthRef.current = nextWidth
-    setWidth (nextWidth)
+    applyWidth (nextWidth)
     window.localStorage.removeItem (storageKeyForSidebar (sidebarKey, side))
-  }, [getClampedWidth, getContainerWidth, sidebarKey, side])
+  }, [applyWidth, getClampedWidth, getContainerWidth, sidebarKey, side])
 
   const handleDoubleClick = (ev: MouseEvent<HTMLDivElement>) => {
     ev.preventDefault ()
@@ -251,9 +267,14 @@ const SidebarComponent: FC<Props> = ({
     const nextWidth = getClampedWidth (
 	readStoredSidebarWidth (sidebarKey, side),
 	containerWidth)
-    widthRef.current = nextWidth
-    setWidth (nextWidth)
-  }, [getClampedWidth, getContainerWidth, sidebarKey, side])
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth, sidebarKey, side])
+
+  useEffect (() => {
+    const containerWidth = getContainerWidth ()
+    const nextWidth = getClampedWidth (widthRef.current, containerWidth)
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth])
 
   useEffect (() => {
     if (typeof window === 'undefined')
@@ -262,16 +283,12 @@ const SidebarComponent: FC<Props> = ({
     const handleResize = () => {
       const containerWidth = getContainerWidth ()
       const nextWidth = getClampedWidth (widthRef.current, containerWidth)
-      if (nextWidth === widthRef.current)
-	return
-
-      widthRef.current = nextWidth
-      setWidth (nextWidth)
+      applyWidth (nextWidth)
     }
 
     window.addEventListener ('resize', handleResize)
     return () => window.removeEventListener ('resize', handleResize)
-  }, [getClampedWidth, getContainerWidth])
+  }, [applyWidth, getClampedWidth, getContainerWidth])
 
   useEffect (() => {
     onWidthChange?.(width)

frontend/src/pages/materials/MaterialBasePage.tsx

@@ -6,7 +6,9 @@ import type { FC } from 'react'
 
 
 const MaterialBasePage: FC = () => (
-    <div className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
+    <div
+	data-sidebar-container
+	className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
       <MaterialSidebar/>
       <Outlet/>
     </div>)

frontend/src/pages/posts/PostDetailPage.tsx

@@ -92,16 +92,16 @@ const PostDetailPage: FC<Props> = ({ user }) => {
 		       : 'bg-gray-500 hover:bg-gray-600')
 
   return (
-      <div className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
+      <div
+	  data-sidebar-container
+	  className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
 	<Helmet>
 	  {(post?.thumbnail || post?.thumbnailBase) && (
 	      <meta name="thumbnail" content={post.thumbnail! || post.thumbnailBase!}/>)}
 	  {post && <title>{`${ post.title || post.url } | ${ SITE_TITLE }`}</title>}
 	</Helmet>
 
-	<div className="hidden md:block">
-	  {post && <TagDetailSidebar post={post}/>}
-	</div>
+	{post && <TagDetailSidebar post={post} className="hidden md:block"/>}
 
 	<MainArea className="relative">
 	  {post
@@ -179,9 +179,7 @@ const PostDetailPage: FC<Props> = ({ user }) => {
 	   : 'Loading...'}
 	</MainArea>
 
-	<div className="md:hidden">
-	  {post && <TagDetailSidebar post={post} sp/>}
-	</div>
+	{post && <TagDetailSidebar post={post} sp className="md:hidden"/>}
       </div>)
 }
 

frontend/src/pages/posts/PostListPage.tsx

@@ -70,6 +70,7 @@ const PostListPage: FC = () => {
 
   return (
       <div
+	  data-sidebar-container
 	  className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden"
 	  ref={containerRef}>
 	<Helmet>