frontend/src/App.tsx

@@ -21,6 +21,7 @@ import { applyClientAppearance,
 	 setCachedUserThemeSlots,
 	 seedClientThemeMode } from '@/lib/settings'
 import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { UnsavedChangesGuardProvider } from '@/lib/useUnsavedChangesGuard'
 
 import { KeyboardShortcutsProvider } from '@/lib/useKeyboardShortcuts'
 import DeerjikistDetailPage from '@/pages/deerjikists/DeerjikistDetailPage'
@@ -210,8 +211,9 @@ const App: FC = () => {
 	{import.meta.env.DEV && <DevModeWatermark/>}
 
 	<BrowserRouter>
-	  <KeyboardShortcutsProvider>
 	  <DialogueProvider>
+	    <UnsavedChangesGuardProvider>
+	      <KeyboardShortcutsProvider>
 	      <MotionConfig
 		  reducedMotion={
 		      animationMode === 'normal'
@@ -232,8 +234,9 @@ const App: FC = () => {
 	      </MotionConfig>
 
 	      <Toaster/>
-	    </DialogueProvider>
 	      </KeyboardShortcutsProvider>
+	    </UnsavedChangesGuardProvider>
+	  </DialogueProvider>
 	</BrowserRouter>
       </>)
 }

frontend/src/components/PrefetchLink.tsx

@@ -6,6 +6,7 @@ import { createPath, useNavigate } from 'react-router-dom'
 import { useOverlayStore } from '@/components/RouteBlockerOverlay'
 import { prefetchForURL } from '@/lib/prefetchers'
 import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { useUnsavedChangesGuard } from '@/lib/useUnsavedChangesGuard'
 import { cn } from '@/lib/utils'
 
 import type { AnchorHTMLAttributes, MouseEvent, TouchEvent } from 'react'
@@ -35,11 +36,19 @@ export default forwardRef<HTMLAnchorElement, Props> (({
   const navigate = useNavigate ()
   const qc = useQueryClient ()
   const behaviourSettings = useClientBehaviourSettings ()
+  const { confirmDiscardNavigation } = useUnsavedChangesGuard ()
   const linkPreloadMode = behaviourSettings.linkPreload ?? 'intent'
+  const path = useMemo (
+      () => typeof to === 'string' ? to : createPath (to),
+      [to],
+  )
   const url = useMemo (() => {
-    const path = (typeof to === 'string') ? to : createPath (to)
+    return (new URL (path, window.location.origin)).toString ()
-    return (new URL (path, location.origin)).toString ()
+  }, [path])
-  }, [to])
+  const nextPathname = useMemo (
+      () => (new URL (path, window.location.origin)).pathname,
+      [path],
+  )
   const setOverlay = useOverlayStore (s => s.setActive)
 
   const doPrefetch = async () => {
@@ -84,6 +93,13 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 
       ev.preventDefault ()
 
+      if (nextPathname !== window.location.pathname)
+	{
+	  const confirmed = await confirmDiscardNavigation ()
+	  if (!(confirmed))
+	    return
+	}
+
       flushSync (() => {
 	setOverlay (true)
       })
@@ -106,7 +122,7 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 
   return (
       <a ref={ref}
-	 href={typeof to === 'string' ? to : createPath (to)}
+	 href={path}
 	 onMouseEnter={handleMouseEnter}
 	 onTouchStart={handleTouchStart}
 	 onClick={handleClick}

frontend/src/components/users/BehaviourSettingsSection.tsx

@@ -158,7 +158,7 @@ const BehaviourSettingsSection: FC<Props> = (
 	  <div className="flex flex-wrap gap-2">
 	    <Button
 		type="button"
-		variant="outline"
+		variant="destructive"
 		disabled={hasUnsavedChanges === false}
 		onClick={handleDiscard}>
 	      変更を破棄

frontend/src/components/users/KeyboardSettingsSection.tsx

@@ -167,7 +167,7 @@ const KeyboardSettingsSection: FC<Props> = (
 	    </Button>
 	    <Button
 		type="button"
-		variant="outline"
+		variant="destructive"
 		disabled={!(hasUnsavedChanges)}
 		onClick={handleDiscard}>
 	      変更を破棄

frontend/src/lib/useKeyboardShortcuts.tsx

@@ -25,6 +25,7 @@ import {
     getEffectiveKeyBindings,
     setClientKeyboardSettings,
 } from '@/lib/settings'
+import { useUnsavedChangesGuard } from '@/lib/useUnsavedChangesGuard'
 
 import type {
     KeyBinding,
@@ -96,6 +97,7 @@ const focusSearchTarget = (): void => {
 export const KeyboardShortcutsProvider = ({ children }: PropsWithChildren) => {
   const location = useLocation ()
   const navigate = useNavigate ()
+  const { confirmDiscardNavigation } = useUnsavedChangesGuard ()
 
   const [keyboardSettings, setKeyboardSettingsState] =
       useState<ClientKeyboardSettings> (() => getClientKeyboardSettings ())
@@ -146,6 +148,13 @@ export const KeyboardShortcutsProvider = ({ children }: PropsWithChildren) => {
     }
   }, [])
 
+  const guardedNavigate = useCallback ((path: string) => {
+    confirmDiscardNavigation ().then (confirmed => {
+      if (confirmed)
+	navigate (path)
+    })
+  }, [confirmDiscardNavigation, navigate])
+
   const builtinHandlers = useMemo<ShortcutHandlers> (
       () => ({
 	  'global.openShortcutHelp': () => {
@@ -154,16 +163,16 @@ export const KeyboardShortcutsProvider = ({ children }: PropsWithChildren) => {
 	  'global.focusSearch': () => {
 	    focusSearchTarget ()
 	  },
-	  'navigation.posts': () => navigate ('/posts'),
+	  'navigation.posts': () => guardedNavigate ('/posts'),
-	  'navigation.tags': () => navigate ('/tags'),
+	  'navigation.tags': () => guardedNavigate ('/tags'),
-	  'navigation.materials': () => navigate ('/materials'),
+	  'navigation.materials': () => guardedNavigate ('/materials'),
-	  'navigation.wiki': () => navigate ('/wiki'),
+	  'navigation.wiki': () => guardedNavigate ('/wiki'),
-	  'settings.account': () => navigate ('/users/settings?tab=account'),
+	  'settings.account': () => guardedNavigate ('/users/settings?tab=account'),
-	  'settings.theme': () => navigate ('/users/settings?tab=theme'),
+	  'settings.theme': () => guardedNavigate ('/users/settings?tab=theme'),
-	  'settings.keyboard': () => navigate ('/users/settings?tab=keyboard'),
+	  'settings.keyboard': () => guardedNavigate ('/users/settings?tab=keyboard'),
-	  'settings.behavior': () => navigate ('/users/settings?tab=behavior'),
+	  'settings.behavior': () => guardedNavigate ('/users/settings?tab=behavior'),
       }),
-      [navigate],
+      [guardedNavigate],
   )
 
   const availableActionIds = useMemo<Set<ShortcutActionId>> (

frontend/src/lib/useUnsavedChangesGuard.tsx

@@ -0,0 +1,69 @@
+import { createContext, useCallback, useContext, useMemo, useState } from 'react'
+
+import { useDialogue } from '@/components/dialogues/DialogueProvider'
+
+import type { FC, PropsWithChildren } from 'react'
+
+type UnsavedChangesSource = {
+    dirty:    boolean
+    discard:  () => void | Promise<void> }
+
+type UnsavedChangesGuardContextValue = {
+    hasUnsavedChanges:             boolean
+    registerUnsavedChangesSource:  (
+	source: UnsavedChangesSource | null,
+    ) => void
+    confirmDiscardNavigation:      () => Promise<boolean> }
+
+const UnsavedChangesGuardContext =
+    createContext<UnsavedChangesGuardContextValue | null> (null)
+
+
+export const UnsavedChangesGuardProvider: FC<PropsWithChildren> = ({ children }) => {
+  const dialogue = useDialogue ()
+  const [source, setSource] = useState<UnsavedChangesSource | null> (null)
+
+  const registerUnsavedChangesSource = useCallback ((
+      nextSource: UnsavedChangesSource | null,
+  ) => {
+    setSource (nextSource)
+  }, [])
+
+  const confirmDiscardNavigation = useCallback (async (): Promise<boolean> => {
+    if (!(source?.dirty))
+      return true
+
+    const confirmed = await dialogue.confirm ({
+	title: '未保存の変更があります',
+	description: 'このまま移動すると、保存していない変更は失われます。',
+	cancelText: 'このページに残る',
+	confirmText: '変更を破棄して移動',
+	variant: 'danger' })
+    if (!(confirmed))
+      return false
+
+    await source.discard ()
+    return true
+  }, [dialogue, source])
+
+  const value = useMemo<UnsavedChangesGuardContextValue> (() => ({
+      hasUnsavedChanges: source?.dirty === true,
+      registerUnsavedChangesSource,
+      confirmDiscardNavigation,
+  }), [confirmDiscardNavigation, registerUnsavedChangesSource, source?.dirty])
+
+  return (
+      <UnsavedChangesGuardContext.Provider value={value}>
+	{children}
+      </UnsavedChangesGuardContext.Provider>)
+}
+
+
+export const useUnsavedChangesGuard = (): UnsavedChangesGuardContextValue => {
+  const context = useContext (UnsavedChangesGuardContext)
+
+  if (context == null)
+    throw new Error ('UnsavedChangesGuardProvider が必要です．')
+
+  return context
+}

frontend/src/pages/users/SettingPage.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useMemo, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
-import { useBeforeUnload, useBlocker, useLocation, useNavigate } from 'react-router-dom'
+import { useBeforeUnload, useLocation, useNavigate } from 'react-router-dom'
 
 import FieldError from '@/components/common/FieldError'
 import FormField from '@/components/common/FormField'
@@ -28,7 +28,6 @@ import {
     getClientThemeMode,
     getDefaultUserThemeSlot,
     hasStoredClientThemeSelection,
-    getUserThemeSlotSelection,
     normaliseUserThemeSlots,
     resolveDisplayedTheme,
     setCachedUserThemeSlots,
@@ -36,6 +35,7 @@ import {
     upsertUserThemeSlot,
     USER_THEME_SLOT_SELECTIONS,
 } from '@/lib/settings'
+import { useUnsavedChangesGuard } from '@/lib/useUnsavedChangesGuard'
 import { useKeyboardShortcutSettings, useKeyboardShortcuts } from '@/lib/useKeyboardShortcuts'
 import { cn, inputClass } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
@@ -99,7 +99,7 @@ type ThemeSectionProps = {
     draftThemeMode:          ClientThemeMode
     draftActiveLightThemeSlotNo: UserThemeSlotNo
     draftActiveDarkThemeSlotNo: UserThemeSlotNo
-    editingThemeSlot:        UserThemeSlotSelection
+    currentDisplayedThemeSlot: UserThemeSlotSelection
     selectedTheme:           ClientTheme
     displayedThemeLabel:     string
     systemThemeLabel:        string
@@ -109,10 +109,9 @@ type ThemeSectionProps = {
     onSelectThemeMode:       (themeMode: ClientThemeMode) => void
     onSelectLightThemeSlotNo: (slotNo: UserThemeSlotNo) => void
     onSelectDarkThemeSlotNo: (slotNo: UserThemeSlotNo) => void
-    onSelectEditingThemeSlot: (selection: UserThemeSlotSelection) => void
     onThemeTokenChange:      (key: ThemeTokenKey, value: string) => void
     onTagColourChange:       (category: Category, colour: string) => void
-    onResetThemeSlot:        (selection: UserThemeSlotSelection) => void
+    onResetThemeSlot:        () => void
     onThemeSubmit:           () => void
     onThemeDiscard:          () => void }
 
@@ -124,8 +123,16 @@ type ThemeDraftState = {
     themeMode:              ClientThemeMode
     activeLightThemeSlotNo: UserThemeSlotNo
     activeDarkThemeSlotNo:  UserThemeSlotNo
-    themeSlots:             UserThemeSlotMap
+    themeSlots:             UserThemeSlotMap }
-    editingThemeSlot:       UserThemeSlotSelection }
+
+type ThemeSegmentedOption<T extends string | number> = {
+    value: T
+    label: string }
+
+type ThemeSegmentedControlProps<T extends string | number> = {
+    value:     T
+    options:   ThemeSegmentedOption<T>[]
+    onChange:  (value: T) => void }
 
 const tabs: TabSpec[] = [
     { id: 'account', label: 'アカウント' },
@@ -138,6 +145,11 @@ const themeModeSelections: ThemeModeItem[] = [
     { id: 'light', label: 'ライト' },
     { id: 'dark', label: 'ダーク' } ]
 
+const themeSlotNoSelections: ThemeSegmentedOption<UserThemeSlotNo>[] = [
+    { value: 1, label: '1' },
+    { value: 2, label: '2' },
+    { value: 3, label: '3' } ]
+
 const sectionClassName =
     'space-y-4 rounded-xl border border-border bg-background/80 p-4'
 
@@ -181,6 +193,32 @@ const themeTokenGroups: ThemeTokenGroupSpec[] = [
       ] },
 ]
 
+
+const ThemeSegmentedControl = <T extends string | number,> (
+    { value, options, onChange }: ThemeSegmentedControlProps<T>,
+) => (
+    <div
+	role="radiogroup"
+	className="flex flex-wrap gap-2 rounded-xl border border-border bg-muted/40 p-1">
+      {options.map (option => (
+	  <button
+	      key={String (option.value)}
+	      type="button"
+	      role="radio"
+	      aria-checked={value === option.value}
+	      className={cn (
+		  'min-w-0 rounded-lg px-3 py-2 text-sm font-medium',
+		  'transition-colors focus-visible:outline-none focus-visible:ring-2',
+		  'focus-visible:ring-ring focus-visible:ring-offset-2',
+		  value === option.value
+		  ? 'bg-primary text-primary-foreground shadow-sm ring-1 ring-primary/40'
+		  : 'bg-transparent text-muted-foreground hover:bg-background/70 hover:text-foreground',
+	      )}
+	      onClick={() => onChange (option.value)}>
+	    {option.label}
+	  </button>))}
+    </div>)
+
 const previewTag = (
     id:         number,
     name:       string,
@@ -221,7 +259,6 @@ const parseTab = (search: string): SettingsTab => {
 
 const tabButtonId = (tab: SettingsTab): string => `settings-tab-${ tab }`
 const tabPanelId = (tab: SettingsTab): string => `settings-panel-${ tab }`
-const SETTINGS_PATH = '/users/settings'
 
 const themePreviewStyle = (tagColours: ThemeTagColours): CSSProperties =>
     Object.fromEntries (
@@ -249,6 +286,27 @@ const ensureCompleteThemeSlots = (
 	{ ...themeSlots },
     )
 
+const comparableThemeTokensForSelection = (
+    themeSlots:  UserThemeSlotMap,
+    selection:   UserThemeSlotSelection,
+): ThemeTokens => {
+  const [_, baseTheme, slotNo] = selection.split (':')
+  const fallback =
+      getDefaultUserThemeSlot (
+	  baseTheme as BuiltinThemeId,
+	  Number (slotNo) as UserThemeSlotNo,
+      ).tokens
+
+  return {
+      ...fallback,
+      ...(themeSlots[selection]?.tokens ?? { }),
+      tagColours: {
+	  ...fallback.tagColours,
+	  ...(themeSlots[selection]?.tokens.tagColours ?? { }),
+      },
+  }
+}
+
 const serialiseThemeDraft = (
     themeMode:              ClientThemeMode,
     activeLightThemeSlotNo: UserThemeSlotNo,
@@ -261,7 +319,7 @@ const serialiseThemeDraft = (
 	activeDarkThemeSlotNo,
 	themeSlots: USER_THEME_SLOT_SELECTIONS.map (selection => ({
 	    selection,
-	    tokens: themeSlots[selection]?.tokens,
+	    tokens: comparableThemeTokensForSelection (themeSlots, selection),
 	})),
     })
 
@@ -454,7 +512,7 @@ const ThemeSection: FC<ThemeSectionProps> = (
     { draftThemeMode,
       draftActiveLightThemeSlotNo,
       draftActiveDarkThemeSlotNo,
-      editingThemeSlot,
+      currentDisplayedThemeSlot,
       selectedTheme,
       displayedThemeLabel,
       systemThemeLabel,
@@ -464,15 +522,12 @@ const ThemeSection: FC<ThemeSectionProps> = (
       onSelectThemeMode,
       onSelectLightThemeSlotNo,
       onSelectDarkThemeSlotNo,
-      onSelectEditingThemeSlot,
       onThemeTokenChange,
       onTagColourChange,
       onResetThemeSlot,
       onThemeSubmit,
       onThemeDiscard },
 ) => {
-  const currentEditableSelection = editingThemeSlot
-
   return (
       <section className={sectionClassName}>
 	<div className="flex flex-wrap items-start justify-between gap-3">
@@ -486,7 +541,7 @@ const ThemeSection: FC<ThemeSectionProps> = (
 		  システム設定: {systemThemeLabel}
 		</p>)}
 	    <p className="text-sm text-muted-foreground">
-	      編輯対象: {themeLabelBySelection (currentEditableSelection)}
+	      保存先: {themeLabelBySelection (currentDisplayedThemeSlot)}
 	    </p>
 	    {hasUnsavedChanges && (
 		<p className="text-sm text-amber-700 dark:text-amber-300">
@@ -497,7 +552,7 @@ const ThemeSection: FC<ThemeSectionProps> = (
 	  <div className="flex flex-wrap gap-2">
 	    <Button
 		type="button"
-		variant="outline"
+		variant="destructive"
 		disabled={!(hasUnsavedChanges)}
 		onClick={onThemeDiscard}>
 	      変更を破棄
@@ -506,7 +561,7 @@ const ThemeSection: FC<ThemeSectionProps> = (
 		type="button"
 		disabled={!(hasUnsavedChanges)}
 		onClick={onThemeSubmit}>
-	      保存
+	      {`${ themeLabelBySelection (currentDisplayedThemeSlot) } に保存`}
 	    </Button>
 	  </div>
 	</div>
@@ -517,29 +572,23 @@ const ThemeSection: FC<ThemeSectionProps> = (
 	<div className="space-y-3 rounded-xl border border-border/70 bg-background/70 p-4">
 	  <div className="space-y-2">
 	    <Label>表示モード</Label>
-	    <select
+	    <ThemeSegmentedControl
-		className={inputClass (false)}
 		value={draftThemeMode}
-		onChange={ev =>
+		options={themeModeSelections.map (selection => ({
-		    onSelectThemeMode (ev.target.value as ClientThemeMode)}>
+		    value: selection.id,
-	      {themeModeSelections.map (selection => (
+		    label: selection.label }))}
-		    <option key={selection.id} value={selection.id}>
+		onChange={value => onSelectThemeMode (value as ClientThemeMode)}/>
-		      {selection.label}
-		    </option>))}
-	    </select>
 	  </div>
 
 	  <div className="space-y-2">
 	    <Label>ライト用テーマ</Label>
 	    <select
-		className={inputClass (false)}
+		className={cn (inputClass (false), 'w-full')}
 		value={draftActiveLightThemeSlotNo}
 		onChange={ev =>
 		    onSelectLightThemeSlotNo (Number (ev.target.value) as UserThemeSlotNo)}>
-	      {themeSelections
+	      {themeSlotNoSelections.map (selection => (
-	       .filter (selection => selection.baseTheme === 'light')
+		    <option key={selection.value} value={selection.value}>
-	       .map (selection => (
-		   <option key={selection.id} value={selection.slotNo}>
 		      {selection.label}
 		    </option>))}
 	    </select>
@@ -548,45 +597,28 @@ const ThemeSection: FC<ThemeSectionProps> = (
 	  <div className="space-y-2">
 	    <Label>ダーク用テーマ</Label>
 	    <select
-		className={inputClass (false)}
+		className={cn (inputClass (false), 'w-full')}
 		value={draftActiveDarkThemeSlotNo}
 		onChange={ev =>
 		    onSelectDarkThemeSlotNo (Number (ev.target.value) as UserThemeSlotNo)}>
-	      {themeSelections
+	      {themeSlotNoSelections.map (selection => (
-	       .filter (selection => selection.baseTheme === 'dark')
+		    <option key={selection.value} value={selection.value}>
-	       .map (selection => (
-		   <option key={selection.id} value={selection.slotNo}>
 		      {selection.label}
 		    </option>))}
 	    </select>
 	  </div>
 
-	  <div className="space-y-2">
+	  <div className="flex flex-wrap items-center gap-2">
-	    <Label htmlFor="theme-slot-select">編輯対象</Label>
-	    <div className="flex flex-col gap-2 sm:flex-row sm:items-center">
-	      <select
-		  id="theme-slot-select"
-		  className={cn (inputClass (false), 'w-full min-w-0 sm:w-64')}
-		  value={currentEditableSelection}
-		  onChange={ev =>
-		      onSelectEditingThemeSlot (ev.target.value as UserThemeSlotSelection)}>
-		{themeSelections.map (selection => (
-		    <option key={selection.id} value={selection.id}>
-		      {selection.label}
-		    </option>))}
-	      </select>
-
 	    <Button
 		type="button"
-		  variant="ghost"
+		variant="outline"
-		  onClick={() => onResetThemeSlot (currentEditableSelection)}>
+		onClick={onResetThemeSlot}>
 	      既定に戻す
 	    </Button>
 	  </div>
-	  </div>
 
 	  <div className="space-y-1 text-sm text-muted-foreground">
-	    <p>変更は保存時に反映されます。</p>
+	    <p>保存するまで反映は確定しません。</p>
 	  </div>
 
 	  <div style={themePreviewStyle (selectedTheme.tokens.tagColours)}>
@@ -672,6 +704,7 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
   const location = useLocation ()
   const navigate = useNavigate ()
   const dialogue = useDialogue ()
+  const { registerUnsavedChangesSource } = useUnsavedChangesGuard ()
 
   const [inheritVsbl, setInheritVsbl] = useState (false)
   const [loading, setLoading] = useState (true)
@@ -693,10 +726,6 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       useState<UserThemeSlotMap> (() => ensureCompleteThemeSlots ({ }))
   const [draftThemeSlots, setDraftThemeSlots] =
       useState<UserThemeSlotMap> (() => ensureCompleteThemeSlots ({ }))
-  const [savedEditingThemeSlot, setSavedEditingThemeSlot] =
-      useState<UserThemeSlotSelection> ('user:light:1')
-  const [editingThemeSlot, setEditingThemeSlot] =
-      useState<UserThemeSlotSelection> ('user:light:1')
   const [dirtyStates, setDirtyStates] =
       useState<Partial<Record<SettingsTab, SettingsTabDirtyState>>> ({ })
   const [userCodeVsbl, setUserCodeVsbl] = useState (false)
@@ -724,7 +753,9 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
   const selectedTheme = useMemo<ClientTheme> (
       () => {
 	const currentSelection =
-	    themeSelections.find (selection => selection.id === editingThemeSlot)
+	    themeSelections.find (
+		selection => selection.id === displayedThemeSelection.selection,
+	    )
 	    ?? themeSelections[0]
 	const themeSlot =
 	    draftThemeSlots[currentSelection.id]
@@ -736,25 +767,23 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	    baseTheme: currentSelection.baseTheme,
 	    tokens: themeSlot.tokens }
       },
-      [draftThemeSlots, editingThemeSlot])
+      [displayedThemeSelection.selection, draftThemeSlots])
   const hasUnsavedThemeChanges = useMemo (
       () =>
 	  serialiseThemeDraft (draftThemeMode,
 			       draftActiveLightThemeSlotNo,
 			       draftActiveDarkThemeSlotNo,
 			       draftThemeSlots)
-	  !== (serialiseThemeDraft (savedThemeMode,
+	  !== serialiseThemeDraft (savedThemeMode,
 				   savedActiveLightThemeSlotNo,
 				   savedActiveDarkThemeSlotNo,
-				    savedThemeSlots)),
+				   savedThemeSlots),
       [draftActiveDarkThemeSlotNo,
        draftActiveLightThemeSlotNo,
        draftThemeMode,
        draftThemeSlots,
-       editingThemeSlot,
        savedActiveDarkThemeSlotNo,
        savedActiveLightThemeSlotNo,
-       savedEditingThemeSlot,
        savedThemeMode,
        savedThemeSlots])
   const savedName = user?.name ?? ''
@@ -812,18 +841,15 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	 activeLightThemeSlotNo = draftActiveLightThemeSlotNo,
 	 activeDarkThemeSlotNo = draftActiveDarkThemeSlotNo,
 	 themeSlots = draftThemeSlots,
-	 nextEditingThemeSlot = editingThemeSlot,
 	 }: { themeMode?:               ClientThemeMode
 	      activeLightThemeSlotNo?:  UserThemeSlotNo
 	      activeDarkThemeSlotNo?:   UserThemeSlotNo
-	      themeSlots?:              UserThemeSlotMap
+	      themeSlots?:              UserThemeSlotMap },
-	      nextEditingThemeSlot?:    UserThemeSlotSelection },
   ) => {
     setDraftThemeMode (themeMode)
     setDraftActiveLightThemeSlotNo (activeLightThemeSlotNo)
     setDraftActiveDarkThemeSlotNo (activeDarkThemeSlotNo)
     setDraftThemeSlots (themeSlots)
-    setEditingThemeSlot (nextEditingThemeSlot)
     setCachedUserThemeSlots (themeSlots)
     applyThemeAppearanceState ({
 	themeMode,
@@ -840,22 +866,19 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       themeMode: draftThemeMode,
       activeLightThemeSlotNo: draftActiveLightThemeSlotNo,
       activeDarkThemeSlotNo: draftActiveDarkThemeSlotNo,
-      themeSlots: draftThemeSlots,
+      themeSlots: draftThemeSlots })
-      editingThemeSlot })
 
   const savedThemeDraftState = (): ThemeDraftState => ({
       themeMode: savedThemeMode,
       activeLightThemeSlotNo: savedActiveLightThemeSlotNo,
       activeDarkThemeSlotNo: savedActiveDarkThemeSlotNo,
-      themeSlots: savedThemeSlots,
+      themeSlots: savedThemeSlots })
-      editingThemeSlot: savedEditingThemeSlot })
 
   const discardThemeChanges = () => {
     setDraftThemeMode (savedThemeMode)
     setDraftActiveLightThemeSlotNo (savedActiveLightThemeSlotNo)
     setDraftActiveDarkThemeSlotNo (savedActiveDarkThemeSlotNo)
     setDraftThemeSlots (savedThemeSlots)
-    setEditingThemeSlot (savedEditingThemeSlot)
     setCachedUserThemeSlots (savedThemeSlots)
     setClientThemeAppearance ({
 	themeMode: savedThemeMode,
@@ -864,6 +887,18 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
     applyClientAppearance (savedThemeSlots)
   }
 
+  const discardAllDirtyChanges = async (): Promise<void> => {
+    const currentDirtyStates = Object.values (dirtyStates)
+
+    for (const dirtyState of currentDirtyStates)
+      {
+	if (dirtyState?.dirty)
+	  await dirtyState.discard ()
+      }
+
+    setDirtyStates ({ })
+  }
+
   const discardCurrentTabChanges = async (): Promise<void> => {
     const currentDirtyState = dirtyStates[activeTab]
 
@@ -903,10 +938,7 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       cancelText = 'このまま編集する',
       confirmText = '変更を破棄して切り替える',
   ): Promise<void> => {
-    const baseState =
+    const baseState = currentThemeDraftState ()
-	hasUnsavedThemeChanges
-	? savedThemeDraftState ()
-	: currentThemeDraftState ()
 
     if (hasUnsavedThemeChanges)
       {
@@ -916,52 +948,52 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	    confirmText)
 	if (!(confirmed))
 	  return
+
+	discardThemeChanges ()
       }
 
-    const nextState = buildNextState (baseState)
+    const nextState = buildNextState (
+	hasUnsavedThemeChanges
+	? savedThemeDraftState ()
+	: baseState)
 
     applyDraftThemeState ({
 	themeMode: nextState.themeMode,
 	activeLightThemeSlotNo: nextState.activeLightThemeSlotNo,
 	activeDarkThemeSlotNo: nextState.activeDarkThemeSlotNo,
-	themeSlots: nextState.themeSlots,
+	themeSlots: nextState.themeSlots })
-	nextEditingThemeSlot: nextState.editingThemeSlot })
   }
 
-  const routeBlocker = useBlocker (({ currentLocation, nextLocation }) =>
+  const requestThemeMode = async (
-      hasPageUnsavedChanges
+      themeMode: ClientThemeMode,
-      && currentLocation.pathname === SETTINGS_PATH
+  ): Promise<void> => {
-      && nextLocation.pathname !== currentLocation.pathname)
+    if (themeMode === draftThemeMode)
-
-  useEffect (() => {
-    if (routeBlocker.state !== 'blocked')
       return
 
-    let active = true
+    await requestThemeStateChange (baseState => ({ ...baseState, themeMode }))
-
-    void (async () => {
-      const confirmed = await confirmDiscardChanges (
-	  'このまま移動すると、保存していない変更は失われます。',
-	  'このページに残る',
-	  '変更を破棄して移動',
-      )
-      if (!(active))
-	return
-
-      if (!(confirmed))
-	{
-	  routeBlocker.reset ()
-	  return
   }
 
-      await discardCurrentTabChanges ()
+  const requestLightThemeSlotNo = async (
-      routeBlocker.proceed ()
+      slotNo: UserThemeSlotNo,
-    }) ()
+  ): Promise<void> => {
+    if (slotNo === draftActiveLightThemeSlotNo)
+      return
 
-    return () => {
+    await requestThemeStateChange (baseState => ({
-      active = false
+	...baseState,
+	activeLightThemeSlotNo: slotNo }))
+  }
+
+  const requestDarkThemeSlotNo = async (
+      slotNo: UserThemeSlotNo,
+  ): Promise<void> => {
+    if (slotNo === draftActiveDarkThemeSlotNo)
+      return
+
+    await requestThemeStateChange (baseState => ({
+	...baseState,
+	activeDarkThemeSlotNo: slotNo }))
   }
-  }, [routeBlocker])
 
   useBeforeUnload (event => {
     if (!(hasPageUnsavedChanges))
@@ -972,9 +1004,9 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
   }, { capture: true })
 
   const updateDraftThemeSlot = (
-      selection: UserThemeSlotSelection,
       updater:   (tokens: ThemeTokens) => ThemeTokens,
   ) => {
+    const selection = displayedThemeSelection.selection
     const currentThemeSlot =
 	draftThemeSlots[selection]
 	?? ensureCompleteThemeSlots ({ })[selection]
@@ -982,7 +1014,7 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	...draftThemeSlots,
 	[selection]: { ...currentThemeSlot, tokens: updater (currentThemeSlot.tokens) } }
 
-    applyDraftThemeState ({ themeSlots: nextThemeSlots, nextEditingThemeSlot: selection })
+    applyDraftThemeState ({ themeSlots: nextThemeSlots })
   }
 
   const handleTabKeyDown = (event: KeyboardEvent<HTMLButtonElement>) => {
@@ -1044,21 +1076,13 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 
     try
     {
+      const selection = displayedThemeSelection.selection
       let nextSavedThemeSlots = { ...savedThemeSlots }
-
-      for (const selection of USER_THEME_SLOT_SELECTIONS)
-	{
       const draftThemeSlot = draftThemeSlots[selection]
       const savedThemeSlot = savedThemeSlots[selection]
-	  const requiresPersist =
-	      selection === editingThemeSlot
-	      && savedThemeSlot?.createdAt == null
-
-	  if ((JSON.stringify (draftThemeSlot?.tokens)
-	       === JSON.stringify (savedThemeSlot?.tokens))
-	      && !(requiresPersist))
-	    continue
 
+      if (JSON.stringify (draftThemeSlot?.tokens) !== JSON.stringify (savedThemeSlot?.tokens))
+	{
 	  const persisted = await upsertUserThemeSlot (
 	      draftThemeSlot?.baseTheme ?? selection.split (':')[1] as BuiltinThemeId,
 	      draftThemeSlot?.slotNo ?? Number (selection.split (':')[2]) as UserThemeSlotNo,
@@ -1075,8 +1099,6 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       setSavedActiveDarkThemeSlotNo (draftActiveDarkThemeSlotNo)
       setSavedThemeSlots (completeThemeSlots)
       setDraftThemeSlots (completeThemeSlots)
-      setSavedEditingThemeSlot (editingThemeSlot)
-      setEditingThemeSlot (editingThemeSlot)
       // Display mode and active slot numbers are browser-local state.
       setClientThemeAppearance ({
 	  themeMode: draftThemeMode,
@@ -1128,10 +1150,6 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	    : settings.theme
 	const activeLightThemeSlotNo = getClientActiveLightThemeSlotNo ()
 	const activeDarkThemeSlotNo = getClientActiveDarkThemeSlotNo ()
-	const initialEditingThemeSlot = resolveDisplayedTheme ({
-	    themeMode,
-	    activeLightThemeSlotNo,
-	    activeDarkThemeSlotNo }, completeThemeSlots).selection
 
 	setSavedThemeMode (themeMode)
 	setDraftThemeMode (themeMode)
@@ -1141,8 +1159,6 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	setDraftActiveDarkThemeSlotNo (activeDarkThemeSlotNo)
 	setSavedThemeSlots (completeThemeSlots)
 	setDraftThemeSlots (completeThemeSlots)
-	setSavedEditingThemeSlot (initialEditingThemeSlot)
-	setEditingThemeSlot (initialEditingThemeSlot)
 	setCachedUserThemeSlots (completeThemeSlots)
 	applyThemeAppearanceState ({ themeMode,
 				     activeLightThemeSlotNo,
@@ -1218,6 +1234,16 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 	discard: handleThemeDiscard })
   }, [hasUnsavedThemeChanges, savedThemeSlots])
 
+  useEffect (() => {
+    registerUnsavedChangesSource ({
+	dirty: hasPageUnsavedChanges,
+	discard: discardAllDirtyChanges })
+
+    return () => {
+      registerUnsavedChangesSource (null)
+    }
+  }, [discardAllDirtyChanges, hasPageUnsavedChanges, registerUnsavedChangesSource])
+
   useKeyboardShortcuts ({
       ['settings.account']: () => {
 	requestActiveTab ('account')
@@ -1236,7 +1262,7 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       draftThemeMode,
       draftActiveLightThemeSlotNo,
       draftActiveDarkThemeSlotNo,
-      editingThemeSlot,
+      currentDisplayedThemeSlot: displayedThemeSelection.selection,
       selectedTheme,
       displayedThemeLabel: themeLabelBySelection (displayedThemeSelection.selection),
       systemThemeLabel: displayedThemeSelection.baseTheme === 'dark' ? 'ダーク' : 'ライト',
@@ -1244,36 +1270,27 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       settingsBaseErrors,
       settingsFieldErrors,
       onSelectThemeMode: themeMode => {
-	requestThemeStateChange (baseState => ({ ...baseState, themeMode }))
+	requestThemeMode (themeMode)
       },
       onSelectLightThemeSlotNo: slotNo => {
-	requestThemeStateChange (baseState => ({
+	requestLightThemeSlotNo (slotNo)
-	    ...baseState,
-	    activeLightThemeSlotNo: slotNo,
-	    editingThemeSlot: getUserThemeSlotSelection ('light', slotNo) }))
       },
       onSelectDarkThemeSlotNo: slotNo => {
-	requestThemeStateChange (baseState => ({
+	requestDarkThemeSlotNo (slotNo)
-	    ...baseState,
-	    activeDarkThemeSlotNo: slotNo,
-	    editingThemeSlot: getUserThemeSlotSelection ('dark', slotNo) }))
-      },
-      onSelectEditingThemeSlot: selection => {
-	requestThemeStateChange (baseState => ({ ...baseState, editingThemeSlot: selection }))
       },
       onThemeTokenChange: (key, value) => {
-	updateDraftThemeSlot (editingThemeSlot, tokens => ({ ...tokens, [key]: value }))
+	updateDraftThemeSlot (tokens => ({ ...tokens, [key]: value }))
       },
       onTagColourChange: (category, colour) => {
-	updateDraftThemeSlot (editingThemeSlot, tokens => ({
+	updateDraftThemeSlot (tokens => ({
 	    ...tokens, tagColours: { ...tokens.tagColours, [category]: colour } }))
       },
-      onResetThemeSlot: selection => {
+      onResetThemeSlot: () => {
+	const selection = displayedThemeSelection.selection
 	const baseTheme =
 	    draftThemeSlots[selection]?.baseTheme
 	    ?? selection.split (':')[1] as BuiltinThemeId
 	updateDraftThemeSlot (
-	    selection,
 	    () => getDefaultUserThemeSlot (
 		baseTheme,
 		(draftThemeSlots[selection]?.slotNo
@@ -1313,7 +1330,7 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 			 : ['border-border bg-background text-foreground']),
 		    )}
 		    onClick={() => {
-		      void requestActiveTab (tab.id)
+		      requestActiveTab (tab.id)
 		    }}>
 		  {tab.label}
 		  {settingsTabErrors[tab.id] ? ' !' : ''}
@@ -1367,7 +1384,7 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 			      'dark:border-slate-700 dark:bg-slate-900 dark:text-slate-100']),
 		      )}
 		      onClick={() => {
-			void requestActiveTab (tab.id)
+			requestActiveTab (tab.id)
 		      }}
 		      onKeyDown={handleTabKeyDown}>
 		    {tab.label}