a11y: semantic headings (UI33) + command-palette listbox semantics (UI27)

UI33 — render titles as real headings so Narrator heading-navigation works:
the shared ScreenHeader title is now <Subtitle2 as="h1"> (one h1 per screen in
one place — Downloads/History/Library/Settings/Terminal); DownloadsView "Queue
(N)" and all 11 settings cards are <Subtitle2 as="h2"> sections; Onboarding
"Welcome" is <Title2 as="h1">. A minimal h1–h6 margin reset in base.css zeroes
the UA heading margin (Fluent's typography classes out-specify the element
selector, so the visual ramp is unchanged) so layout matches the former spans.

UI27 — give the command palette proper combobox/listbox semantics: the input is
role="combobox" with aria-controls/aria-activedescendant/aria-autocomplete, the
list is role="listbox", and each row is role="option" with aria-selected, so the
active row is announced to screen readers via active-descendant. Focus stays on
the input (standard combobox pattern), so the rows became non-focusable divs;
onMouseEnter is kept to unify pointer + keyboard highlight on one sel state.

Also corrected UI30's checkbox in the audit (already implemented via the shared
SegmentedControl radiogroup; only the marker lagged).

typecheck + 253 tests + eslint + prettier + production build all green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/renderer/src/assets/base.css

@@ -9,6 +9,24 @@
   outline-offset: 2px;
 }
 
+/*
+ * Reset the UA heading styles (UI33). Titles are rendered as real headings
+ * (h1/h2) for Narrator heading-navigation, but they carry Fluent's typography
+ * classes for their visual ramp; those classes out-specify this element
+ * selector, so only the browser's default heading margin needs zeroing to keep
+ * the layout identical to the former styled-span titles.
+ */
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+  margin: 0;
+  font-size: inherit;
+  font-weight: inherit;
+}
+
 html,
 body {
   margin: 0;

src/renderer/src/components/CommandPalette.tsx

@@ -98,6 +98,9 @@ export function CommandPalette({
   const listRef = useRef<HTMLDivElement>(null)
 
   const filtered = actions.filter((a) => a.label.toLowerCase().includes(q.trim().toLowerCase()))
+  const listId = 'cmdpalette-list'
+  const optionId = (id: string): string => `cmdpalette-option-${id}`
+  const activeId = filtered[sel] ? optionId(filtered[sel].id) : undefined
 
   useEffect(() => {
     inputRef.current?.focus()
@@ -106,8 +109,8 @@ export function CommandPalette({
     setSel(0)
   }, [q])
   useEffect(() => {
-    const btn = listRef.current?.querySelector<HTMLElement>(`[data-sel="true"]`)
-    btn?.scrollIntoView({ block: 'nearest' })
+    const row = listRef.current?.querySelector<HTMLElement>(`[data-sel="true"]`)
+    row?.scrollIntoView({ block: 'nearest' })
   }, [sel])
 
   function onKeyDown(e: React.KeyboardEvent): void {
@@ -144,22 +147,29 @@ export function CommandPalette({
           onChange={(e) => setQ(e.target.value)}
           onKeyDown={onKeyDown}
           placeholder="Type a command…"
+          role="combobox"
+          aria-expanded={filtered.length > 0}
+          aria-controls={listId}
+          aria-activedescendant={activeId}
+          aria-autocomplete="list"
           aria-label="Command palette search"
         />
-        <div className={styles.list} ref={listRef}>
+        <div className={styles.list} ref={listRef} id={listId} role="listbox" aria-label="Commands">
           {filtered.length === 0 ? (
             <div className={styles.empty}>No matching commands</div>
           ) : (
             filtered.map((a, i) => (
-              <button
+              // A non-focusable option: focus stays on the combobox input and the
+              // active row is announced via aria-activedescendant (UI27), the
+              // standard combobox+listbox pattern. onMouseEnter keeps the pointer
+              // and keyboard highlight unified on one `sel` state.
+              <div
                 key={a.id}
-                type="button"
+                id={optionId(a.id)}
+                role="option"
+                aria-selected={i === sel}
                 data-sel={i === sel ? 'true' : undefined}
-                className={mergeClasses(
-                  styles.item,
-                  i === sel && styles.itemActive,
-                  focus.focusRing
-                )}
+                className={mergeClasses(styles.item, i === sel && styles.itemActive)}
                 onClick={() => {
                   a.run()
                   onClose()
@@ -168,7 +178,7 @@ export function CommandPalette({
               >
                 <span>{a.label}</span>
                 {a.hint && <span className={styles.itemHint}>{a.hint}</span>}
-              </button>
+              </div>
             ))
           )}
         </div>

src/renderer/src/components/DownloadsView.tsx

@@ -115,7 +115,7 @@ export function DownloadsView(): React.JSX.Element {
       )}
 
       <div className={styles.queueHeader}>
-        <Subtitle2>Queue ({queueCount})</Subtitle2>
+        <Subtitle2 as="h2">Queue ({queueCount})</Subtitle2>
         <div className={styles.headerActions}>
           {summary.failed > 0 && (
             <Button

src/renderer/src/components/Onboarding.tsx

@@ -142,7 +142,7 @@ export function Onboarding(): React.JSX.Element {
           <div className={styles.mark}>
             <ArrowDownloadFilled />
           </div>
-          <Title2>Welcome to AeroFetch</Title2>
+          <Title2 as="h1">Welcome to AeroFetch</Title2>
         </div>
 
         <Body1>

src/renderer/src/components/settings/AboutCard.tsx

@@ -94,7 +94,7 @@ export function AboutCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <InfoRegular className={styles.sectionIcon} />
-        <Subtitle2>About</Subtitle2>
+        <Subtitle2 as="h2">About</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         AeroFetch is a generic frontend for yt-dlp. It bundles ffmpeg and manages its own copy of

src/renderer/src/components/settings/AppearanceCard.tsx

@@ -24,7 +24,7 @@ export function AppearanceCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <PaintBucketRegular className={styles.sectionIcon} />
-        <Subtitle2>Appearance</Subtitle2>
+        <Subtitle2 as="h2">Appearance</Subtitle2>
       </div>
 
       <Field label="Theme">

src/renderer/src/components/settings/BackupCard.tsx

@@ -51,7 +51,7 @@ export function BackupCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <DocumentArrowDownRegular className={styles.sectionIcon} />
-        <Subtitle2>Backup &amp; restore</Subtitle2>
+        <Subtitle2 as="h2">Backup &amp; restore</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         Save your settings and custom-command templates to a JSON file, or restore them on another

src/renderer/src/components/settings/CookiesCard.tsx

@@ -68,7 +68,7 @@ export function CookiesCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <CookiesRegular className={styles.sectionIcon} />
-        <Subtitle2>Cookies</Subtitle2>
+        <Subtitle2 as="h2">Cookies</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         Some sites only serve full quality, age-restricted, or members-only video to a logged-in

src/renderer/src/components/settings/CustomCommandsCard.tsx

@@ -17,7 +17,7 @@ export function CustomCommandsCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <CodeRegular className={styles.sectionIcon} />
-        <Subtitle2>Custom commands</Subtitle2>
+        <Subtitle2 as="h2">Custom commands</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         Named templates of extra yt-dlp flags -- your own power-user recipes (e.g.

src/renderer/src/components/settings/DiagnosticsCard.tsx

@@ -28,7 +28,7 @@ export function DiagnosticsCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <BugRegular className={styles.sectionIcon} />
-        <Subtitle2>Diagnostics</Subtitle2>
+        <Subtitle2 as="h2">Diagnostics</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         Failed downloads are logged here even after you clear the queue, so you can copy the details

src/renderer/src/components/settings/DownloadsCard.tsx

@@ -55,7 +55,7 @@ export function DownloadsCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <ArrowDownloadRegular className={styles.sectionIcon} />
-        <Subtitle2>Downloads</Subtitle2>
+        <Subtitle2 as="h2">Downloads</Subtitle2>
       </div>
 
       <Field

src/renderer/src/components/settings/FilenamesCard.tsx

@@ -14,7 +14,7 @@ export function FilenamesCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <DocumentRegular className={styles.sectionIcon} />
-        <Subtitle2>Filenames</Subtitle2>
+        <Subtitle2 as="h2">Filenames</Subtitle2>
       </div>
       <Field
         label="Filename template"

src/renderer/src/components/settings/NetworkCard.tsx

@@ -20,7 +20,7 @@ export function NetworkCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <GlobeRegular className={styles.sectionIcon} />
-        <Subtitle2>Network</Subtitle2>
+        <Subtitle2 as="h2">Network</Subtitle2>
       </div>
 
       <Field

src/renderer/src/components/settings/PostProcessingCard.tsx

@@ -14,7 +14,7 @@ export function PostProcessingCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <OptionsRegular className={styles.sectionIcon} />
-        <Subtitle2>Format &amp; post-processing</Subtitle2>
+        <Subtitle2 as="h2">Format &amp; post-processing</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         Defaults applied to every new download (yt-dlp and ffmpeg do the work).

src/renderer/src/components/settings/SoftwareUpdateCard.tsx

@@ -78,7 +78,7 @@ export function SoftwareUpdateCard(): React.JSX.Element {
     <Card className={styles.card}>
       <div className={styles.sectionHeader}>
         <ArrowSyncRegular className={styles.sectionIcon} />
-        <Subtitle2>Software update</Subtitle2>
+        <Subtitle2 as="h2">Software update</Subtitle2>
       </div>
       <Caption1 className={styles.hint}>
         {appVersion

src/renderer/src/components/ui/Screen.tsx

@@ -65,7 +65,7 @@ export function ScreenHeader({
   return (
     <div className={styles.header}>
       <div className={styles.titleBlock}>
-        <Subtitle2>{title}</Subtitle2>
+        <Subtitle2 as="h1">{title}</Subtitle2>
         {description && <Caption1 className={styles.description}>{description}</Caption1>}
       </div>
       {actions && <div className={styles.actions}>{actions}</div>}