Connect Apple Music and Spotify-via-Last.fm on iPhone

- Local Expo module (Swift): MusicKit authorization, Music User Token via
  MusicUserTokenProvider, and live Music app now-playing while the app is
  open (MediaPlayer notifications), reported through the device endpoint
- One-tap Apple Music onboarding on iOS; Apple Music row in Settings
- Sign in with Last.fm, plus a guided Spotify-via-Last.fm flow when direct
  Spotify sign-in is capped
- Device registration moved to shared code used by Android and iOS
Not yet compiled for iOS (no Xcode here); needs an EAS build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/mobile/src/app/(tabs)/settings.tsx

@@ -18,6 +18,7 @@ import { SharingControls } from '@/components/SharingControls';
 import { Body, Button, Card, Chip, Field, Heading, Row, Title } from '@/components/ui';
 import { api } from '@/lib/api';
 import { showError } from '@/lib/errors';
+import { AppleMusicPermissionError, appleMusicAvailable, connectAppleMusic } from '@/lib/appleMusic';
 import { openReaderSettings, useReader } from '@/lib/nowPlayingReader';
 import { useDebounced } from '@/lib/useDebounced';
 import { useSession } from '@/lib/session';
@@ -127,18 +128,54 @@ function Connections() {
     await mutate();
   };
 
-  const connectOAuth = (provider: 'spotify' | 'plex') =>
+  /** Sign in on the service's site and come back via deep link. Returns true when connected. */
+  const signIn = async (provider: 'spotify' | 'plex' | 'lastfm'): Promise<boolean> => {
+    // Deep link back into the app; in Expo Go this is an exp:// URL, in builds musicshare://
+    const returnTo = Linking.createURL('settings');
+    const { url } = await api.authorizeUrl(provider, { client: 'mobile', returnTo });
+    const result = await WebBrowser.openAuthSessionAsync(url, returnTo);
+    if (result.type !== 'success') return false;
+    const error = Linking.parse(result.url).queryParams?.error;
+    if (error === 'spotify_limited') {
+      offerSpotifyViaLastfm();
+      return false;
+    }
+    if (typeof error === 'string') {
+      Alert.alert(`Couldn't connect ${SERVICE_LABELS[provider]}`, error);
+      return false;
+    }
+    return true;
+  };
+
+  const connectOAuth = (provider: 'spotify' | 'plex' | 'lastfm') => run(() => signIn(provider));
+
+  /**
+   * Spotify only lets small apps sign in a handful of accounts. Spotify's own
+   * Last.fm link works for everyone: sign in to Last.fm here, then approve
+   * "Spotify Scrobbling" on Last.fm.
+   */
+  const linkSpotifyOnLastfm = () =>
+    WebBrowser.openBrowserAsync('https://www.last.fm/settings/applications').catch((e) => showError(e));
+
+  const setUpSpotifyViaLastfm = () =>
     run(async () => {
-      // Deep link back into the app; in Expo Go this is an exp:// URL, in builds musicshare://
-      const returnTo = Linking.createURL('settings');
-      const { url } = await api.authorizeUrl(provider, { client: 'mobile', returnTo });
-      const result = await WebBrowser.openAuthSessionAsync(url, returnTo);
-      if (result.type === 'success') {
-        const error = Linking.parse(result.url).queryParams?.error;
-        if (typeof error === 'string') Alert.alert(`Couldn't connect ${SERVICE_LABELS[provider]}`, error);
-      }
+      if (!byProvider.has('lastfm') && !(await signIn('lastfm'))) return;
+      Alert.alert('Last step: link Spotify', 'On the next page, tap Connect next to "Spotify Scrobbling" and approve.', [
+        { text: 'Open Last.fm', onPress: linkSpotifyOnLastfm },
+      ]);
     });
 
+  function offerSpotifyViaLastfm() {
+    Alert.alert(
+      'Spotify sign-in is limited during beta',
+      "Spotify only allows a few accounts to sign in to new apps directly. You can still share Spotify through Last.fm: two quick approvals, and it works for everyone.",
+      [
+        { text: 'Not now', style: 'cancel' },
+        { text: 'Set up', onPress: setUpSpotifyViaLastfm },
+      ],
+    );
+  }
+
   const disconnect = (provider: NowPlayingProvider) =>
     Alert.alert(`Disconnect ${SERVICE_LABELS[provider]}?`, 'Friends will stop seeing what you play there.', [
       { text: 'Cancel', style: 'cancel' },
@@ -159,6 +196,16 @@ function Connections() {
 
   const isActive = (p: NowPlayingProvider) => byProvider.get(p)?.status === 'active';
 
+  const linkAppleMusic = () =>
+    run(async () => {
+      try {
+        await connectAppleMusic();
+      } catch (err) {
+        if (err instanceof AppleMusicPermissionError) Alert.alert('Apple Music access needed', err.message);
+        else throw err;
+      }
+    });
+
   return (
     <Card>
       <Heading>Music services</Heading>
@@ -166,6 +213,20 @@ function Connections() {
         Connect where you listen. Friends see what you&apos;re playing in real time.
       </Body>
 
+      {appleMusicAvailable && (
+        <View style={[styles.connectionColumn, styles.connection]}>
+          <View style={{ flex: 1 }}>
+            <Text style={styles.provider}>Apple Music</Text>
+            {status('apple_music', 'One tap. Live while the app is open, recently played otherwise.')}
+          </View>
+          {isActive('apple_music') ? (
+            <Button small title="Disconnect" onPress={() => disconnect('apple_music')} />
+          ) : (
+            <Button small variant="primary" title={byProvider.has('apple_music') ? 'Reconnect' : 'Connect'} onPress={linkAppleMusic} />
+          )}
+        </View>
+      )}
+
       {(['spotify', 'plex'] as const).map((p) => (
         <View key={p} style={[styles.connectionColumn, styles.connection]}>
           <View style={{ flex: 1 }}>
@@ -180,16 +241,30 @@ function Connections() {
         </View>
       ))}
 
-      {(['lastfm', 'listenbrainz'] as const).map((p) => (
-        <UsernameConnection
-          key={p}
-          provider={p}
-          status={status(p, p === 'lastfm' ? 'Anything that scrobbles: YouTube Music, Tidal, Deezer…' : 'Open-source scrobbling')}
-          active={byProvider.has(p)}
-          onConnect={(username) => run(() => api.connectUsername(p, username))}
-          onDisconnect={() => disconnect(p)}
-        />
-      ))}
+      <View style={styles.connectionColumn}>
+        <View style={styles.connection}>
+          <View style={{ flex: 1 }}>
+            <Text style={styles.provider}>Last.fm</Text>
+            {status('lastfm', 'Also the way to share Spotify for everyone (via Spotify’s Last.fm link).')}
+          </View>
+          {byProvider.has('lastfm') ? (
+            <Button small title="Disconnect" onPress={() => disconnect('lastfm')} />
+          ) : (
+            <Button small variant="primary" title="Sign in" onPress={() => connectOAuth('lastfm')} />
+          )}
+        </View>
+        {byProvider.has('lastfm') && (
+          <Button small title="Link Spotify to Last.fm" onPress={linkSpotifyOnLastfm} style={{ alignSelf: 'flex-start' }} />
+        )}
+      </View>
+
+      <UsernameConnection
+        provider="listenbrainz"
+        status={status('listenbrainz', 'Open-source scrobbling')}
+        active={byProvider.has('listenbrainz')}
+        onConnect={(username) => run(() => api.connectUsername('listenbrainz', username))}
+        onDisconnect={() => disconnect('listenbrainz')}
+      />
 
       <JellyfinConnection
         status={status('jellyfin', 'Sign in to your Jellyfin server. Your password isn’t stored.')}