feat(navidrome): Instant Mix probe, ping identity, and AudioMuse UX

Parse type and serverVersion from Subsonic ping; persist per-server identity and
run a background Instant Mix probe (random songs + getSimilarSongs) for
Navidrome 0.60+. Hide the AudioMuse server toggle when the probe returns no
similar tracks; clear prefs when the server is no longer eligible.

Artist pages fall back to Last.fm similar artists when AudioMuse is enabled but
the server returns none. Instant Mix failures set a per-server issue flag with a
settings warning and toast. Settings description links the official plugin repo
via i18n Trans.

src/api/subsonic.ts

@@ -3,6 +3,11 @@ import md5 from 'md5';
 import { invoke } from '@tauri-apps/api/core';
 import { useAuthStore } from '../store/authStore';
 import { version } from '../../package.json';
+import {
+  isNavidromeAudiomuseSoftwareEligible,
+  type InstantMixProbeResult,
+  type SubsonicServerIdentity,
+} from '../utils/subsonicServerIdentity';
 
 // ─── Secure random salt ────────────────────────────────────────
 function secureRandomSalt(): string {
@@ -265,8 +270,14 @@ export async function ping(): Promise<boolean> {
   }
 }
 
+export type PingWithCredentialsResult = SubsonicServerIdentity & { ok: boolean };
+
 /** Test a connection with explicit credentials — does NOT depend on store state. */
-export async function pingWithCredentials(serverUrl: string, username: string, password: string): Promise<boolean> {
+export async function pingWithCredentials(
+  serverUrl: string,
+  username: string,
+  password: string,
+): Promise<PingWithCredentialsResult> {
   try {
     const base = serverUrl.startsWith('http') ? serverUrl.replace(/\/$/, '') : `http://${serverUrl.replace(/\/$/, '')}`;
     const salt = secureRandomSalt();
@@ -277,12 +288,108 @@ export async function pingWithCredentials(serverUrl: string, username: string, p
       timeout: 15000,
     });
     const data = resp.data?.['subsonic-response'];
-    return data?.status === 'ok';
+    const ok = data?.status === 'ok';
+    return {
+      ok,
+      type: typeof data?.type === 'string' ? data.type : undefined,
+      serverVersion: typeof data?.serverVersion === 'string' ? data.serverVersion : undefined,
+      openSubsonic: data?.openSubsonic === true,
+    };
   } catch {
-    return false;
+    return { ok: false };
   }
 }
 
+function restBaseFromUrl(serverUrl: string): string {
+  const base = serverUrl.startsWith('http') ? serverUrl.replace(/\/$/, '') : `http://${serverUrl.replace(/\/$/, '')}`;
+  return `${base}/rest`;
+}
+
+async function apiWithCredentials<T>(
+  serverUrl: string,
+  username: string,
+  password: string,
+  endpoint: string,
+  extra: Record<string, unknown> = {},
+  timeout = 15000,
+): Promise<T> {
+  const params = { ...getAuthParams(username, password), ...extra };
+  const resp = await axios.get(`${restBaseFromUrl(serverUrl)}/${endpoint}`, {
+    params,
+    paramsSerializer: { indexes: null },
+    timeout,
+  });
+  const data = resp.data?.['subsonic-response'];
+  if (!data) throw new Error('Invalid response from server (possibly not a Subsonic server)');
+  if (data.status !== 'ok') throw new Error(data.error?.message ?? 'Subsonic API error');
+  return data as T;
+}
+
+const INSTANT_MIX_PROBE_RANDOM_SIZE = 8;
+const INSTANT_MIX_PROBE_SIMILAR_COUNT = 12;
+const INSTANT_MIX_PROBE_MAX_TRACKS = 4;
+
+/**
+ * Probes whether `getSimilarSongs` returns any tracks (Instant Mix / Navidrome agent chain).
+ * Does not pass `musicFolderId` — probes the whole library as seen by the account.
+ * Note: if `ND_AGENTS` includes Last.fm, a positive result does not prove AudioMuse alone.
+ */
+export async function probeInstantMixWithCredentials(
+  serverUrl: string,
+  username: string,
+  password: string,
+): Promise<InstantMixProbeResult> {
+  try {
+    const data = await apiWithCredentials<{ randomSongs: { song: SubsonicSong | SubsonicSong[] } }>(
+      serverUrl,
+      username,
+      password,
+      'getRandomSongs.view',
+      { size: INSTANT_MIX_PROBE_RANDOM_SIZE, _t: Date.now() },
+      12000,
+    );
+    const raw = data.randomSongs?.song;
+    const songs: SubsonicSong[] = !raw ? [] : Array.isArray(raw) ? raw : [raw];
+    if (songs.length === 0) return 'skipped';
+
+    let anyError = false;
+    for (const song of songs.slice(0, INSTANT_MIX_PROBE_MAX_TRACKS)) {
+      try {
+        const simData = await apiWithCredentials<{ similarSongs: { song: SubsonicSong | SubsonicSong[] } }>(
+          serverUrl,
+          username,
+          password,
+          'getSimilarSongs.view',
+          { id: song.id, count: INSTANT_MIX_PROBE_SIMILAR_COUNT },
+          12000,
+        );
+        const sRaw = simData.similarSongs?.song;
+        const list: SubsonicSong[] = !sRaw ? [] : Array.isArray(sRaw) ? sRaw : [sRaw];
+        if (list.some(s => s.id !== song.id)) return 'ok';
+      } catch {
+        anyError = true;
+      }
+    }
+    return anyError ? 'error' : 'empty';
+  } catch {
+    return 'error';
+  }
+}
+
+/** After a successful ping, probe Instant Mix in the background (Navidrome ≥ 0.60 only). */
+export function scheduleInstantMixProbeForServer(
+  serverId: string,
+  serverUrl: string,
+  username: string,
+  password: string,
+  identity: SubsonicServerIdentity,
+): void {
+  if (!isNavidromeAudiomuseSoftwareEligible(identity)) return;
+  void probeInstantMixWithCredentials(serverUrl, username, password).then(result =>
+    useAuthStore.getState().setInstantMixProbe(serverId, result),
+  );
+}
+
 export async function getRandomAlbums(size = 6): Promise<SubsonicAlbum[]> {
   const data = await api<{ albumList2: { album: SubsonicAlbum[] } }>('getAlbumList2.view', {
     type: 'random',