fix(audio): support ADPCM WAV, validate format on selection, remove unsupported FLAC filter

Three related fixes for issue #389, where custom notification sounds
silently fell back to the built-in default on Windows.

Root cause: Rodio 0.22 uses Symphonia for decoding. The compiled
Symphonia crates only included PCM WAV support. ADPCM-encoded WAV
(the default output of Windows Sound Recorder) failed to decode
silently, and FLAC — offered in the file picker — was never decodable.
Failures were never surfaced to the user; they would see their filename
in settings but hear the wrong sound.

- Add symphonia-codec-adpcm as a direct dependency so ADPCM WAV files
  decode correctly via the existing Decoder::new() path.
- Add audio::probe_audio_file() which attempts to construct a Decoder
  from a copied file before committing it. On failure, the orphan is
  deleted and the in-memory custom path is cleared so playback falls
  back to the embedded default cleanly.
- Call probe_audio_file() in audio_set_custom after the file is copied;
  return an Err to the frontend if the format is unsupported.
- Add per-cue inline error state to NotificationsSection.svelte so the
  error message is displayed below the failing row. Error clears on a
  successful selection or when the user restores the default.
- Remove 'flac' from the openAudioFilePicker filter; FLAC decoding is
  not available and the option was misleading.

Author: Splode

src-tauri/Cargo.lock

@@ -37,6 +37,7 @@ axum = { version = "0.8", features = ["ws"] }
 futures-util = "0.3"
 
 rodio = { version = "0.22", default-features = false, features = ["playback", "wav", "mp3", "vorbis"] }
+symphonia-codec-adpcm = "0.5.5"
 tiny-skia = "0.12"
 notify = "8"
 

src-tauri/Cargo.toml

@@ -209,6 +209,18 @@ pub fn find_custom_files(audio_dir: &Path) -> CustomAudioPaths {
     }
 }
 
+/// Probe `path` by attempting to construct a `rodio::Decoder`.
+/// Returns `Ok(())` if the format and codec are recognised, or an error
+/// string suitable for returning to the frontend.
+pub fn probe_audio_file(path: &Path) -> Result<(), String> {
+    let reader = std::fs::File::open(path)
+        .map(std::io::BufReader::new)
+        .map_err(|e| format!("cannot open file: {e}"))?;
+    Decoder::new(reader)
+        .map(|_| ())
+        .map_err(|e| format!("audio format not supported: {e}"))
+}
+
 // ---------------------------------------------------------------------------
 // Audio thread
 // ---------------------------------------------------------------------------

src-tauri/src/audio/mod.rs

@@ -451,6 +451,15 @@ pub fn audio_set_custom(
     let dest = audio_dir.join(format!("{stem}.{ext}"));
     std::fs::copy(src, &dest).map_err(|e| e.to_string())?;
 
+    // Verify the copied file is decodable before committing. If it fails,
+    // clean up the orphan and sync in-memory state to default (the old file
+    // was already deleted above).
+    if let Err(e) = audio::probe_audio_file(&dest) {
+        let _ = std::fs::remove_file(&dest);
+        audio_state.clear_custom_path(&cue);
+        return Err(e);
+    }
+
     audio_state.set_custom_path(&cue, dest);
 
     let display_name = src

src-tauri/src/commands.rs

@@ -43,6 +43,22 @@
     else longBreakAlert = val;
   }
 
+  let workAlertError = $state<string | null>(null);
+  let shortBreakAlertError = $state<string | null>(null);
+  let longBreakAlertError = $state<string | null>(null);
+
+  function getError(id: CueKey): string | null {
+    if (id === 'work_alert') return workAlertError;
+    if (id === 'short_break_alert') return shortBreakAlertError;
+    return longBreakAlertError;
+  }
+
+  function setError(id: CueKey, val: string | null) {
+    if (id === 'work_alert') workAlertError = val;
+    else if (id === 'short_break_alert') shortBreakAlertError = val;
+    else longBreakAlertError = val;
+  }
+
   async function refreshAudioInfo() {
     try {
       const info: CustomAudioInfo = await getCustomAudioInfo();
@@ -76,6 +92,7 @@
   }
 
   async function pickAudio(id: CueKey) {
+    setError(id, null);
     let path: string | null = null;
     try {
       path = await openAudioFilePicker();
@@ -87,15 +104,18 @@
     try {
       const displayName = await setCustomAudio(id, path);
       setFileName(id, displayName);
+      setError(id, null);
     } catch (err) {
       await logError(`[audio] setCustomAudio failed: ${err}`);
+      setError(id, String(err));
     }
   }
 
   async function restoreAudio(id: CueKey) {
     try {
       await clearCustomAudio(id);
       setFileName(id, null);
+      setError(id, null);
     } catch (err) {
       await logError(`[audio] clearCustomAudio failed: ${err}`);
     }
@@ -122,6 +142,9 @@
         <button class="btn-choose" onclick={() => pickAudio(id)}>{m.notif_btn_choose()}</button>
       </div>
     </div>
+    {#if getError(id)}
+      <p class="audio-error">{getError(id)}</p>
+    {/if}
   {/each}
 
   <div class="group-heading">{m.notif_group_desktop()}</div>
@@ -324,4 +347,12 @@
     background: color-mix(in oklch, var(--color-foreground) 14%, transparent);
     color: var(--color-foreground);
   }
+
+  .audio-error {
+    margin: 0;
+    padding: 2px 20px 8px;
+    font-size: 0.72rem;
+    color: var(--color-danger, #e05252);
+    font-family: monospace;
+  }
 </style>

src/lib/components/settings/sections/NotificationsSection.svelte

@@ -60,7 +60,7 @@ export const clearCustomAudio = (cue: string) => invoke<void>('audio_clear_custo
 export const openAudioFilePicker = (): Promise<string | null> =>
   dialogOpen({
     multiple: false,
-    filters: [{ name: 'Audio', extensions: ['mp3', 'wav', 'ogg', 'flac'] }],
+    filters: [{ name: 'Audio', extensions: ['mp3', 'wav', 'ogg'] }],
   }) as Promise<string | null>;
 
 // --- Diagnostic log commands ---