refactor(tauri): decompose lib command surface into domain modules

Split the large lib command module into nested app_api, cache, sync, and ui submodules while preserving command signatures and behavior. This keeps command responsibilities isolated and makes further extraction safer.

src-tauri/src/lib_commands/app_api/integration.rs

@@ -0,0 +1,108 @@
+use super::*;
+
+#[tauri::command]
+pub(crate) fn register_global_shortcut(
+    app: tauri::AppHandle,
+    shortcut_map: tauri::State<ShortcutMap>,
+    shortcut: String,
+    action: String,
+) -> Result<(), String> {
+    use tauri_plugin_global_shortcut::{GlobalShortcutExt, Shortcut, ShortcutState};
+
+    let mut map = shortcut_map.lock().unwrap();
+
+    // Idempotent: if this exact shortcut+action is already registered, skip.
+    // This prevents on_shortcut() from accumulating duplicate handlers when
+    // registerAll() is called again after a JS HMR reload or StrictMode double-effect.
+    if map.get(&shortcut).map(|a| a == &action).unwrap_or(false) {
+        return Ok(());
+    }
+
+    // Unregister any existing OS grab for this shortcut before re-registering.
+    if let Ok(s) = shortcut.parse::<Shortcut>() {
+        let _ = app.global_shortcut().unregister(s);
+    }
+    map.insert(shortcut.clone(), action.clone());
+    drop(map); // release lock before the blocking OS call
+
+    let parsed: Shortcut = shortcut.parse().map_err(|_| format!("Invalid shortcut: {shortcut}"))?;
+    app.global_shortcut()
+        .on_shortcut(parsed, move |app, _shortcut, event| {
+            if event.state == ShortcutState::Pressed {
+                let event_name = match action.as_str() {
+                    "play-pause"  => "media:play-pause",
+                    "next"        => "media:next",
+                    "prev"        => "media:prev",
+                    "volume-up"   => "media:volume-up",
+                    "volume-down" => "media:volume-down",
+                    _             => return,
+                };
+                let _ = app.emit(event_name, ());
+            }
+        })
+        .map_err(|e| e.to_string())
+}
+
+#[tauri::command]
+pub(crate) fn unregister_global_shortcut(
+    app: tauri::AppHandle,
+    shortcut_map: tauri::State<ShortcutMap>,
+    shortcut: String,
+) -> Result<(), String> {
+    use tauri_plugin_global_shortcut::{GlobalShortcutExt, Shortcut};
+    shortcut_map.lock().unwrap().remove(&shortcut);
+    let parsed: Shortcut = shortcut.parse().map_err(|_| format!("Invalid shortcut: {shortcut}"))?;
+    app.global_shortcut().unregister(parsed).map_err(|e| e.to_string())
+}
+
+#[tauri::command]
+pub(crate) fn mpris_set_metadata(
+    controls: tauri::State<MprisControls>,
+    title: Option<String>,
+    artist: Option<String>,
+    album: Option<String>,
+    cover_url: Option<String>,
+    duration_secs: Option<f64>,
+) -> Result<(), String> {
+    use souvlaki::MediaMetadata;
+    use std::time::Duration;
+
+    let duration = duration_secs.map(|s| Duration::from_secs_f64(s));
+    let mut guard = controls.lock().unwrap();
+    let Some(ctrl) = guard.as_mut() else { return Ok(()); };
+    ctrl.set_metadata(MediaMetadata {
+        title: title.as_deref(),
+        artist: artist.as_deref(),
+        album: album.as_deref(),
+        cover_url: cover_url.as_deref(),
+        duration,
+    })
+    .map_err(|e| format!("MPRIS set_metadata failed: {e:?}"))
+}
+
+#[tauri::command]
+pub(crate) fn mpris_set_playback(
+    controls: tauri::State<MprisControls>,
+    playing: bool,
+    position_secs: Option<f64>,
+) -> Result<(), String> {
+    use souvlaki::{MediaPlayback, MediaPosition};
+    use std::time::Duration;
+
+    let progress = position_secs.map(|s| MediaPosition(Duration::from_secs_f64(s)));
+    let playback = if playing {
+        MediaPlayback::Playing { progress }
+    } else {
+        MediaPlayback::Paused { progress }
+    };
+    let mut guard = controls.lock().unwrap();
+    let Some(ctrl) = guard.as_mut() else { return Ok(()); };
+    ctrl.set_playback(playback)
+        .map_err(|e| format!("MPRIS set_playback failed: {e:?}"))
+}
+
+/// Returns true if `path` is an accessible directory (used for pre-flight checks in the frontend).
+#[tauri::command]
+pub(crate) fn check_dir_accessible(path: String) -> bool {
+    std::path::Path::new(&path).is_dir()
+}