fix: prevent Last.fm auth loss from Ctrl+C or crash

src/frontend_bridge/config.rs

@@ -277,11 +277,22 @@ pub(super) fn save_settings(settings: &BridgeSettings) {
     let Some(path) = settings_path() else {
         return;
     };
-    if let Some(parent) = path.parent() {
-        let _ = fs::create_dir_all(parent);
-    }
+    let Some(parent) = path.parent() else {
+        return;
+    };
+    let _ = fs::create_dir_all(parent);
     let text = format_settings_text(settings);
-    let _ = fs::write(path, text);
+
+    // Atomic write: write to a temp file in the same directory, then rename.
+    // This prevents a crash during write from truncating/corrupting the settings file.
+    let tmp_path = path.with_extension("tmp");
+    if let Err(err) = fs::write(&tmp_path, &text) {
+        eprintln!("Failed to write settings temp file: {err}");
+        return;
+    }
+    if let Err(err) = fs::rename(&tmp_path, &path) {
+        eprintln!("Failed to rename settings temp file: {err}");
+    }
 }
 
 pub(super) fn format_settings_text(settings: &BridgeSettings) -> String {

src/frontend_bridge/events.rs

@@ -430,6 +430,10 @@ pub(super) fn process_lastfm_event(
             if state.settings.integrations.lastfm_username != runtime.username {
                 state.settings.integrations.lastfm_username = runtime.username;
                 *settings_dirty = true;
+                // Flush immediately — the username is the lookup key for the
+                // session in the keyring.  Losing it (e.g. Ctrl+C before the
+                // periodic 2 s save) makes the session irrecoverable.
+                super::config::save_settings(&state.settings);
                 urgency = SnapshotUrgency::Immediate;
             }
             urgency

src/lastfm/mod.rs

@@ -316,14 +316,22 @@ impl Service {
                 self.flush_queue();
             }
             Ok(None) => {
+                eprintln!(
+                    "Last.fm: no session key found in keyring for user \"{username}\" — \
+                     was the keyring cleared or is the keyring daemon unavailable?"
+                );
                 self.state.username = username;
                 self.state.auth_state = AuthState::Disconnected;
                 self.state.status_text = "Reconnect Last.fm to resume scrobbling.".to_string();
             }
             Err(err) => {
+                let message = request_error_message(err);
+                eprintln!(
+                    "Last.fm: keyring error loading session for user \"{username}\": {message}"
+                );
                 self.state.username = username;
                 self.state.auth_state = AuthState::Error;
-                self.state.status_text = request_error_message(err);
+                self.state.status_text = message;
             }
         }
     }