fix: audit fixes — blur offset, lock-before-IO, FP signal lifecycle, TOCTOU (v0.6.6)

Third triple audit (quality, performance, security). Key fixes:
- Blur padding offset: texture at (-pad,-pad) prevents edge darkening on all sides
- Wallpaper loads after lock.lock() — disk I/O no longer delays lock acquisition
- begin_verification disconnects old signal handler before registering new one
- resume_async resets failed_attempts to prevent premature exhaustion
- Unknown VerifyStatus with done=true triggers restart instead of hanging
- symlink_metadata() replaces separate is_file()+is_symlink() (TOCTOU)
- faillock_warning dead code removed, blur sigma clamped to [0,100]
- Redundant Zeroizing<Vec<u8>> removed, on_verify_status restricted to pub(crate)
- Warn logging for non-UTF-8 GECOS and avatar path errors
- Default impl for FingerprintListener, 3 new tests (47 total)

src/fingerprint.rs

@@ -35,10 +35,8 @@ pub struct FingerprintListener {
     on_exhausted: Option<Box<dyn Fn() + 'static>>,
 }
 
-impl FingerprintListener {
-    /// Create a lightweight FingerprintListener without any D-Bus calls.
-    /// Call `init_async().await` afterwards to connect to fprintd.
-    pub fn new() -> Self {
+impl Default for FingerprintListener {
+    fn default() -> Self {
         FingerprintListener {
             device_proxy: None,
             signal_id: None,
@@ -50,6 +48,14 @@ impl FingerprintListener {
             on_exhausted: None,
         }
     }
+}
+
+impl FingerprintListener {
+    /// Create a lightweight FingerprintListener without any D-Bus calls.
+    /// Call `init_async().await` afterwards to connect to fprintd.
+    pub fn new() -> Self {
+        Self::default()
+    }
 
     /// Connect to fprintd and get the default device asynchronously.
     pub async fn init_async(&mut self) {
@@ -171,6 +177,7 @@ impl FingerprintListener {
         listener: &Rc<RefCell<FingerprintListener>>,
         username: &str,
     ) {
+        listener.borrow_mut().failed_attempts = 0;
         Self::begin_verification(listener, username).await;
     }
 
@@ -181,11 +188,16 @@ impl FingerprintListener {
         username: &str,
     ) {
         let proxy = {
-            let inner = listener.borrow();
-            match inner.device_proxy.clone() {
+            let mut inner = listener.borrow_mut();
+            let proxy = match inner.device_proxy.clone() {
                 Some(p) => p,
                 None => return,
+            };
+            // Disconnect any previous signal handler to prevent duplicates on resume
+            if let Some(old_id) = inner.signal_id.take() {
+                proxy.disconnect(old_id);
             }
+            proxy
         };
 
         // Claim the device
@@ -265,7 +277,7 @@ impl FingerprintListener {
     }
 
     /// Process a VerifyStatus signal from fprintd.
-    pub fn on_verify_status(&mut self, status: &str, done: bool) {
+    pub(crate) fn on_verify_status(&mut self, status: &str, done: bool) {
         if !self.running {
             return;
         }
@@ -305,6 +317,9 @@ impl FingerprintListener {
         }
 
         log::debug!("Unhandled fprintd status: {status}");
+        if done {
+            self.restart_verify_async();
+        }
     }
 
     /// Restart fingerprint verification asynchronously after a completed attempt.
@@ -403,11 +418,13 @@ mod tests {
         let called_clone = called.clone();
         let mut listener = FingerprintListener::new();
         listener.running = true;
+        listener.running_flag.set(true);
         listener.on_failure = Some(Box::new(move || { called_clone.set(true); }));
 
         listener.on_verify_status("verify-no-match", false);
         assert!(called.get());
         assert!(listener.running);
+        assert!(listener.running_flag.get());
         assert_eq!(listener.failed_attempts, 1);
     }