mount: prefer boot disk ESP and run cargo fmt

* choose ESP matching the primary data disk when multiple ESPs exist,
  falling back gracefully for single-disk layouts
* keep new helper to normalize device names and reuse the idempotent
  mount logic
* apply cargo fmt across the tree

src/device/discovery.rs

@@ -186,7 +186,10 @@ pub fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>> {
     discover_with_provider(&provider, filter)
 }
 
-fn discover_with_provider<P: DeviceProvider>(provider: &P, filter: &DeviceFilter) -> Result<Vec<Disk>> {
+fn discover_with_provider<P: DeviceProvider>(
+    provider: &P,
+    filter: &DeviceFilter,
+) -> Result<Vec<Disk>> {
     let mut candidates = provider.list_block_devices()?;
     // Probe properties if provider needs to enrich
     for d in &mut candidates {
@@ -210,10 +213,15 @@ fn discover_with_provider<P: DeviceProvider>(provider: &P, filter: &DeviceFilter
         .collect();
 
     if filtered.is_empty() {
-        return Err(Error::Device("no eligible disks found after applying filters".to_string()));
+        return Err(Error::Device(
+            "no eligible disks found after applying filters".to_string(),
+        ));
     }
 
-    debug!("eligible disks: {:?}", filtered.iter().map(|d| &d.path).collect::<Vec<_>>());
+    debug!(
+        "eligible disks: {:?}",
+        filtered.iter().map(|d| &d.path).collect::<Vec<_>>()
+    );
     Ok(filtered)
 }
 
@@ -259,9 +267,10 @@ fn read_disk_size_bytes(name: &str) -> Result<u64> {
     let p = sys_block_path(name).join("size");
     let sectors = fs::read_to_string(&p)
         .map_err(|e| Error::Device(format!("read {} failed: {}", p.display(), e)))?;
-    let sectors: u64 = sectors.trim().parse().map_err(|e| {
-        Error::Device(format!("parse sectors for {} failed: {}", name, e))
-    })?;
+    let sectors: u64 = sectors
+        .trim()
+        .parse()
+        .map_err(|e| Error::Device(format!("parse sectors for {} failed: {}", name, e)))?;
     Ok(sectors.saturating_mul(512))
 }
 
@@ -287,11 +296,7 @@ fn read_optional_string(p: PathBuf) -> Option<String> {
             while s.ends_with('\n') || s.ends_with('\r') {
                 s.pop();
             }
-            if s.is_empty() {
-                None
-            } else {
-                Some(s)
-            }
+            if s.is_empty() { None } else { Some(s) }
         }
         Err(_) => None,
     }
@@ -324,9 +329,27 @@ mod tests {
     fn filter_by_size_and_include_exclude() {
         let provider = MockProvider {
             disks: vec![
-                Disk { path: "/dev/sda".into(), size_bytes: 500 * 1024 * 1024 * 1024, rotational: true, model: None, serial: None }, // 500 GiB
-                Disk { path: "/dev/nvme0n1".into(), size_bytes: 128 * 1024 * 1024 * 1024, rotational: false, model: None, serial: None }, // 128 GiB
-                Disk { path: "/dev/loop0".into(), size_bytes: 8 * 1024 * 1024 * 1024, rotational: false, model: None, serial: None }, // 8 GiB pseudo (but mock provider supplies it)
+                Disk {
+                    path: "/dev/sda".into(),
+                    size_bytes: 500 * 1024 * 1024 * 1024,
+                    rotational: true,
+                    model: None,
+                    serial: None,
+                }, // 500 GiB
+                Disk {
+                    path: "/dev/nvme0n1".into(),
+                    size_bytes: 128 * 1024 * 1024 * 1024,
+                    rotational: false,
+                    model: None,
+                    serial: None,
+                }, // 128 GiB
+                Disk {
+                    path: "/dev/loop0".into(),
+                    size_bytes: 8 * 1024 * 1024 * 1024,
+                    rotational: false,
+                    model: None,
+                    serial: None,
+                }, // 8 GiB pseudo (but mock provider supplies it)
             ],
         };
 
@@ -346,7 +369,13 @@ mod tests {
     fn no_match_returns_error() {
         let provider = MockProvider {
             disks: vec![
-                Disk { path: "/dev/sdb".into(), size_bytes: 50 * 1024 * 1024 * 1024, rotational: true, model: None, serial: None }, // 50 GiB
+                Disk {
+                    path: "/dev/sdb".into(),
+                    size_bytes: 50 * 1024 * 1024 * 1024,
+                    rotational: true,
+                    model: None,
+                    serial: None,
+                }, // 50 GiB
             ],
         };
 
@@ -363,4 +392,4 @@ mod tests {
             other => panic!("unexpected error: {:?}", other),
         }
     }
-}
+}