seaweed-volume: propagate directory fsync failures on the compaction commit path

fsync_dir dropped every sync_all error, so the commit could proceed with an
undurable marker or rename and a later restart could recover the wrong
generation. Return the error and check it at the commit call sites (marker write
and the swap), matching the Go fsyncDir which already propagates. Directory
fsync stays a no-op on Windows, where it is unsupported.

seaweed-volume/src/storage/volume.rs

@@ -2953,7 +2953,7 @@ impl Volume {
             .open(&marker_path)?;
         f.sync_all()?;
         drop(f);
-        fsync_dir(&marker_path);
+        fsync_dir(&marker_path)?;
         Ok(())
     }
 
@@ -3007,9 +3007,9 @@ impl Volume {
             fs::rename(self.file_name(".cpx"), &idx_path)?;
         }
         if cpd_exists || cpx_exists {
-            fsync_dir(&dat_path);
+            fsync_dir(&dat_path)?;
             if self.dir != self.dir_idx {
-                fsync_dir(&idx_path);
+                fsync_dir(&idx_path)?;
             }
             let _ = fs::remove_dir_all(self.file_name(".ldb"));
             let _ = fs::remove_file(self.file_name(".rdb"));
@@ -3023,7 +3023,7 @@ impl Volume {
             Err(e) if e.kind() == io::ErrorKind::NotFound => {}
             Err(e) => return Err(e.into()),
         }
-        fsync_dir(&marker_path);
+        fsync_dir(&marker_path)?;
         Ok(())
     }
 
@@ -3415,13 +3415,24 @@ fn get_append_at_ns(last: u64) -> u64 {
 /// Remove all files associated with a volume.
 /// .dat/.idx removals log at info level so destructive calls are traceable.
 /// fsync the parent directory of `path` so a rename/create/unlink inside it is
-/// durable. Best-effort: a platform that does not support directory fsync (or a
-/// path with no parent) is silently tolerated, matching the Go fsyncDir helper.
-fn fsync_dir(path: &str) {
-    if let Some(parent) = Path::new(path).parent() {
-        if let Ok(d) = File::open(parent) {
-            let _ = d.sync_all();
+/// durable, propagating a sync failure so the commit path can abort rather than
+/// proceed with an undurable rename or marker. A path with no openable parent is
+/// tolerated; directory fsync is unsupported on Windows, so it is a no-op there
+/// (matching the Go fsyncDir helper, which ignores that error).
+fn fsync_dir(path: &str) -> io::Result<()> {
+    #[cfg(windows)]
+    {
+        let _ = path;
+        Ok(())
+    }
+    #[cfg(not(windows))]
+    {
+        if let Some(parent) = Path::new(path).parent() {
+            if let Ok(d) = File::open(parent) {
+                return d.sync_all();
+            }
         }
+        Ok(())
     }
 }