refactor(reflinking): add windows ReFS filesystem support

documentation/docs/features/cross-seed/hardlink-mode.md

@@ -88,7 +88,7 @@ Reflink mode creates copy-on-write clones of the matched files. Unlike hardlinks
 ### When to Use Reflink Mode
 
 - You want to cross-seed torrents that hardlink mode would skip due to "extra files share pieces with content"
-- Your filesystem supports copy-on-write clones (BTRFS, XFS on Linux; APFS on macOS)
+- Your filesystem supports copy-on-write clones (BTRFS, XFS on Linux; APFS on macOS; ReFS on Windows)
 - You prefer the safety of copy-on-write over hardlinks
 
 ### Reflink Requirements
@@ -99,7 +99,12 @@ Reflink mode creates copy-on-write clones of the matched files. Unlike hardlinks
 - The filesystem must support reflinks:
   - **Linux**: BTRFS, XFS (with reflink=1), and similar CoW filesystems
   - **macOS**: APFS
-  - **Windows/FreeBSD**: Not currently supported
+  - **Windows**: ReFS on the same volume as the source files and reflink base directory
+  - **FreeBSD**: Not currently supported
+
+:::note
+Windows reflink mode uses ReFS block cloning (requiring an ReFS filesystem). NTFS is not supported. If reflink creation fails, fallback still depends on the existing "Fallback to regular mode" setting.
+:::
 
 :::tip
 On Linux, check the filesystem type with `df -T /path` (you want `xfs`/`btrfs`, not `fuseblk`/`fuse.mergerfs`/`overlayfs`).

internal/services/crossseed/service.go

@@ -11081,7 +11081,11 @@ func (s *Service) processReflinkMode(
 
 	// Create reflink tree on disk
 	if err := reflinktree.Create(plan); err != nil {
-		log.Error().
+		logEvent := log.Error()
+		if errors.Is(err, reflinktree.ErrReflinkUnsupported) {
+			logEvent = log.Warn()
+		}
+		logEvent.
 			Err(err).
 			Int("instanceID", candidate.InstanceID).
 			Str("torrentName", torrentName).

pkg/reflinktree/reflink_test.go

@@ -17,8 +17,8 @@ func TestSupportsReflink(t *testing.T) {
 
 	supported, reason := SupportsReflink(tmpDir)
 
-	// On unsupported platforms, should return false
-	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
+	// On unsupported platforms, should return false.
+	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" && runtime.GOOS != "windows" {
 		if supported {
 			t.Errorf("SupportsReflink should return false on %s", runtime.GOOS)
 		}
@@ -28,8 +28,8 @@ func TestSupportsReflink(t *testing.T) {
 		return
 	}
 
-	// On supported platforms, the result depends on filesystem
-	// We just verify the function doesn't panic and returns sensible values
+	// On supported platforms, the result depends on filesystem.
+	// We just verify the function doesn't panic and returns sensible values.
 	t.Logf("SupportsReflink(%s): supported=%v, reason=%s", tmpDir, supported, reason)
 
 	if !supported {

pkg/reflinktree/reflink_unsupported.go

@@ -1,12 +1,12 @@
 // Copyright (c) 2025-2026, s0up and the autobrr contributors.
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-//go:build !linux && !darwin
+//go:build !linux && !darwin && !windows
 
 package reflinktree
 
 // SupportsReflink returns false on unsupported platforms.
-// Windows and FreeBSD do not have a standard reflink mechanism that we support.
+// FreeBSD do not have a standard reflink mechanism that we support.
 func SupportsReflink(_ string) (supported bool, reason string) {
 	return false, "reflink is not supported on this operating system"
 }