mount: leave an unlinked file out of the periodic metadata flush

flushFileMetadata did not check the handle's delete mark. A file
unlinked while open before its deferred create reached the filer was
created again by the next periodic flush, which expects no entry.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

weed/mount/weedfs_metadata_flush.go

@@ -99,6 +99,10 @@ func (wfs *WFS) flushFileMetadata(fh *FileHandle) error {
 	if !fh.dirtyMetadata {
 		return nil
 	}
+	// Unlink marks under this lock; publishing would recreate the name.
+	if fh.isDeleted {
+		return nil
+	}
 
 	fileFullPath := fh.FullPath()
 	dir, name := fileFullPath.DirAndName()

weed/mount/weedfs_metadata_flush_unlinked_test.go

@@ -0,0 +1,31 @@
+//go:build !freebsd
+
+package mount
+
+import (
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+)
+
+// A file unlinked while open, before its deferred create reached the filer,
+// must not be created by the periodic metadata flush.
+func TestPeriodicFlushSkipsUnlinkedHandle(t *testing.T) {
+	wfs, fake, fh, inode := openLinkTestFile(t)
+	fake.mu.Lock()
+	delete(fake.records, "tmp")
+	fake.mu.Unlock()
+	fh.baseEntry.Store(nil)
+	wfs.markHandleDeleted(inode)
+	fh.UpdateEntry(func(e *filer_pb.Entry) {
+		e.Chunks = append(e.Chunks, linkHandleChunk(2, 100))
+		e.Attributes.FileSize = 200
+	})
+	fh.dirtyMetadata = true
+	if err := wfs.flushFileMetadata(fh); err != nil {
+		t.Fatalf("periodic flush: %v", err)
+	}
+	if fake.stored("tmp") != nil {
+		t.Fatal("the periodic flush recreated the unlinked name")
+	}
+}