mount: refuse a merge that puts inline content next to chunks

A read inside the inline bytes returns them without looking at chunks,
so one side's inline content merged with the other side's chunks hid
data after a successful flush.

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

weed/mount/content_flush_condition_test.go

@@ -307,6 +307,18 @@ func TestMergeContentEntry(t *testing.T) {
 	if _, ok := mergeContentEntry(stored, base, local, local); ok {
 		t.Fatal("merged into a replaced file")
 	}
+
+	empty := flushConditionEntry()
+	inline := proto.Clone(empty).(*filer_pb.Entry)
+	inline.Content = []byte("peer")
+	appended := proto.Clone(empty).(*filer_pb.Entry)
+	appended.Chunks = flushConditionEntry(5).Chunks
+	if _, ok := mergeContentEntry(inline, empty, appended, appended); ok {
+		t.Fatal("merged chunks next to inline content")
+	}
+	if _, ok := mergeContentEntry(appended, empty, inline, inline); ok {
+		t.Fatal("merged inline content next to chunks")
+	}
 }
 
 // A miss on state no peer changed is republished once against the stored

weed/mount/weedfs_file_sync.go

@@ -373,8 +373,9 @@ const maxContentFlushMerges = 3
 // content it changed, taking those values from sent (local in stored's id
 // space). Everything else keeps the stored value. A local truncation keeps
 // its size and clips stored chunks to it; otherwise the larger size wins.
-// A different file at the path, or inline content changed on both sides,
-// cannot be merged.
+// A different file at the path, inline content changed on both sides, or
+// inline content next to chunks (reads stop at the inline bytes) cannot be
+// merged.
 func mergeContentEntry(stored, base, local, sent *filer_pb.Entry) (*filer_pb.Entry, bool) {
 	if stored == nil || base == nil || stored.IsDirectory || !bytes.Equal(stored.HardLinkId, base.HardLinkId) {
 		return nil, false
@@ -410,6 +411,9 @@ func mergeContentEntry(stored, base, local, sent *filer_pb.Entry) (*filer_pb.Ent
 			merged.Chunks = append(merged.Chunks, proto.Clone(c).(*filer_pb.FileChunk))
 		}
 	}
+	if len(merged.Content) > 0 && len(merged.Chunks) > 0 {
+		return nil, false
+	}
 
 	if merged.Attributes == nil {
 		merged.Attributes = &filer_pb.FuseAttributes{}