.

wcfs/internal/zdata/δftail.go

@@ -640,7 +640,7 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 				return δfTail
 			}
 			if !(tail < δfTail.Rev) {
-				panic("tail not ↓")
+				panic("BUG: tail not ↓")
 			}
 		}
 
@@ -680,6 +680,8 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 		var head zodb.Tid // head] of current epoch coverage
 		// state of Zinblk as we are scanning ← current epoch
 		// initially corresponds to head of the epoch (= @head for latest epoch)
+		//
+		// XXX -> ZinblkOverlay(.base = Zinblk@head w/o Clone; .adj = δZinblk)
 		Zinblk := map[zodb.Oid]setI64{} // zblk -> which #blk refers to it
 		var ZinblkAt zodb.Tid           // Zinblk covers [ZinblkAt,<next δT>)
 		if ie+1 == le {