distribution: the holder's test follows the rule that a chunk 0 again starts a part afresh

mesh-delivery's parts.Receiver.Take took a chunk 0 again on purpose (276412d7, design 51 Publishing, 1966/AC203-1,
AC203-2); the holder's test still expected it refused and failed on every run, on trunk too. The test now expects a
chunk out of sequence refused and a chunk 0 again taken.

Builds: design 51 Publishing, the bullet "The file travels in parts through the seat"; issue 1975's group check

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/distribution/internal/holder/holder_test.go

@@ -242,8 +242,13 @@ func TestTheHolderOfTheTwoImageSeats(t *testing.T) {
 		if a, _ := b.h.Publish(ArtifactSeat, builder, req("t1")); !reflect.DeepEqual(a.Missing, []string{part.Digest}) {
 			t.Errorf("resumed publish = %+v", a)
 		}
-		if _, err := b.h.PublishPart(ArtifactSeat, builder, PartRequest{Transfer: "t1", Digest: part.Digest, Sequence: 0, Data: blob[:1000]}); err == nil {
-			t.Error("a chunk sent twice was taken: the transfer goes on from the chunks held")
+		// A chunk that is neither the cursor nor 0 is refused; a chunk 0 again is a part lacked travelling whole again
+		// (mesh-delivery's parts.Receiver.Take, 1966/AC203-1, AC203-2): its earlier chunks are dropped and it is taken.
+		if _, err := b.h.PublishPart(ArtifactSeat, builder, PartRequest{Transfer: "t1", Digest: part.Digest, Sequence: 2, Data: blob[:1000]}); err == nil {
+			t.Error("a chunk out of sequence was taken: the transfer goes on from the chunks held")
+		}
+		if _, err := b.h.PublishPart(ArtifactSeat, builder, PartRequest{Transfer: "t1", Digest: part.Digest, Sequence: 0, Data: blob[:1000]}); err != nil {
+			t.Errorf("a chunk 0 again was refused: %v", err)
 		}
 		a, err = b.h.PublishPart(ArtifactSeat, builder, PartRequest{Transfer: "t1", Digest: part.Digest, Sequence: 1, Last: true, Data: blob[1000:]})
 		if err != nil || !a.Ended || len(b.said) != 1 || b.said[0].event != EventPublished || b.said[0].body.Reference == "" {