Fix sequence number comparison.

host/peer/sequence_number.go

@@ -46,7 +46,7 @@ func (s sequenceNumber) nextEpoch() sequenceNumber {
 //	== 0 if this is equal to the provided sequenceNumber
 //	 > 0 if this is greater than the provided sequenceNumber
 func (s sequenceNumber) cmp(o sequenceNumber) int {
-	if ecmp := int(s.epoch - o.epoch); ecmp != 0 {
+	if ecmp := int(int32(s.epoch - o.epoch)); ecmp != 0 {
 		return ecmp
 	}
 	return int(s.seq - o.seq)

host/peer/sequence_number_test.go

@@ -0,0 +1,49 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package peer
+
+import (
+	"testing"
+)
+
+func TestSequenceNumberCmp(t *testing.T) {
+	for _, test := range []struct {
+		a    sequenceNumber
+		b    sequenceNumber
+		want int
+	}{
+		{
+			a:    sequenceNumber{epoch: 1, seq: 1},
+			b:    sequenceNumber{epoch: 1, seq: 1},
+			want: 0,
+		},
+		{
+			a:    sequenceNumber{epoch: 2, seq: 1},
+			b:    sequenceNumber{epoch: 1, seq: 1},
+			want: 1,
+		},
+		{
+			a:    sequenceNumber{epoch: 1, seq: 2},
+			b:    sequenceNumber{epoch: 1, seq: 1},
+			want: 1,
+		},
+		{
+			a:    sequenceNumber{epoch: 20, seq: 1},
+			b:    sequenceNumber{epoch: 1, seq: 1},
+			want: 19,
+		},
+		{
+			a:    sequenceNumber{epoch: 1, seq: 20},
+			b:    sequenceNumber{epoch: 1, seq: 1},
+			want: 19,
+		},
+	} {
+		if got := test.a.cmp(test.b); got != test.want {
+			t.Errorf("%#v cmp> %#v: want %d got %d", test.a, test.b, test.want, got)
+		}
+		if got := test.b.cmp(test.a); got != -test.want {
+			t.Errorf("%#v <cmp %#v: want %d got %d", test.a, test.b, -test.want, got)
+		}
+	}
+}