Enforce durable D&D evidence ranges

internal/modules/dnd/codec/locationoccurrences/codec_test.go

@@ -140,6 +140,41 @@ func TestCodecCandidateDecodeOwnsValues(t *testing.T) {
 	}
 }
 
+func TestCodecRejectsInvalidDurableRangesWhileCandidatesPreserveThem(t *testing.T) {
+	codec := New()
+	for _, test := range []struct {
+		name   string
+		mutate func(*dnd.LocationOccurrenceList)
+		want   string
+	}{
+		{name: "nonpositive start", mutate: func(value *dnd.LocationOccurrenceList) { value.Occurrences[0].SourceRefs[0].StartUnitID = 0 }, want: "start_unit_id"},
+		{name: "nonpositive end", mutate: func(value *dnd.LocationOccurrenceList) { value.Occurrences[0].SourceRefs[0].EndUnitID = 0 }, want: "end_unit_id"},
+		{name: "reversed", mutate: func(value *dnd.LocationOccurrenceList) {
+			value.Occurrences[0].SourceRefs[0].StartUnitID = 2
+			value.Occurrences[0].SourceRefs[0].EndUnitID = 1
+		}, want: "must not exceed"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			candidate := validList()
+			test.mutate(&candidate)
+			content, err := codec.EncodeCandidate(candidate)
+			if err != nil {
+				t.Fatalf("EncodeCandidate() error = %v", err)
+			}
+			decoded, err := codec.DecodeCandidate(content)
+			if err != nil || !reflect.DeepEqual(decoded, candidate) {
+				t.Fatalf("DecodeCandidate() = %#v, %v; want %#v", decoded, err, candidate)
+			}
+			if _, err := codec.Encode(candidate); err == nil || !strings.Contains(err.Error(), test.want) {
+				t.Fatalf("Encode() error = %v, want %q", err, test.want)
+			}
+			if _, err := codec.Decode(content); err == nil || !strings.Contains(err.Error(), test.want) {
+				t.Fatalf("Decode() error = %v, want %q", err, test.want)
+			}
+		})
+	}
+}
+
 func TestCodecRejectsStructuralJSONBeforeSemanticApproval(t *testing.T) {
 	valid := `{"occurrences":[{"location_id":"location:sha256:0000000000000000000000000000000000000000000000000000000000000000","name":"The Tavern","kind":"visited","source_refs":[{"source_id":"session","start_unit_id":1,"end_unit_id":1}]}]}`
 	for _, test := range []struct{ name, raw, want string }{