Harden scan robustness and tests

plugins/services/telnet_test.go

@@ -0,0 +1,17 @@
+//go:build plugin_telnet || !plugin_selective
+
+package services
+
+import (
+	"strings"
+	"testing"
+	"unicode/utf8"
+)
+
+func TestTelnetExtractEvidenceTruncatesByRune(t *testing.T) {
+	p := NewTelnetPlugin()
+	got := p.extractEvidence("CMD_START\n" + strings.Repeat("界", 105) + "\nCMD_END")
+	if !utf8.ValidString(got) || len([]rune(got)) != 103 || !strings.HasSuffix(got, "...") {
+		t.Fatalf("extractEvidence() = %q", got)
+	}
+}