fix(logs): don't panic masking a JWT with a short signature

internal/logs/sanitizer.go

@@ -114,6 +114,9 @@ func (s *SecretSanitizer) registerDefaultPatterns() {
 			if len(parts) != 3 {
 				return "****"
 			}
+			if len(parts[2]) < 4 {
+				return parts[0] + ".***.***"
+			}
 			// Show first part (header) but mask payload and signature
 			return parts[0] + ".***." + parts[2][len(parts[2])-4:]
 		},

internal/logs/sanitizer_jwt_short_signature_test.go

@@ -0,0 +1,28 @@
+package logs
+
+import (
+	"strings"
+	"testing"
+)
+
+// The jwt regex accepts a 1-3 character signature segment; masking it must
+// not slice out of range (a panic inside the zap core takes the caller down).
+func TestSanitizer_JWTShortSignatureDoesNotPanic(t *testing.T) {
+	s := newTestSanitizer()
+	const payload = "eyJzdWIiOiIxIn0"
+	for _, sig := range []string{"x", "ab", "abc"} {
+		in := "jwt eyJhbGciOiJub25lIn0." + payload + "." + sig
+		var out string
+		func() {
+			defer func() {
+				if r := recover(); r != nil {
+					t.Errorf("sanitizeString(%q) panicked: %v", in, r)
+				}
+			}()
+			out = s.sanitizeString(in)
+		}()
+		if strings.Contains(out, payload) {
+			t.Errorf("payload leaked: %q", out)
+		}
+	}
+}