#Centipede fix flag description for --feature_frequency_threshold

PiperOrigin-RevId: 564433183

centipede/environment.cc

diff --git a/centipede/environment.cc b/centipede/environment.cc
index 44451d1..ed780c6 100644
--- a/centipede/environment.cc
+++ b/centipede/environment.cc
@@ -242,7 +242,13 @@
           "Internal flag. When a given feature is present in the corpus this "
           "many times Centipede will stop recording it for future corpus "
           "elements. Larger values will use more RAM but may improve corpus "
-          "weights. Valid values are 1 - 255.");
+          "weights. Valid values are 2 - 255.")
+    .OnUpdate([]() {
+      size_t threshold = absl::GetFlag(FLAGS_feature_frequency_threshold);
+      QCHECK(threshold >= 2 && threshold <= 255)
+          << "--" << FLAGS_feature_frequency_threshold.Name()
+          << " must be in [2,255] but has value " << threshold;
+    });
 ABSL_FLAG(bool, require_pc_table, true,
           "If true, Centipede will exit if the --pc_table is not found.");
 ABSL_FLAG(int, telemetry_frequency, 0,