diff --git a/game/reconstructed/mech4.cpp b/game/reconstructed/mech4.cpp
index 2f1ba3b..09cca72 100644
--- a/game/reconstructed/mech4.cpp
+++ b/game/reconstructed/mech4.cpp
@@ -6961,10 +6961,16 @@ void
 				// there, moving caret gone".  Re-seed instead of propagating.
 				if (!(trueRange == trueRange) || !(sShownRange == sShownRange))
 				{
-					if (getenv("BT_RANGE_LOG"))
+					// #147: ALWAYS-ON (capped) -- the trap is the ONLY evidence
+					// that can name the NaN source in a field log, and Friday's
+					// fleet does not set BT_RANGE_LOG.  Fires once per poisoning
+					// (the re-seed clears it); the #172 rare-forensic precedent.
+					static int s_nanPrints = 0;
+					if (s_nanPrints < 20 && ++s_nanPrints)
 						DEBUG_STREAM << "[range] NaN TRAPPED (true=" << trueRange
-							<< " shown=" << sShownRange << ") -- re-seeded to 1200\n"
-							<< std::flush;
+							<< " shown=" << sShownRange << ") -- re-seeded to 1200"
+							<< ((s_nanPrints == 20) ? " (cap reached)" : "")
+							<< "\n" << std::flush;
 					trueRange   = 1200.0f;
 					sShownRange = 1200.0f;
 				}