fleetd #609 review: repair a garbled comment carried over from the brief

The brief's sentence about a null token count at HIGH was broken, and the
worker copied it into the source verbatim. The code was already right; only
the comment was unreadable.

Says what is actually true: a HIGH reading always carries a non-null token
count today, because LeadContextGauge only reaches HIGH by comparing a number
against HIGH_THRESHOLD_TOKENS. That invariant lives in another class and
nothing asserts it, so the branch stays.

fleetd/src/main/java/dev/ltms/fleet/msg/LeadHeartbeatLoop.java

@@ -360,8 +360,10 @@ public final class LeadHeartbeatLoop {
             sb.append(": ").append(reading.tokens()).append(" tokens used, ")
                     .append(reading.compactions()).append(' ').append(compactionWord).append(" so far.");
         } else {
-            // tokens() can be null even at HIGH is not true today, but do not assume it — leave the
-            // token clause out rather than print "null tokens".
+            // A HIGH reading always carries a non-null token count today: LeadContextGauge only
+            // reaches HIGH by comparing a number against HIGH_THRESHOLD_TOKENS. That invariant
+            // lives in another class and nothing asserts it, so this branch does not rely on it —
+            // it drops the token clause rather than printing "null tokens".
             sb.append(" (").append(reading.compactions()).append(' ').append(compactionWord)
                     .append(" so far).");
         }