Gate readiness on stable viewport frames

docs/renderer-performance.md

@@ -40,7 +40,9 @@ INITIALIZING generation=N waiting_for=world_state,viewport target_fps=10
 
 The framework gate opens only after the region-scoped world state exists, the
 first scene/assets have converged, and at least two complete viewport frames
-have been published without render errors. The terminal then emits
+have been published after the last missed deadline, within the frame budget,
+and without render errors. One-time warm-up misses are reported separately and
+do not contaminate the post-`READY` stability window. The terminal then emits
 `INITIALIZED ...` followed by one unambiguous `READY ...` line when the session
 and agent services are released. The default readiness allowance is two
 minutes; the measured scene convergence window was about 30.05 seconds.