diff --git a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
index 6492891c..9d6f13b1 100644
--- a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
+++ b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
@@ -619,3 +619,7 @@ names the principle that settles it, and is cited as "design 47 G A-n".
   mesh-sdk's seat server (`conn.AnswerSeat`) and the tool runner's `serveSeats` read `seatdef.EffectiveCallers` and
   refuse a caller outside them, the unproven one included, before the holder runs; a holder keeps no caller check of
   its own.
+- **A-166** (A-164, §76, §495; principles 1 and 7) The runner keeps a state `consumers` (history 1, a key per
+  consumer) holding the time its oldest unacknowledged message was delivered, written when a message is delivered or
+  acknowledged; `runner_health` works the age out as now minus that time when it is read, so nothing is read on a
+  timer.