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 43da4f84..6492891c 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
@@ -615,3 +615,7 @@ names the principle that settles it, and is cited as "design 47 G A-n".
 - **A-164** (§468, §76, §495, A-115; principles 4 and 7) The runner's process writes each durable consumer's oldest
   unacknowledged age into a state of the runner's own when it changes; the bundle's `runner_health` reads that state,
   its own module's, and asks no seat verb of itself; tools stay the bundle's (A-115).
+- **A-165** (§610, A-156; principles 3 and 7) The class defaults of §610 are applied where a seat's verb is answered:
+  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.