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 4428779f..26864c96 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
@@ -684,3 +684,7 @@ names the principle that settles it, and is cited as "design 47 G A-n".
   catalog seat's `catalog-revision` for the candidate `run-<id>` (a candidate's revision, its subject naming it),
   reading the candidate's entries and fingerprints through the seat's `revision` verb with the candidate's group;
   `<id>` is a random 12-hex id the runner makes, so two runs of one commit are two pipelines.
+- **A-181** (amends A-100 and A-162; §556; principles 1 and 2) The builder's `build.ended` stream keeps the last
+  message per subject (one per fingerprint), and the assigner reads it whole at its start as §556 reads a kept
+  stream, then hears it; so what was built, and a failed build's error, survive its restart and it reads no builder
+  bucket. `assigner_put`'s fingerprint-prefix form goes: a put names the whole fingerprint.