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 32c1c586..02c7c60d 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
@@ -332,3 +332,7 @@ names the principle that settles it, and is cited as "design 47 G A-n".
   each entry by fingerprint; it reads each entry through `mesh-catalog.entry` (repository and commit are the member's
   head) and needs no pull request number, a build being per fingerprint. Its read of the indexer's `candidates` view
   goes.
+- **A-85** (§291, ADR 0666 §6, §9, §614, A-83; principle 7) The indexer keeps a catalog revision per watched branch, as
+  it keeps the trunk's: objects `branch.<branch>.<n>` (the branch escaped as a name) beside `trunk.<n>`, the trunk being
+  the first watched branch's; the branch follower's per-branch `revision` reads them, and `BuildEdges.fp` is the entry's
+  fingerprint in the revision whose `source` the build names.