memory: U5 adoption is a prediction with a re-measure date

Operator declined the fleetwide announcement (2026-09-22) and chose to
let the convention propagate through the README alone, specifically so
adoption can be distinguished from design. Baseline 0 of 26 booths at
landing; re-count 2026-09-29. Near-zero means nobody heard about it,
which is a different failure from nobody wanting it.

persistent-memory.md

@@ -59,6 +59,17 @@ _As of 2026-09-22:_
 
 ## Recent decisions
 
+- `[2026-09-22]` **U5's adoption is a stated, falsifiable prediction — RE-MEASURE
+  2026-09-29.** Operator declined the fleetwide announcement and chose to let the
+  convention sit, explicitly so that adoption can be told apart from design:
+  **count how many booths under `~/booth-data` carry a `.booth.json` a week
+  after landing.** A near-zero count means the convention was never heard of
+  (an adoption failure — fix by announcing), NOT that the shape was wrong. A
+  non-zero count from handles that only read the README means it propagates on
+  its own. Baseline at landing: **0 of 26**. Same instrument as the `.forever`
+  prediction below, and for the same reason — a diagnosis nobody re-measures is
+  a belief.
+  `find ~/booth-data -maxdepth 2 -name .booth.json | wc -l`
 - `[2026-09-22]` **The U2 bug-hunt panel landed and it was not ceremony —
   `v0.2.2`.** Nine adopted findings across four arms; eight were real against
   live code and one was already fixed. The headline was **4/4 convergent from