DECISIONS.md, RUST.md: Iris decided iris over Masonry, 2026-09-05

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/RUST.md

@@ -36,6 +36,10 @@ session spending an afternoon on them again.
 
 ## Where things stand (2026-09-05)
 
+- **Decided 2026-09-05: iris over Masonry**, by Iris, from the host-GPU
+  numbers in I5's box and E1/E2's findings. See the Recommendation's item
+  3 and `DECISIONS.md`. Next: the remaining screens and the app on iris —
+  a new ordered list is the next thing to write into this file.
 - **I5 is now `[x]`: a clean, single-session, like-for-like 24-swipe
   scroll comparison between Compose and iris exists, 2026-09-05.** Same
   sandbox session content for both apps, same emulator, `EMU_GPU=software`
@@ -692,7 +696,13 @@ light" has a knob inside the same stack.
    names; winit on the desktop. On top of it, **Masonry as the yardstick**
    (E1, E2) and **iris as the thing being built** (I0–I5), both aimed at
    the same transcript screen with the same pass conditions.
-3. **Decide when the transcript screen exists in both**, from the
+3. **Decided, 2026-09-05: iris.** Iris made the call from the host-GPU
+   comparison in I5's box (iris p50 15.0 ms, Compose 20.0 ms, same
+   content, same emulator) and from what E1/E2 found Masonry cannot do on
+   Android today (touch scroll, per-span rich text, cross-row selection,
+   the keyboard bridge). `DECISIONS.md` has the entry. The paragraph
+   below is what the decision was to be made from, kept for the record.
+   **Decide when the transcript screen exists in both**, from the
    measurements, and record the decision here with the numbers. If iris
    carries the screen within the Compose baseline, it is the app's
    framework and Masonry was the calibration. If it does not, the