iris bench: one ScrollController for every scroll area (ai-app-2 4fdabc3)

README.md

@@ -11,6 +11,51 @@ no enrolment and no permissions.
 
 The rest of this file is the runbook that was delivered with the APKs.
 
+**2026-09-08 (newest): scrolling is one mechanism, and this build is
+mostly structure.** `iris-bench-arm64.apk` rebuilt from ai-app-2
+`4fdabc3`, four commits on from the last one. **There is deliberately no
+new feature here and little that should look different** -- it is the
+scrolling rework you asked for after reading `docs/SCROLL.md`, plus the
+two changes before it, so what this build is for is catching anything
+that got *worse*.
+
+- Everything a scroll position is made of now lives in one
+  `ScrollController` that the two scrolling widgets own, instead of a
+  protocol between a `Scroll` and the list inside it. The list is no
+  longer wrapped in a scroll area at all -- it is one widget doing its own
+  layout and its own scrolling -- and the `Widget` trait lost the three
+  scrolling methods that existed only to connect the two.
+- A scroll delta's sign is now a screen direction (positive scrolls up or
+  left) rather than "toward earlier content", which pointed the opposite
+  way for a list laid out backwards. Nothing in this build lays one out
+  backwards yet, so this is a latent fix rather than something to see.
+- The one behaviour that genuinely changed: a scroll delta is now applied
+  by the next frame's layout rather than the instant it arrives, because
+  the layout is the only thing that knows where the content ends. Input is
+  always followed by a frame, so this should be invisible -- if any
+  gesture feels a frame behind your finger, that is the change to suspect
+  and worth saying so.
+- Earlier in the same run: one fling and one drag implementation for every
+  scroll area (a code fence, the composer and the transcript now share
+  exactly the same code), and the list's pin ("stay at the newest
+  message") is separate from which way it is laid out.
+
+What to look for -- all of it is "does this still work", not "is this
+new":
+
+- Flick the transcript hard both ways: it should decelerate and stop
+  exactly on the first and last message, never past either.
+- Put a finger down on a coasting transcript: it should stop dead under
+  your finger and then follow it.
+- Flick a code block sideways while scrolling the transcript vertically
+  somewhere else -- the two should not interfere.
+- Scroll the composer's text when a message is long enough to need it.
+- While a reply is streaming, the view should stay stuck to the bottom;
+  scroll away and it should stop following, and coming back to the bottom
+  should re-stick.
+- Selecting text with a long press should still work and should not pan.
+
+
 **2026-09-08 (later still): the scroll lock, and the input box's clip.**
 `iris-bench-arm64.apk` rebuilt from ai-app-2 `5e34dba`. Both are from
 your report on the bench build, and both have a test that fails without