RUST.md, DECISIONS.md, IRIS_TODO.md: the port plan, P1-P7, after iris-over-Masonry

Adds "The port, in order (decided 2026-09-05)" to RUST.md: seven ordered
steps building the app on iris now that the framework is decided, each
naming the Kotlin files it replaces, the client-core pieces it needs
(and which are not yet covered and must be ported first), the missing
iris widgets it needs (recorded in IRIS_TODO.md's new "Build (for the
port)" section), and a pass condition a later agent can run. Ordered by
risk to the daily-use path: session screen parity, then the shell merge
and a real phone install, then root tabs, the file explorer,
settings/enrolment, desktop parity, and the cutover itself.

Crate-shape decision recorded in DECISIONS.md: one UI crate, app-ui,
grown out of transcript-ui rather than started beside it, with
desktop-app/android-app as thin entry points over it and platform-only
code staying in the E3/E5 Java shell.

Updates RUST.md's "Where things stand" and "For the next agent" to point
at P1 rather than the now-closed framework decision.

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

docs/IRIS_TODO.md

@@ -292,6 +292,42 @@ order and what "done" looks like. Tick and date them in place.
   everything, the same way input is**. Whatever the mechanism, a widget
   that does not animate must pay nothing and import nothing for it.
 
+## Build (for the port)
+
+Widgets `RUST.md`'s "The port, in order (decided 2026-09-05)" needs and
+iris does not have yet, one entry per gap, named against the P-step that
+first needs it. Move an entry up to "Fix" or tick it in place once built;
+do not duplicate it there.
+
+- [ ] **A history-paging cushion measured in on-screen viewports, not a
+  row count.** (**P1**.) `iris::widget::List` has no equivalent of the
+  Compose app's `HISTORY_SCREENS` — AGENTS.md's "Things that have
+  bitten" is explicit that a fixed row count under-fills a screen on a
+  tool-heavy transcript and over-fills one on a text-heavy one, so
+  whatever loads the next page has to ask the list how many viewports
+  are actually on screen, not assume a constant.
+- [ ] **A scaled thumbnail/image widget for an in-transcript image.**
+  (**P1**.) `SessionImage.kt`'s bitmap decode-and-downscale has no iris
+  counterpart; iris's own image widget (used by `bench_images.rs`) draws
+  a loaded texture but does nothing about sourcing or scaling one from a
+  server-produced attachment.
+- [ ] **A modal/dialog primitive.** (**P1**, reused by **P3** and
+  **P5**.) Needed for the session settings dialog, `UsageDialog`'s
+  equivalent, and the delete-with-`deleteForeign` confirmation with its
+  toggle switch. Build once, wherever it is first needed, rather than
+  once per screen that wants one.
+- [ ] **A horizontal gauge/bar widget.** (**P1**.) For
+  `SessionUsageBar`'s equivalent — a bounded fill reflecting a fraction,
+  nothing fancier.
+- [ ] **A `BusyItem` equivalent: a dimmed row carrying an operation
+  label that does not block its list's own scroll/drag.** (**P3**.) The
+  Compose version tried an overlay first and it swallowed the drag along
+  with the tap (AGENTS.md's "Shared appearance") — worth not repeating
+  that attempt in iris before building the row-level version directly.
+- [ ] **A toggle switch.** (**P3**.) For the delete dialog's
+  `deleteForeign` control; iris has no switch/checkbox widget yet as far
+  as this pass found.
+
 ## Reconsider
 
 - [ ] **`WidgetView`.** Iris is unsure of it: what she wants is an easy way