Document deferred layout requests and verification on Iris PR 19

docs/PLAN.md

@@ -870,8 +870,11 @@ span rather than silently discarding its `rest` component.
 the box a parent asks a widget in is its *region*, where the drawing ends up
 is its *placement*, and the length a fraction resolves against is its *rel
 base*. A container says all three in one `PlaceDesc` argument. `Widget::draw`
-remains the only layout body. The invariants, the measured costs, the fuzzing
-method and the failed hypotheses are all in `docs/LAYOUT.md`; the app's pin at
+remains the only layout body. PR #19 also has optional size-request discovery
+for deferred min/max/clamp expressions (2026-09-20); ordinary widgets still
+return `Size`, and plain requests retain symbolic allocation. The invariants,
+the measured costs, the fuzzing method and the failed hypotheses are all in
+`docs/LAYOUT.md`; the app's pin at
 `32f6ad8` predates every part of it, so nothing here depends on it until the
 integration described in `docs/HANDOFF.md` lands.