Document deferred layout requests and verification on Iris PR 19

docs/HANDOFF.md

@@ -4,10 +4,33 @@ Where the work in flight stands. The settled layout design, the vocabulary
 and the measurement method are in `docs/LAYOUT.md`; what the review of #19
 found is in `docs/LAYOUT_LOG.md`.
 
+## Deferred comparisons are submitted on PR #19
+
+The `layout/one-ask` tip is `8780b40`, in `/home/bob/repos/iris-deferred`.
+`/home/bob/repos/iris` remains on `layout/bounds`; that branch's `de1eb7e` was
+fast-forwarded into #19 before this work. The app's Iris pin is untouched.
+
+The new request path composes min/max/clamp before assigning leftover slots,
+while ordinary widgets keep returning `Size`. Known requests skip provisional
+painting; measured leaves can complete a nested expression. The implementation
+uses a reusable expression arena and retained draw buffers. The allocation rig
+checks zero allocations after warm-up for unchanged plain and clamped trees.
+Generalized cross-axis maxima are deferred because hidden main-axis shares
+must not contribute to them. The current design is in `docs/LAYOUT.md`.
+
+Format, workspace Clippy with and without layout diagnostics, and all 197
+workspace tests pass. The broad scans passed: 400 depth-5 trees through the
+shrinker, 1,000 depth-6 and 2,000 depth-4 generated trees, plus 400 depth-5
+expression trees and 400 relative-bound trees. All 34,986 unbounded cold boxes
+match `de1eb7e`. The forced-redraw allocation fixtures report zero allocations
+across 100 resize frames after warm-up. The text resize benchmark uses 5.89%
+more retired instructions than `de1eb7e`; this is not a universal speedup.
+See `docs/LAYOUT.md` for the measurements and remaining measured paths.
+
 ## The Iris layout repair is submitted
 
-**Iris PR #19** (`layout/one-ask`) replaces closed #18. The tip is `2dba90b`,
-and past the reviewed `cadfba0` it is twelve rounds, each described in
+**Iris PR #19** (`layout/one-ask`) replaces closed #18. Before the deferred
+comparison work above, its review rounds past `cadfba0` are described in
 `docs/LAYOUT_LOG.md`:
 
 - **The repair**, `add6774` and `84dad21` -- collapsed-share placement,
@@ -68,9 +91,8 @@ over 2026-09-17 to 19; it is current, not frozen.
 
 The core design remains sound. Round-to-nearest is still unchanged.
 
-Two checkouts share one Git storage: `/home/bob/repos/iris` is the active
-`layout/one-ask` worktree, and `ai-app-2/iris` stays on `app-pin` at the
-app's `32f6ad8` pin until the integration below is ready.
+The Iris worktrees share Git storage. `ai-app-2/iris` stays on `app-pin` at
+the app's `32f6ad8` pin until the integration below is ready.
 
 ### The branch layout, and the trap that used to be here
 
@@ -198,17 +220,19 @@ glyphs do not follow a shortened entry.
   are caller bugs under `debug_assert`, but the fallbacks differ.
 - `docs/LAYOUT.md` §4, §5 and the density section name `Painter::place`,
   `Painter::region()`, `SetSize`, `desired_width`, `apply_rest`, `Len::dp`,
-  `Aligned` and `MaxSize`, none of which exist. Do not restore
-  `OnResize::Translate` or `OrthoSize`.
-- **`layout/bounds` (`de1eb7e`) is green and ready to review**, kept off #19
-  so that branch stays one subject. A rule holds what a widget answers
+  `Aligned`, which no longer exist; `MaxSize` now exists with the bounds API.
+  Do not restore `OnResize::Translate` or `OrthoSize`.
+- **`layout/bounds` (`de1eb7e`) is included in #19** for the deferred
+  comparison implementation. A rule holds what a widget answers
   (`SizeRule::{Min, Max, Clamp}`); a widget holds the box (`MaxSize`, which
   `.max_width`/`.max_height` build). Bryan settled the split on 2026-09-20
-  after four readings were measured; the reasoning and the one remaining hole
-  -- a retained answer re-placed under a different rel base, which is older
-  than bounds -- are in `docs/LAYOUT_LOG.md`. A bound may not contain
-  `leftover`, and the generated trees grow bounds in pixels until that hole is
-  closed.
+  after four readings were measured; the reasoning is in `docs/LAYOUT_LOG.md`.
+  The deferred-request work fixes stale relative-bound reuse by tracking the
+  input base and comparing resolved bounds, with a reduced natural-size-hint
+  regression and 400 depth-5 relative-bound trees. Intrinsic bounds remain
+  `Len`s; comparisons involving leftover use `SizeRequest`. Ordinary generated
+  trees retain pixel bounds; `deferred_generated` supplies relative bounds and
+  expressions in separate corpora.
 - `LazySpan`.
 - `Scroll` taking a direction rather than one axis.