Record the region/placement sweep and prune the handoff

The `extent` rename landed as iris `5642f20`; the handoff had not listed it
as pending at all, and its item 2 named renames that are already upstream.
Say which vocabulary the app has still to absorb, drop the retired-clone
and archive chronicle, and strike the three clarity findings now done.

docs/HANDOFF.md

@@ -6,33 +6,38 @@ in `docs/LAYOUT_LOG.md`.
 
 ## The Iris layout repair is submitted
 
-**Iris PR #19** (`layout/one-ask`) replaces closed #18. The current tip is
-`84dad21`: `add6774` fixes collapsed-share placement, retained mask ownership,
-and a redraw-on-reparent defect; `84dad21` removes repeated work in the test
-harness. `docs/LAYOUT_LOG.md` records the review and its regression coverage.
-The core design remains sound; naming and round-to-nearest are unchanged.
+**Iris PR #19** (`layout/one-ask`) replaces closed #18. The tip is `5642f20`:
+`add6774` fixes collapsed-share placement, retained mask ownership and a
+redraw-on-reparent defect, `84dad21` removes repeated work in the test
+harness, and `5642f20` is the naming sweep below. The core design remains
+sound; round-to-nearest is still unchanged.
 
-There is one Iris Git repository, stored with this checkout's submodule:
+Two checkouts share one Git storage. `/home/bob/repos/iris` is the active
+`layout/one-ask` worktree; `ai-app-2/iris` stays on `main` at the app's
+`32f6ad8` pin, and is kept until the app's integration is ready.
 
-- `/home/bob/repos/iris` is the active `layout/one-ask` worktree.
-- `/home/bob/repos/ai-app-2/iris` stays on `main` at the app's `32f6ad8` pin.
-  It shares Git storage with the active worktree, rather than being a second
-  development repository. Keep it until the app's integration is ready.
-- The standalone `iris-layout-experiment` clone is retired. Superseded fork
-  branches are removed; unique experiment tips and the #18 measurement
-  baseline are preserved under `archive/2026-09-19/` tags. A complete bundle
-  is also under `~/.local/state/iris/archive/`.
+Each round was checked with format, workspace clippy under `-D warnings`, the
+workspace tests with and without `layout-diagnostics`, the release fast
+oracle, and the three prescribed seed scans — 400 at depth 5, 1,000 at depth
+6, 2,000 at depth 4. The cold dump covers 34,488 boxes: the fixes moved 650 of
+them, all from the collapsed-share correction, and the naming sweep moved
+none.
 
-Verification of the fixes: format and workspace clippy with `-D warnings`,
-workspace tests with and without `layout-diagnostics` (128 suite tests,
-20 core tests, 21 with diagnostics, and 11 generated tests), and the release fast oracle pass.
-The 400-seed depth-5 shrinker, 1,000-seed depth-6 run, and 2,000-seed
-breadth scan all pass. The cold dump covers 34,488 boxes; 650 change because
-of the collapsed-share correction. With only that correction withheld,
-the remaining fixes reproduce the baseline dump exactly.
-The headless `tabs` example and the exact collapsed-share repro were rendered
-and inspected; the latter places the blue tail at x=220..400. The machine's
-Vulkan device is the RX 7900 XT through RADV native context.
+## The naming sweep is done
+
+`5642f20` finished the rename decided on 2026-09-17, which `frame`'s return as
+a length had left half-applied. The box a parent asks a widget in is the
+**region**, and where its drawing ends up is its **placement**:
+
+- `Painter::extent` → `region`, and its `extent_len()` → `region_len()`.
+- `ActiveData::{part, extent}` → `{region, placement}`, and with them
+  `DrawInfo::part` and `Placing::extent`.
+- `LayoutHolds::{extent, extent_len}` → `{region, region_len}`, and
+  `Counter::OutsideExtent` → `OutsideRegion`.
+- `placed_extent` → `placement`, `frame_and_extent` → `frame_and_region`,
+  `part_of` → `region_of`.
+- `Painter`'s `window_own`, `extent_own`, `frame_own_len` and `extent_len`
+  become the one `own: LayoutHolds` they were assembled into.
 
 ## What is next, in order
 
@@ -44,8 +49,10 @@ Vulkan device is the RX 7900 XT through RADV native context.
 2. **Integrate the app's Iris capabilities before changing its pin.**
    `32f6ad8` has 45 commits not reachable from the review branch; shared UI
    ownership, richer masks, Android support, and app-side performance work
-   must survive the integration. Then migrate `SizeRule` beside widgets,
-   alignment properties, `rest` to `leftover`, and removal of `OrthoSize`.
+   must survive the integration. The app then absorbs the branch's
+   vocabulary, all of it already upstream: `rest` → `leftover`, `SizeRule`
+   beside widgets, alignment properties, the removal of `OrthoSize`, and the
+   region/placement names above.
 3. **Round-to-nearest**, CPU and shader together as one verified change.
    Bryan approved it on 2026-09-17 and neither half has landed; the
    derivation, the form to use and what to re-check are in `docs/LAYOUT.md`
@@ -64,9 +71,9 @@ Vulkan device is the RX 7900 XT through RADV native context.
   composing through `FULL` "is not quite the identity in f32"; on the grid it
   is exact and the shortcut is performance only.
 - `docs/LAYOUT.md` §4, §5 and the density section name `Painter::place`,
-  `SetSize`, `desired_width`, `apply_rest`, `Len::dp`, `Aligned` and
-  `MaxSize`, none of which exist. Do not restore `OnResize::Translate` or
-  `OrthoSize`.
+  `Painter::region()`, `SetSize`, `desired_width`, `apply_rest`, `Len::dp`,
+  `Aligned` and `MaxSize`, none of which exist. Do not restore
+  `OnResize::Translate` or `OrthoSize`.
 - `LazySpan`, then `SizeRule::{Min, Max, Clamp}`. A cap may not contain
   `leftover`; whether `Max` narrows the child's drawing box is a product
   decision.