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
+**Iris PR #19** (`layout/one-ask`) replaces closed #18. The tip is `5642f20`:
-`84dad21`: `add6774` fixes collapsed-share placement, retained mask ownership,
+`add6774` fixes collapsed-share placement, retained mask ownership and a
-and a redraw-on-reparent defect; `84dad21` removes repeated work in the test
+redraw-on-reparent defect, `84dad21` removes repeated work in the test
-harness. `docs/LAYOUT_LOG.md` records the review and its regression coverage.
+harness, and `5642f20` is the naming sweep below. The core design remains
-The core design remains sound; naming and round-to-nearest are unchanged.
+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.
+Each round was checked with format, workspace clippy under `-D warnings`, the
-- `/home/bob/repos/ai-app-2/iris` stays on `main` at the app's `32f6ad8` pin.
+workspace tests with and without `layout-diagnostics`, the release fast
-  It shares Git storage with the active worktree, rather than being a second
+oracle, and the three prescribed seed scans — 400 at depth 5, 1,000 at depth
-  development repository. Keep it until the app's integration is ready.
+6, 2,000 at depth 4. The cold dump covers 34,488 boxes: the fixes moved 650 of
-- The standalone `iris-layout-experiment` clone is retired. Superseded fork
+them, all from the collapsed-share correction, and the naming sweep moved
-  branches are removed; unique experiment tips and the #18 measurement
+none.
-  baseline are preserved under `archive/2026-09-19/` tags. A complete bundle
-  is also under `~/.local/state/iris/archive/`.
 
-Verification of the fixes: format and workspace clippy with `-D warnings`,
+## The naming sweep is done
-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.
+`5642f20` finished the rename decided on 2026-09-17, which `frame`'s return as
-The 400-seed depth-5 shrinker, 1,000-seed depth-6 run, and 2,000-seed
+a length had left half-applied. The box a parent asks a widget in is the
-breadth scan all pass. The cold dump covers 34,488 boxes; 650 change because
+**region**, and where its drawing ends up is its **placement**:
-of the collapsed-share correction. With only that correction withheld,
+
-the remaining fixes reproduce the baseline dump exactly.
+- `Painter::extent` → `region`, and its `extent_len()` → `region_len()`.
-The headless `tabs` example and the exact collapsed-share repro were rendered
+- `ActiveData::{part, extent}` → `{region, placement}`, and with them
-and inspected; the latter places the blue tail at x=220..400. The machine's
+  `DrawInfo::part` and `Placing::extent`.
-Vulkan device is the RX 7900 XT through RADV native context.
+- `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,
+   must survive the integration. The app then absorbs the branch's
-   alignment properties, `rest` to `leftover`, and removal of `OrthoSize`.
+   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
+  `Painter::region()`, `SetSize`, `desired_width`, `apply_rest`, `Len::dp`,
-  `MaxSize`, none of which exist. Do not restore `OnResize::Translate` or
+  `Aligned` and `MaxSize`, none of which exist. Do not restore
-  `OrthoSize`.
+  `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.

docs/LAYOUT.md

@@ -387,7 +387,7 @@ can name -- a division of two lengths, which a `rel + px` length cannot hold.
 A widget's own declaration *is* a fraction, of whichever of those reached it,
 and it is the only one of them that also places the box inside the part.
 
-Validity has a pin for each: `LayoutHolds::extent_len` for the box's symbolic
+Validity has a pin for each: `LayoutHolds::region_len` for the box's symbolic
 length and `frame_len` for the frame's. A range of window pixels cannot say
 which frame an answer is a fraction of, since two frames are different
 lengths at the same window size. Resolving any of these lengths in pixels is

docs/LAYOUT_LOG.md

@@ -136,18 +136,10 @@ The descriptions above preserve the original failure at `cadfba0`.
 
 ### Clarity, in the order worth doing
 
-- **`extent` is back.** `core/src/ui` says `extent` 138 times, its comments
+The first three -- the unswept `extent`, the two same-typed boxes on
-  say "box" 153 times, and the types are all `UiRegion`. Bryan renamed this
+`ActiveData`, and `Painter`'s four holds accumulators -- were done in
-  to `placement` on 2026-09-17; `frame` survived with its new meaning as a
+`5642f20`. What is left:
-  length, `extent` did not. One sweep over `Painter::extent`,
+
-  `ActiveData::{extent, part}`, `placed_extent`, `frame_and_extent` and
-  `LayoutHolds::{extent, extent_len}`.
-- `ActiveData::part` and `::extent` are both boxes told apart only by
-  prose, and `draw_at` writes `part: extent` from one value. `asked_in` and
-  `drawn_in` would say it in the names.
-- `Painter` accumulates a `LayoutHolds` under four names that do not match
-  the four fields they become (`window_own`, `extent_own`, `frame_own_len`,
-  `extent_len`). One `own: LayoutHolds` field deletes the mapping.
 - `draw_inner` returns `(Size, LayoutHolds, LayoutHolds)`, two same-typed
   values ordered by convention. A named pair makes the swap unwriteable.
 - `DrawInfo::px` is computed at all four construction sites and read only by