Record the twelfth sweep, over the request arena

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/HANDOFF.md

@@ -53,6 +53,23 @@ and `revision_cost` resize -0.79% in release instruction medians.
 the three deferred corpora, 206 and 210 tests, and the cold dump byte-identical
 to `2ac0843` across all 34,986 boxes.
 
+## A quality sweep of the request arena is submitted on PR #19
+
+The twelfth sweep landed at `f48e04e`. It is the first review of `05e6ced` --
+one node type for a request, an arena per owner, and `Widgets::edit_bound`.
+Four findings, the largest being that the one path copying a request into
+another arena was run by nothing: all 206 tests passed with a `panic!` in it,
+because every expression in the corpora and in the cases compares an
+expression against a plain length. A fixture with absolute geometry and a
+fourth arm in the deferred corpus cover it now, and the path was already
+correct. The other three: `Debug` on a request still printed the derived
+arena its own new `Display` was written to avoid, a method asked nothing of
+its receiver, and a closure parameter shadowed the rule it was called on.
+`docs/LAYOUT_LOG.md` has all four, with the four rules it tripped and left.
+Verified: format, clippy both ways, 207 and 211 tests, the cold dump
+byte-identical to `05e6ced` across all 34,986 boxes, and 400 depth-5 trees in
+each of the three deferred corpora in 200.95s.
+
 ## A quality sweep of the bounds work is submitted on PR #19
 
 The eleventh sweep landed at `ea1f836`. It is the first review of `2ac0843`
@@ -184,6 +201,8 @@ comparison work above, its review rounds past `cadfba0` are described in
 - **One node type for a request**, `05e6ced` -- the expression a rule holds
   and the expression the pass allocates were two shapes of one thing, with
   the fold written twice and an `Arc` where nothing shares.
+- **The request arena's own sweep**, `f48e04e` -- the join that copies one
+  request's nodes into another's, which nothing in the suite ran.
 
 The settled design of the vocabulary rounds is in `docs/LAYOUT.md` under
 "Three names, and the one argument that says them". Bryan settled the API
@@ -239,7 +258,7 @@ the name it is reachable by.
 **Always**, because they cost nothing: format, workspace clippy under
 `-D warnings` with and without `layout-diagnostics`, the workspace tests, and
 the **cold dump**. `layout_dump` over 400 depth-5 trees is **34,986** boxes
-since `76aaf06` grew bounds in the trees, and is unchanged through `05e6ced`.
+since `76aaf06` grew bounds in the trees, and is unchanged through `f48e04e`.
 It was 34,571 from `2dba90b`, which grew the images, and 34,488 before those; the fourth through eighth sweeps all
 repeated 34,492, which is a `wc -l` of the whole run rather than of its box
 lines, so count the lines that are a box (`grep -cE '^[0-9]+ [0-9]+ '`). It is the only thing that catches two
@@ -271,6 +290,11 @@ a compile error, which reads exactly like a fuzzer failure.
    adds a third: where a round fixed a class of defect one instance at a
    time, put the check in the shared helper, which both closes the class and
    tests the instances that round said were already fine.
+   The twelfth adds a fourth, about coverage rather than about a defect: a
+   branch only a combination of the public API reaches can be reached by
+   nothing and still look covered, since every test around it passes. Put a
+   `panic!` in the arm and run the suite; it costs one build and it answers
+   the question the test names cannot.
 2. **A review of everything written before the review gate existed.**
    `pre-submit-review` and the rule that nothing is submitted unreviewed
    arrived on 2026-09-13, well after the Rust port and most of Iris were