Record the thirteenth sweep, a full pass over #19

Seven findings at cbccfb6, the largest being a length of zero that printed
as the empty string -- which the twelfth sweep made load-bearing by pointing
Debug at Display, and which scenario::describe rendered as "no rule at all".
Also re-measured the hole Sow::bound's comment recorded: the seeds it named
stopped naming those trees when the leaves grew images, and 600 depth-5
trees now agree with every bound a fraction.

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

docs/LAYOUT_LOG.md

@@ -6,6 +6,97 @@ nothing here is rediscovered. Each entry says who found it and when.
 it (settled design, the measurement method) belongs in `docs/LAYOUT.md`, and
 the current plan is in `docs/HANDOFF.md`.
 
+## Thirteenth sweep: a full pass over #19 (2026-09-20)
+
+Over the whole branch rather than one commit, and the first review of
+`f48e04e`. Seven findings, all in `cbccfb6`.
+
+- **A length of zero printed as nothing.** `Display for LayoutLen` leaves out
+  each part that is zero, so `LayoutLen::ZERO` is the empty string -- and
+  `f48e04e` pointed `Debug` at `Display`, so the four `assert_eq!`s in
+  `cases/deferred.rs` print nothing where a request of zero is. Worse in
+  `scenario::describe`, which prints a `.width(0)` rule as `-` -- the same
+  thing it prints for a widget with no rule. That function exists so a tree a
+  fuzzer found "can be written out by hand"; a value it cannot say is a hole
+  in the one thing it is for. Measured before the fix:
+  `format!("{}", px(0).min(px(40)))` was `""`, and `Size::ZERO` was `"(, )"`.
+  It is `0 px;` now, with a test over all four shapes of length.
+- **A ceiling that stepped off the top of the grid.** `ceil_from_f32` takes
+  `next_up` of a `from_f32` that has already clamped, and `next_up` wraps, so
+  `Px::ceil_from_f32(1e12)` was `Px::MIN` -- the most negative length there
+  is, from the largest measurement. `from_f32` clamps deliberately ("a float
+  has further to come from"); the ceiling is the other way in from a float
+  and the rule governs both. The assertion goes beside the one `from_f32`
+  already had, which is where the class lives.
+- **`Moves::depth` walked the chain a second way**, with its own copy of
+  `CHAIN_LIMIT` and without the debug assertion `walk` makes. It is
+  `self.walk(idx, |_| depth += 1)` now, so the CPU counts a move chain in one
+  place and the constant the shader is handed reaches both.
+- **A harness setter that did not do what it said.** `Harness::set_len` said
+  "the way `.width()` sets one" and called `set_size_rule`, which writes the
+  whole rule -- so it dropped any bound beside the length, where
+  `Widgets::set_len` keeps one on purpose. A case that set a bound and then a
+  length would have passed with no bound at all. It calls `Widgets::set_len`.
+- **Three spellings of "one seed, or a range of them."** `generated.rs`,
+  `shrink.rs` and `deferred_generated.rs` each wrote the `std::env::var(..)
+  .parse()` match by hand -- the class the eleventh sweep closed for *reading*
+  a parameter and not for this one. One `rig::seeds`, carrying an
+  `#[allow(dead_code)]` because the module is compiled into each rig target
+  and the measurement rigs choose no seeds.
+- **A refusal that could go uncounted.** `diag::outside` writes out
+  `AxisHolds::contains`'s four clauses to say *which* one refused a reuse. A
+  fifth clause added there and not here would leave a refusal counted by
+  `ReuseOutside` and explained by nothing; a debug assertion catches that now,
+  which is the cheap guard rather than machinery to derive the reasons.
+- **`cases/deferred` sat last** in `suite.rs`'s otherwise alphabetical list.
+
+**A stale record, re-measured.** `Sow::bound` grows bounds in pixels and its
+comment said why: a fraction survives a `place_at` into a different rel base,
+"seeds 4 (shuffle-all-but-first) and 196 (resize-size) at depth 5 are where
+that showed". But `generated.rs` says in its own comment that a seed names a
+tree only while the generator draws the same things in the same order, and
+that adding images to the leaves moved every one of them -- which is
+`2dba90b`, after that hole was recorded. Re-measured: 600 depth-5 trees over
+all sixteen cases agree warm against cold with every bound a fraction
+(93.18s, release). The generator still grows pixels, because
+`deferred_generated.rs` already varies that dimension in its relative-bound
+corpus and growing fractions here would move every box in the cold dump for
+overlap; the comment now says that rather than describing an open defect.
+
+Five things the sweep **looked at and left**:
+
+- **`independent_order` compares two lengths by `leftover` where their pixels
+  and fractions are equal**, which is only sound while a leftover resolves at
+  a nonnegative ratio. Worked through: `allocate` starts at `Ratio::ZERO` and
+  breaks before moving when the fixed parts already exceed the room, so `at`
+  is never negative and a larger weight is never a shorter length. Recorded so
+  the next reader does not derive it again.
+- **`Bound::outside`'s assertion that a floor does not sit over a cap fires
+  only for some boxes.** With `min` 100 and `max` 50 it fires where the box is
+  under 100 and passes where it is over, because the floor only binds on one
+  side. Left: the two ends can be a fraction and a pixel length, so which is
+  larger is not a question `set_min_len` can answer, and the box is where it
+  becomes one.
+- **A bound has no remover.** `set_min_len`/`set_max_len` only ever write
+  `Some`, and clearing one means writing the whole rule -- which drops the
+  preferred length, the mirror of the defect fixed above. Left because
+  nothing asks for it yet and the preferred length has no remover either; the
+  asymmetry is uniform.
+- **`Moves::clear` replaces its arena rather than clearing it**, throwing away
+  capacity where `RequestArena::reset` deliberately keeps it. Left: it runs
+  only on a full redraw, and `Arena` has no `clear`.
+- **`TextEditCtx::apply_event` reads `if undo && let Some(..)` with an `else
+  if` after it**, so an undo with an empty history now falls into the branch
+  that pushes history. It is equivalent only because an undo command does not
+  itself change the text, so the `!=` guarding that push is false. Left as
+  correct; noted because the guard is somebody else's invariant.
+
+Verified at `cbccfb6`: format, workspace clippy under `-D warnings` with and
+without `layout-diagnostics`, 208 ordinary and 212 diagnostic tests (207 and
+211 before, plus the one this adds), and the cold dump byte-identical to
+`f48e04e` across all **34,986** boxes. The three seed scans were not run:
+nothing here can move a box, which the dump confirms.
+
 ## Twelfth sweep: the request arena (2026-09-20)
 
 Over `05e6ced`, which no earlier round reviewed -- one node type for a