Record the eleventh sweep, over the built-in bounds work

docs/LAYOUT_LOG.md

@@ -6,6 +6,99 @@ 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`.
 
+## Eleventh sweep: the built-in bounds work (2026-09-20)
+
+Over `2ac0843`, which no earlier round reviewed -- `SizeRule` from an enum to
+a preferred length beside an independent `Bound`, the offer constrained in
+`Placing::ask`, and `MaxSize` removed. 554 inserted lines over 18 files. Eight
+findings, all in `ea1f836`.
+
+- **A hint read that answered "cannot say" was counted as no read at all.**
+  The bound check moved out of `Painter::size_request` and into
+  `Painter::size_hint`, where it returns above `diag::hint_read` and the
+  `HintHits`/`HintMisses` bump. So a bounded child was neither a hit nor a
+  miss and left no trace event, in the one place the counters exist to watch.
+  It is a miss now -- the bound makes the hint `None` rather than returning
+  early -- with the reason written on it, since the obvious simplification
+  back to an early return silently loses the counter again.
+- **Two loops over both axes, writing the same value.** `draw_widget` grew a
+  second `for axis in Axis::BOTH` when the rel-base pin moved up to join the
+  bound's, separated only by a comment. One loop; the pin goes first because
+  the bound block `continue`s on a share.
+- **A twelve-line comment left describing the wrong line.** The new
+  one-liner about combining the ask's holds was inserted between the comment
+  about holding an answer to its bound and the code that comment is about.
+- **Three things nothing reads.** `Declared::from_axes` lost its only caller
+  with `Widgets::declared_lens`; `Bounds::from_axes` and `SizeRule::declared`
+  never had one. `PlaceDesc::from_axes` is the only member of that family
+  anything calls, so nothing is left half-complete.
+- **The shrinker printed a rule with derived `Debug`.** `describe`'s
+  hand-written printer was replaced by `format!("{r:?}")` and the comment
+  saying why it was hand-written deleted. Measured: one axis prints as
+  `SizeRule { request: Some(Linear(LayoutLen { px: 0, rel: 0, leftover: 1 })),
+  bound: Bound { min: None, max: Some(Len { rel: 0, px: 80 }) } }` -- 130
+  characters, twice per widget, in a line that joins every ancestor with
+  `" < "`. That is the one function whose stated job is output a tree can be
+  rebuilt from. It prints its parts again: `[x:1 leftover;<80 px;,y:-]`.
+- **Five spellings of reading one environment variable.** `bounds_cost` wrote
+  three in one function (`var().unwrap_or_else`, `var().is_ok_and(== "1")`,
+  `var().ok().and_then(parse)`) where an identical `fn env<T: FromStr>`
+  already stood in `layout_dump.rs`, `layout_diagnostics.rs`,
+  `revision_cost.rs` and `scenario/mod.rs`. This is the class the tenth sweep
+  found one commit earlier and fixed one instance of. It is now one function
+  in `tests/rig/`, used by all six rigs, and a switch is `env(NAME, 0_u8) != 0`
+  everywhere.
+- **A measurement rig verifying inside its measured loop.** `bounds_cost`
+  asserted 128 regions every frame, where `revision_cost` prints its geometry
+  once before the loop and asserts nothing inside it. Measured at `MODE=cap
+  FRAMES=2000`: 5.780B instructions with the per-frame assertions against
+  5.743B without, three runs each, stable to 0.005% -- 0.65%, which is far
+  less than it looked and still not layout. The check now runs once on each
+  side of the crossing before the loop, and the number is in the comment so
+  nobody re-adds it or deletes it for the wrong reason. Its module comment
+  also said it compares against "the former wrapper", which this tree no
+  longer contains, without saying the other side has to be run at an earlier
+  commit; and it documented `MODE` and `REDRAW` but not `FRAMES`, and gave no
+  invocation line where every neighbouring rig gives one.
+- **The same fixture built by two tests, and a half-test that could no longer
+  decide anything.** `a_bound_holds_what_a_widget_answers` and
+  `a_cap_holds_an_answer_that_overflowed_its_box` both built a 250 window
+  holding two 200-wide rects in a row under a 300 cap; the first lost its doc
+  comment in `2ac0843` and the second kept one. They are one test, with the
+  corners assertion folded into the cap arm and a corrected explanation --
+  corrected because the old one said a bound "leaves the box alone", which is
+  no longer true in general and is true of this fixture only because 300 does
+  not bind a 250 box. Separately, the second half of
+  `a_cap_attribute_narrows_the_widgets_box` lost the assertion that
+  distinguished it when `MaxSize` went (the wrapper measuring 400 while its
+  child measured 300), leaving `rect().max_width(300)` at root in a 400
+  window -- which is the opening of
+  `a_cap_attribute_is_decided_again_on_either_side_of_the_crossing`, verbatim.
+  It is now `width(leftover(1)).max_width(300)`, the allocator's path, which
+  nothing covered at the root.
+
+Two things the sweep **looked at and left**:
+
+- **`SizeRule` now holds `Option<SizeRequest>` inline** where the enum held
+  `Request(Arc<SizeRequest>)`, so `at_least` and `at_most` clone the request
+  to edit a bound. Left because `SizeRequest` is `Linear(LayoutLen)` or an
+  `Arc` pair, so that clone is a discriminant copy or a refcount bump, never
+  a deep copy. `size_of::<SizeRule>()` is 40 bytes, which the rig prints.
+- **`Widgets::set_len` writes the `SizeRule` literally** where `set_min_len`
+  and `set_max_len` go through `SizeRule::at_least`/`at_most`. A matching
+  builder was considered and rejected: the two bound helpers exist because a
+  bound is half of a pair that has to be preserved, and a request has no
+  other half to preserve -- a method would be a name in front of one field
+  assignment.
+
+Verified at `ea1f836`: format, workspace clippy under `-D warnings` with and
+without `layout-diagnostics`, 206 ordinary and 210 diagnostic tests (207 and
+211 before, less the merged test), 400 depth-5 trees warm against cold in
+64.19s, and the cold dump byte-identical to `2ac0843` across all **34,986**
+boxes. The scan was run because the `size_hint` restructure touches what a
+container records as a dependency; the dump because nothing here was meant to
+move a box.
+
 ## Tenth sweep: the deferred request system (2026-09-20)
 
 Over the part of #19 no earlier round reviewed -- `76aaf06` and `de1eb7e`