Record the rule/widget split for bounds

A rule holds what a widget answers and a widget holds the box (Bryan,
2026-09-20). `layout/bounds` is green on all three scans; the hole left is a
retained answer re-placed under a different rel base, which predates bounds.

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

docs/LAYOUT_LOG.md

@@ -70,6 +70,25 @@ to it: a rule that is a fraction must pin its rel base, which `Exact` was
 already missing for bounds-shaped reasons; and `widget_trait!` dropped
 attributes, so no method it defines could carry a doc comment.
 
+**Settled (Bryan, 2026-09-20): a rule holds the answer, a widget holds the
+box.** `de1eb7e`. `SizeRule::{Min, Max, Clamp}` holds the length a widget
+answers and leaves its box alone, which is stable because an answer is a
+function of what the widget drew. `MaxSize` is the box version and is a widget
+because a widget is drawn again whenever its own box changes, so the
+comparison is made where the answer can be kept. `.max_width`/`.max_height`
+are that widget; `.min_width`/`.min_height` stay a rule. All three seed scans
+pass. The capped scroll -- 400 px of content under a 100 px cap, a 100 px
+viewport and 300 to scroll -- is the app's `MaxSize` capability, and it comes
+back through the widget.
+
+One hole is left and is **older than bounds**: `place_at` hands a parent a
+retained answer without checking that the answer still holds for the rel base
+that place gives, so a fraction resolved against one rel base survives into
+another. A fraction in a bound is the first thing to reach it (seeds 4 and 196
+at depth 5), which is why the generated trees grow bounds in pixels only, said
+where the tree is grown. An `Exact` rule that is a fraction can reach it too.
+The fix is a holds check at the re-place site, not anything about bounds.
+
 ## Images in the generated trees (2026-09-20)
 
 `Image` is the only widget here whose size hint is a length in pixels, so it is