Record the step 5 result: hints skip the room ask, and the far pin is not the cost

Measured at a888717 and at the new f6242aa on wip/hint-first, with the
inset experiment recorded as tested and rejected. The plan is now review,
render and land.

docs/LAYOUT_LOG.md

@@ -7,6 +7,78 @@ must outlive it (settled design, the measurement method) is already in
 `docs/LAYOUT.md`, and the current plan is in `docs/HANDOFF.md`. Commit ids
 are in `/home/bob/repos/iris-layout-experiment` unless said otherwise.
 
+## What the step 5 measurements found (planner, 2026-09-19)
+
+Re-measured `a888717` first: every number in the handoff's table reproduced
+exactly (342/288, 118/95, 3/3, 1, 44/13 at seed 1; 1278/982, 429/366 at
+seed 13), so the table was trusted. What the counters said beyond it:
+
+- **Most redraws never reached the reuse check.** `many` at seed 1 made 118
+  draws and only 78 reuse attempts, 4 of them rejected; the other draws
+  came from `retained_answer` failing before `try_reuse` ran. Mechanism: a
+  share child is asked in the room and then in its slot, one record holds
+  one answer, and each ask overwrites it -- so the room ask finds the slot
+  answer (pinned to the slot's length) and the slot ask finds the room
+  answer, and each draws. Every ancestor redraw pays it twice per share
+  child, multiplied down nested shares.
+- **#18 avoided the room ask where a hint or rule gave the length.** Its
+  `Span` called `painter.known_len` first; `3091fb8` dropped that with the
+  offer machinery. Restored at `f6242aa` as `Painter::size_hint`, which now
+  resolves a fraction against the asking widget's frame (it returned the raw
+  rule before, which no caller had noticed because its one caller read
+  `px`) and pins that frame where it did. `Scroll`, `Masked`, a `Stack`
+  without a sizing child and the fixture's `Branch` gained `LEFTOVER`
+  hints. A hinted child is asked once, in its slot; a hinted share with no
+  room is never asked and is undrawn. Cost (draws / distinct, depth 8):
+  seed 1 cold 264/232, many 41/41, size 3/3, scroll 1, resize 36/13; seed
+  13 cold 758/627, many 16/16, resize nothing. `many` is at its floor:
+  every draw is a marked widget or the parent one deferred to. Cold layout
+  of 400 trees at depth 5 is byte-identical to `a888717` (the new
+  `tests/layout_dump.rs`), and the three long fuzzers agree.
+- **What is left is reported shares.** With hints in, the hottest widget
+  in seed 1's resize frame is a `Span` drawn 8 times, two more drawn 4 and a
+  `Branch` drawn 4: a span whose children report `leftover` has no hint, is
+  asked in the room and in its slot, and both draw because the room drawing
+  divided the room (`far` read, pinned to that length). Under the root's
+  resize redraw that is 2 per level of nesting. It is also the whole of
+  cold's draws over its distinct count.
+
+  The design that removes it, not implemented: keep two answers on the
+  record, the room answer from a measuring ask and the slot answer from the
+  placing ask, with the drawing belonging to the placing ask. A measuring
+  ask (`Painter::measure`, a new call the parent makes explicitly, so
+  "which ask is the measurement" is stated rather than inferred) reuses the
+  room answer when its holds contain the room and touches no drawing;
+  otherwise it draws in the room and records the answer as the room's. The
+  placing ask is `widget_at` as now. A local redraw of a twice-asked child
+  re-asks both questions, marks the parent if either answer moved, and puts
+  the drawing back otherwise -- which also retires `re_asked`'s deferral.
+  The cost is a second `Option<(Size, LayoutHolds)>` on `ActiveData` and a
+  measuring path through `draw_inner` that skips `try_reuse` and `relocate`.
+  This is the one-record-two-questions bookkeeping the earlier plans died
+  of, made explicit at the call site instead of recovered from the ask; it
+  is worth doing only once an app screen shows reported shares nested
+  under a resize, and that screen should be measured first.
+- **Dropping the span's `far` pin does nothing** (`wip/inset` at `5b181bc`,
+  pushed, one commit over `f6242aa`): `Part::Of` replaced by
+  `Part::Inset { lead, trail }` in window lengths, an exact `in_parent` arm
+  for a pixel inset (the range moved by the pixels, `Holds::longer_by`) and
+  a pinned own length plus a window range for one with a fraction, `Pad`
+  speaking it, and `Span` reading `extent_len` only with shares or in the
+  negative direction. Suite, oracle and clippy green; counters identical to
+  `f6242aa` at every phase of both seeds. Why: a symbolic pin survives a
+  resize because every ask box is symbolically stable across one -- the
+  viewport a scroll asks its content in is `rel 1`, a slot is a sum of
+  pixel answers, a stack's sized part is an answer -- so the pin only fails
+  where an answer changed, which is a real relayout. The worker's "44 to
+  20" at `a888717` was a deliberately unsound read, and what it saved was
+  share spans reusing the drawing that divided the room in the slot that
+  is narrower: wrong layout, not spared work. Not to be repeated; the
+  branch is evidence.
+- **The frame pin on a rule that is a fraction costs nothing** to speak of:
+  `reuse outside: a frame length` is 3 of 264 cold draws at seed 1 and 1 of
+  758 at seed 13. Dropped from the plan.
+
 ## What making the frame a length found (worker, 2026-09-19)
 
 Step 2 of the handoff, implemented over `0ef87eb` in