Record the renders and the counters for the frame-as-length step

Step 3 is done: against #18 the render set is byte-identical but for two
pixels of antialiasing in random and one padded block in text moving a
pixel, and a live resize of random matches a cold render at that size
exactly. The cost table is re-measured at adbedaf, where the fuzzer's own
Branch was found pinning the window and hiding what the change costs.

docs/HANDOFF.md

@@ -14,12 +14,12 @@ detached comparison checkout is `/home/bob/repos/iris-layout-baseline`. It is
 the reviewed baseline this work must preserve or improve.
 
 The continuation is `/home/bob/repos/iris-layout-experiment`, now on branch
-**`wip/one-ask`** at **`23523ee`**, four commits over `4328eac` (the head of
+**`wip/one-ask`** at **`adbedaf`**, five commits over `4328eac` (the head of
 `wip/transparent-frames`, which is unchanged). It replaces the old step 3
 plan with the one-ask protocol below, and `1512d84` and `23523ee` make the
 frame a length of the window. It passes every check:
 
-| check at `23523ee` | result |
+| check at `adbedaf` | result |
 | --- | --- |
 | `cargo fmt --all --check`, clippy `-D warnings`, with and without `layout-diagnostics` | clean |
 | `cargo test --workspace` (debug) | 122 suite, 20 core, 11 generated, all green |
@@ -35,8 +35,14 @@ over two pads relocating the column under them instead of dividing it again,
 and a resize leaving a short scroll's window-tall content where it was. Each
 is pinned as a named test.
 
-Not done: the renders and the `tabs` replay, the retained-cost work, the
+The renders and the replay are done and recorded in `docs/LAYOUT_LOG.md`:
-renames, and a pre-submit review of the three commits as one diff.
+against #18, `minimal` and `tabs` are byte-identical (before and after the
+reference gesture), `random` differs in two pixels of glyph antialiasing,
+`text` moves one padded block one pixel, and a live resize of `random`
+matches a cold render at that size byte for byte.
+
+Not done: the retained-cost work, the renames, and a pre-submit review of
+the five commits as one diff.
 
 The worker's older step 3/4 experiment is preserved as branch
 `wip/step3-experiment` (one commit over `4328eac`) and as
@@ -244,7 +250,7 @@ Unchanged; see `docs/LAYOUT.md`.
 ## Implementation plan
 
 Work in `/home/bob/repos/iris-layout-experiment` on `wip/one-ask` from
-`23523ee`. Make each step a warning-clean commit and run its named checks
+`adbedaf`. Make each step a warning-clean commit and run its named checks
 before the next. If a step exposes a different mechanism, stop and update
 this handoff rather than papering over it.
 
@@ -254,30 +260,29 @@ frame, ask, box and size warm against cold), pinned as a named test in
 `tests/cases/unsettled.rs`, then fixed under the two rules above. Do not add
 a second draw back.
 
-### 1. Review the four commits
+### 1. Review the five commits
 
-Run the pre-submit review over `3091fb8`, `0ef87eb`, `1512d84` and `23523ee`
+Run the pre-submit review over the five commits as one diff against
-as one diff against `4328eac`. `1512d84` rewrote much of what the first two did to
+`4328eac`. `1512d84` rewrote much of what the first two did to `painter.rs`
-`painter.rs` and `render_state.rs` and was reviewed as it was written, but
+and `render_state.rs` and was reviewed as it was written, but the five have
-the three have never been read as one change, and the parts of the one-ask
+never been read as one change, and the parts of the one-ask protocol it did
-protocol it did not touch -- `place_at`, the twice-asked deferral, `Span`'s
+not touch -- `place_at`, the twice-asked deferral, `Span`'s two passes --
-two passes -- were written as a probe and reviewed only by their tests.
+were written as a probe and reviewed only by their tests.
 
 ### 2. Make the frame a length and the box a region
 
-**Done at `1512d84` and `23523ee`.** The settled rule is in `docs/LAYOUT.md` under
+**Done at `1512d84` and `23523ee`.** The settled rule is in `docs/LAYOUT.md`
-"Frames, decided boxes and padding"; what implementing it corrected in the
+under "Frames, decided boxes and padding"; what implementing it corrected in
-plan -- three of them wrong layout that would have shipped -- is in
+the plan -- four of them wrong layout that would have shipped -- is in
 `docs/LAYOUT_LOG.md`.
 
 ### 3. Render and replay
 
-Read the installed graphics skill and confirm the renderer. Render `view`,
+**Done at `adbedaf`**, against `e44dea3` (#18); what each render showed is
-`minimal`, `random`, `tabs` and `text` at 1920x1200 against `34cafb6` and
+in `docs/LAYOUT_LOG.md`. `view` has no counterpart in the baseline, so it
-`e44dea3`, replay `tabs`, and compare a live resize of `random` with a cold
+was rendered but not compared. Run the set again after any further change
-render at the same size (commands under **Full verification** below). A
+here -- the commands are under **Full verification** below, and a text
-text placed by re-expression rather than a second draw is the change most
+placed by re-expression rather than by a second draw is what shows first.
-likely to show here; inspect every intentional difference and record it.
 
 ### 4. Rename and delete
 
@@ -293,26 +298,36 @@ Suite, oracle.
 
 ### 5. Restore the expected retained cost
 
-Work counters at `3091fb8`, seed 1 and 13, depth 8, widget draws / distinct
+Work counters, seed 1 and 13, depth 8, widget draws / distinct widgets,
-widgets, beside `e44dea3` (#18) and `49cec82` (the branch head before this):
+beside `e44dea3` (#18) and `0ef87eb` (before the frame became a length):
 
-| seed 1  | e44dea3 | 49cec82 | 0ef87eb |
+| seed 1  | e44dea3 | 0ef87eb | adbedaf |
 | ---     | ---     | ---     | ---     |
-| cold    | 369/261 | 516/288 | 331/288 |
+| cold    | 369/261 | 331/288 | 342/288 |
-| many    | 157/95  | 187/119 | 110/92  |
+| many    | 157/95  | 110/92  | 118/95  |
 | size    | 16/12   | 3/3     | 3/3     |
 | scroll  | 2       | 1       | 1       |
-| resize  | 13/13   | 24/76   | 40/15   |
+| resize  | 13/13   | 40/15   | 44/13   |
 
-| seed 13 | e44dea3  | 49cec82  | 0ef87eb  |
+| seed 13 | e44dea3  | 0ef87eb  | adbedaf  |
 | ---     | ---      | ---      | ---      |
-| cold    | 1330/707 | 2940/982 | 1179/982 |
+| cold    | 1330/707 | 1179/982 | 1278/982 |
-| many    | 524/159  | 1091/423 | 424/364  |
+| many    | 524/159  | 424/364  | 429/366  |
-| resize  | nothing  | 2215/510 | nothing  |
+| resize  | nothing  | nothing  | nothing  |
 
-`many` and `size` are better than #18 at seed 1 and `many` draws fewer times
+`many`, `size` and `scroll` are better than #18 and within a few draws of
-at seed 13, but it touches twice as many distinct widgets there, and `resize`
+`0ef87eb`; `cold` is 3% and 8% more than `0ef87eb` for the same distinct
-at seed 1 draws 40 times where #18 drew 13. Two mechanisms, both understood:
+widgets, which is the frame pins making a widget answer again where it used
+to be reused on a box that happened to match. `resize` at seed 1 still draws
+44 times where #18 drew 13.
+
+Measuring this is what found `adbedaf`: the fuzzer's own `Branch` pinned the
+window rather than saying which side of its threshold it was on, which put
+seed 1's resize at 131 and seed 13's at 828. A fixture that redraws
+everything on a resize cannot tell a change that reuses well from one that
+does not, so check the fixture before believing a regression.
+
+Three mechanisms behind what is left, all understood:
 
 - **A share child is asked twice per span draw** -- in the measuring room
   with the frame forwarded, then in its slot with the frame narrowed. Each
@@ -331,6 +346,11 @@ at seed 1 draws 40 times where #18 drew 13. Two mechanisms, both understood:
   so a resize redraws it. Read `extent_len` only where a slot depends on it
   (shares, or `Sign::Neg`), and express the measuring room's far end without
   the length. Measure `resize` at seed 1 before and after.
+- **A rule that is a fraction of the frame pins the frame**, which is what
+  `cold` grew by. The answer for such an axis is a pure function of the rule
+  and the frame, so a reuse could resolve it again from the record instead
+  of redrawing -- `placed_extent` already takes `declared`. Worth trying
+  before anything subtler; the pin stays for the axes that read the frame.
 
 Report every phase at both seeds, work counters first, medians only when the
 work agrees.

docs/LAYOUT_LOG.md

@@ -75,13 +75,21 @@ after the step lands.
 - **The clipping debug assert compared the reported size with the frame**
   rather than with the box it is a claim about.
 
-Two rig changes came out of it, both kept:
+Three rig changes came out of it, all kept:
 
 - The shrinker prints the *shrunk* tree's divergence rather than the grown
   tree's, and the divergence now lists, for the failing widget and every
   ancestor, warm and cold `frame`, `ask`, `box` and `size`. Reading that
   table is what found the box-arm defect; reconstructing a 20-widget plan by
   hand would not have.
+- The fuzzer's `Branch` states the range it branched on rather than pinning
+  the window it read the measurement against (`adbedaf`). It is the only
+  widget in the fixture that reads a length in pixels and chooses a subtree
+  from it, so with a pin every one of them redrew on every resize: seed 1's
+  resize was 131 widget draws and seed 13's 828, against 44 and nothing once
+  it says the range. That is a fixture that cannot tell a change that reuses
+  well from one that does not, and it looked exactly like a regression in
+  the change being measured.
 - A `size-resize` case: a size change and *then* a resize. Every other case
   changes something and compares at once or resizes first, so an answer kept
   as a fraction of the wrong length agreed at the window it was made at and
@@ -93,6 +101,26 @@ generated, the 400-seed depth-5 shrinker over all sixteen cases, the
 1000-seed depth-6 oracle, and the 2000-seed depth-4 scan over all sixteen
 cases.
 
+What the renders showed, at 1920x1200 against `e44dea3` (#18), with the
+examples identical in both checkouts and Vulkan confirmed (the example asks
+for `Backends::PRIMARY` and would have aborted on the GL fallback):
+
+- `minimal` and `tabs` are byte-identical, and so is `tabs` after the
+  reference replay -- which changes 94% of the screen, so it is a real
+  comparison and not two pictures of nothing.
+- `random` differs in two pixels, each by one grey level: glyph
+  antialiasing, nothing deleted.
+- `text` differs only in its third block, the `rel(0.5)` padded paragraph in
+  a row: the block is the same width (945 px) and wraps the same lines, and
+  sits one pixel further right. Its box is 948 px, so the drawing is centred
+  with a 1.5 px remainder and the two expressions round that half-pixel the
+  other way. The first two blocks, which have no declared width, are
+  identical -- padding coming off the frame does not move a text that wraps
+  at the box it was given.
+- A live resize of `random` to 900x1200 is byte-identical to a cold render
+  at 900x1200, which is the warm/cold rule checked in pixels rather than in
+  regions.
+
 One thing is unexplained and worth knowing about: seed 30 at depth 5
 (`shuffle-all-but-first`) failed once, with a span keeping an answer of
 `1 rel` for an axis whose frame had become `78 px`, and then stopped failing