# Layout findings log What the sessions working on Iris's retained layout found, planner and worker alike, kept so that nothing here is rediscovered. Each entry says who found it and when. **Delete this file when transparent frames lands**; what 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 one-ask protocol found (planner, 2026-09-18, third session) Branch `wip/one-ask` at `3091fb8` over `4328eac`. The change is described in `docs/HANDOFF.md`; this is what building and fuzzing it turned up, in order. - **The step 3 assertion was the wrong check.** At the worker's stopping point every generated case stopped on `assert_eq!(extent, info.part)` in `place`, on a `Text` asked at 45 px in `Within(All)` whose longest word is 89.5 px: its drawing holds for `[45, 45]` and its answer box is 89.5 px wide. No leaf can promise its drawing holds for a box chosen from its answer; the plan's sentence "every drawing must hold for the answer box it supplies" was the defect, not `Text`. Removing the check *and the redraw it guarded* -- placement is re-expression, unconditionally -- made the suite green including both decided-box pins, with nothing else changed. - **Six retained tests encoded the paired draw** (`settled + 2`, "drawn once" expecting two): they now expect one draw. Two more failed because `Stack` had been changed to ask non-sizing children with `Fill(All)`; they need `Within(All)` so a smaller answer sits inside the stack, with the frame narrowed to the sizing answer. That is the whole of the suite churn. - **Seed 2 at depth 4 (`repaint-some`, `region-node`)** shrinks to a `Stack` sized by one text. A local redraw of the text asked it again in the box the stack was *asked* in and left it filling that; cold puts it in the box the stack's *answer* chose. A local redraw must put the fresh drawing back at the retained place of the parent's answer box, always, not only when the asked and placed places differ. - **Six seeds at depth 5** (60 `repaint`, 308 `every-size`, 20 `region-node`, 248, 384, 162 `reorder`) shrink to one shape: a zero `Pad` round a widget reading `extent_len` (a span with a share rect, or a `Branch`), as a share child of a span beside a fixed sibling. Seed 248 reproduced: **cold** was wrong. In the measuring pass the inner span read `far = rel 1 - 17.6px` and wrote slots in it; in the placing pass the pad got a narrowed frame of the same pixel length, was reused (its contract had no pin, because `in_parent`'s `Part::Of` arm drops a child's `extent_len`), and its child was re-expressed into a frame where `rel 1` means 17.6 px less. The inner span's own record had the pin; only the composition lost it. Composing the pin through `Of` -- exactly where the part is the whole box less pixels, `pinned - part.px`, and pinning the parent's own length otherwise -- fixed all six; the planner's earlier version of the same experiment broke seeds under the old protocol because the second draw was still there. - Cost after the fix (widget draws / distinct widgets, depth 8): seed 1 cold 331/288, many 78/78, size 3/3, scroll 1, resize 40/15; seed 13 cold 1179/982, many 335/333, resize nothing drawn. The table with the baselines is in the handoff. `many` at seed 13 touches 333 distinct widgets because a share child is asked twice per span draw, and `resize` at seed 1 draws 40 because positive-direction spans without shares pin `far`; both are step 4 there. - At `3091fb8` the 2000-seed depth-4 scan agreed over all fifteen cases (82,203 widgets, 269 s) and the 1000-seed depth-6 oracle found **seed 946, `shuffle-all-but-first`**, which shrinks to nine widgets: `Span{LEFT}[Rect, Span{RIGHT}[Rect, Span{DOWN}[Wrapped, Rect, Wrapped].height(159), Rect]]`, the column emptied to its first text. Reproduced with the records printed: the column reports a share along the row while its rect has room (both texts wrap at the whole row, 35 px each, under 159) and a fixed width once asked in its third of the row (each text 88 px, no room, rect undrawn, cross-axis answer a pixel width). So the row asked it twice and built its slots on the first answer and its cross size on the second. Emptying the column changes only the first; the local redraw re-asked the second, found it unchanged, and told nobody. Cold has the column 874 px wide. Fixed in `0ef87eb` by deferring any widget its parent asked twice in one draw to that parent, pinned as `unsettled::emptying_a_column_the_row_asked_twice_asks_the_row_again` (checked red without the deferral, green with it). Cost: `many` at depth 8 went from 78/78 to 110/92 draws/distinct at seed 1 and from 335/333 to 424/364 at seed 13; still under #18's 157/95 and 524/159 draws. At `0ef87eb` the 1000-seed depth-6 oracle (148 s) and the 2000-seed depth-4 scan (262 s) both agree over all fifteen cases. ## What the step 3 plan got wrong (planner, 2026-09-18, third session) Three things, each a different kind of mistake: 1. **It kept the question the machinery could not answer.** The offer bit existed because a widget was drawn twice, once where asked and once where its answer placed it, and something had to say which draw was the measurement. Both plans of 2026-09-18 tried to define that bit better (the worker's four rules, the planner's two experiments). The repair is to have one draw, after which the bit has nothing to name. A plan that proposes bookkeeping for a distinction should first ask whether the distinction has to exist. 2. **It stated the contract at the wrong box.** "Every drawing must hold for the answer box it supplies" reads as a tightening and is actually unsatisfiable for any widget that reads its box. The right statement is the opposite: the answer box is never a question, so nothing is demanded of the drawing there; `Holds` is about the ask box only. 3. **It narrowed frames by region.** The worker's share frames were `extent_part(axis, From(span))`, a position in the span's frame; a frame given as a position does not move when its part moves, and `re_ask` had no way to put it back. A narrowed frame must be a *length* of the parent's frame, placed into the part by alignment on every placement, exactly as a declared rule already was. The requirements did change under the plans (transparent frames, then shares narrowing frames, then `Scroll`'s content length), which explains some churn but not the three above; those were reasoning errors that a five-widget reproduction with the retained records printed would have caught in minutes. Print the records before proposing the next rule. ## The two shrinker seeds that were open on `wip/transparent-frames` (planner, 2026-09-18) -- closed by `wip/one-ask` Both were the rule in `draw_inner` that decided which answer places a widget's box: `measured = if info.offer() { fresh } else { retained }` with `offer() := place == offer_place`. That bit is meant to say "this ask is a measurement" and has no consistent value once a container's body runs in more than one box. - **Seed 2, `repaint`, depth 5** shrinks to `Stack{sized by child 0}[x: leftover] > [OneLine, Pad{0} > Span{DOWN}[Rect, OneLine], Branch]`. The stack's box is one text line tall. The span measured in the stack's room has leftover room, draws the rect and reports `leftover` across; in the stack's box it has none, undraws the rect and reports the text's width. Cold kept the first because the stack's placing evaluation reused the pad's retained answer, which looked valid only because `in_parent`'s `Part::Of` arm drops the span's `extent_len` pin. Warm re-asked the span in the box and got the second. The correct layout is the second: the stack's non-sizing children belong in the stack's box, and the measuring pass drew them in a box the stack never has. - **Seed 108, `reorder`, depth 5** shrinks to `Span{LEFT} > [Span{LEFT} > [Span{DOWN} > [Branch{probe Rect, wide Rect, narrow Wrapped, 483}, Wrapped], Rect], Rect]`. A draw trace shows the `DOWN` span evaluated at 900, 450, 600 and 300 px across in one cold layout (room of the outer span, slot inside the inner span's measuring pass, slot of the inner span, slot inside that), the wrapping text re-shaped at each. In the last one the branch's narrow text is drawn in its real 300 px box and answers 286 px; `draw_inner` discards that for the retained 438.9 px answer from the 450 px evaluation because the branch's `below` place embeds `extent_len(Y)`, which moved when the sibling text's height changed, so `place != offer_place`; the text is redrawn 438.9 px wide in a 300 px box. Warm does the same with a different stale answer (286 px from the first frame). The same shape is `unsettled::a_widget_under_a_region_node_is_asked_in_the_box_that_node_was_offered`. Two one-line experiments, both reverted, run at `49cec82` with the fast oracle, the debug suite and the shrinker at 400 seeds of depth 5: | change | seed 2 | seed 108 | else | | --- | --- | --- | --- | | compose the pin through `Part::Of` (`len.px - part_len.px` where `part_len.rel == ONE`) | fixed | fails | seed 220 `reorder` and one suite test fail | | `measured = answer.0` always, and every ask records `answer`/`offer_part` | fails | fixed | seeds 184, 246, 292, 372 and two suite tests fail, all under `Scroll` | The second experiment's failures are the case the gate was secretly holding up: a container re-drawn in a box its own answer derived. The specific one is `Scroll`, whose `apply_leftover` content length adds a whole viewport on top of the content's pixels (a row reporting `600 px + leftover` in a 900 px viewport gets a 1500 px content box), so the wrapping text inside is offered 900 px more room than it was measured in and re-wraps; the layout drifts one iteration per evaluation, and warm and cold differ by how many they ran. Bryan: that content length was always wrong; a share is the room left in the viewport, so `content = max(viewport, px + rel*viewport)`. With it the content box never re-offers room and `Scroll` needs no own-answer evaluation. The `many`/`resize` cost is the same mechanism in miniature: four evaluations of a ten-widget subtree in one cold layout, from `Within(cursor.. far)` measuring rooms followed by `Fill(slot)` placing, with the span's `extent_len` pin forcing a redraw at every box length. ## Original step 3 plan, preserved verbatim (planner, 2026-09-18) This is the original idea from ai-app-2 `280fad7`, kept here even as the handoff's stop notice changes with new evidence: > ### 3. Evaluate children in parent-decided boxes > > Change placement so an answer-derived box never runs a container body. > Placing becomes reuse-or-translate. Remove the offer/measurement gate and > its retained bookkeeping only as each caller stops needing it; do not leave > a parallel old path. > > Three current widgets must stop depending on measuring boxes they will never > own: > > - `Span`: do not read `extent_len` unconditionally. Slots depend on `far` > only when shares exist (the decided slot fills its part) or for negative > direction; compute negative-direction slots from `total`. Pin the extent > length only in those cases. > - `Stack`: draw non-sizing children in `From(0..size)` on an axis where the > sizing child's answer is `px`/`rel`, and `All` where it is `leftover`, > instead of drawing them in `All` of the measuring room. > - `Branch` in the random rig: express "the rest of my box" as > `Of(40px..FULL)` rather than reading `extent_len(Y)`. > > Every drawing must hold for the answer box it supplies. The two focused tests > from step 1 and the existing region-node and decided-box tests must pass here. The surrounding seven-step implementation plan remains in `docs/HANDOFF.md`; the quoted text above is the part whose interpretation is now blocked, so it must remain available even if the live handoff is rewritten. ## Step 3 experiment after verifying the tests (worker, 2026-09-18) The initial 17 suite failures mixed obsolete expectations with real defects. `ReadsBox`, `ReadsWidth`, and `Measured` used pixel reads to compute only their answer; failing `Counted` cases installed a box dependency without drawing anything. Those fixtures encoded the old second draw inside the answer box. Giving the painter answer-only pixel reads preserved their invalidation and geometry claims while removing the obsolete paired-draw count. Separate fixtures still exercise actual drawing dependencies with ordinary pixel reads. The experiment then reached a green 114-test suite. Its substantive findings: - answer validity and final-drawing validity must remain independent all the way through `draw_inner`; returning their old combined contract falsely pinned wrappers such as `Pad` to provisional boxes; - a repeated ask of one child replaces that child's provisional final-drawing contract rather than intersecting both drawings forever; - provisional `Span` asks fill their measuring room; `Within` immediately tries to put the child in its own answer before the span decides anything; - only an actually allocated share pins final span slots to `far`; an overfull row with a requested but unallocated share uses fixed slots; - a narrowed share frame is `Part::From(slot)` of the span's *extent*, not a zero-based span in the forwarded frame; - a local redraw re-asks the question that produced the retained answer and marks the parent to restore any distinct final placement. The release fast oracle then failed all eleven ordinary cases during cold layout. Most failures were `Text`: its provisional drawing was pinned to a pixel width that did not include the smaller box its answer selected. A generated `Stack` showed the same class through a symbolic `FULL` pin. This is stronger evidence than the original suite failures: the generated tests are not asserting draw counts or the old two-draw protocol, and no warm state exists yet. The open decision is whether the guarantee quoted above applies to every leaf and how `Text` can establish it, or whether answer-derived leaf evaluation remains legal while container evaluation does not. ## What the plan of 2026-09-18 got wrong (planner, same day) The plan claimed the retained model rests on the frame's length being the same on every ask. Answers depend on the *part* (the box offered), not the frame, for every widget that reads its box, so transparent frames fixed fraction resolution and moved the second geometry from the frame to the extent rather than removing it. Step 6 ("redraw without the deferral; both seeds must pass now because the frame no longer changes under the widget") followed from that claim and was false for the same reason. The plan also carried `offer_place` ("from the first ask of the parent's draw at the offer") forward from the old protocol without noticing it is undefinable once a container is evaluated in several boxes, and its `Inset` sketch assumed a narrowed frame and a placed extent could coexist, which `frame_and_extent` collapses ("a narrowed frame is its own extent") and which the extent-in-frame-coordinates representation cannot express in general (`(0.5*B - 20)/(B - 20)` is not `rel + px`). The plan also wrote "a frame is narrowed only by a declared length, an inset or the root" and the code's `declared_lens` filters `leftover` out; Bryan: a share was always meant to narrow the frame like the other two. The worker executed the plan as written, found exactly this ("whether a given draw is a measurement cannot be recovered from the ask"), tried four bookkeeping rules (first-ness alone, place matching the retained offer place, box matching the measured box, a retained flag on the drawing), each fixing some seeds and breaking others, restored the deferral and stopped. That was the right call. The plan as handed over is at ai-app-2 `152bed7` if the wording is ever needed. ## What the worker measured on `wip/transparent-frames` (worker, 2026-09-18) Widget draws / distinct widgets / update ms from `tests/layout_diagnostics.rs` at depth 8; draw counts are deterministic so these are single runs. `e44dea3` is #18's head, `34cafb6` the commit the branch starts from, `49cec82` its head. | seed 1 | e44dea3 | 34cafb6 | 49cec82 | 3091fb8 | 0ef87eb | | --- | --- | --- | --- | --- | --- | | cold | 369/261/10.6 | 463/274/13.3 | 516/288/12.0 | 331/288/12.3 | 331/288/12.0 | | repaint | 1 | 1 | 1 | 1 | 1 | | many | 157/95/0.33 | 263/108/0.59 | 187/119/0.52 | 78/78/0.13 | 110/92/0.23 | | size | 16/12/0.018 | 3/3 | 3/3/0.010 | 3/3/0.008 | 3/3/0.008 | | scroll | 2/0.002 | 1 | 1/0.004 | 1/0.001 | 1/0.001 | | resize | 13/13/0.019 | 22/15/0.032 | 24/76/0.090 | 40/15/0.096 | 40/15/0.096 | | seed 13 | e44dea3 | 49cec82 | 3091fb8 | 0ef87eb | | --- | --- | --- | --- | --- | | cold | 1330/707/20.3 | 2940/982/28.3 | 1179/982/24.6 | 1179/982/24.6 | | many | 524/159/1.09 | 1091/423/2.39 | 335/333/0.62 | 424/364/0.87 | | resize | nothing drawn | 2215/510/6.56 | nothing drawn | nothing drawn | The last two columns are single runs from the third session; `cold` and `resize` at seed 1 are after the `Part::Of` pin composition, which added 18 and 19 draws respectively over the version without it, and `many` at `0ef87eb` includes the deferral of twice-asked share children. Three findings, each applied on the branch: - **Lazy `Within` placement costs more than it saves.** Leaving a child's answer to be placed at the end of the parent's draw puts the drawing in the part first and in the answer's box after; where it does not hold for both that is two drawings. Seed 1's resize went from 391 widget draws to 29 with it removed. - **An inset said in frame lengths makes a container read its own box.** "Less eleven pixels at the end" needs the length, and a container whose box is its own answer then depends on its own answer: `Pad` drew sixty-four times in one resize frame at seed 13. `Part::Of` says it as a part of the box and composes without a length. - **Pin one axis at a time.** `extent_len` pinning both axes made a span dividing one hold for one length of the other. `Part::Of`'s `in_parent` arm drops a child's `extent_len` pin (only `All` composes one), which is what let seed 2's pad reuse an answer for a box its span had never been measured in. Reference renders at `49cec82` against `34cafb6`: `view` and `minimal` byte-identical; `tabs` 2,332 pixels; `text` shows `wtext(..).width(rel(1.0))` inside `.pad(16)` at the window's edges. Under the decided share rule that example is correct as written: once the share narrows the frame, `rel(1.0)` is the padded share and fits. The clipped render records the current bug. `random` moves where nested spans do. ## Defects landed before transparent frames, and their lessons (2026-09-17 review) - **A report is a fraction of the containing widget** (`ffd79f3`). A report used to come back composed through the box it was offered, and a span offers each child the room from its cursor, so a nested span taking half of what it was given took a quarter of a row whose first half was spoken for. Consequence: a span can overflow itself without bound, so its `fixed <= 0` branches are ordinary and boxes of negative length reach children; nothing yet states what a widget may assume about one. - **An answer is not an answer while anything under it is dirty** (`0e0d4af`, superseded by `a0693ac`). `dirty_size_under` was what made an answer an answer until the settling walk made the state it guarded against unreachable. Found at seed 564, depth 6, `shuffle-every-other`. - **A frame settles strictly bottom-up** (`a92c6ac`, `a0693ac`). A widget that cannot settle defers to its parent rather than drawing the parent from inside itself; `update` marks the root for a resize instead of drawing it top-down, and only where the new output falls outside what the root's answer holds for. Sound by induction on depth. Bryan: "then that entire category of issue can't even occur." - **A text is handed back a box its own line fits in** (`4bd8607`): report `ceil` of the shaped size; the two tolerances that were holding it together (`BREAK_EPSILON_PX`, a nearest-step `Holds` start) both went. - **A subtree that changes hands is recorded on both sides** (`e44dea3`): the old parent's child list is repaired and the subtree's depths re-walked where its top moved. The fuzzer never re-parents, which is why nothing generated reached it. - **A span's leftover boundary is its own inverse** (`53b00c6`): forty lines became twelve and one `div` left layout. - **`wip/stack-fraction-twice`** (a stack sized by a child reporting `rel(0.5)` applied it twice) is closed by transparent frames: `placed_extent` takes the reported length *from* the part rather than composing it into the part. No oracle could see it; the branch's test pins it. **`wip/padding-outset-and-inset`** is superseded: padding goes outside what it pads, and its `rel(0.5)`-under-inset failure was the same second application. - Four findings from the frame/extent prototype still shape the code: an answer and a drawing each retain their dependencies (`answer_under` and `under`); a wider contract does not invalidate an existing guarantee; no measurement is different from a measured zero (`ActiveData::answer` is optional); the settling walk takes the deepest mark from a `BTreeSet` keyed by depth and what ends it is the mark set. ## Failed hypotheses worth not repeating - **The placement pin was blamed for the `many` gap and is not the cause** (2026-09-17). Disabling it still redrew 487 distinct widgets a frame at seed 13 against 159; the per-widget trace showed local redraws deferring to their parents in chains to the root because a span handed its children its own placement as their frame. Transparent frames fixed that part. - **`wip/local-reask`** re-asked a dirty widget at its offer instead of deferring, under the old protocol, and diverged at seeds 532 and 398 of depth 6. Superseded; the branch can be deleted. - **An offer composed back up the move chain** fell back to `FULL` under a region node and was resolved against that node's *placed* box, so everything under a `Scroll` was re-asked at the content's width. Pinned by `unsettled::a_widget_under_a_region_node_is_asked_in_the_box_that_node_was_offered`. - **Four bookkeeping rules for "which draw is a measurement"** (worker) and **the two experiments above** (planner): each fixes some seeds and breaks others. The bit is undefinable; `wip/one-ask` removes the second draw, so there is nothing left for it to name. - **Asserting that a placed drawing holds for its answer box** (worker's step 3): unsatisfiable for `Text` and for any widget that reads its box and reports something else. The answer box is not a question. - **Choosing between a fixed and a relative child in pixels at the span's current width** admits multiple self-sizing fixed points; seed 13 settled differently warm and cold under it. The same circularity is what a cap containing `leftover` would put into `SizeRule::Max`. - **A tolerant endpoint on the span's leftover split** retained zero-height children at seed 16. Pinned by `unsettled::a_box_that_only_rounds_past_its_fixed_children_leaves_nothing_over`. - **`Scroll` returning the final placed answer** rather than the first box's advanced one fixed-point iteration (seed 86). Moot once the content box never re-offers room, but keep the test until that is measured. - **A `git bisect`** once named a commit that could not be the cause; read the tree rather than the bisect when that happens. ## Fuzzer coverage - Seeds 1121 and 1839 at depth 4 failed on every commit before `4bd8607` and nothing routine reached them: the fast oracle takes ten seeds, the shrinker 400 at depth 5, the long oracle 1000 at depth 6. The scan that found them (2000 seeds at depth 4 over all fifteen cases, 261 s) should be run after any layout change. `Rng::new` is `seed | 1`, so an even seed and the odd one above it are one tree. - The shrinker panics per thread at the first failing seed, so a run reports at most one seed per chunk of about 58; a seed listed as new after a change may have been hidden behind another in the same chunk. Check a single seed against the unpatched code before calling it new (seed 220 was checked this way and is new under the pin experiment). - Depth finds things and so does breadth; widen one axis at a time and record which. ## Smaller open items (carried from the old handoff) - An undrawn `leftover` child still contributes its gap, so a vanished child leaves a double gap. - Nested spans pass `leftover` weight up, so three leftover children in one inner span beside one in another get three quarters to one quarter. No other layout system does that; confirm it is wanted. - `Fixed::div` by zero answers `MIN`/`MAX` while `ratio` answers `ZERO`; both are caller bugs under `debug_assert`, but the fallbacks differ. - The comment on the `local == UiRegion::FULL` shortcut in `widget_at` says composing through `FULL` "is not quite the identity in f32"; on the grid it is exact and the shortcut is performance only. - `docs/LAYOUT.md` §4, §5 and the density section name `Painter::place`, `SetSize`, `desired_width`, `apply_rest`, `Len::dp`, `Aligned` and `MaxSize`, none of which exist. Do not restore `OnResize::Translate` or `OrthoSize`. - `tabs` changed twice across `d3b0ebf` with nobody looking; take the oracle as the reference and the five renders as a spot check.