ai-app/docs/IRIS_EXTRACTION_HANDOFF.md

Iris extraction handoff

Operational handoff for pulling Iris out of ai-app into a standalone framework. Not a decisions log; delete it when the extraction is done.

Where things stand

Canonical main is ca2b4b2 (#17, the headless rig). Sixteen slices are in; #16's size work and #17's rig both merged on 2026-09-14.

#18 split/18-position-chain is open, worktree /home/bob/repos/iris-pr18, head db1751f, five commits. LAYOUT.md §2's O(1) subtree movement, plus the Remap retirement the owner asked for on top of it.

• Every active widget owns a slot in UiRenderState::moves -- a translation in physical pixels and the slot it is relative to. A primitive instance and a mask each name one, and prelude.wgsl walks the chain and adds the accumulated delta. A mask resolves its own chain rather than the drawn primitive's, so a stationary viewport can clip content moving inside it.
• try_reuse's translation case writes one slot instead of remapping a subtree: 100 primitive region writes to 0 on a span of 20 rows five primitives deep.
• window_region walks the same chain on the CPU, so hit testing and anyone asking in window pixels agree with the shader. Moves::resolve stops at CHAIN_LIMIT as the shader does, and debug-asserts that it reached the end.
• Vec2 is repr(align(8)), WGSL's alignment for a vec2<f32>, so a GPU struct holding one is laid out the way its shader reads it without saying so itself. GlyphPrimitive no longer states its own alignment; both it and MoveOffset keep a manual unsafe impl Pod, because the trailing padding that alignment introduces is what derive(Pod) refuses. No manual padding fields -- the owner rejected one on 2026-09-14.
• Remap is gone, with UiScalar::outside, UiSpan::outside and LerpUtil::lerp_inv. A translation never needed an inversion: shifting a box shifts everything composed into it by the same amount, since lerp(s + d, e + d, t) == lerp(s, e, t) + d on both channels, whatever the box's relative extent. Only a change of length needs each part's fraction recovered, which is UiRegion::stretch behind UiRegion::stretchable. The decision is made once before the walk and neither relocation method branches, which is how the owner asked for it.

Two invariants everything here rests on. resolved = region + resolve(slot), so anything that rewrites a region owes that slot a zero -- stretch does it for the subtree it rewrites, draw_inner for the widget it draws. And a stretch is only expressible out of a box with a relative extent; a fixed length holds its parts as offsets from its start and keeps no fraction.

The plan after #18, agreed with the owner on 2026-09-14

Three changes, done together as one slice on top of #18, because each decides the shape of the others.

• Slots are opt-in, created by the container that re-places children. A draw call asks for one; a widget that did not asks nothing and composes into its nearest ancestor's slot. #18 gives every widget a slot, which puts a primitive's walk at full tree depth for no benefit, since almost every slot is zero. Span, Scroll and Aligned re-place children after drawing them and are the ones that ask. That keeps the chain 2-4 deep, which chain_cost measured as free.
• A stretch is a rewalk from the widget whose box changed, not a flat pass. #18's stretch takes the top widget's old and new window boxes and rewrites every descendant against that one pair, which works only while a composite fraction of the top box is recoverable from a window rel -- and a fixed-length box destroys that for everything beneath it, whatever is stored. Instead: keep the parent-relative region -- the argument widget_within, primitive_within and set_mask already receive -- on each widget, primitive and mask, and recompose it against the new box. For each child, compute its new window box from its local; the same length on both axes is one slot write where it has a slot and a recomposition where it does not, and a changed length asks that child's on_resize and recurses or redraws. Nothing is inverted, so stretchable, UiScalar::stretch's division and its debug assertion all go. It also fixes two things #18 gets away with only because nothing but leaves says Scale: try_reuse asks on_resize of the top widget alone, and stretch never rewrites Mask::region.
• Containers say Scale. Span on both axes: it hands every child UiSpan::FULL on the orthogonal axis, and its aligned-axis placement is written in fractions and offsets of its own box, so the children's local regions do not change when the box does. A child's length can, if one without a hint reports differently after a redraw, and that reaches the span through size_deps as it does today. The general rule: a widget is Scale on an axis unless its draw reads the pixel length of its box on that axis, which is text. The default stays Redraw.

Open, and the owner's to decide: a slot that carries a box instead of a translation. Everything under a slot would store its region relative to that box, and the shader would compose the chain with within instead of adding deltas. A move and a stretch of a Scale subtree are then both one slot write: no rewalk over primitives, no stored locals, and Translate comes free, since a glyph at an abs offset from its row's start stays there when the row grows. The CPU work on a resize becomes asking on_resize down the widgets and redrawing the ones that say so -- one ask for a transcript row against a few hundred glyph rewrites. It replaces #18's chain rather than extending it, and it contradicts LAYOUT.md §2's line that slots carry translation only. Before choosing it, run chain_cost with a region per slot in place of a Vec2: the per-level cost was measured as the dependent load rather than the arithmetic, so the extra lerps should be free, but that is an assumption until the rig says so.

What is settled either way: recalculating rather than repositioning is in, as the Remap retirement above. It costs the per-axis carry: a box that changed length on one axis and not the other is redrawn rather than remapped. Six of tabs's fourteen relocations and five of text's sixteen, all single- primitive leaves, and one extra redraw per frame on replace_cost -- 354,310,889 instructions against 354,272,387, noise. The rewalk restores that carry, and generalises it to a subtree.

Measured, so the next attempt is compared rather than argued:

rig	what it says
tests/chain_cost.rs	GPU pass time by chain depth at 200k instances: free to depth 8 (+5%), then ~3 us per level -- +42.6% at 16, +221% at 64. Each step is a storage load addressed by the previous one, so it is the chaining that costs, not the arithmetic at a level; a slot carrying a whole region should measure the same, but has not been.
tests/replace_cost.rs	Instructions per frame re-placing 200 rows: 1.98M writing each row's slot, 2.38M rewriting its regions, 7.13M redrawing it. A load for perf, not a check. Five primitives per row; the regime that decides whether the chain is worth it is a transcript row of a few hundred glyphs, so re-run it with 200 characters of text per row before concluding.
tests/draw_cost.rs	Pre-existing: what recording a frame costs on the CPU by layer count.

Irrelevant at an example's couple of hundred primitives; a transcript's glyphs are tens of thousands, which is the regime chain_cost measures.

Check for a review before starting anything, and read the newest submitted_at rather than the first result:

TOKEN=$(cat ~/.config/gitea/token)
N=18
curl -s -H "Authorization: token $TOKEN" \
  https://git.arirex.me/api/v1/repos/iris/iris/pulls/$N/reviews
curl -s -H "Authorization: token $TOKEN" \
  https://git.arirex.me/api/v1/repos/iris/iris/pulls/$N/reviews/<id>/comments
curl -s -H "Authorization: token $TOKEN" \
  https://git.arirex.me/api/v1/repos/iris/iris/issues/$N/comments

My replies are ordinary issue comments on the same PR and say what each change was for. /home/bob/repos/ai-app-2 is on rustify, worktree clean.

How the work is sequenced

Most fundamental first, from the owner on 2026-09-13: "please do more fundamental changes first, such as library updates and core framework changes, so that code only has to be written once", and "should probably start adding tests early on rather than later, so you don't have to make separate test scripts and stuff. This might involve making the harness eventually, depends on what needs tested."

So slices are ordered by how much depends on them, not by what is nearest ready, and a slice arrives with tests rather than with a script in /tmp.

Agree a design before sending another variation of it. The owner stopped the fourth round of #11 with "we should probably agree on the design here rather than you keep submitting variations that I review". When a review comes back about the shape of something rather than a defect in it, put the options and a recommendation in front of her and implement what she picks.

Nothing is submitted without a separate review pass — the installed pre-submit-review skill: build clean, review the code, review the comments on their own once the code has settled, then verify the claim by running it. The fixes a review produces are themselves unreviewed code, so the passes repeat until a round finds nothing. It has earned its place repeatedly: four defects on #11 that format, clippy, tests and five headless renders had all passed, and on #12 a regression introduced by the review's own first draft. audit.sh in the skill directory prints every comment line a branch adds against a base ref; the owner's standing complaint is verbose agent comments, and the default verdict is delete. Machine-specific notes do not belong in the repository — they live in ~/.claude/MACHINE.md or a this-machine-* skill.

Other standing instructions from the owner:

• Pull Iris out even if the Rust application switchover is not accepted. No app, session, transcript, setup or server concepts in Iris; the dependency runs one way from app/ to Iris.
• Small, coherent PRs. The original extraction PR was too large to review. A slice may be redone rather than transplanted, and need not remove every old feature. Non-conflicting pull requests may be open at once — disjoint path sets, each branched from current upstream/main rather than stacked. The owner reviews small ones as they arrive and only avoids having two large ones in flight, which is one more reason to keep a slice small.
• Order by dependency, largest reach first. On 2026-09-13: "do the large reaching framework changes first so less has to be redone." Pick the next slice by how much sits on top of it, not by what is nearest ready, so each piece of code is written once against the framework that will exist.
• Do not recreate an ai branch in canonical Iris; the fork is the boundary.
• Never rewrite a pushed branch. Follow review with additive commits, and merge upstream/main in rather than rebasing when a branch falls behind.
• Respond to each review finding with a fix or a concise explanation. Do not add a ceremonial comment when the changed code already answers it.
• A test has to guard something that could break again. The owner deleted #14's test as pointless: the rename it guarded cannot regress. When a fix is structural, the structure is the test.

The next slice

The plan above, as one slice on #18: opt-in slots, the rewalk stretch over stored locals, and Span saying Scale -- after the owner has answered whether a slot carries a box, since that decides whether the locals are stored beside window regions or are the regions. Then set_child_offset and LazySpan to finish LAYOUT.md §2, then built-in alignment.

The archive is not a patch here: it writes Widget::draw against painter.set_size, which #16 replaced with a returned Size, and it writes lengths against LayoutLen and density, which canonical does not have. Recreate on today's Len and let the dp slice follow.

Still in the target, roughly in dependency order:

• The rest of the position chain (LAYOUT.md §2), on top of the slice above: set_child_offset for a container that moves its children as a group, and LazySpan.

• Built-in alignment, and probably size, after the chain rather than before it: the owner reordered the two on 2026-09-14. Reproduced in the harness -- .width(rel(0.5)) inside a Dir::DOWN span reports 200 of 400 and is handed the whole 400, and a Pad in between does not change that. Do not "fix" that by reading the child's ortho size_hint: a Pad between the SetSize and the span has no hint of its own, so the declared width silently goes back to filling. It works only when nothing is in the way. Alignment has to belong to the widget rather than be discovered through whatever happens to sit on top of it.

  Two things beyond the bug argue for it. Built-in size removes SetSize, and with it the mismatch that made OnResize's old default unsafe -- a wrapper reporting one size while handing its child the whole box. And built-in alignment is what would let OnResize::Translate apply to centred content, which otherwise has to say Redraw because only its own draw knows where the middle was.

  Size is the harder half: a declared size beside the one draw returns is two sources of truth for one thing, so settle what each means before building it.

• OnResize::Translate, which still does nothing. ActiveData::region is both the box a widget was given and the box its primitives occupy, and mov remaps out of it; keeping a drawing at its old size while the box grows leaves the two disagreeing and the next move stretches it. Found by rendering tabs against main, not by a test. Whatever the chain does, the drawn box and the offered box have to stop being one field.

• UiRenderState behind Rc<RefCell<..>>, queued by the owner on 2026-09-13 as fundamental, and especially so for text.

• Len, LayoutLen and dp. The archive splits the type so that rest is unrepresentable where it is meaningless (a padding), and folds a density in at resolve time. 21 files mention Len, so it is wide but shallow. After the draw-size slice, not before: that one deletes the desired_* bodies this would otherwise have to be threaded through.

• The input restructure — src/default/sense.rs becomes src/rsc/sense.rs (308 lines to 2313), plus core/src/event/controller.rs, desktop/input.rs, android/input.rs and sense_tests.rs: pointer capture, drag slop and axis, platform cancellation, mask-aware hit testing, event timestamps. The archive's own consumes is what #12 landed, so that part transplants; tests/pointer_routing.rs is the acceptance criterion.

• Retained span, scrolling and layout placement.

• Retained paints, selection, overlays and shared UI runtime state.

• Generic desktop/Android framework hosts and reusable example/APK tooling.

• Application-owned fonts and application-named font families.

• Shared resource-handle bookkeeping and replaceable glyph-atlas buckets.

• Positioned text overflow and cluster-safe ellipsis.

Dependencies are current apart from winit, which stays on 0.30.12 until 0.31 leaves prerelease. parley 0.11.1 and image 0.25.10 are latest.

cd /home/bob/repos/iris && git fetch upstream
git diff --stat upstream/main..origin/archive/full-extraction

The archive is a reference, not a patch to apply. Recreate a change on top of canonical main, leave app-specific behaviour out, and verify it independently. Pick disjoint path sets when two PRs are open, and branch each from the latest upstream/main rather than stacking — unless the slice fixes code another open branch replaces, in which case say so and stack deliberately.

How the renderer works now

Current invariants, not history. Worth reading before touching core/render.

• A primitive registers itself by being drawn. The type carries its own WGSL, and PrimitiveRegistry keys ids by TypeId, so the kind comes from the type and there are no RECT/GLYPH/TEXTURE constants. Nothing is seeded, so an id depends on what a ui drew first and a ui pays only for the pipelines it uses.
• Each primitive records its own draws. Primitive::render makes a PrimitiveRender that states the layout its shader reads, uploads whatever it owns, and records its draws. GlyphRender owns the atlas and binds it once per list; ImageRender owns the images and binds one per instance; the default owns nothing and draws every instance in one call. The renderer sets the pipeline, the shared group, the list's data and its vertex buffer, and knows nothing else. Dispatch per list was measured at 6 instructions, 0.1% of a frame at 256 and at 1024 layers, against the ~5,400 wgpu spends recording one list; tests/draw_cost.rs is that measurement.
• The shared bind group is the window, the masks and the move chain, given to every draw. A mask texture would go here too. What a primitive samples is its own group, and a primitive that samples nothing has no such group in its pipeline.
• Every binding size is stated. A None minimum puts the binding on wgpu-core's late-sized list, which is_ready scans on every draw.
• shader/prelude.wgsl plus one file per primitive, because one module cannot declare two types at the same binding. The prelude carries only what every primitive uses — window, masks, vertex shader, masked() — and its header is where binding numbers are written down; what a shader samples is declared by that shader.
• A texture handle is drawn like anything else. Painter::primitive takes impl PrimitiveLike: a primitive, or something that yields one and does whatever else drawing it needs — a &TextureHandle retains its share on the way through, which a Pod primitive cannot.
• Order within a layer means nothing, and the widgets do not rely on it: Stack gives each child its own layer and TextEdit draws its view in a child layer above the selection rectangles.
• Images are one texture and one bind group each, so each drawn image is a draw call. The owner chose that on 2026-09-13 over packing images into arrays like atlas pages; a bindless binding_array was ruled out by Android support. Revisit only with her.
• Layers are never freed (TODO in primitive/layer.rs), so every layer a session creates is walked every frame thereafter. Measured at ~2ns per empty layer per frame, which is why it is the TODO's problem and not a bug of its own.

Repository topology

ai-app checkout

• /home/bob/repos/ai-app-2, origin = git@git.arirex.me:iris/ai-app.git, branch rustify.
• iris/ is a submodule pinned at 32f6ad8, the complete extracted snapshot, and .gitmodules points at the bot fork, not canonical Iris.
• Do not change either casually: ai-app needs the complete snapshot while canonical Iris is only partly caught up. Reconcile when canonical contains what ai-app needs, or when the owner accepts a temporarily non-building pin.

standalone Iris checkout

• /home/bob/repos/iris, origin = fork, upstream = canonical.
• Fork main and origin/archive/full-extraction both name 32f6ad8, the target snapshot. history/full names the source-history result a615bcd.
• Do not reset, overwrite or force-push fork main: it is both the target reference and the commit ai-app pins.
• Start each new branch from current upstream/main in its own worktree:

cd /home/bob/repos/iris && git fetch upstream
git worktree add -b split/19-name /home/bob/repos/iris-pr19 upstream/main

/home/bob/repos/iris-pr18 is the live one. Every other iris-pr* worktree holds a merged branch; they are readable references, not places to build.

Every other /home/bob/repos/iris-pr* worktree holds a merged branch. They are readable references; do not build new work on them.

Verifying a slice

iris runs its own rig now (#17), so a rendering claim no longer has to be driven from ai-app's submodule:

cd <iris-worktree>
./scripts/run-headless.sh tabs --mode 1920x1200@60Hz --shot /tmp/out.png
./scripts/run-headless.sh tabs --replay /tmp/taps.touch --shot /tmp/out.png

The reference shots this session compared against are tabs, view, minimal and text at 1920x1200, plus tabs with a replay that switches to the image tab and adds two images. A .touch line is <ms> down|move|up <x> <y> in the output's own pixels; the tab strip is at y=24 and the five tabs at x = 192, 576, 960, 1344 and 1728, with the image tab's add button near (1836, 1116).

A resize is its own case and the harness cannot see it. Start an example, change the output mode under it with swaymsg output HEADLESS-1 mode WxH@60Hz, screenshot, and compare against a cold start at that size -- they must match byte for byte. That is what caught both of #16's defects, and neither showed up in 40 tests.

cd <iris-worktree>
cargo fmt --all --check
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace

42 tests pass on #18's head. --workspace matters: rig-input is a crate of its own.

Two drawing paths still have no shot of their own, and each needs a ui the examples do not have, so both are throwaway examples written into the worktree and deleted after:

1. An image alone in a layer, which is the case that failed GPU validation when every other test happened to have a rectangle in the same layer.
2. Six lines of 400px text, which forces the atlas to four pages and proves the array grew and its group was rebuilt.

tabs with the image replay covers rects, glyphs and images together, so that one is an ordinary check now.

Cautions

• Read /home/bob/repos/ai-app-2/AGENTS.md and the machine-wide rules first. Anything about this machine — the GPU that comes and goes, measuring a small performance difference, the emulator — is in ~/.claude/MACHINE.md and the this-machine-* skills, and belongs there rather than here.
• Keep Iris generic: session drivers, transcripts, setup and server concepts, app icons and product fonts stay in ai-app. Android and desktop code is Iris work only when it is a generic host or platform integration.
• Preserve the dirty-worktree rule. All worktrees were clean at handoff; anything found later may be the owner's or another agent's.
• Do not delete the archived snapshot or the fork main ai-app pins.
• A complete target branch is not permission to recreate the giant PR.
• Another agent was freeing disk on this VM and removed target/ from the iris-pr* worktrees once. Sources and git state were untouched. Tell peers before changing shared machine tooling, and expect a cold rebuild sometimes.

Merged so far

PR	On canonical main
#2	Build on the current nightly (4275314)
#3	Request a frame after resize (936fbdd)
#4	Decouple iris-core from winit (465e430)
#5	Use vsync by default (ec2b5d4)
#6	Notify winit before presenting (db9b0f2)
#7	Keep unsafe reference helpers internal (0191f20)
#8	Initialize the window uniform from the surface (6e271e8)
#9	Preserve primitive-count recursion (b90c855)
#10	Text layout and rendering on Parley (0f6a28b)
#11	Atlas as an array texture, and the primitive rendering overhaul (b234497)
#13	Build on wgpu 30 (00d2230)
#14	Rename the Sized widget to SetSize (32b1038)
#15	Run a ui without a window, and test one (c8ac669)
#12	Route pointer input per kind (43ce8c7)
#16	Size a widget while drawing it, not in a pass of its own (f942385)
#17	Bring the headless rig into the repository (ca2b4b2)

URLs are https://git.arirex.me/iris/iris/pulls/{number}.