ai-app/docs/IRIS_TODO.md

# iris: known problems and things still to build

Iris's own list for the library, recorded 2026-09-04 in her words where it
matters, so the agents working through RUST.md pick these up in a sensible
order rather than rediscovering them. Each item says where it sits in the
order and what "done" looks like. Tick and date them in place.

## Fix

- [x] **`request_device` asked for compute-shader limits it never uses
  (2026-09-05).** `Limits::default()` (both `iris/src/android/render.rs`
  and `iris/src/default/render.rs`) requests desktop-tier compute limits
  unconditionally, even though nothing in `iris`/`iris-core` creates a
  `ComputePipeline` or writes a `@compute` shader stage — confirmed by
  grepping the whole tree, not assumed. That crashed device creation
  outright on the Android emulator's software GL path (`EMU_GPU=software`,
  `--features force-gles`): SwiftShader's GL reports itself as OpenGL ES
  3.0, which has no compute shaders, so the adapter's real limit is 0
  against the unconditional request for 65535 — the same would happen on
  any real GLES-3.0-only Android device. Fixed by a new, shared
  `iris_core::device_limits()` (`iris/core/src/render/mod.rs`) that zeros
  exactly the six `max_compute_*` fields rather than switching to a
  downlevel `Limits` preset — `downlevel_webgl2_defaults()` also zeros
  `max_storage_buffers_per_shader_stage`, which `shader.wgsl`'s vertex
  stage needs (four `var<storage>` buffers), so that preset would trade
  this crash for a bind-group-layout one on the same hardware.
  `rigs/gpu-probe`'s own hand-mirrored `Limits` (it is deliberately its
  own crate, not able to call `device_limits()` directly) was updated to
  match. See `DECISIONS.md` and RUST.md's I5 box for the account,
  including what could not be re-verified on-device this pass (the
  emulator was in concurrent use by another session).

- [x] **Input does not fall through by input type (2026-09-04).**
  `SensorUi::run_sensors` (`src/default/sense.rs`) used to set "consumed,
  stop checking lower layers" from mere hover — a widget registered for
  nothing but `click()` blocked a `Scroll` meant for whatever was behind
  it, since "the cursor is over this widget" and "this widget handled the
  event" were the same check. Fixed by judging consumption per input
  kind: with no button transition and no scroll happening this frame
  ("momentary" activity), the topmost hovered widget still wins, same as
  before; when something momentary *is* happening, only a widget whose
  registered senses actually include a matching non-hover one (checked
  via a new `TypeEventManager::registered`, which lists what a widget
  registered without running anything) consumes it, so a widget with only
  `Hovering`/click handlers can no longer block a scroll from reaching a
  list underneath. `iris/src/sense_tests.rs` builds a button-over-a-list
  `Stack` with a plain `HasEvents` impl (no GPU or window) and checks both
  directions: a scroll over the button reaches the list, and a real click
  still reaches the button — confirmed to fail on the pre-fix code and
  pass after.

- [x] **Appending one image to an already-loaded list rebuilds every other
  image's bind group (2026-09-05, fixed 2026-09-05).** Found by the
  benchmark below: `GpuTextures::update` (`core/src/render/texture.rs`)
  triggered `rebuild_image_bind_groups` — a loop over *every live
  standalone image*, rebuilding its `BindGroup` — whenever the shared
  `masks` or `move_offsets` GPU buffer was resized (`masks_resized ||
  moves_resized` in `UiRenderNode::update`, `core/src/render/mod.rs`), and
  a widget getting its *first* move-offset slot (LAYOUT.md section 2 —
  every widget gets one on first draw) could be exactly what grows that
  buffer. So one new message with one new image, appended to a transcript
  that already has N images loaded, did not cost O(1): it cost one
  `create_image` for the new image plus one `make_image_bind_group` per
  *existing* image, because the new widget's own move slot pushed the
  arena past its capacity. Measured directly in
  `iris/examples/bench_images.rs`: appending a 1,001st image to 1,000
  already-settled ones reported **1,001** bind-group creates for that one
  frame, not 1 (`./run-bench.sh images`, frame 5 in the transcript below).

  **Fix**: `masks`/`move_offsets` never belonged in a standalone image's own
  bind group (group 2) in the first place — the group also holds that
  image's own texture view, which is the only thing that is genuinely
  per-image, so a buffer shared by *everything* forced a rebuild of
  *every* group the moment it moved. Gave masks/move_offsets their own
  bind group (group 3 in `shader.wgsl` and `UiRenderNode`: `masks_layout`/
  `masks_group`), bound once per frame in `UiRenderNode::draw` rather than
  once per draw call, instead of duplicating them into every per-image
  group. `GpuTextures` and its image bind groups now know nothing about
  either buffer — `rebuild_image_bind_groups` is called only from
  `grow_array` (the atlas array texture growing, which genuinely does
  change what every image's own bind group must reference) — so a
  masks/move_offsets resize now touches exactly one bind group, ever,
  regardless of how many images are live. Numbers after the fix, same
  benchmark and command:

      ./run-bench.sh images
      frame=1 bind_group_creates=1000   (cold load, unchanged)
      frame=2 bind_group_creates=0      (was 1000 -- see the item below)
      frame=3 bind_group_creates=0
      frame=4 bind_group_creates=0
      (append one image here)
      frame=5 bind_group_creates=1      (was 1001)
      frame=6 bind_group_creates=0

  `run-headless.sh tabs --shot` still 27266 bytes, byte-for-byte unchanged,
  confirming the bind-group restructuring changed nothing about what is
  drawn.
- [x] **Bind-group creation takes two frames to reach the steady state, not
  one (2026-09-05, closed by the fix above, 2026-09-05).** Same benchmark:
  loading 1,000 images cold used to report 1,000 creates on frame 1
  (expected — `create_image`, one per new image) *and again* 1,000 on
  frame 2, before settling to 0 from frame 3. This was `rebuild_image_bind_groups`
  firing a second time for the same masks/move-offsets buffer-growth
  reason as the item above, confirming the guess recorded here — the two
  were exactly the same root cause measured two different ways. Frame 2
  now reports 0 (see the numbers above); not a separate fix.

- [ ] **A read-only text display has no widget of its own — P0's bench
  report area is a `TextEdit` standing in for one (2026-09-05).** The only
  way to get selectable text on screen today is `.editable(...)` plus
  `.attr::<Selectable>(())` (`Selectable` is only implemented for
  `TextEdit`, `iris/src/attr.rs`), which also makes the field focusable —
  tapping the bench report opens the soft keyboard over text nothing lets
  you type into. Harmless for a bench-only debug screen (not fixed this
  pass), but a real "selectable, not editable" text primitive would
  remove the keyboard side effect and is worth having before another
  screen wants the same thing (P1's own transcript rows already read
  their content from a `TextEdit` for the same reason).

## From the phone, 2026-09-06

Found on Iris's own phone while working RUST.md's P0 box's phone-report
follow-ups. Recorded here rather than fixed in that pass, so a follow-up
agent takes them without colliding with that pass's `bench_client.rs`/
`android/view.rs`/`android/sense.rs` changes.

- [x] **Swiping has no momentum, fixed 2026-09-06.** `List::fling`/
  `VelocityTracker`/`FlingCalculator` (`iris/src/widget/list.rs`,
  `iris/src/sense.rs`) -- IRIS.md's 2026-09-06 entry has the full account.
  Wired through `Selection::drag`'s release path, cancelled by the next
  touch-down, clamped at the loaded content's start/end. Verified by unit
  test (fling distance against the closed-form spline result, cancel-on-
  touch, the clamp), not yet by an on-device or emulator feel-check --
  that is still open.
- [x] **Scrolling down sometimes jitters the text, fixed 2026-09-06.**
  Root-caused by reading `DragArbiter::update`'s `Undecided`-to-`Panning`
  transition rather than by an on-device trace (no emulator was used this
  pass): it was the first named suspect, not the second. `self.last` stays
  at the press origin for every `Undecided` frame (nothing pans while the
  gesture might still be a selection), so the frame that finally crosses
  `DRAG_SLOP` returned `Pan(dy)` with `dy` measured from `press_start` --
  the *whole* pre-threshold drag, applied to the list in one step, however
  many frames it had taken to get there. Fixed by applying only the
  excess past `DRAG_SLOP` on that one frame (`dy - DRAG_SLOP.copysign
  (dy)`), the same "consume the slop, don't replay it" rule Android's own
  touch handling follows. New regression test,
  `crossing_the_slop_by_a_little_pans_by_a_little` (`iris/src/sense.rs`).
  **Not yet done**: an emulator trace of the real per-frame offset
  confirming this was the whole story on real touch input rather than
  only the arbiter's own unit tests -- worth a follow-up pass before
  calling it fully closed.
- [x] **Composing text held back until a space, caret not moving, fixed
  2026-09-06.** `InputMethodManager.updateSelection` was never called --
  see IRIS.md's 2026-09-06 entry and RUST.md's P0 box, item 1, for the
  full account and the emulator evidence.
- [x] **Swipe over the composer summons the keyboard, fixed 2026-09-06.**
  `Selector`/`Selectable` now wait for a completed tap -- see IRIS.md's
  2026-09-06 entry and RUST.md's P0 box, item 5. Verified via `dumpsys
  input_method`'s `mInputShown` on the emulator, not yet on the phone.
- [x] **Text disappears again after leaving and returning to the app,
  fixed 2026-09-06.** `GlyphAtlas::clear`/`Textures::reset` on a
  genuinely new renderer -- see IRIS.md's 2026-09-06 entry and RUST.md's
  P0 box, item 4. Verified on the emulator (home, reopen, screenshot);
  not yet on the phone.
- [ ] **Composed/typed text never becomes visible at all -- found
  2026-09-06, not fixed.** The composer bar stays empty even once the
  buffer genuinely holds the typed text (confirmed indirectly: Gboard's
  own suggestion strip reacts correctly to each keystroke). A new unit
  test proves the widget tree's own layout math resolves the field's
  region correctly across a keyboard resize, so the bug is downstream of
  that -- most likely `UiRenderState::redraw`'s single-widget redraw path,
  or specific to this emulator's forced `force-gles` backend (untested on
  Vulkan or the real phone). RUST.md's P0 box, item 2, has the full
  writeup, what was ruled out, and where to look next. **Also unverified
  because of this**: item 3's composer rebuild (one `Stack`-based widget,
  a capped/scrollable height, bottom padding tied to the IME/nav-bar
  inset) -- structurally in place and unit-tested, but its own visual
  correctness cannot be screenshotted until text actually renders.
- [ ] **The composer has no touch-drag scroll for overflowing text.** The
  2026-09-06 rebuild caps the field at ~6 lines and wraps it in
  `.scrollable()` for a wheel/trackpad scroll, but a real finger drag over
  text that has overflowed the cap does not scroll it -- `Scroll`'s touch
  handling is a follow-up, the same shape `List`'s own touch-drag pan
  needed before I3/I5.

## Build

- [x] **Benchmarks**, not unit tests, run on demand (2026-09-05; a
  `benches/` or a script under `iris/`, never in `cargo test`). The
  scenario that matters most is a **message list** — chat apps and this
  app's transcript alike — stressed with many messages and many images.
  One case in particular: **resizing an input box** (typing enough text to
  grow it) that pushes a long list of messages above it must stay very
  fast and recalculate almost nothing — a move of everything above, not a
  re-layout. That is exactly the O(1) move chain in LAYOUT.md; the
  benchmark is what proves it. Done when the numbers are in this file with
  the command, and the input-box case reports draws re-run, not just frame
  time.

  **Built as two rigs**, chosen per scenario by whether a real `wgpu`
  device is needed (`UiRenderState`/`Widgets` touch no GPU or window, so
  most of this runs as an ordinary binary — the same property
  `layout_tests.rs` relies on):

  - `iris/benches/message_list.rs` — a plain `Instant`-timed binary
    (`[[bench]] harness = false` in `iris/Cargo.toml`), not criterion: see
    the file's own header for why (short version — every scenario here
    reduces to a *count* `UiRenderState::take_counters` already produces,
    which criterion's statistical machinery adds nothing to and which a
    new dependency is not worth pulling in for). Covers (a) first-frame
    cost of a message list of N wrapped-text rows (one in 20 also carrying
    a small in-memory image) for N = 100/1,000/10,000; (b) per-frame cost
    of scrolling that list, 200 ticks; (c) the input-box case — a
    fixed-height field at the bottom of the screen growing by a line 40
    times, with the message list above it filling the rest of the screen.
    Run: `cd iris && cargo bench --bench message_list` (always release —
    `cargo bench` builds the `bench` profile, which is optimized).
  - `iris/examples/bench_images.rs` — needs a real device, so it runs
    through `iris/run-headless.sh bench_images`, printing
    `UiRenderNode::take_image_bind_group_creates()` (a new counter, added
    in `core/src/render/texture.rs` and `core/src/render/mod.rs`,
    mirroring `UiRenderState::take_counters`) each frame. Covers (d): 1,000
    image rows, checked both cold (does bind-group creation reach zero
    once loaded) and after appending one more image once settled (does
    *that* stay cheap) — the second question is what actually matters for
    a live transcript and is what turned up the two Fix items above.
  - `iris/run-bench.sh [list|images]` runs either or both and is what to
    run before/after touching `Scroll`, `Span`, `Sized`, the move-offset
    chain, or `GpuTextures`.

  **Numbers (2026-09-05, release, `cargo bench`/`run-headless.sh`, this
  VM: AMD Ryzen 7 3800X, 8 cores, rustc 1.98.0 nightly-2026-09-03):**

      cd iris && cargo bench --bench message_list
      (a) first frame, N=100:    30.30ms  draws=227   rewrites=15   moves=0
      (a) first frame, N=1000:  186.04ms  draws=2252  rewrites=150  moves=0
      (a) first frame, N=10000:1770.36ms  draws=22502 rewrites=1500 moves=0
      (b) scroll, N=100/1000/10000, 200 ticks each:
          draws=200 rewrites=0 moves=200 (identical at every N)
          per-tick average: 0.0002ms (identical at every N)
      (c) input grows 40 lines, N=100/1000/10000 rows above it:
          draws=320 rewrites=40 moves=160 (identical at every N)
          per-line average: 0.0012-0.0013ms (identical at every N)

      cd iris && ./run-bench.sh images        (2026-09-05, before the fix)
      frame=1 bind_group_creates=1000   (cold load)
      frame=2 bind_group_creates=1000   (see Fix item above)
      frame=3 bind_group_creates=0
      frame=4 bind_group_creates=0
      (append one image here)
      frame=5 bind_group_creates=1001   (see Fix item above)
      frame=6 bind_group_creates=0

      cd iris && ./run-bench.sh images        (2026-09-05, after the fix)
      frame=1 bind_group_creates=1000   (cold load, unchanged -- genuine work)
      frame=2 bind_group_creates=0
      frame=3 bind_group_creates=0
      frame=4 bind_group_creates=0
      (append one image here)
      frame=5 bind_group_creates=1      (one image's own create_image, O(1))
      frame=6 bind_group_creates=0

  **Reading it**: (a) is real, necessary work — shaping and laying out N
  never-before-seen text rows — and scales with N as it must, ~10x cost
  per 10x N. (b) and (c) are the pass conditions that matter: both are
  **exactly flat across N = 100 to 10,000**, confirming LAYOUT.md's O(1)
  move chain holds for both scrolling and for a growing input box pushing
  the message list — draws/moves per tick or per line do not grow with
  list size, and the per-operation cost (a fraction of a microsecond) is
  nowhere near a frame budget. (d)'s cold-load and steady-state halves
  behave as designed; its *append* half did not, until the fix above moved
  masks/move_offsets out of the per-image bind group — now flat at O(1)
  the same way (b) and (c) are.

- **I5's transcript screen (`iris/transcript-ui/`, 2026-09-05) — what it
  left, each recorded at the point in the code it would go rather than
  silently dropped. See RUST.md's I5 box for the full account of what
  *was* built (the screen, `SpanStyle`, cross-row selection, the growing
  composer).**
  - [x] **Android integration for this screen — done, 2026-09-05.**
    `iris-android-app`'s `transcript-screen` Cargo feature
    (`transcript_client.rs`) runs this screen against a real `ai-server`
    through `client-core`, confirmed on-device: real scrolling, real
    touch-drag panning, tap-by-name on the composer. Two real bugs found
    and fixed along the way (a missing `INTERNET` permission; a
    background-thread redraw request that crashed via a `Looper`
    requirement, fixed by routing through `View::post_delayed` — see
    `IRIS.md`'s `Tasks::redraw_handle` entry). See RUST.md's I5 box,
    "The Android integration, done 2026-09-05" for the full account.
  - [x] **A render-time number for iris, comparable to Compose's
    `transcript-bench.sh` report — instrumentation done and a real number
    obtained, 2026-09-05 (later the same day); the clean comparable loop
    is not.** `iris_core::FrameReport` (`iris/core/src/render/
    frame_report.rs`, `IRIS.md`'s new entry) times every frame from
    `render()`'s redraw start to after `queue.submit`+`present()`, exposed
    as two named on-screen controls ("Frame report", "Reset frame
    report"). Driven against a real on-device touch-drag it read
    `frames=34 janky%=61.76 p50=26.5ms p90=48.0ms p99=98.1ms
    worst=98.1ms` — real, not inferred, but accumulated across several
    gestures rather than one clean 24-swipe loop, because of the new
    finding below. See RUST.md's I5 box, "Update, 2026-09-05, later the
    same day" for the full account.
  - [ ] **New, 2026-09-05: intermittent touch delivery to iris's
    `SurfaceView` under this checkout's `EMU_GPU=software` emulator.**
    The same swipe coordinates, confirmed (by scanning a screenshot
    column for the first non-black pixel) to sit over real row text,
    sometimes produced 30+ real frames and a screenshot diff and
    sometimes produced zero of either, across otherwise-identical
    `ui-trace` invocations. Not the already-understood "already at that
    scroll edge" case (reproduced with content confirmed taller than the
    viewport, in both directions). Leading candidate, not yet confirmed:
    this checkout's emulator was independently observed at ~78% of one
    CPU core, continuously, while idle on-screen — SwiftShader's software
    rasterisation is CPU-bound by design, and a synthetic touch competing
    with that load for delivery is plausible but unmeasured *during* a
    failing gesture (the standing rule against diagnosing from
    after-the-fact measurements applies here). Needs a sampler (load,
    `dumpsys input`, a `-i 0` `ui-trace` capture) running while a failing
    gesture is driven, and ideally a comparison under `-gpu host` (real
    Vulkan) to see whether it is specific to software rendering. This is
    what blocks the clean, comparable 24-swipe loop above.
  - [x] **Long-press-then-drag-to-select — confirmed on-device, 2026-09-05
    (later the same day).** `ui-trace` gained a `holddrag X1 Y1 X2 Y2
    HOLD_MS MOVE_MS` action (`emulator-tools`, additive, extends the same
    `MotionEvent`/`injectInputEvent` mechanism `swipe` already used):
    press, hold past `LONG_PRESS`, move, release, as one continuous touch.
    Driven against a real row (`holddrag 300 1850 300 2050 600 300`) it
    produced `iris selection: begin at row ...` then a sequence of
    `iris selection: extend to row ...` log lines
    (`transcript-ui/src/selection.rs`, a new small `log` dependency since
    selection has no accessibility label of its own yet — see the next
    item), and a screenshot taken right after shows the expected
    highlighted selection spanning multiple rows. `DragArbiter`'s own
    unit tests already covered this sequence against a synthetic clock;
    this is the first time it has been driven by a real device touch.
  - [x] **Touch-drag panning over a row's own rendered text — done,
    2026-09-05.** `row.rs` used to register `CursorSense::click_or_drag()`
    on each row's `TextEdit` for cross-row selection; `TextEdit::draw`'s
    `painter.child_layer()` (`iris/src/widget/text/edit.rs:87`) meant that
    registration won `core/src/sense.rs::run_sensors`'s per-layer
    arbitration on every frame it was pressed, not just the frame the
    press started, so a list pan gesture registered on `List` itself never
    got a turn while a row was under the finger. Fixed with
    `iris::sense::DragArbiter` (recorded in `IRIS.md`), one small state
    machine per list deciding pan vs. select the way Android does (a
    vertical drag pans immediately; a stationary press held `LONG_PRESS`
    (500ms) starts a selection which further drag extends; a horizontal
    drag while something is already selected extends immediately) —
    `transcript-ui/src/selection.rs`'s `Selection::drag` is the one place
    every row's drag now routes through. 8 new unit tests
    (`iris/src/sense.rs`'s `drag_arbiter_tests`); `cargo fmt/clippy/test
    --workspace` and `cargo ndk` (both `iris` and `transcript-ui`) all
    clean; `run-headless.sh` screenshot byte-identical to before the
    change (38578 bytes). See RUST.md's I5 box, "Gap closed, 2026-09-05".
  - [x] **Intermittent touch-scroll dropout — root-caused and fixed,
    2026-09-05.** Not the coalesced-`ACTION_MOVE` hypothesis the earlier
    pass suspected (ruled out): a gesture's `ACTION_DOWN` can land on a
    row's own padding/gap or its header, which no `CursorSense` covers,
    so `DragArbiter` never gets `press_start` and sits in `Idle`
    (answers `Undecided` forever) for that whole gesture. Fixed via a new
    `DragArbiter::is_idle()` that `Selection::drag`
    (`transcript-ui/src/selection.rs`) checks to recover a missed press
    on the next `Pressing` frame. Four new unit tests. See RUST.md's I5
    box, "Touch-scroll dropout root-caused, 2026-09-05", for the trace and
    what a peer session sharing this checkout's emulator mid-pass
    prevented from being re-verified end-to-end (the aggregate
    `iris-scroll.sh` three-run confirmation and a re-taken FrameReport
    row) — a future pass should finish that once the emulator is free.
  - [ ] **Row-level accessibility names.** The composer carries
    `.label("Message")`; transcript rows do not carry a `.label()` of
    their own yet, so `Widgets::named()` (I4) does not include them —
    `row.rs`'s `build_text_row` is where one would go, keyed to something
    stable per row (its sender + a short excerpt, matching what a screen
    reader announcing a chat message would say).
  - [ ] **A tappable link and a background chip behind inline code.**
    Both need per-range glyph geometry that `TextEditCtx` does not expose
    outside `iris::widget::text` (`edit.rs`'s `layout()` helper is
    private) — see `markdown.rs`'s module doc for the exact shape the fix
    would take (the same primitive `TextEdit::draw`'s own selection
    highlight already uses internally,
    `iris/src/widget/text/edit.rs:99`).
  - [ ] **`Selection`'s anchor-row shortcut.** The row a drag started in
    is selected in full (`select_all`) the moment the drag leaves it,
    rather than "from the click point to whichever edge points away from
    the drag" — needs the same private `layout()` access as the item
    above. `selection.rs`'s module doc has the exact reasoning.
  - [ ] **No syntax highlighting inside a fenced code block.**
    `client_core::highlight` exists (built for the file explorer) and
    could feed per-token `SpanStyle`s into a code block's span; wiring it
    in was not attempted this pass.

- [ ] **Masks defined relative to each other.** Wanted: mask A multiplies
  by something *and also* applies mask B — a mask can reference a parent
  mask, the way the move chain references a parent offset. Today masks
  are independent regions. Design it beside the move chain (same shape:
  a parent index and a bounded walk in the shader); do it when a real
  widget needs it, not before.
- [ ] **Positions as a single float per scroll.** Iris raised, and half
  rejected, letting a scroll update one float rather than positions:
  input handling cares about most elements in a list, so absolute
  positions must be computed on the CPU anyway. LAYOUT.md's design
  already lands here (GPU walks the chain, CPU resolves on demand for
  hit tests). Keep the CPU resolution lazy and per query; do not
  materialise every row's absolute position per frame.
- [ ] **Animations, last.** Cosmetic, so after everything above. Must be
  **modular — a piece of the library rather than a core part forced into
  everything, the same way input is**. Whatever the mechanism, a widget
  that does not animate must pay nothing and import nothing for it.

## Build (for the port)

Widgets `RUST.md`'s "The port, in order (decided 2026-09-05)" needs and
iris does not have yet, one entry per gap, named against the P-step that
first needs it. Move an entry up to "Fix" or tick it in place once built;
do not duplicate it there.

- [ ] **A history-paging cushion measured in on-screen viewports, not a
  row count.** (**P1**.) `iris::widget::List` has no equivalent of the
  Compose app's `HISTORY_SCREENS` — AGENTS.md's "Things that have
  bitten" is explicit that a fixed row count under-fills a screen on a
  tool-heavy transcript and over-fills one on a text-heavy one, so
  whatever loads the next page has to ask the list how many viewports
  are actually on screen, not assume a constant.
- [ ] **A scaled thumbnail/image widget for an in-transcript image.**
  (**P1**.) `SessionImage.kt`'s bitmap decode-and-downscale has no iris
  counterpart; iris's own image widget (used by `bench_images.rs`) draws
  a loaded texture but does nothing about sourcing or scaling one from a
  server-produced attachment.
- [ ] **A modal/dialog primitive.** (**P1**, reused by **P3** and
  **P5**.) Needed for the session settings dialog, `UsageDialog`'s
  equivalent, and the delete-with-`deleteForeign` confirmation with its
  toggle switch. Build once, wherever it is first needed, rather than
  once per screen that wants one.
- [ ] **A horizontal gauge/bar widget.** (**P1**.) For
  `SessionUsageBar`'s equivalent — a bounded fill reflecting a fraction,
  nothing fancier.
- [ ] **A `BusyItem` equivalent: a dimmed row carrying an operation
  label that does not block its list's own scroll/drag.** (**P3**.) The
  Compose version tried an overlay first and it swallowed the drag along
  with the tap (AGENTS.md's "Shared appearance") — worth not repeating
  that attempt in iris before building the row-level version directly.
- [ ] **A toggle switch.** (**P3**.) For the delete dialog's
  `deleteForeign` control; iris has no switch/checkbox widget yet as far
  as this pass found.

## Reconsider

- [ ] **`WidgetView`.** Iris is unsure of it: what she wants is an easy way
  to compose a widget from others (a button is the main case). With
  sizing folded into `draw`, composing may be easy enough that `View` is
  redundant. Decide after the layout change lands, by writing a button
  both ways and keeping the one that is shorter to explain; delete the
  other rather than keeping two ways.

## Build (asked for by Iris, 2026-09-06): a density-independent length unit

- [x] **A third length kind beside relative and pixels, so display scales
  "just work".** Done 2026-09-06 — `Len::dp`/`len_fns::dp`, resolved
  against `UiRenderState`/`Painter::density()` at `apply_rest` time; text
  additionally rasterises at the resolved (physical) size instead of
  scaling a low-resolution bitmap afterward, which was making text blurry.
  `Span::gap`/`Padding` moved from `f32` to `Len` so they take `dp(...)`
  too; transcript-ui's row/composer padding and one example migrated.
  `em` was not added — nothing in this pass needed a text-relative unit,
  and `dp`'s own doc says why it and physical pixels are kept as separate
  fields rather than one the caller pre-multiplies. Not yet verified on
  Iris's own phone at two densities (this pass had no device) — see
  docs/RUST.md's P0 box and docs/IRIS.md's 2026-09-06 entry for what to
  check. Iris's words: "another length type similar to absolute &
  relative, so instead there would be relative, pixels, and another unit
  like em or whatever is standard. That way different display scales
  should just work." Today a length is either a fraction of the parent
  (`rest`/relative) or physical pixels, and the phone drew 16 px text at
  roughly a third of its intended size until the P0 fixes applied the
  display's scale factor globally. That global scale is a stopgap for the
  benchmark; the real shape is a unit resolved against the display's
  density at layout time — Android's `dp` / CSS's reference pixel is the
  standard (1 unit = 1/160 in), with `em` as the text-relative option —
  so a widget author writes `16.dp()` once and never sees the scale.
  Done when: `Length` (or whatever the enum is called) has the third
  variant; every place that resolves a length takes the density; the
  examples and `transcript-ui` use the new unit for text sizes, padding
  and control sizes; the emulator at two densities and the phone draw the
  same layout at the same physical size. After the bench setup is
  finished, before P1 draws any new screen.