paseo/docs/floating-panels.md

# Floating Panels

Anchored popovers — tooltips, hover cards, dropdowns, autocompletes — that visually
float above an anchor element on iOS, Android, and web. This doc captures the
non-obvious traps. It is **not** a tutorial; it assumes you have seen the
canonical files and are trying to add or change one.

## Canonical files

| File                                     | Use case                                                       |
| ---------------------------------------- | -------------------------------------------------------------- |
| `components/ui/combobox.tsx`             | Anchored picker with search; mobile falls back to bottom sheet |
| `components/ui/tooltip.tsx`              | Non-interactive hover/long-press tooltip                       |
| `components/workspace-hover-card.tsx`    | Desktop-web hover card with measure + computePosition + Portal |
| `components/ui/autocomplete-popover.tsx` | Inline slash-command autocomplete above a focused TextInput    |

Each handles a different mix of concerns: combobox owns input focus, tooltip is
non-interactive, hover-card is web-only desktop, autocomplete coexists with a
focused TextInput. There is no shared "floating panel" primitive yet — when a
fifth use case shows up we can revisit; until then prefer copying the closest
file and trimming. The four gotchas below are what each of them re-learned.

## Gotcha 1 — Android touch hit-test by parent bounds

On Android, a child View whose bounds fall outside its parent's bounds renders
correctly (with `overflow: visible`, the default) but **does not receive touch
events**. `ViewGroup.dispatchTouchEvent` filters touches by the parent's hit
rect first, then iterates children. A touch in the overflowing region never
reaches the parent, let alone the child. iOS and web do not share this rule —
iOS hit-test descends into overflowing children, web uses standard CSS pointer
events. This is the bug that put autocomplete on this path: the popover was
positioned `bottom: 100%` of its parent and worked on iOS/web for months;
Android touches sailed straight through to the chat scroll view behind it.

Two escape hatches in the codebase:

- **`Modal`** (combobox, tooltip on native) — opens a new Android window, so
  hit-testing starts fresh in that window. Side effect: a Modal opening on
  Android can detach the IME from an underlying TextInput. Fine for combobox
  (it has its own input) and tooltip (no input). **Not** fine for autocomplete
  (the composer's input must stay focused so the user keeps typing).
- **`<Portal>` from `@gorhom/portal`** (hover-card, autocomplete-popover) —
  hoists the React subtree to a fixed mount point (`PortalHost name="root"` in
  `app/_layout.tsx`) whose bounds cover the screen. Same window, same IME,
  hit-test works because the new parent is full-screen. This is the right
  default when you must keep IME attachment.

Choose Modal vs Portal by whether you need the underlying input to keep its
keyboard.

## Gotcha 2 — Portal breaks lifecycle and coordinate-system inheritance

A Portal escapes Android's hit-test, but it also escapes two things you were
quietly relying on:

- **Lifecycle.** The portal'd subtree mounts at the app root, not inside your
  component's natural ancestor chain. When the user navigates away, your
  component may stay mounted (offscreen, in a tab) — the popover stays with it.
  Gate `visible` on a screen-focus signal. For panes inside `agent-panel`, the
  `isPaneFocused` prop already exists and flips on pane switches; pass
  `visible={isYourOwnVisible && isPaneFocused}`. See
  `composer.tsx:1604` and `autocomplete-popover.tsx`.
- **Transforms.** The composer is wrapped in a Reanimated `Animated.View` with
  `translateY: -keyboardShift` (see `use-keyboard-shift-style.ts`). The chat
  content has the same transform applied (`agent-panel.tsx:939`). They move
  together because they share the SharedValue. A portal'd popover is at the
  app root — it does not get that transform unless you apply it yourself.

The fix for transforms is Gotcha 3.

## Gotcha 3 — Reanimated transforms vs `measureInWindow`

`measureInWindow` returns the view's _current_ screen position. In theory that
includes Reanimated-applied transforms (Reanimated updates native view
properties, and Android's `getLocationInWindow` reads transformed coords). In
practice it's racy — the measurement may snapshot mid-animation, and on Android
with Reanimated worklets the result is not always stable.

Do not try to track the keyboard by re-measuring on every frame. Instead,
**slave the popover's transform to the same SharedValue the composer uses**:

1. Snapshot `openShift = shift.value` at the moment you measure the anchor.
2. Apply `useAnimatedStyle(() => ({ transform: [{ translateY: openShift.value - shift.value }] }))`
   to the popover wrapper.

When `shift` equals `openShift`, the translate is 0 and the popover sits at
the measured position. When the keyboard moves afterward, the delta translates
the popover by exactly the amount the composer translates. They move in
lockstep, no re-measurement needed. See `autocomplete-popover.tsx` —
`openShift` / `shift` / `animatedTransformStyle`.

Re-measure on `Keyboard.addListener('keyboardDidShow'|'keyboardDidHide')` only
to refresh the snapshot if the keyboard was mid-transition when the popover
opened.

## Gotcha 4 — Status-bar offset for Portal-based positioning on Android

On Android, `measureInWindow` returns coords **below** the status bar (the
status bar is system-owned space). A Portal overlay positioned at `top: 0`
inside the `PortalProvider` may start at the **top of the window** (above the
status bar) depending on the wrapper chain. The result: position the popover
at the measured `rect.y` and it sits `StatusBar.currentHeight` higher than the
anchor on Android.

Mirror what tooltip does: shift the measured rect down by the status bar height
on Android only.

```ts
const statusBarOffset = Platform.OS === "android" ? (StatusBar.currentHeight ?? 0) : 0;
setAnchorRect({ ...rect, y: rect.y + statusBarOffset });
```

See `tooltip.tsx` and `autocomplete-popover.tsx`. iOS and web do not need this.

## Gotcha 5 — The two-measurement flash

If your popover needs `top` (or `left`) computed from both:

- the anchor's screen position (`anchorRect` from `measureInWindow`), **and**
- the popover's own size (`contentSize` from `onLayout`),

then a naïve implementation will flash through three positions on every open:

1. **Frame 1** — render with `top: -9999` (or any placeholder) while waiting
   for either measurement. Wrapper has no `width`, so the inner content lays
   out at its natural (often narrow) intrinsic width.
2. **Frame 2** — `anchorRect` lands. Wrapper now has `width: anchorRect.width`.
   But the stale `onLayout` from frame 1 has already set `contentSize` to the
   narrow-width dimensions. `top = anchorRect.y - wrongHeight - gap` — visible
   at the wrong spot.
3. **Frame 3** — real `onLayout` fires with the correct width. `contentSize`
   updates. Position snaps to the right place.

The visible jump in frame 2 is the flash. Two pieces solve it, and you need
both:

- **Do not mount the floating content until `anchorRect` is set.** Return
  `null` until then. This prevents the bad-width onLayout from happening at
  all.
- **Once `anchorRect` is set but `contentSize` isn't, render the wrapper with
  the final width but `opacity: 0`.** The first visible paint is at the
  correct position. This is the combobox pattern —
  `shouldHideDesktopContent` at `combobox.tsx:481, 876`. **Do not** use
  `top: -9999` as the placeholder; the layout work still happens at -9999 and
  any subsequent state-flash is visible when you flip back.

The "render invisible to measure, then reveal" pattern is the canonical
solution to chicken-and-egg positioning in this codebase. Reach for it before
anything fancier.

## Recipe for a new anchored panel

Before you write a new one, ask:

1. **Can the underlying input lose its keyboard?** If yes, use Modal (simpler).
   If no, use Portal.
2. **Does the panel need to dismiss on screen change?** Almost always yes —
   gate `visible` on an upstream focus prop (`isPaneFocused` or similar).
3. **Does the panel sit above something that moves with the keyboard?** If
   yes, slave a Reanimated transform to the same SharedValue (Gotcha 3).
   If no, you can probably skip the transform entirely.
4. **Will the panel's content height vary?** If yes, you need both
   `anchorRect` and `contentSize` for positioning → apply Gotcha 5 (return
   null until anchor, then opacity-0 until contentSize). If no — content has
   a known fixed max height — you might be able to use bottom-anchored
   positioning (`bottom: windowHeight - anchor.y + gap`) and skip the
   `contentSize` round-trip entirely. **But only if the height is genuinely
   bounded** — autocomplete's inner detail card escapes the 220-cap
   container, which is why bottom-anchored looked clean but rendered
   wrong. Verify before you commit.
5. **Are you on Android with Portal?** Add the status-bar offset (Gotcha 4).

Then copy the closest canonical file and trim.