fix(app): close the autocomplete popover while its retained panel is hidden

A workspace stays mounted with display: none while another route shows, and the popover stayed open inside it. On native its frame then failed to measure the hidden composer, stopped tracking, and kept the stale placement after the user came back. The popover now closes with its panel and reopens with a fresh measurement.

docs/floating-panels.md

@@ -7,12 +7,12 @@ 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/ui/hover-card.tsx`           | Desktop-web hover card the pointer can move onto; Portal          |
-| `components/ui/autocomplete-popover.tsx` | Slash-command autocomplete anchored to the focused composer input |
+| 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/ui/hover-card.tsx`        | Desktop-web hover card the pointer can move onto; Portal          |
+| `components/ui/autocomplete-popover/` | Slash-command autocomplete anchored to the focused composer input |
 
 Each handles a different mix of concerns: combobox owns input focus, tooltip is
 non-interactive, hover-card is web-only desktop, autocomplete keeps the composer
@@ -280,6 +280,22 @@ popover or leaves it behind the keyboard. `measureAtRest` measures through
 Fabric's transform-free `measureLayout` instead. Re-measure when `isMoving`
 settles; the composer's resting position changes as the draft grows.
 
+A measured rect is an asynchronous copy, so it lands after the anchor's new
+layout has painted. The composer resizes while the autocomplete is open: a
+wrapped line, cleared text, a window resize. On web a `ResizeObserver` reads
+the anchor's rect against the layer and commits the placement with `flushSync`,
+which runs after layout and before paint. On native a Reanimated frame callback
+reads only the anchor's height on the UI thread and holds its bottom edge at
+the rest measurement. A height carries no transform. On iOS the absolute
+position does not reliably include one: the keyboard lift runs on the native
+driver and reaches the shadow tree only when the view re-renders. The
+fixed-bottom model is wrong for the centered New workspace composer on tablets,
+which grows around its middle, and for width or x changes. The popover is off
+there by half the growth, or by the old width, until the next rest measurement.
+Keep the portal's `KeyboardTranslateView` host-sized with
+`pointerEvents="box-none"` and position the popover inside it, so the popover
+moves without leaving its parent's bounds (Gotcha 1).
+
 The provider also reconciles iOS from the controller's native `onEnd` event.
 The controller's stock iOS shared values update at move start and during an
 interactive move, but not at the terminal event, so JS contention can otherwise

packages/app/src/components/ui/autocomplete-popover.browser.test.tsx

@@ -1,10 +1,12 @@
 import React, { act, type ReactNode } from "react";
+import { flushSync } from "react-dom";
 import { createRoot, type Root } from "react-dom/client";
 import { PortalProvider } from "@gorhom/portal";
 import { View } from "react-native";
 import { KeyboardProvider } from "react-native-keyboard-controller";
 import { SafeAreaProvider } from "react-native-safe-area-context";
 import { afterEach, beforeEach, expect, it, vi } from "vitest";
+import { RetainedPanel } from "@/components/retained-panel";
 import { KeyboardShiftProvider } from "@/keyboard/shift";
 import type { AutocompleteOption } from "./autocomplete";
 import { AutocompletePopover } from "./autocomplete-popover";
@@ -14,19 +16,20 @@ import { FloatingPanelPortalHost } from "./floating-panel-portal";
 beforeEach(() => vi.stubGlobal("React", React));
 
 /**
- * The popover's height bound is a Reanimated style. Reanimated computes a style's first value
- * when its hook first runs and sends later values from an effect, after the commit that mounts
- * the view. Native paints that commit: a bound computed while the popover was closed painted the
- * popover at its minimum height, hanging down over the composer, for a frame on every open.
- * Web runs the effect before paint, so the wrong value only shows as the first style the DOM
- * receives.
+ * The popover must paint its first frame at its place. On native, Reanimated computes a style's
+ * first value when its hook first runs and sends later values after the mounting commit, which
+ * native paints: a bound computed while the popover was closed hung the popover over the composer
+ * for a frame on every open. The frame now mounts only with a measured anchor. This suite runs the
+ * web frame; the native frame was checked frame by frame on Android.
  */
 
 const SAFE_AREA = {
   frame: { x: 0, y: 0, width: 390, height: 844 },
   insets: { top: 0, left: 0, right: 0, bottom: 0 },
 };
-const COMPOSER_TOP = 600;
+// The composer rests on the dock's bottom edge and grows upward, as in the app.
+const COMPOSER_BOTTOM = 124;
+const OFFSET_FROM_ANCHOR = 12;
 const OPTIONS: AutocompleteOption[] = ["help", "hello", "history"].map((name) => ({
   id: name,
   label: `/${name}`,
@@ -44,8 +47,25 @@ afterEach(() => {
 });
 
 const SCREEN_STYLE = { width: 390, height: 844 };
-const COMPOSER_STYLE = { position: "absolute" as const, top: COMPOSER_TOP, left: 16, width: 358 };
-const INPUT_STYLE = { height: 120 };
+const styleCache = new Map<string, object>();
+function cachedStyle<T extends object>(key: string, create: () => T): T {
+  const cached = styleCache.get(key);
+  if (cached) return cached as T;
+  const style = create();
+  styleCache.set(key, style);
+  return style;
+}
+function composerStyle(width: number): object {
+  return cachedStyle(`composer:${width}`, () => ({
+    position: "absolute" as const,
+    bottom: COMPOSER_BOTTOM,
+    left: 16,
+    width,
+  }));
+}
+function inputStyle(height: number): object {
+  return cachedStyle(`input:${height}`, () => ({ height }));
+}
 function ignoreSelection(): void {}
 
 function Providers({ children }: { children: ReactNode }): ReactNode {
@@ -60,22 +80,36 @@ function Providers({ children }: { children: ReactNode }): ReactNode {
   );
 }
 
-function Screen({ visible }: { visible: boolean }): ReactNode {
+interface ScreenProps {
+  visible: boolean;
+  panelActive?: boolean;
+  inputHeight?: number;
+  composerWidth?: number;
+}
+
+function Screen({
+  visible,
+  panelActive = true,
+  inputHeight = 120,
+  composerWidth = 358,
+}: ScreenProps): ReactNode {
   return (
     <Providers>
-      <View style={SCREEN_STYLE}>
-        <View style={COMPOSER_STYLE}>
-          <AutocompletePopover
-            visible={visible}
-            options={OPTIONS}
-            selectedIndex={OPTIONS.length - 1}
-            onSelect={ignoreSelection}
-          >
-            <View style={INPUT_STYLE} />
-          </AutocompletePopover>
+      <RetainedPanel active={panelActive}>
+        <View style={SCREEN_STYLE}>
+          <View style={composerStyle(composerWidth)}>
+            <AutocompletePopover
+              visible={visible}
+              options={OPTIONS}
+              selectedIndex={OPTIONS.length - 1}
+              onSelect={ignoreSelection}
+            >
+              <View testID="composer-input" style={inputStyle(inputHeight)} />
+            </AutocompletePopover>
+          </View>
+          <FloatingPanelPortalHost />
         </View>
-        <FloatingPanelPortalHost />
-      </View>
+      </RetainedPanel>
     </Providers>
   );
 }
@@ -89,6 +123,43 @@ function render(node: ReactNode): void {
   act(() => root?.render(node));
 }
 
+/** Commits a change to the screen synchronously and lets the browser paint it. */
+async function changeAndPaint(node: ReactNode): Promise<void> {
+  flushSync(() => root?.render(node));
+  await new Promise<void>((resolve) => {
+    requestAnimationFrame(() => {
+      const channel = new MessageChannel();
+      channel.port1.addEventListener("message", () => resolve(), { once: true });
+      channel.port1.start();
+      channel.port2.postMessage(null);
+    });
+  });
+}
+
+function rectOf(testID: string): DOMRect | null {
+  return document.querySelector(`[data-testid="${testID}"]`)?.getBoundingClientRect() ?? null;
+}
+
+/** Where the popover sits against the composer, or null when it is not painted. */
+function placementAgainstComposer(): { gap: number; x: number; width: number } | null {
+  const popover = rectOf("composer-autocomplete-popover");
+  const composer = rectOf("composer-input");
+  if (!popover || !composer) return null;
+  return {
+    gap: Math.round(composer.top - popover.bottom),
+    x: Math.round(popover.x - composer.x),
+    width: Math.round(popover.width - composer.width),
+  };
+}
+
+async function openSettled(props: Omit<ScreenProps, "visible"> = {}): Promise<void> {
+  render(<Screen visible={false} {...props} />);
+  render(<Screen visible {...props} />);
+  await waitForPopover();
+  await new Promise((resolve) => setTimeout(resolve, 200));
+  expect(placementAgainstComposer()).toEqual({ gap: OFFSET_FROM_ANCHOR, x: 0, width: 0 });
+}
+
 /** Every max-height the popover's frame has held, starting with the one it mounted with. */
 function recordPopoverMaxHeights(): { values: string[]; stop: () => void } {
   const values: string[] = [];
@@ -150,3 +221,42 @@ it("opens with its height bound instead of the bound it had while closed", async
   expect(Number.parseFloat(settled)).toBeGreaterThan(0);
   expect(recording.values[0]).toBe(settled);
 });
+
+/**
+ * The popover lives in a portal and copies the composer's rect. A copy taken after the composer's
+ * layout paints the composer at its new size against the popover's old place: the popover overlapped
+ * a composer that grew a line, floated above one that shrank, and kept the old width after a resize.
+ */
+it("moves with the composer in the frame the composer grows", async () => {
+  await openSettled();
+  await changeAndPaint(<Screen visible inputHeight={160} />);
+  expect(placementAgainstComposer()).toEqual({ gap: OFFSET_FROM_ANCHOR, x: 0, width: 0 });
+});
+
+it("follows the composer down when its text clears before the popover closes", async () => {
+  // The input relayouts on the cleared text before the autocomplete hides the popover.
+  await openSettled({ inputHeight: 160 });
+  await changeAndPaint(<Screen visible inputHeight={120} />);
+  expect(placementAgainstComposer()).toEqual({ gap: OFFSET_FROM_ANCHOR, x: 0, width: 0 });
+});
+
+it("matches the composer's width in the frame the composer resizes", async () => {
+  await openSettled();
+  await changeAndPaint(<Screen visible composerWidth={240} />);
+  expect(placementAgainstComposer()).toEqual({ gap: OFFSET_FROM_ANCHOR, x: 0, width: 0 });
+});
+
+/**
+ * A retained workspace stays mounted while another route shows. A popover left open there tracked a
+ * composer it could not measure, and on native stopped following the composer after the user came
+ * back.
+ */
+it("closes while its retained panel is hidden and reopens in place when it shows again", async () => {
+  await openSettled();
+  render(<Screen visible panelActive={false} />);
+  expect(rectOf("composer-autocomplete-popover")).toBeNull();
+  render(<Screen visible />);
+  await waitForPopover();
+  await new Promise((resolve) => setTimeout(resolve, 200));
+  expect(placementAgainstComposer()).toEqual({ gap: OFFSET_FROM_ANCHOR, x: 0, width: 0 });
+});

packages/app/src/components/ui/autocomplete-popover/index.tsx

@@ -1,19 +1,13 @@
+import { useCallback, useEffect, useRef, useState, type ReactElement, type ReactNode } from "react";
 import {
-  useCallback,
-  useEffect,
-  useMemo,
-  useRef,
-  useState,
-  type ReactElement,
-  type ReactNode,
-} from "react";
-import { View, useWindowDimensions, type StyleProp, type ViewStyle } from "react-native";
+  StyleSheet,
+  View,
+  useWindowDimensions,
+  type StyleProp,
+  type ViewStyle,
+} from "react-native";
 import { Portal } from "@gorhom/portal";
-import Animated, {
-  useAnimatedReaction,
-  useAnimatedStyle,
-  type DerivedValue,
-} from "react-native-reanimated";
+import { useAnimatedReaction, useAnimatedRef } from "react-native-reanimated";
 import { scheduleOnRN } from "react-native-worklets";
 import { useSafeAreaInsets } from "react-native-safe-area-context";
 import {
@@ -25,18 +19,10 @@ import {
   measureFloatingPanelPortalHost,
   useFloatingPanelPortalHostName,
 } from "@/components/ui/floating-panel-portal";
+import { useRetainedPanelActive } from "@/components/retained-panel";
 import { KeyboardTranslateView, useKeyboardAnchor, useKeyboardShift } from "@/keyboard/shift";
-import { SPACING } from "@/styles/theme";
-import { inlineUnistylesStyle } from "@/styles/unistyles-inline-style";
-
-const OFFSET_FROM_ANCHOR = SPACING[3];
-
-interface RelativeAnchorRect {
-  x: number;
-  y: number;
-  width: number;
-  hostHeight: number;
-}
+import { PopoverFrame } from "./internal/frame";
+import type { AnchorAtRest } from "./internal/placement";
 
 interface AutocompletePopoverProps {
   visible: boolean;
@@ -59,8 +45,16 @@ export function AutocompletePopover({
 }: AutocompletePopoverProps): ReactElement | null {
   "use no memo";
   // React Compiler memoizes effect captures by reading SharedValue.value during render.
-  const anchorRef = useRef<View>(null);
-  const [relativeAnchorRect, setRelativeAnchorRect] = useState<RelativeAnchorRect | null>(null);
+  const anchorRef = useAnimatedRef<View>();
+  // The animated ref returns its native handle, which React 19 would call as a ref cleanup.
+  // The anchor stays a plain View: its style is the caller's Unistyles style.
+  const setAnchorElement = useCallback(
+    (element: View | null) => {
+      anchorRef(element);
+    },
+    [anchorRef],
+  );
+  const [anchorAtRest, setAnchorAtRest] = useState<AnchorAtRest | null>(null);
   const windowDimensions = useWindowDimensions();
   const safeAreaInsets = useSafeAreaInsets();
   const portalHostName = useFloatingPanelPortalHostName();
@@ -68,7 +62,9 @@ export function AutocompletePopover({
   const anchor = useKeyboardAnchor();
   const { measureAtRest } = anchor;
   const measurementGeneration = useRef(0);
-  const canMeasure = visible && (options.length === 0 || selectedIndex >= 0);
+  // A retained panel stays mounted while hidden; its anchor cannot be measured until it shows.
+  const isPanelActive = useRetainedPanelActive();
+  const canMeasure = isPanelActive && visible && (options.length === 0 || selectedIndex >= 0);
 
   const remeasure = useCallback(() => {
     if (!canMeasure) return;
@@ -82,10 +78,11 @@ export function AutocompletePopover({
       if (generation !== measurementGeneration.current || !anchorRect || !hostRect) {
         return undefined;
       }
-      setRelativeAnchorRect({
+      setAnchorAtRest({
         x: anchorRect.x - hostRect.x,
         y: anchorRect.y - hostRect.y,
         width: anchorRect.width,
+        height: anchorRect.height,
         hostHeight: hostRect.height,
       });
       return undefined;
@@ -95,7 +92,7 @@ export function AutocompletePopover({
   useEffect(() => {
     measurementGeneration.current += 1;
     if (!canMeasure) {
-      setRelativeAnchorRect(null);
+      setAnchorAtRest(null);
       return;
     }
 
@@ -118,27 +115,22 @@ export function AutocompletePopover({
     [isMoving, remeasure],
   );
 
-  // Lay out at the anchor's resting position; the KeyboardTranslateView below lifts
-  // it with the anchor. Height changes only at keyboard boundaries.
-  const baseStyle = useMemo(() => {
-    if (!relativeAnchorRect) return null;
-    return inlineUnistylesStyle({
-      position: "absolute" as const,
-      left: relativeAnchorRect.x,
-      width: relativeAnchorRect.width,
-      bottom: relativeAnchorRect.hostHeight - relativeAnchorRect.y + OFFSET_FROM_ANCHOR,
-    });
-  }, [relativeAnchorRect]);
-
-  // The translate view is the popover's own frame, so it lifts only the popover.
+  // The layer covers the host and rides the anchor's keyboard translation; the frame inside it
+  // places the popover. A layer that spans the host keeps the popover inside its parent's bounds,
+  // which Android hit-testing requires.
   return (
-    <View ref={anchorRef} onLayout={remeasure} style={anchorStyle} collapsable={false}>
+    <View ref={setAnchorElement} onLayout={remeasure} style={anchorStyle} collapsable={false}>
       {children}
-      {canMeasure && relativeAnchorRect && baseStyle ? (
+      {canMeasure && anchorAtRest ? (
         <Portal hostName={portalHostName}>
-          <KeyboardTranslateView {...anchor.translation} style={baseStyle}>
+          <KeyboardTranslateView
+            {...anchor.translation}
+            style={StyleSheet.absoluteFill}
+            pointerEvents="box-none"
+          >
             <PopoverFrame
-              anchorY={relativeAnchorRect.y}
+              anchorRef={anchorRef}
+              anchorAtRest={anchorAtRest}
               reservedLift={anchor.reservedLift}
               topInset={safeAreaInsets.top}
             >
@@ -155,37 +147,3 @@ export function AutocompletePopover({
     </View>
   );
 }
-
-interface PopoverFrameProps {
-  anchorY: number;
-  reservedLift: DerivedValue<number>;
-  topInset: number;
-  children: ReactNode;
-}
-
-/**
- * Bounds the popover's height to the space above the anchor. It mounts only with a measured
- * anchor: Reanimated computes the first style when the hook first runs and sends later values
- * after the mounting commit, which native paints. A bound computed before the measurement painted
- * the popover at its minimum height, hanging over the composer, for a frame on every open.
- */
-function PopoverFrame({
-  anchorY,
-  reservedLift,
-  topInset,
-  children,
-}: PopoverFrameProps): ReactElement {
-  "use no memo";
-  // React Compiler memoizes effect captures by reading SharedValue.value during render.
-  const heightStyle = useAnimatedStyle(
-    () => ({
-      maxHeight: Math.max(0, anchorY - reservedLift.value - topInset - OFFSET_FROM_ANCHOR * 2),
-    }),
-    [anchorY, reservedLift, topInset],
-  );
-  return (
-    <Animated.View testID="composer-autocomplete-popover" style={heightStyle}>
-      {children}
-    </Animated.View>
-  );
-}

packages/app/src/components/ui/autocomplete-popover/internal/frame.tsx

@@ -0,0 +1,68 @@
+import { useCallback, type ReactElement } from "react";
+import Animated, {
+  measure,
+  useAnimatedStyle,
+  useFrameCallback,
+  useSharedValue,
+} from "react-native-reanimated";
+import { placeAboveAnchor, type PopoverFrameProps } from "./placement";
+
+/**
+ * The composer grows upward from a fixed bottom edge as its text wraps. Its height is read on the
+ * UI thread every frame, so the popover moves in the frame the composer's new layout mounts; an
+ * asynchronous measurement through JS painted the composer over or away from the popover first.
+ *
+ * The frame mounts only with a measured anchor. Reanimated computes the first style when the hook
+ * first runs and sends later values after the mounting commit, which native paints: a placement
+ * computed before the measurement painted the popover over the composer for a frame on every open.
+ */
+export function PopoverFrame({
+  anchorRef,
+  anchorAtRest,
+  reservedLift,
+  topInset,
+  children,
+}: PopoverFrameProps): ReactElement {
+  "use no memo";
+  // React Compiler memoizes effect captures by reading SharedValue.value during render.
+  const anchorHeight = useSharedValue(anchorAtRest.height);
+  const anchorLost = useSharedValue(false);
+  const readAnchorHeight = useCallback(() => {
+    "worklet";
+    if (anchorLost.value) return;
+    const measured = measure(anchorRef);
+    if (!measured) {
+      // The anchor left the shadow tree, usually as the composer unmounts; the portal removes the
+      // frame a commit later. Each failed measure() logs a warning, and a busy JS thread holds
+      // that commit for many frames, so stop measuring and follow the rest measurement.
+      anchorLost.value = true;
+      return;
+    }
+    if (measured.height !== anchorHeight.value) {
+      anchorHeight.value = measured.height;
+    }
+  }, [anchorHeight, anchorLost, anchorRef]);
+  useFrameCallback(readAnchorHeight);
+
+  const style = useAnimatedStyle(() => {
+    const anchorBottom = anchorAtRest.y + anchorAtRest.height;
+    const liveHeight = anchorLost.value ? anchorAtRest.height : anchorHeight.value;
+    return {
+      position: "absolute",
+      left: anchorAtRest.x,
+      width: anchorAtRest.width,
+      ...placeAboveAnchor({
+        anchorTop: anchorBottom - liveHeight,
+        hostHeight: anchorAtRest.hostHeight,
+        reservedLift: reservedLift.value,
+        topInset,
+      }),
+    };
+  }, [anchorAtRest, anchorHeight, anchorLost, reservedLift, topInset]);
+
+  return (
+    <Animated.View testID="composer-autocomplete-popover" style={style}>
+      {children}
+    </Animated.View>
+  );
+}

packages/app/src/components/ui/autocomplete-popover/internal/frame.web.tsx

@@ -0,0 +1,68 @@
+import { useLayoutEffect, useRef, useState, type ReactElement } from "react";
+import { flushSync } from "react-dom";
+import { View } from "react-native";
+import { inlineUnistylesStyle } from "@/styles/unistyles-inline-style";
+import { placeAboveAnchor, type AnchorAtRest, type PopoverFrameProps } from "./placement";
+
+type AnchorRect = Omit<AnchorAtRest, "height">;
+
+function rectWithin(anchor: HTMLElement, host: HTMLElement): AnchorRect {
+  const anchorRect = anchor.getBoundingClientRect();
+  const hostRect = host.getBoundingClientRect();
+  return {
+    x: anchorRect.x - hostRect.x,
+    y: anchorRect.y - hostRect.y,
+    width: anchorRect.width,
+    hostHeight: hostRect.height,
+  };
+}
+
+/**
+ * The composer resizes as its text wraps and as the window resizes. ResizeObserver callbacks run
+ * after layout and before paint, so committing the new placement synchronously there paints the
+ * popover against the composer's new rect in the same frame.
+ */
+export function PopoverFrame({
+  anchorRef,
+  anchorAtRest,
+  reservedLift,
+  topInset,
+  children,
+}: PopoverFrameProps): ReactElement {
+  "use no memo";
+  // React Compiler memoizes effect captures by reading SharedValue.value during render.
+  const frameRef = useRef<View>(null);
+  const [anchor, setAnchor] = useState<AnchorRect>(anchorAtRest);
+
+  useLayoutEffect(() => {
+    const anchorElement = anchorRef.current as unknown as HTMLElement | null;
+    // The frame's parent is the portal layer, which covers the host.
+    const host = (frameRef.current as unknown as HTMLElement | null)?.parentElement;
+    if (!anchorElement || !host) return undefined;
+    setAnchor(rectWithin(anchorElement, host));
+    const observer = new ResizeObserver(() => {
+      flushSync(() => setAnchor(rectWithin(anchorElement, host)));
+    });
+    observer.observe(anchorElement);
+    observer.observe(host);
+    return () => observer.disconnect();
+  }, [anchorAtRest, anchorRef]);
+
+  const style = inlineUnistylesStyle({
+    position: "absolute" as const,
+    left: anchor.x,
+    width: anchor.width,
+    ...placeAboveAnchor({
+      anchorTop: anchor.y,
+      hostHeight: anchor.hostHeight,
+      reservedLift: reservedLift.value,
+      topInset,
+    }),
+  });
+
+  return (
+    <View ref={frameRef} testID="composer-autocomplete-popover" style={style}>
+      {children}
+    </View>
+  );
+}

packages/app/src/components/ui/autocomplete-popover/internal/placement.ts

@@ -0,0 +1,41 @@
+import type { ReactNode } from "react";
+import type { View } from "react-native";
+import type { AnimatedRef, DerivedValue } from "react-native-reanimated";
+import { SPACING } from "@/styles/theme";
+
+const OFFSET_FROM_ANCHOR = SPACING[3];
+
+/** The anchor's resting rect, relative to the portal host the popover renders in. */
+export interface AnchorAtRest {
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+  hostHeight: number;
+}
+
+export interface PopoverFrameProps {
+  anchorRef: AnimatedRef<View>;
+  /** Taken asynchronously; the frame follows the anchor's live size between measurements. */
+  anchorAtRest: AnchorAtRest;
+  reservedLift: DerivedValue<number>;
+  topInset: number;
+  children: ReactNode;
+}
+
+/** Places the popover above an anchor whose top edge is `anchorTop` within the host. */
+export function placeAboveAnchor(input: {
+  anchorTop: number;
+  hostHeight: number;
+  reservedLift: number;
+  topInset: number;
+}): { bottom: number; maxHeight: number } {
+  "worklet";
+  return {
+    bottom: input.hostHeight - input.anchorTop + OFFSET_FROM_ANCHOR,
+    maxHeight: Math.max(
+      0,
+      input.anchorTop - input.reservedLift - input.topInset - OFFSET_FROM_ANCHOR * 2,
+    ),
+  };
+}