fix(menu): keep a click on a menu item inside its own panel

frontend/common/useContainClicks.ts

@@ -0,0 +1,29 @@
+import { RefObject, useEffect } from 'react'
+
+/**
+ * Keeps clicks inside `ref` from reaching the outside-click watchers, so a
+ * subtree portalled elsewhere still counts as part of whatever opened it.
+ *
+ * Without this, an InlineModal holding a portalled menu closes on the very item
+ * you picked, because the menu is not a DOM descendant of the modal. Native
+ * listeners rather than React's onMouseUp, because those sit below document,
+ * which is where useOutsideClick listens.
+ */
+const useContainClicks = (
+  ref: RefObject<HTMLElement | null>,
+  active = true,
+) => {
+  useEffect(() => {
+    const node = ref.current
+    if (!active || !node) return
+    const stop = (e: Event) => e.stopPropagation()
+    node.addEventListener('mouseup', stop)
+    node.addEventListener('touchend', stop)
+    return () => {
+      node.removeEventListener('mouseup', stop)
+      node.removeEventListener('touchend', stop)
+    }
+  }, [ref, active])
+}
+
+export default useContainClicks

frontend/web/components/base/DropdownMenu.tsx

@@ -2,6 +2,7 @@ import React, { useLayoutEffect, useRef, useState } from 'react'
 import Icon, { IconName } from 'components/icons/Icon'
 import classNames from 'classnames'
 import useOutsideClick from 'common/useOutsideClick'
+import useContainClicks from 'common/useContainClicks'
 import { createPortal } from 'react-dom'
 import { calculateListPosition } from 'common/utils/calculateListPosition'
 
@@ -37,6 +38,10 @@ const DropdownMenu: React.FC<DropdownMenuProps> = ({
   const dropDownRef = useRef<HTMLDivElement>(null)
   useOutsideClick(dropDownRef, () => setIsOpen(false))
 
+  // The menu is portalled to the body, so it belongs to its trigger rather
+  // than to wherever it is drawn.
+  useContainClicks(dropDownRef, isOpen)
+
   useLayoutEffect(() => {
     if (!isOpen || !dropDownRef.current || !btnRef.current) return
     const listPosition = calculateListPosition(