Extract useClickOutside hook, dedupe popover close-on-outside-click logic

RegexHelpIcon and LogPreview's ColumnPicker each reimplemented the same
mousedown-outside-ref-closes-popover effect; share it via a small hook.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TeyhRfMYjMditek6geDRoQ

webapp/src/components/LogPreview.tsx

@@ -1,5 +1,6 @@
 import { useEffect, useRef, useState } from 'react'
 import { metricPrimitiveToDisplayString, type LogEntry, type ParamDeclaration } from '../lib/api'
+import { useClickOutside } from '../lib/useClickOutside'
 import { sectionHeaderClassName, sectionHeaderLeftClassName } from './CollapsibleSection'
 import { HelpIcon } from './HelpIcon'
 
@@ -37,14 +38,7 @@ function ColumnPicker({
   const [open, setOpen] = useState(false)
   const ref = useRef<HTMLDivElement>(null)
 
-  useEffect(() => {
-    if (!open) return
-    function onClickOutside(e: MouseEvent) {
-      if (ref.current && !ref.current.contains(e.target as Node)) setOpen(false)
-    }
-    document.addEventListener('mousedown', onClickOutside)
-    return () => document.removeEventListener('mousedown', onClickOutside)
-  }, [open])
+  useClickOutside(ref, () => setOpen(false), open)
 
   return (
     <div ref={ref} className="relative">

webapp/src/components/RegexHelpIcon.tsx

@@ -1,4 +1,5 @@
-import { useEffect, useRef, useState } from 'react'
+import { useRef, useState } from 'react'
+import { useClickOutside } from '../lib/useClickOutside'
 
 // Regex syntax cheat sheet, scoped to what the Rust `regex` crate actually supports (used server-side
 // for message-match/field-match regexes and the filter bar's `regex(...)`) — no PCRE-only lookaround
@@ -30,14 +31,7 @@ export function RegexHelpIcon({ label }: { label?: string }) {
   const open = pinned || hovering
   const ref = useRef<HTMLDivElement>(null)
 
-  useEffect(() => {
-    if (!pinned) return
-    function onClickOutside(e: MouseEvent) {
-      if (ref.current && !ref.current.contains(e.target as Node)) setPinned(false)
-    }
-    document.addEventListener('mousedown', onClickOutside)
-    return () => document.removeEventListener('mousedown', onClickOutside)
-  }, [pinned])
+  useClickOutside(ref, () => setPinned(false), pinned)
 
   return (
     <div

webapp/src/lib/useClickOutside.ts

@@ -0,0 +1,14 @@
+import { useEffect, type RefObject } from 'react'
+
+// Shared by popover-style UI (RegexHelpIcon, LogPreview's ColumnPicker) that closes itself when a
+// mousedown lands outside its container ref, while `active`.
+export function useClickOutside(ref: RefObject<HTMLElement | null>, onOutside: () => void, active: boolean) {
+  useEffect(() => {
+    if (!active) return
+    function onClickOutside(e: MouseEvent) {
+      if (ref.current && !ref.current.contains(e.target as Node)) onOutside()
+    }
+    document.addEventListener('mousedown', onClickOutside)
+    return () => document.removeEventListener('mousedown', onClickOutside)
+  }, [active, ref, onOutside])
+}