fix(chat): warm resource lists on editor focus so fast mentions resolve

Deferring the lists to menu-open left a window where `selectActive()` saw an
empty candidate list, and its `false` return falls through to submitting the
message with the mention unresolved. Start hydrating on first focus — the
earliest reliable signal a mention may be coming — which closes the window
while keeping the lists off the page-load path.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/plus-menu-dropdown/plus-menu-dropdown.tsx

@@ -41,6 +41,14 @@ const MENTION_ONLY_RESOURCE_TYPES = new Set<MothershipResourceType>(['integratio
 
 interface PlusMenuDropdownProps {
   workspaceId: string
+  /**
+   * Starts hydrating the resource lists before the menu opens. The editor sets
+   * this on focus: `@`-mention confirmation reads the candidate list
+   * synchronously on Enter, and an empty list falls through to submitting the
+   * message with the mention unresolved. Focus is the earliest reliable signal
+   * that a mention may be coming, and still keeps these lists off page load.
+   */
+  warm?: boolean
   onResourceSelect: (resource: MothershipResource) => void
   onClose: () => void
   textareaRef: React.RefObject<HTMLTextAreaElement | null>
@@ -51,7 +59,7 @@ interface PlusMenuDropdownProps {
 
 export const PlusMenuDropdown = React.memo(
   React.forwardRef<PlusMenuHandle, PlusMenuDropdownProps>(function PlusMenuDropdown(
-    { workspaceId, onResourceSelect, onClose, textareaRef, pendingCursorRef, mentionQuery },
+    { workspaceId, warm, onResourceSelect, onClose, textareaRef, pendingCursorRef, mentionQuery },
     ref
   ) {
     const [open, setOpen] = useState(false)
@@ -62,8 +70,8 @@ export const PlusMenuDropdown = React.memo(
     const searchRef = useRef<HTMLInputElement>(null)
     const contentRef = useRef<HTMLDivElement>(null)
 
-    // Gated on `open` so an idle chat surface never fetches the workspace lists.
-    const availableResources = useAvailableResources(workspaceId, { enabled: open })
+    // Gated so an idle chat surface never fetches the workspace lists.
+    const availableResources = useAvailableResources(workspaceId, { enabled: open || !!warm })
 
     const doOpen = useCallback(
       (anchor: { left: number; top: number }, options?: { mention?: boolean }) => {

apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/prompt-editor/prompt-editor.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { useCallback, useEffect, useLayoutEffect, useMemo, useRef } from 'react'
+import { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react'
 import { cn } from '@sim/emcn'
 import { ContextMentionIcon } from '@/app/workspace/[workspaceId]/home/components/context-mention-icon'
 import {
@@ -72,6 +72,12 @@ export function PromptEditor({
 }: PromptEditorProps) {
   const { textareaRef, value } = editor
   const scrollerRef = useRef<HTMLDivElement>(null)
+  /**
+   * Latched on first focus and never cleared: it only starts the resource
+   * lists early so an `@`-mention has candidates by the time Enter is pressed.
+   * Un-warming on blur would just re-open the race on the next focus.
+   */
+  const [hasFocused, setHasFocused] = useState(false)
 
   /**
    * Autosize: grow the textarea to its full content height; the scroller caps
@@ -203,6 +209,7 @@ export function PromptEditor({
           onKeyDown={
             readOnly ? undefined : (e) => editor.handleKeyDown(e, { onSubmit, onArrowUpOnEmpty })
           }
+          onFocus={readOnly ? undefined : () => setHasFocused(true)}
           onPaste={readOnly ? undefined : editor.handlePaste}
           onCopy={editor.handleCopy}
           onCut={readOnly ? undefined : editor.handleCut}
@@ -220,6 +227,7 @@ export function PromptEditor({
           <PlusMenuDropdown
             ref={editor.plusMenuRef}
             workspaceId={editor.workspaceId}
+            warm={hasFocused}
             onResourceSelect={editor.insertResource}
             onClose={editor.handlePlusMenuClose}
             textareaRef={editor.textareaRef}