💻 feat: Deeper MCP UI integration in the Chat UI (#9669)

* 💻 feat: deeper MCP UI integration in the chat UI using plugins

---------

Co-authored-by: Samuel Path <samuel.path@shopify.com>
Co-authored-by: Pierre-Luc Godin <pierreluc.godin@shopify.com>

* 💻 refactor: Migrate MCP UI resources from index-based to ID-based referencing

- Replace index-based resource markers with stable resource IDs
- Update plugin to parse \ui{resourceId} format instead of \ui0
- Refactor components to use useMessagesOperations instead of useSubmitMessage
- Add ShareMessagesProvider for UI resources in share view
- Add useConversationUIResources hook for cross-turn resource lookups
- Update parsers to generate resource IDs from content hashes
- Update all tests to use resource IDs instead of indices
- Add sandbox permissions for iframe popups
- Remove deprecated MCP tool context instructions

---------

Co-authored-by: Pierre-Luc Godin <pierreluc.godin@shopify.com>

client/src/store/misc.ts

@@ -1,4 +1,4 @@
-import { atom } from 'recoil';
+import { atom, selectorFamily } from 'recoil';
 import { TAttachment } from 'librechat-data-provider';
 import { atomWithLocalStorage } from './utils';
 import { BadgeItem } from '~/common';
@@ -10,6 +10,43 @@ const messageAttachmentsMap = atom<Record<string, TAttachment[] | undefined>>({
   default: {},
 });
 
+/**
+ * Selector to get attachments for a specific conversation.
+ */
+const conversationAttachmentsSelector = selectorFamily<
+  Record<string, TAttachment[]>,
+  string | undefined
+>({
+  key: 'conversationAttachments',
+  get:
+    (conversationId) =>
+    ({ get }) => {
+      if (!conversationId) {
+        return {};
+      }
+
+      const attachmentsMap = get(messageAttachmentsMap);
+      const result: Record<string, TAttachment[]> = {};
+
+      // Filter to only include attachments for this conversation
+      Object.entries(attachmentsMap).forEach(([messageId, attachments]) => {
+        if (!attachments) {
+          return;
+        }
+
+        const relevantAttachments = attachments.filter(
+          (attachment) => attachment.conversationId === conversationId,
+        );
+
+        if (relevantAttachments.length > 0) {
+          result[messageId] = relevantAttachments;
+        }
+      });
+
+      return result;
+    },
+});
+
 const queriesEnabled = atom<boolean>({
   key: 'queriesEnabled',
   default: true,
@@ -30,6 +67,7 @@ const chatBadges = atomWithLocalStorage<Pick<BadgeItem, 'id'>[]>('chatBadges', [
 export default {
   hideBannerHint,
   messageAttachmentsMap,
+  conversationAttachmentsSelector,
   queriesEnabled,
   isEditingBadges,
   chatBadges,