diff --git a/api/server/middleware/__tests__/validateMessageReq.spec.js b/api/server/middleware/__tests__/validateMessageReq.spec.js
index 2570c9a8d8..997286dfe7 100644
--- a/api/server/middleware/__tests__/validateMessageReq.spec.js
+++ b/api/server/middleware/__tests__/validateMessageReq.spec.js
@@ -1,5 +1,5 @@
 jest.mock('~/models', () => ({
-  getConvo: jest.fn(),
+  getConvoOwnership: jest.fn(),
 }));
 
 jest.mock('@librechat/api', () => ({
@@ -18,7 +18,7 @@ jest.mock('@librechat/data-schemas', () => ({
 }));
 
 const validateMessageReq = require('../validateMessageReq');
-const { getConvo } = require('~/models');
+const { getConvoOwnership } = require('~/models');
 const { GenerationJobManager } = require('@librechat/api');
 const { logger } = require('@librechat/data-schemas');
 
@@ -52,7 +52,7 @@ describe('validateMessageReq', () => {
 
     expect(res.status).toHaveBeenCalledWith(400);
     expect(res.json).toHaveBeenCalledWith({ error: 'Conversation ID mismatch' });
-    expect(getConvo).not.toHaveBeenCalled();
+    expect(getConvoOwnership).not.toHaveBeenCalled();
     expect(next).not.toHaveBeenCalled();
   });
 
@@ -69,7 +69,7 @@ describe('validateMessageReq', () => {
 
     expect(res.status).toHaveBeenCalledWith(400);
     expect(res.json).toHaveBeenCalledWith({ error: 'Conversation ID mismatch' });
-    expect(getConvo).not.toHaveBeenCalled();
+    expect(getConvoOwnership).not.toHaveBeenCalled();
     expect(next).not.toHaveBeenCalled();
   });
 
@@ -81,11 +81,11 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue({ conversationId: 'convo-owned', user: userId });
+    getConvoOwnership.mockResolvedValue({ conversationId: 'convo-owned', user: userId });
 
     await validateMessageReq(req, res, next);
 
-    expect(getConvo).toHaveBeenCalledWith(userId, 'convo-owned');
+    expect(getConvoOwnership).toHaveBeenCalledWith(userId, 'convo-owned');
     expect(next).toHaveBeenCalledTimes(1);
   });
 
@@ -98,7 +98,7 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
     GenerationJobManager.getJob.mockResolvedValue({
       status: 'running',
       metadata: { userId, tenantId: 'tenant-a' },
@@ -120,7 +120,7 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
     GenerationJobManager.getJob.mockResolvedValue({
       status: 'running',
       metadata: { userId },
@@ -141,7 +141,7 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
     GenerationJobManager.getJob.mockResolvedValue({
       status: 'running',
       metadata: { userId: 'another-user' },
@@ -163,7 +163,7 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
     GenerationJobManager.getJob.mockResolvedValue({
       status: 'running',
       metadata: { userId, tenantId: 'tenant-b' },
@@ -185,7 +185,7 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
 
     await validateMessageReq(req, res, next);
 
@@ -205,7 +205,7 @@ describe('validateMessageReq', () => {
     const res = createResponse();
     const next = jest.fn();
     const error = new Error('job store unavailable');
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
     GenerationJobManager.getJob.mockRejectedValue(error);
 
     await validateMessageReq(req, res, next);
@@ -229,7 +229,7 @@ describe('validateMessageReq', () => {
     };
     const res = createResponse();
     const next = jest.fn();
-    getConvo.mockResolvedValue(null);
+    getConvoOwnership.mockResolvedValue(null);
 
     await validateMessageReq(req, res, next);
 
diff --git a/api/server/middleware/messageValidation.js b/api/server/middleware/messageValidation.js
index a7047dbc0c..83c4ff61a8 100644
--- a/api/server/middleware/messageValidation.js
+++ b/api/server/middleware/messageValidation.js
@@ -4,10 +4,10 @@ const {
   isPendingActionStale,
 } = require('@librechat/api');
 const { logger } = require('@librechat/data-schemas');
-const { getConvo } = require('~/models');
+const { getConvoOwnership } = require('~/models');
 
 module.exports = createMessageRequestMiddleware({
-  getConvo,
+  getConvo: getConvoOwnership,
   getJob: (conversationId) => GenerationJobManager.getJob(conversationId),
   isPendingActionStale,
   logger,
diff --git a/api/server/routes/__tests__/messages-get-real-validation.spec.js b/api/server/routes/__tests__/messages-get-real-validation.spec.js
index 7e8b24a3cc..bafb54977f 100644
--- a/api/server/routes/__tests__/messages-get-real-validation.spec.js
+++ b/api/server/routes/__tests__/messages-get-real-validation.spec.js
@@ -1,3 +1,4 @@
+const { CLIENT_MESSAGE_SELECT } = require('@librechat/data-schemas');
 const express = require('express');
 const request = require('supertest');
 
@@ -49,7 +50,7 @@ jest.mock('librechat-data-provider', () => ({
 
 jest.mock('~/models', () => ({
   saveConvo: jest.fn(),
-  getConvo: jest.fn(),
+  getConvoOwnership: jest.fn(),
   getMessage: jest.fn(),
   saveMessage: jest.fn(),
   getMessages: jest.fn(),
@@ -90,7 +91,7 @@ jest.mock('~/db/models', () => ({
 
 describe('GET /api/messages/:conversationId with real validation middleware', () => {
   let app;
-  const { getConvo, getMessages } = require('~/models');
+  const { getConvoOwnership, getMessages } = require('~/models');
   const authenticatedUserId = 'user-owner-123';
 
   beforeAll(() => {
@@ -114,7 +115,7 @@ describe('GET /api/messages/:conversationId with real validation middleware', ()
 
     expect(response.status).toBe(200);
     expect(response.body).toEqual([]);
-    expect(getConvo).not.toHaveBeenCalled();
+    expect(getConvoOwnership).not.toHaveBeenCalled();
     expect(getMessages).not.toHaveBeenCalled();
   });
 
@@ -125,7 +126,7 @@ describe('GET /api/messages/:conversationId with real validation middleware', ()
       resolveConvo = resolve;
     });
 
-    getConvo.mockImplementation(() => {
+    getConvoOwnership.mockImplementation(() => {
       events.push('convo-started');
       return convoPromise;
     });
@@ -156,10 +157,10 @@ describe('GET /api/messages/:conversationId with real validation middleware', ()
     const response = await responsePromise;
 
     expect(eventsBeforeValidation).toEqual(['convo-started', 'messages-started']);
-    expect(getConvo).toHaveBeenCalledWith(authenticatedUserId, 'convo-1');
+    expect(getConvoOwnership).toHaveBeenCalledWith(authenticatedUserId, 'convo-1');
     expect(getMessages).toHaveBeenCalledWith(
       { conversationId: 'convo-1', user: authenticatedUserId },
-      '-_id -__v -user',
+      CLIENT_MESSAGE_SELECT,
     );
     expect(response.status).toBe(200);
     expect(response.body).toEqual([{ messageId: 'message-1', conversationId: 'convo-1' }]);
diff --git a/api/server/routes/__tests__/messages-get.spec.js b/api/server/routes/__tests__/messages-get.spec.js
index fc9971bb95..bf3daea5bf 100644
--- a/api/server/routes/__tests__/messages-get.spec.js
+++ b/api/server/routes/__tests__/messages-get.spec.js
@@ -1,3 +1,4 @@
+const { CLIENT_MESSAGE_SELECT } = require('@librechat/data-schemas');
 const express = require('express');
 const request = require('supertest');
 
@@ -171,7 +172,7 @@ describe('message route conversation ownership filters', () => {
     expect(response.status).toBe(200);
     expect(getMessages).toHaveBeenCalledWith(
       { conversationId: 'convo-1', user: authenticatedUserId },
-      '-_id -__v -user',
+      CLIENT_MESSAGE_SELECT,
     );
   });
 
@@ -216,7 +217,7 @@ describe('message route conversation ownership filters', () => {
     expect(eventsBeforeValidation).toEqual(['messages-started']);
     expect(getMessages).toHaveBeenCalledWith(
       { conversationId: 'convo-1', user: authenticatedUserId },
-      '-_id -__v -user',
+      CLIENT_MESSAGE_SELECT,
     );
 
     expect(response.status).toBe(200);
@@ -242,7 +243,7 @@ describe('message route conversation ownership filters', () => {
 
     expect(getMessages).toHaveBeenCalledWith(
       { conversationId: 'convo-1', user: authenticatedUserId },
-      '-_id -__v -user',
+      CLIENT_MESSAGE_SELECT,
     );
     expect(response.status).toBe(404);
     expect(response.body).toEqual({ error: 'Conversation not found' });
@@ -256,7 +257,7 @@ describe('message route conversation ownership filters', () => {
     expect(response.status).toBe(200);
     expect(getMessages).toHaveBeenCalledWith(
       { conversationId: 'convo-1', messageId: 'message-1', user: authenticatedUserId },
-      '-_id -__v -user',
+      CLIENT_MESSAGE_SELECT,
     );
   });
 });
diff --git a/api/server/routes/messages.js b/api/server/routes/messages.js
index 0d130ca5a8..d95a755015 100644
--- a/api/server/routes/messages.js
+++ b/api/server/routes/messages.js
@@ -1,6 +1,6 @@
 const express = require('express');
 const { v4: uuidv4 } = require('uuid');
-const { logger } = require('@librechat/data-schemas');
+const { logger, CLIENT_MESSAGE_SELECT } = require('@librechat/data-schemas');
 const {
   ContentTypes,
   feedbackSchema,
@@ -289,7 +289,7 @@ router.get('/:conversationId', prepareMessageRequestValidation, async (req, res)
     // This intentionally starts a user-scoped read before validation resolves;
     // the response remains gated on validation success below.
     const messagesPromise = validation.shouldFetchMessages
-      ? db.getMessages({ conversationId, user: req.user.id }, '-_id -__v -user').then(
+      ? db.getMessages({ conversationId, user: req.user.id }, CLIENT_MESSAGE_SELECT).then(
           (messages) => ({ messages }),
           (error) => ({ error }),
         )
@@ -350,7 +350,7 @@ router.get('/:conversationId/:messageId', validateMessageReq, async (req, res) =
     const { conversationId, messageId } = req.params;
     const message = await db.getMessages(
       { conversationId, messageId, user: req.user.id },
-      '-_id -__v -user',
+      CLIENT_MESSAGE_SELECT,
     );
     if (!message) {
       return res.status(404).json({ error: 'Message not found' });
diff --git a/client/src/components/Chat/Messages/Content/ActivityPhaseGroup.tsx b/client/src/components/Chat/Messages/Content/ActivityPhaseGroup.tsx
index 431b285ce1..87ccc807d2 100644
--- a/client/src/components/Chat/Messages/Content/ActivityPhaseGroup.tsx
+++ b/client/src/components/Chat/Messages/Content/ActivityPhaseGroup.tsx
@@ -6,6 +6,7 @@ import type { TMessageContentParts } from 'librechat-data-provider';
 import type { CSSProperties, ReactNode } from 'react';
 import {
   useExpandCollapse,
+  useLazyCollapseBody,
   scheduleMessageContentLayoutReconcile,
   EXPAND_TRANSITION,
 } from '~/hooks';
@@ -54,12 +55,14 @@ export default function ActivityPhaseGroup({
   hasContent,
   showCursor = false,
   animateEntrance = false,
+  hasPendingApproval = false,
 }: {
   labelPart: ActivityPhasePart;
   children: ReactNode;
   hasContent: boolean;
   showCursor?: boolean;
   animateEntrance?: boolean;
+  hasPendingApproval?: boolean;
 }) {
   const label = getActivityLabelText(labelPart);
   const hasFailure = labelPart.status === 'failed' || labelPart.status === 'partial';
@@ -85,6 +88,14 @@ export default function ActivityPhaseGroup({
   const previousIsExpandedRef = useRef(isExpanded);
   const userOverrideRef = useRef(false);
   const { style: expandStyle, ref: expandRef } = useExpandCollapse(isExpanded);
+  /** A phase label can resolve while an approval card inside it is still
+   *  pending (see ApprovalContext), and ToolApproval owns unsent local
+   *  edit/respond/reason state — so a collapsed phase retains its body until
+   *  every nested approval resolves, exactly like ToolCallGroup. */
+  const { shouldRenderBody, mountBody, handleTransitionEnd } = useLazyCollapseBody(
+    isExpanded,
+    hasPendingApproval,
+  );
 
   useEffect(() => {
     if (!foldsIn || userOverrideRef.current) {
@@ -124,9 +135,10 @@ export default function ActivityPhaseGroup({
     userOverrideRef.current = true;
     cancelEntranceRef.current?.();
     cancelEntranceRef.current = null;
+    mountBody();
     setIsSettled(true);
     setIsExpanded((expanded) => !expanded);
-  }, []);
+  }, [mountBody]);
 
   /** Only the folding entrance drives the header off its natural height.
    *  History and reduced-motion render the plain, unstyled row. */
@@ -211,24 +223,27 @@ export default function ActivityPhaseGroup({
       <div
         id={panelId}
         style={expandStyle}
+        onTransitionEnd={handleTransitionEnd}
         aria-hidden={!isExpanded}
         data-testid="activity-phase-panel"
       >
-        <div className="overflow-hidden" ref={expandRef}>
-          {/** Padding and the divider ride the same curve as the fold: the
-           *   children occupy the exact position they held before the marker
-           *   arrived and settle into the card as it materializes, instead of
-           *   stepping sideways by the card's inset on the first frame. */}
-          <div
-            className={cn(
-              'border-t transition-[border-color,padding]',
-              FOLD_EASING,
-              isSettled ? 'border-border-light px-3 py-2' : 'border-transparent px-0 py-0',
-            )}
-          >
-            {children}
+        {shouldRenderBody && (
+          <div className="overflow-hidden" ref={expandRef}>
+            {/** Padding and the divider ride the same curve as the fold: the
+             *   children occupy the exact position they held before the marker
+             *   arrived and settle into the card as it materializes, instead of
+             *   stepping sideways by the card's inset on the first frame. */}
+            <div
+              className={cn(
+                'border-t transition-[border-color,padding]',
+                FOLD_EASING,
+                isSettled ? 'border-border-light px-3 py-2' : 'border-transparent px-0 py-0',
+              )}
+            >
+              {children}
+            </div>
           </div>
-        </div>
+        )}
       </div>
     </div>
   );
diff --git a/client/src/components/Chat/Messages/Content/ContentParts.tsx b/client/src/components/Chat/Messages/Content/ContentParts.tsx
index 3709e12f8a..0afa4ab1be 100644
--- a/client/src/components/Chat/Messages/Content/ContentParts.tsx
+++ b/client/src/components/Chat/Messages/Content/ContentParts.tsx
@@ -15,6 +15,7 @@ import MemoryArtifacts, { hasMemoryArtifacts } from './MemoryArtifacts';
 import { MessageContext, SearchContext } from '~/Providers';
 import PendingSkillCall from './Parts/PendingSkillCall';
 import ActivityPhaseGroup from './ActivityPhaseGroup';
+import { hasPendingApprovalInPart } from '~/utils';
 import EditContentParts from './EditContentParts';
 import { EmptyText, AgentUpdate } from './Parts';
 import ApprovalProvider from './ApprovalContext';
@@ -530,6 +531,9 @@ const ContentParts = memo(function ContentParts({
                 key={`activity-phase-${messageId}-${segment.labelIndex}`}
                 labelPart={segment.labelPart}
                 hasContent={segment.hasContent}
+                hasPendingApproval={segment.content.some(
+                  (part) => part != null && hasPendingApprovalInPart(part),
+                )}
                 animateEntrance={
                   previousPhaseIndices != null && !previousPhaseIndices.has(segment.labelIndex)
                 }
diff --git a/client/src/components/Chat/Messages/Content/Parts/Reasoning.tsx b/client/src/components/Chat/Messages/Content/Parts/Reasoning.tsx
index b1b96424b6..520daf441b 100644
--- a/client/src/components/Chat/Messages/Content/Parts/Reasoning.tsx
+++ b/client/src/components/Chat/Messages/Content/Parts/Reasoning.tsx
@@ -3,8 +3,8 @@ import { useAtomValue } from 'jotai';
 import { ContentTypes } from 'librechat-data-provider';
 import type { MouseEvent, FocusEvent } from 'react';
 import { ThinkingContent, ThinkingButton, FloatingThinkingBar } from './Thinking';
+import { useLocalize, useExpandCollapse, useLazyCollapseBody } from '~/hooks';
 import useSmoothStreaming from '~/hooks/Messages/useSmoothStreaming';
-import { useLocalize, useExpandCollapse } from '~/hooks';
 import { showThinkingAtom } from '~/store/showThinking';
 import { useMessageContext } from '~/Providers';
 import { cn } from '~/utils';
@@ -47,6 +47,7 @@ const Reasoning = memo((props: ReasoningProps) => {
   const [isBarVisible, setIsBarVisible] = useState(false);
   const containerRef = useRef<HTMLDivElement>(null);
   const { style: expandStyle, ref: expandRef } = useExpandCollapse(isExpanded);
+  const { shouldRenderBody, mountBody, handleTransitionEnd } = useLazyCollapseBody(isExpanded);
   const { isSubmitting, isLatestMessage, nextType } = useMessageContext();
 
   // Strip <think> tags from the reasoning content (modern format)
@@ -57,10 +58,14 @@ const Reasoning = memo((props: ReasoningProps) => {
       .trim();
   }, [reasoning]);
 
-  const handleClick = useCallback((e: MouseEvent<HTMLButtonElement>) => {
-    e.preventDefault();
-    setIsExpanded((prev) => !prev);
-  }, []);
+  const handleClick = useCallback(
+    (e: MouseEvent<HTMLButtonElement>) => {
+      e.preventDefault();
+      mountBody();
+      setIsExpanded((prev) => !prev);
+    },
+    [mountBody],
+  );
 
   const handleFocus = useCallback(() => {
     setIsBarVisible(true);
@@ -127,20 +132,25 @@ const Reasoning = memo((props: ReasoningProps) => {
           aria-hidden={!isExpanded || undefined}
           className={cn(nextType !== ContentTypes.THINK && isExpanded && 'mb-4')}
           style={expandStyle}
+          onTransitionEnd={handleTransitionEnd}
         >
           <div className="relative overflow-hidden" ref={expandRef}>
-            <ThinkingContent
-              animate={smoothStreaming && effectiveIsSubmitting && isLast && isExpanded}
-            >
-              {reasoningText}
-            </ThinkingContent>
-            <FloatingThinkingBar
-              isVisible={isBarVisible && isExpanded}
-              isExpanded={isExpanded}
-              onClick={handleClick}
-              content={reasoningText}
-              contentId={contentId}
-            />
+            {shouldRenderBody && (
+              <>
+                <ThinkingContent
+                  animate={smoothStreaming && effectiveIsSubmitting && isLast && isExpanded}
+                >
+                  {reasoningText}
+                </ThinkingContent>
+                <FloatingThinkingBar
+                  isVisible={isBarVisible && isExpanded}
+                  isExpanded={isExpanded}
+                  onClick={handleClick}
+                  content={reasoningText}
+                  contentId={contentId}
+                />
+              </>
+            )}
           </div>
         </div>
       </div>
diff --git a/client/src/components/Chat/Messages/Content/ToolCall.tsx b/client/src/components/Chat/Messages/Content/ToolCall.tsx
index 862b397846..cdd5096692 100644
--- a/client/src/components/Chat/Messages/Content/ToolCall.tsx
+++ b/client/src/components/Chat/Messages/Content/ToolCall.tsx
@@ -10,7 +10,7 @@ import {
   splitToolCallName,
 } from 'librechat-data-provider';
 import type { TAttachment, PartMetadata } from 'librechat-data-provider';
-import { useLocalize, useProgress, useExpandCollapse } from '~/hooks';
+import { useLocalize, useProgress, useExpandCollapse, useLazyCollapseBody } from '~/hooks';
 import { ToolIcon, getToolIconType, isError } from './ToolOutput';
 import { useMCPIconMap, useMCPServerNames } from '~/hooks/MCP';
 import { useToolCallIntent } from './Parts/intent';
@@ -54,6 +54,7 @@ export default function ToolCall({
   const hasOutput = (output?.length ?? 0) > 0;
   const [showInfo, setShowInfo] = useState(() => autoExpand && hasOutput);
   const { style: expandStyle, ref: expandRef } = useExpandCollapse(showInfo);
+  const { shouldRenderBody, mountBody, handleTransitionEnd } = useLazyCollapseBody(showInfo);
 
   useEffect(() => {
     if (autoExpand && hasOutput) {
@@ -194,6 +195,7 @@ export default function ToolCall({
   const showCancelled = cancelled || (errorState && !output);
 
   const handleToggleInfo = useCallback(() => {
+    mountBody();
     setShowInfo((prev) => {
       const next = !prev;
       if (next) {
@@ -201,7 +203,7 @@ export default function ToolCall({
       }
       return next;
     });
-  }, [onExpand]);
+  }, [mountBody, onExpand]);
 
   const subtitle = useMemo(() => {
     if (isMCPToolCall && mcpServerName) {
@@ -297,9 +299,13 @@ export default function ToolCall({
           error={showCancelled}
         />
       </div>
-      <div style={expandStyle} data-tool-call-output-id={toolCallId}>
+      <div
+        style={expandStyle}
+        onTransitionEnd={handleTransitionEnd}
+        data-tool-call-output-id={toolCallId}
+      >
         <div className="overflow-hidden" ref={expandRef}>
-          {hasInfo && (
+          {hasInfo && shouldRenderBody && (
             <div className="my-2 overflow-hidden rounded-lg border border-border-light bg-surface-secondary">
               <ToolCallInfo input={args ?? ''} output={output} attachments={attachments} />
             </div>
diff --git a/client/src/components/Chat/Messages/Content/ToolCallGroup.tsx b/client/src/components/Chat/Messages/Content/ToolCallGroup.tsx
index 85ea2f778e..46daffdaef 100644
--- a/client/src/components/Chat/Messages/Content/ToolCallGroup.tsx
+++ b/client/src/components/Chat/Messages/Content/ToolCallGroup.tsx
@@ -10,7 +10,13 @@ import type {
   FunctionToolCall,
 } from 'librechat-data-provider';
 import type { PartWithIndex } from './ParallelContent';
-import { cn, getToolDisplayLabel, getBatchActivityLabelPart, getActivityLabelText } from '~/utils';
+import {
+  cn,
+  getToolDisplayLabel,
+  hasPendingApprovalInPart,
+  getBatchActivityLabelPart,
+  getActivityLabelText,
+} from '~/utils';
 import { useLocalize, useExpandCollapse, scheduleMessageContentLayoutReconcile } from '~/hooks';
 import { useMCPIconMap, useMCPServerNames } from '~/hooks/MCP';
 import { isBashProgrammaticToolCall } from './routing';
@@ -25,27 +31,6 @@ interface ToolMeta {
   hasOutput: boolean;
 }
 
-type ToolCallWithNestedContent = Agents.ToolCall & {
-  subagent_content?: TMessageContentParts[];
-};
-
-function hasPendingApprovalInPart(part: TMessageContentParts): boolean {
-  if (part.type !== ContentTypes.TOOL_CALL) {
-    return false;
-  }
-  const toolCall = part[ContentTypes.TOOL_CALL] as ToolCallWithNestedContent | undefined;
-  if (!toolCall) {
-    return false;
-  }
-  if (toolCall.approval != null && (toolCall.output?.length ?? 0) === 0) {
-    return true;
-  }
-  return (
-    Array.isArray(toolCall.subagent_content) &&
-    toolCall.subagent_content.some(hasPendingApprovalInPart)
-  );
-}
-
 function getToolMeta(part: TMessageContentParts): ToolMeta | null {
   if (part.type !== ContentTypes.TOOL_CALL) {
     return null;
diff --git a/client/src/components/Chat/Messages/Content/WebSearch.tsx b/client/src/components/Chat/Messages/Content/WebSearch.tsx
index 970512da71..e6e53a82b0 100644
--- a/client/src/components/Chat/Messages/Content/WebSearch.tsx
+++ b/client/src/components/Chat/Messages/Content/WebSearch.tsx
@@ -9,8 +9,8 @@ import type {
   PartMetadata,
 } from 'librechat-data-provider';
 import { FaviconImage, getCleanDomain } from '~/components/Web/SourceHovercard';
+import { useLocalize, useExpandCollapse, useLazyCollapseBody } from '~/hooks';
 import { StackedFavicons } from '~/components/Web/Sources';
-import { useLocalize, useExpandCollapse } from '~/hooks';
 import { useToolCallIntent } from './Parts/intent';
 import { useSearchContext } from '~/Providers';
 import cn from '~/utils/cn';
@@ -208,6 +208,7 @@ export default function WebSearch({
   const sourceCount = allSources.length;
   const [showSourceList, setShowSourceList] = useState(() => autoExpand && sourceCount > 0);
   const { style: sourceExpandStyle, ref: sourceExpandRef } = useExpandCollapse(showSourceList);
+  const { shouldRenderBody, mountBody, handleTransitionEnd } = useLazyCollapseBody(showSourceList);
 
   useEffect(() => {
     if (autoExpand && sourceCount > 0) {
@@ -216,6 +217,7 @@ export default function WebSearch({
   }, [autoExpand, sourceCount]);
 
   const handleToggleSources = () => {
+    mountBody();
     setShowSourceList((prev) => {
       const next = !prev;
       if (next) {
@@ -272,31 +274,33 @@ export default function WebSearch({
           )}
         </button>
         {hasSourceData && (
-          <div style={sourceExpandStyle}>
+          <div style={sourceExpandStyle} onTransitionEnd={handleTransitionEnd}>
             <div className="overflow-hidden" ref={sourceExpandRef}>
-              <div className="my-2 max-h-[280px] overflow-y-auto rounded-lg border border-border-light">
-                {allSources.map((source, i) => {
-                  const domain = getCleanDomain(source.link);
-                  return (
-                    <a
-                      key={source.link}
-                      href={source.link}
-                      target="_blank"
-                      rel="noopener noreferrer"
-                      className={cn(
-                        'flex items-center gap-2.5 px-3 py-2 transition-colors hover:bg-surface-hover',
-                        i > 0 && 'border-t border-border-light',
-                      )}
-                    >
-                      <FaviconImage domain={domain} className="size-4 shrink-0 rounded-sm" />
-                      <span className="min-w-0 flex-1 truncate text-xs font-medium text-text-primary">
-                        {source.title || domain}
-                      </span>
-                      <span className="shrink-0 text-[11px] text-text-secondary">{domain}</span>
-                    </a>
-                  );
-                })}
-              </div>
+              {shouldRenderBody && (
+                <div className="my-2 max-h-[280px] overflow-y-auto rounded-lg border border-border-light">
+                  {allSources.map((source, i) => {
+                    const domain = getCleanDomain(source.link);
+                    return (
+                      <a
+                        key={source.link}
+                        href={source.link}
+                        target="_blank"
+                        rel="noopener noreferrer"
+                        className={cn(
+                          'flex items-center gap-2.5 px-3 py-2 transition-colors hover:bg-surface-hover',
+                          i > 0 && 'border-t border-border-light',
+                        )}
+                      >
+                        <FaviconImage domain={domain} className="size-4 shrink-0 rounded-sm" />
+                        <span className="min-w-0 flex-1 truncate text-xs font-medium text-text-primary">
+                          {source.title || domain}
+                        </span>
+                        <span className="shrink-0 text-[11px] text-text-secondary">{domain}</span>
+                      </a>
+                    );
+                  })}
+                </div>
+              )}
             </div>
           </div>
         )}
diff --git a/client/src/components/Chat/Messages/Content/__tests__/ActivityPhaseGroup.test.tsx b/client/src/components/Chat/Messages/Content/__tests__/ActivityPhaseGroup.test.tsx
index b4f7d237a2..9576230b4d 100644
--- a/client/src/components/Chat/Messages/Content/__tests__/ActivityPhaseGroup.test.tsx
+++ b/client/src/components/Chat/Messages/Content/__tests__/ActivityPhaseGroup.test.tsx
@@ -13,8 +13,10 @@ jest.mock('~/hooks/Messages/useSmoothStreaming', () => ({
 
 jest.mock('~/hooks', () => {
   const expandCollapse = jest.requireActual('~/hooks/Messages/useExpandCollapse');
+  const lazyCollapseBody = jest.requireActual('~/hooks/Messages/useLazyCollapseBody');
   return {
     useExpandCollapse: expandCollapse.default,
+    useLazyCollapseBody: lazyCollapseBody.default,
     EXPAND_TRANSITION: expandCollapse.EXPAND_TRANSITION,
     scheduleMessageContentLayoutReconcile: (target: HTMLElement | null) =>
       mockScheduleLayoutReconcile(target),
@@ -192,4 +194,72 @@ describe('ActivityPhaseGroup', () => {
     expect(screen.getByText(LABEL)).toHaveClass('text-left');
     expect(pendingFrames()).toBe(0);
   });
+
+  test('keeps a collapsed history phase body unmounted until expanded', () => {
+    render(
+      <ActivityPhaseGroup labelPart={labelPart} hasContent>
+        <div data-testid="phase-content" />
+      </ActivityPhaseGroup>,
+    );
+
+    expect(screen.queryByTestId('phase-content')).not.toBeInTheDocument();
+
+    fireEvent.click(screen.getByRole('button', { name: LABEL }));
+    expect(screen.getByTestId('phase-content')).toBeInTheDocument();
+  });
+
+  test('releases the body only after the collapse transition completes', () => {
+    render(
+      <ActivityPhaseGroup labelPart={labelPart} hasContent>
+        <div data-testid="phase-content" />
+      </ActivityPhaseGroup>,
+    );
+
+    const trigger = screen.getByRole('button', { name: LABEL });
+    fireEvent.click(trigger);
+    expect(screen.getByTestId('phase-content')).toBeInTheDocument();
+
+    fireEvent.click(trigger);
+    expect(screen.getByTestId('phase-content')).toBeInTheDocument();
+
+    fireEvent.transitionEnd(screen.getByTestId('activity-phase-panel'));
+    expect(screen.queryByTestId('phase-content')).not.toBeInTheDocument();
+  });
+
+  test('a pending approval retains the collapsed body until it resolves', () => {
+    const { rerender } = render(
+      <ActivityPhaseGroup labelPart={labelPart} hasContent hasPendingApproval>
+        <div data-testid="phase-content" />
+      </ActivityPhaseGroup>,
+    );
+
+    const trigger = screen.getByRole('button', { name: LABEL });
+    fireEvent.click(trigger);
+    fireEvent.click(trigger);
+    fireEvent.transitionEnd(screen.getByTestId('activity-phase-panel'));
+    expect(screen.getByTestId('phase-content')).toBeInTheDocument();
+
+    rerender(
+      <ActivityPhaseGroup labelPart={labelPart} hasContent hasPendingApproval={false}>
+        <div data-testid="phase-content" />
+      </ActivityPhaseGroup>,
+    );
+    expect(screen.queryByTestId('phase-content')).not.toBeInTheDocument();
+  });
+
+  test('the entrance fold keeps the body mounted, then releases it after settling', () => {
+    render(
+      <ActivityPhaseGroup labelPart={labelPart} hasContent animateEntrance>
+        <div data-testid="phase-content" />
+      </ActivityPhaseGroup>,
+    );
+
+    expect(screen.getByTestId('phase-content')).toBeInTheDocument();
+
+    flushFrames();
+    flushFrames();
+
+    fireEvent.transitionEnd(screen.getByTestId('activity-phase-panel'));
+    expect(screen.queryByTestId('phase-content')).not.toBeInTheDocument();
+  });
 });
diff --git a/client/src/components/Chat/Messages/Content/__tests__/ContentParts.integration.test.tsx b/client/src/components/Chat/Messages/Content/__tests__/ContentParts.integration.test.tsx
index 9d9d1a5830..bb53b13b3d 100644
--- a/client/src/components/Chat/Messages/Content/__tests__/ContentParts.integration.test.tsx
+++ b/client/src/components/Chat/Messages/Content/__tests__/ContentParts.integration.test.tsx
@@ -16,6 +16,7 @@ jest.mock('~/hooks', () => ({
     style: { display: 'grid', gridTemplateRows: isExpanded ? '1fr' : '0fr' },
     ref: { current: null },
   }),
+  useLazyCollapseBody: jest.requireActual('~/hooks/Messages/useLazyCollapseBody').default,
   useProgress: (initial: number) => (initial >= 1 ? 1 : initial),
   scheduleMessageContentLayoutReconcile: jest.fn(() => jest.fn()),
 }));
diff --git a/client/src/components/Chat/Messages/Content/__tests__/ContentParts.test.tsx b/client/src/components/Chat/Messages/Content/__tests__/ContentParts.test.tsx
index 664a1c28cc..b735bc0493 100644
--- a/client/src/components/Chat/Messages/Content/__tests__/ContentParts.test.tsx
+++ b/client/src/components/Chat/Messages/Content/__tests__/ContentParts.test.tsx
@@ -9,6 +9,7 @@ jest.mock('~/utils', () => ({
   mapAttachments: () => ({}),
   filterAttachmentsForPart: (attachments: unknown) => attachments,
   groupSequentialToolCalls: jest.fn(),
+  hasPendingApprovalInPart: jest.requireActual('~/utils/groupToolCalls').hasPendingApprovalInPart,
 }));
 
 jest.mock('~/Providers', () => {
diff --git a/client/src/components/Chat/Messages/Content/__tests__/ToolCall.test.tsx b/client/src/components/Chat/Messages/Content/__tests__/ToolCall.test.tsx
index 463bb24bc1..967a66cfa4 100644
--- a/client/src/components/Chat/Messages/Content/__tests__/ToolCall.test.tsx
+++ b/client/src/components/Chat/Messages/Content/__tests__/ToolCall.test.tsx
@@ -31,6 +31,7 @@ jest.mock('~/hooks', () => ({
     },
     ref: { current: null },
   }),
+  useLazyCollapseBody: jest.requireActual('~/hooks/Messages/useLazyCollapseBody').default,
 }));
 
 jest.mock('~/hooks/MCP', () => {
@@ -291,24 +292,19 @@ describe('ToolCall', () => {
   });
 
   describe('tool call info visibility', () => {
-    it('should toggle tool call info expand/collapse when clicking header', () => {
+    it('should mount tool call info only after expanding via the header', () => {
       renderWithRecoil(<ToolCall {...mockProps} />);
 
-      // ToolCallInfo is always in the DOM (CSS expand/collapse), but initially collapsed
-      const toolCallInfo = screen.getByTestId('tool-call-info');
-      expect(toolCallInfo).toBeInTheDocument();
+      // Collapsed info stays unmounted until the first expansion
+      expect(screen.queryByTestId('tool-call-info')).not.toBeInTheDocument();
 
-      // The expand wrapper starts collapsed (showInfo=false, autoExpand=false)
-      const expandWrapper = toolCallInfo.closest('[style]')?.parentElement;
-      expect(expandWrapper).toBeDefined();
-
-      // Click to expand
       fireEvent.click(screen.getByTestId('progress-text'));
       expect(screen.getByTestId('tool-call-info')).toBeInTheDocument();
     });
 
     it('should pass input and output props to ToolCallInfo', () => {
       renderWithRecoil(<ToolCall {...mockProps} />);
+      fireEvent.click(screen.getByTestId('progress-text'));
 
       const toolCallInfo = screen.getByTestId('tool-call-info');
       const props = JSON.parse(toolCallInfo.textContent!);
@@ -375,6 +371,7 @@ describe('ToolCall', () => {
   describe('edge cases', () => {
     it('should handle undefined args', () => {
       renderWithRecoil(<ToolCall {...mockProps} args={undefined as any} />);
+      fireEvent.click(screen.getByTestId('progress-text'));
 
       const toolCallInfo = screen.getByTestId('tool-call-info');
       const props = JSON.parse(toolCallInfo.textContent!);
@@ -383,6 +380,7 @@ describe('ToolCall', () => {
 
     it('should handle null output', () => {
       renderWithRecoil(<ToolCall {...mockProps} output={null} />);
+      fireEvent.click(screen.getByTestId('progress-text'));
 
       const toolCallInfo = screen.getByTestId('tool-call-info');
       const props = JSON.parse(toolCallInfo.textContent!);
@@ -391,9 +389,9 @@ describe('ToolCall', () => {
 
     it('should handle simple function name without domain', () => {
       renderWithRecoil(<ToolCall {...mockProps} name="simpleName" />);
+      fireEvent.click(screen.getByTestId('progress-text'));
 
-      const toolCallInfo = screen.getByTestId('tool-call-info');
-      expect(toolCallInfo).toBeInTheDocument();
+      expect(screen.getByTestId('tool-call-info')).toBeInTheDocument();
     });
 
     it('should handle complex nested attachments', () => {
diff --git a/client/src/components/Chat/Messages/Content/__tests__/ToolCallGroup.test.tsx b/client/src/components/Chat/Messages/Content/__tests__/ToolCallGroup.test.tsx
index 0426219539..2e916958be 100644
--- a/client/src/components/Chat/Messages/Content/__tests__/ToolCallGroup.test.tsx
+++ b/client/src/components/Chat/Messages/Content/__tests__/ToolCallGroup.test.tsx
@@ -67,6 +67,7 @@ jest.mock('~/utils', () => ({
    *  so stubbing them out would hide the header logic under test. */
   getBatchActivityLabelPart: jest.requireActual('~/utils/activityLabels').getBatchActivityLabelPart,
   getActivityLabelText: jest.requireActual('~/utils/activityLabels').getActivityLabelText,
+  hasPendingApprovalInPart: jest.requireActual('~/utils/groupToolCalls').hasPendingApprovalInPart,
 }));
 
 jest.mock('../Parts', () => ({
diff --git a/client/src/components/Chat/Messages/Content/__tests__/WebSearch.test.tsx b/client/src/components/Chat/Messages/Content/__tests__/WebSearch.test.tsx
index fc29f0391b..a0fef95cc4 100644
--- a/client/src/components/Chat/Messages/Content/__tests__/WebSearch.test.tsx
+++ b/client/src/components/Chat/Messages/Content/__tests__/WebSearch.test.tsx
@@ -1,7 +1,7 @@
 import React from 'react';
 import { RecoilRoot } from 'recoil';
 import { Tools } from 'librechat-data-provider';
-import { render, screen } from '@testing-library/react';
+import { fireEvent, render, screen } from '@testing-library/react';
 import type { TAttachment, SearchResultData, ValidSource } from 'librechat-data-provider';
 import { SearchContext } from '~/Providers';
 import WebSearch from '../WebSearch';
@@ -19,6 +19,7 @@ jest.mock('~/hooks', () => ({
     };
     return translations[key] || key;
   },
+  useLazyCollapseBody: jest.requireActual('~/hooks/Messages/useLazyCollapseBody').default,
   useExpandCollapse: (isExpanded: boolean) => ({
     style: {
       display: 'grid',
@@ -129,6 +130,7 @@ describe('WebSearch', () => {
       const attachments = [makeAttachment(0, searchResults['0'])];
 
       renderWebSearch({ searchResults, attachments });
+      fireEvent.click(screen.getByRole('button', { name: /Searched the web/ }));
 
       const links = screen.getAllByRole('link');
       const hrefs = links.map((l) => l.getAttribute('href'));
@@ -143,6 +145,7 @@ describe('WebSearch', () => {
       const attachments = [makeAttachment(1, searchResults['1'])];
 
       renderWebSearch({ searchResults, attachments });
+      fireEvent.click(screen.getByRole('button', { name: /Searched the web/ }));
 
       const links = screen.getAllByRole('link');
       const hrefs = links.map((l) => l.getAttribute('href'));
@@ -178,6 +181,9 @@ describe('WebSearch', () => {
         </RecoilRoot>,
       );
 
+      fireEvent.click(container0.querySelector('button[aria-expanded]') as HTMLElement);
+      fireEvent.click(container1.querySelector('button[aria-expanded]') as HTMLElement);
+
       const links0 = Array.from(container0.querySelectorAll('a[href]')).map((a) =>
         a.getAttribute('href'),
       );
@@ -195,6 +201,7 @@ describe('WebSearch', () => {
 
     it('falls back to searchResults[ownTurn] when attachments is undefined', () => {
       renderWebSearch({ searchResults });
+      fireEvent.click(screen.getByRole('button', { name: /Searched the web/ }));
 
       const links = screen.getAllByRole('link');
       const hrefs = links.map((l) => l.getAttribute('href'));
diff --git a/client/src/components/Chat/Messages/MessagesView.tsx b/client/src/components/Chat/Messages/MessagesView.tsx
index 37bf2b3dc2..ed76987ccd 100644
--- a/client/src/components/Chat/Messages/MessagesView.tsx
+++ b/client/src/components/Chat/Messages/MessagesView.tsx
@@ -5,9 +5,10 @@ import { Constants } from 'librechat-data-provider';
 import { CSSTransition } from 'react-transition-group';
 import type { TMessage } from 'librechat-data-provider';
 import { useScreenshot, useMessageScrolling, useScrollbarGutter, useLocalize } from '~/hooks';
+import { RowMountProvider, useProgressiveRowMount } from '~/hooks/Messages';
+import { MessagesViewProvider, useChatContext } from '~/Providers';
 import ScrollToBottom from '~/components/Messages/ScrollToBottom';
 import { steerOverlayHeightFamily } from '~/store/steer';
-import { MessagesViewProvider } from '~/Providers';
 import { fontSizeAtom } from '~/store/fontSize';
 import MultiMessage from './MultiMessage';
 import MessageNav from './MessageNav';
@@ -114,6 +115,22 @@ function MessagesViewContent({
 
   const { conversationId } = conversation ?? {};
 
+  const { index, latestMessageDepth } = useChatContext();
+  const isSubmitting = useRecoilValue(store.isSubmittingFamily(index));
+  const autoScroll = useRecoilValue(store.autoScroll);
+  /** Re-arm from the conversation that owns the RENDERED tree: the Recoil
+   *  conversation id lags the route during warm-cache navigation, and keying
+   *  off it would first mount the new tree unwindowed, then narrow it after
+   *  the fact — visibly unmounting rows the user is already reading. */
+  const treeConversationId = _messagesTree?.[0]?.conversationId ?? conversationId;
+  const mountWindow = useProgressiveRowMount({
+    tailDepth: latestMessageDepth,
+    anchorBottom: autoScroll || isSubmitting,
+    isSubmitting,
+    conversationId: treeConversationId,
+    scrollableRef,
+  });
+
   /** The in-flight steer overlay floats above the composer over the bottom of
    *  the thread (see `InFlightSteers`); reserve an equal band here so the
    *  newest message rests above it and older ones scroll behind. */
@@ -133,6 +150,10 @@ function MessagesViewContent({
               height: '100%',
               overflowY: 'auto',
               width: '100%',
+              /** The mount hook pins the anchor row itself (document-space
+               *  measurement); native scroll anchoring reacting to the same
+               *  insertions would double-correct. */
+              overflowAnchor: mountWindow != null ? 'none' : undefined,
             }}
           >
             <div
@@ -156,12 +177,14 @@ function MessagesViewContent({
               ) : (
                 <>
                   <div ref={screenshotTargetRef} data-testid="screenshot-target">
-                    <MultiMessage
-                      messagesTree={_messagesTree}
-                      messageId={conversationId ?? null}
-                      setCurrentEditId={setCurrentEditId}
-                      currentEditId={currentEditId ?? null}
-                    />
+                    <RowMountProvider mountWindow={mountWindow}>
+                      <MultiMessage
+                        messagesTree={_messagesTree}
+                        messageId={conversationId ?? null}
+                        setCurrentEditId={setCurrentEditId}
+                        currentEditId={currentEditId ?? null}
+                      />
+                    </RowMountProvider>
                   </div>
                 </>
               )}
diff --git a/client/src/components/Chat/Messages/MultiMessage.tsx b/client/src/components/Chat/Messages/MultiMessage.tsx
index dc54587aea..5b8a658e58 100644
--- a/client/src/components/Chat/Messages/MultiMessage.tsx
+++ b/client/src/components/Chat/Messages/MultiMessage.tsx
@@ -5,6 +5,7 @@ import type { TMessage } from 'librechat-data-provider';
 import type { ReactElement } from 'react';
 import type { TMessageProps } from '~/common';
 import MessageContent from '~/components/Messages/MessageContent';
+import { useRowMountWindow } from '~/hooks/Messages';
 import MessageParts from './MessageParts';
 import Message from './Message';
 import store from '~/store';
@@ -21,6 +22,7 @@ function MultiMessage({
   setCurrentEditId,
 }: TMessageProps) {
   const [siblingIdx, setSiblingIdx] = useRecoilState(store.messagesSiblingIdxFamily(messageId));
+  const mountWindow = useRowMountWindow();
 
   const setSiblingIdxRev = useCallback(
     (value: number) => {
@@ -165,8 +167,17 @@ function MultiMessage({
     setSiblingIdx: setSiblingIdxRev,
   };
 
-  let row: ReactElement;
-  if (isAssistantsEndpoint(message.endpoint) && message.content) {
+  /** A row outside the progressive mount window renders nothing while the
+   *  recursion continues, so descendants keep their atoms, effects, and
+   *  streaming spine; the window only ever widens, so rows never unmount. */
+  const rowMounted =
+    mountWindow == null ||
+    ((message.depth ?? 0) >= mountWindow.start && (message.depth ?? 0) <= mountWindow.end);
+
+  let row: ReactElement | null = null;
+  if (!rowMounted) {
+    row = null;
+  } else if (isAssistantsEndpoint(message.endpoint) && message.content) {
     row = <MessageParts {...sharedProps} />;
   } else if (message.content) {
     row = <MessageContent {...sharedProps} />;
diff --git a/client/src/components/Chat/Messages/__tests__/MultiMessage.spec.tsx b/client/src/components/Chat/Messages/__tests__/MultiMessage.spec.tsx
index b999d27000..586c1f2231 100644
--- a/client/src/components/Chat/Messages/__tests__/MultiMessage.spec.tsx
+++ b/client/src/components/Chat/Messages/__tests__/MultiMessage.spec.tsx
@@ -193,3 +193,46 @@ describe('MultiMessage sibling selection', () => {
     expect(displayed()).toBe('a1');
   });
 });
+
+describe('MultiMessage row mount window', () => {
+  const { RowMountProvider } =
+    jest.requireActual<typeof import('~/hooks/Messages')>('~/hooks/Messages');
+
+  const chain = (): TMessage => {
+    const leaf = { ...msg('m2'), parentMessageId: 'm1', depth: 2 } as TMessage;
+    const mid = { ...msg('m1'), parentMessageId: 'm0', depth: 1, children: [leaf] } as TMessage;
+    return { ...msg('m0'), depth: 0, children: [mid] } as TMessage;
+  };
+
+  const windowedTree = (mountWindow: { start: number; end: number } | null) => (
+    <RecoilRoot>
+      <RowMountProvider mountWindow={mountWindow}>
+        <MultiMessage
+          messageId="parent-1"
+          messagesTree={[chain()]}
+          currentEditId={null}
+          setCurrentEditId={jest.fn()}
+        />
+      </RowMountProvider>
+    </RecoilRoot>
+  );
+
+  it('renders every row without a window', () => {
+    render(windowedTree(null));
+    expect(screen.getAllByTestId('row').map((r) => r.textContent)).toEqual(['m0', 'm1', 'm2']);
+  });
+
+  it('gates rows outside the window while the recursion continues below them', () => {
+    render(windowedTree({ start: 2, end: 2 }));
+    expect(screen.getAllByTestId('row').map((r) => r.textContent)).toEqual(['m2']);
+  });
+
+  it('mounts newly windowed rows above without disturbing deeper rows', () => {
+    const view = render(windowedTree({ start: 2, end: 2 }));
+    view.rerender(windowedTree({ start: 1, end: 2 }));
+    expect(screen.getAllByTestId('row').map((r) => r.textContent)).toEqual(['m1', 'm2']);
+
+    view.rerender(windowedTree(null));
+    expect(screen.getAllByTestId('row').map((r) => r.textContent)).toEqual(['m0', 'm1', 'm2']);
+  });
+});
diff --git a/client/src/hooks/Messages/__tests__/useLazyCollapseBody.spec.tsx b/client/src/hooks/Messages/__tests__/useLazyCollapseBody.spec.tsx
new file mode 100644
index 0000000000..c51ea766c0
--- /dev/null
+++ b/client/src/hooks/Messages/__tests__/useLazyCollapseBody.spec.tsx
@@ -0,0 +1,99 @@
+import React from 'react';
+import { fireEvent, render, screen } from '@testing-library/react';
+import useLazyCollapseBody from '../useLazyCollapseBody';
+
+const TOGGLE_LABEL = 'toggle';
+
+function Disclosure({
+  initialExpanded,
+  retainBody = false,
+}: {
+  initialExpanded: boolean;
+  retainBody?: boolean;
+}) {
+  const [isExpanded, setIsExpanded] = React.useState(initialExpanded);
+  const { shouldRenderBody, mountBody, handleTransitionEnd } = useLazyCollapseBody(
+    isExpanded,
+    retainBody,
+  );
+  return (
+    <div>
+      <button
+        type="button"
+        onClick={() => {
+          mountBody();
+          setIsExpanded((prev) => !prev);
+        }}
+      >
+        {TOGGLE_LABEL}
+      </button>
+      <div data-testid="panel" onTransitionEnd={handleTransitionEnd}>
+        {shouldRenderBody && <div data-testid="body" />}
+      </div>
+    </div>
+  );
+}
+
+describe('useLazyCollapseBody', () => {
+  it('leaves a collapsed-by-default body unmounted', () => {
+    render(<Disclosure initialExpanded={false} />);
+    expect(screen.queryByTestId('body')).not.toBeInTheDocument();
+  });
+
+  it('mounts an expanded-by-default body immediately', () => {
+    render(<Disclosure initialExpanded={true} />);
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+  });
+
+  it('mounts in the same commit as a user expand', () => {
+    render(<Disclosure initialExpanded={false} />);
+    fireEvent.click(screen.getByRole('button'));
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+  });
+
+  it('keeps the body through the collapse transition, then releases it', () => {
+    render(<Disclosure initialExpanded={false} />);
+    const toggle = screen.getByRole('button');
+    fireEvent.click(toggle);
+    fireEvent.click(toggle);
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+
+    fireEvent.transitionEnd(screen.getByTestId('panel'));
+    expect(screen.queryByTestId('body')).not.toBeInTheDocument();
+  });
+
+  it('ignores transition events bubbling from descendants', () => {
+    render(<Disclosure initialExpanded={false} />);
+    const toggle = screen.getByRole('button');
+    fireEvent.click(toggle);
+    fireEvent.click(toggle);
+
+    fireEvent.transitionEnd(screen.getByTestId('body'));
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+  });
+
+  it('does not release the body when a transition ends while expanded', () => {
+    render(<Disclosure initialExpanded={true} />);
+    fireEvent.transitionEnd(screen.getByTestId('panel'));
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+  });
+
+  it('retains the body across a collapse while retainBody is set', () => {
+    const view = render(<Disclosure initialExpanded={false} retainBody />);
+    const toggle = screen.getByRole('button');
+    fireEvent.click(toggle);
+    fireEvent.click(toggle);
+    fireEvent.transitionEnd(screen.getByTestId('panel'));
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+
+    view.rerender(<Disclosure initialExpanded={false} retainBody={false} />);
+    expect(screen.queryByTestId('body')).not.toBeInTheDocument();
+  });
+
+  it('keeps an expanded body mounted when retention clears', () => {
+    const view = render(<Disclosure initialExpanded={false} retainBody />);
+    fireEvent.click(screen.getByRole('button'));
+    view.rerender(<Disclosure initialExpanded={false} retainBody={false} />);
+    expect(screen.getByTestId('body')).toBeInTheDocument();
+  });
+});
diff --git a/client/src/hooks/Messages/__tests__/useProgressiveRowMount.spec.tsx b/client/src/hooks/Messages/__tests__/useProgressiveRowMount.spec.tsx
new file mode 100644
index 0000000000..911f051f7b
--- /dev/null
+++ b/client/src/hooks/Messages/__tests__/useProgressiveRowMount.spec.tsx
@@ -0,0 +1,148 @@
+import React from 'react';
+import { act, renderHook } from '@testing-library/react';
+import type { RowMountWindow } from '../useProgressiveRowMount';
+import { useProgressiveRowMount, completeProgressiveRowMounts } from '../useProgressiveRowMount';
+
+type HookProps = {
+  tailDepth: number | undefined;
+  anchorBottom: boolean;
+  isSubmitting: boolean;
+  conversationId: string | null | undefined;
+};
+
+describe('useProgressiveRowMount', () => {
+  let frames: Array<FrameRequestCallback | undefined>;
+  const scrollableRef = { current: null } as React.RefObject<HTMLDivElement | null>;
+
+  /** Runs only the frames scheduled BEFORE this flush, so one call advances
+   *  the expansion by exactly one step even though each step schedules the
+   *  next frame during the act() flush. */
+  const flushFrames = () =>
+    act(() => {
+      const pending = frames.length;
+      for (let index = 0; index < pending; index += 1) {
+        const frame = frames[index];
+        frames[index] = undefined;
+        frame?.(index);
+      }
+    });
+
+  beforeEach(() => {
+    frames = [];
+    window.requestAnimationFrame = jest.fn((callback: FrameRequestCallback) => {
+      frames.push(callback);
+      return frames.length;
+    }) as unknown as typeof window.requestAnimationFrame;
+    window.cancelAnimationFrame = jest.fn((handle: number) => {
+      frames[handle - 1] = undefined;
+    }) as unknown as typeof window.cancelAnimationFrame;
+  });
+
+  const setup = (initial: Partial<HookProps> = {}) => {
+    const props: HookProps = {
+      tailDepth: 267,
+      anchorBottom: false,
+      isSubmitting: false,
+      conversationId: 'convo-a',
+      ...initial,
+    };
+    return renderHook(
+      (current: HookProps) => useProgressiveRowMount({ ...current, scrollableRef }),
+      { initialProps: props },
+    );
+  };
+
+  it('does not window short threads', () => {
+    const { result } = setup({ tailDepth: 20 });
+    expect(result.current).toBeNull();
+  });
+
+  it('does not window when a submission is already active', () => {
+    const { result } = setup({ isSubmitting: true });
+    expect(result.current).toBeNull();
+  });
+
+  it('anchors the first window at the top by default', () => {
+    const { result } = setup();
+    expect(result.current).toEqual({ start: 0, end: 15 });
+  });
+
+  it('anchors the first window at the tail for bottom anchoring', () => {
+    const { result } = setup({ anchorBottom: true });
+    expect(result.current).toEqual({ start: 252, end: Number.POSITIVE_INFINITY });
+  });
+
+  it('widens per frame until the whole path is covered, then lifts the restriction', () => {
+    const { result } = setup();
+    const seen: RowMountWindow[] = [result.current];
+
+    for (let i = 0; i < 20 && result.current != null; i += 1) {
+      flushFrames();
+      seen.push(result.current);
+    }
+
+    expect(result.current).toBeNull();
+    const ends = seen.filter((w): w is NonNullable<RowMountWindow> => w != null).map((w) => w.end);
+    for (let i = 1; i < ends.length; i += 1) {
+      expect(ends[i]).toBeGreaterThan(ends[i - 1]);
+    }
+    /** The final widening and the covered-check that lifts the restriction
+     *  land in the same flush, so the last observable window sits within one
+     *  chunk of the tail. */
+    expect(ends[ends.length - 1]).toBeGreaterThanOrEqual(267 - 32);
+  });
+
+  it('completes immediately when a submission starts mid-expansion', () => {
+    const { result, rerender } = setup();
+    expect(result.current).not.toBeNull();
+
+    rerender({
+      tailDepth: 267,
+      anchorBottom: false,
+      isSubmitting: true,
+      conversationId: 'convo-a',
+    });
+    expect(result.current).toBeNull();
+  });
+
+  it('force-completes in-flight mounts for DOM consumers, resolving after paint', async () => {
+    const { result } = setup();
+    expect(result.current).not.toBeNull();
+
+    let resolved = false;
+    let completion: Promise<void> = Promise.resolve();
+    act(() => {
+      completion = completeProgressiveRowMounts().then(() => {
+        resolved = true;
+      });
+    });
+    expect(result.current).toBeNull();
+
+    flushFrames();
+    flushFrames();
+    await act(async () => {
+      await completion;
+    });
+    expect(resolved).toBe(true);
+
+    /** With nothing in flight it resolves immediately, no frames needed. */
+    await expect(completeProgressiveRowMounts()).resolves.toBeUndefined();
+  });
+
+  it('re-arms a fresh window when the conversation changes', () => {
+    const { result, rerender } = setup();
+
+    while (result.current != null) {
+      flushFrames();
+    }
+    expect(result.current).toBeNull();
+
+    rerender({
+      tailDepth: 199,
+      anchorBottom: false,
+      isSubmitting: false,
+      conversationId: 'convo-b',
+    });
+    expect(result.current).toEqual({ start: 0, end: 15 });
+  });
+});
diff --git a/client/src/hooks/Messages/index.ts b/client/src/hooks/Messages/index.ts
index 1818bbc065..7a0eb4d833 100644
--- a/client/src/hooks/Messages/index.ts
+++ b/client/src/hooks/Messages/index.ts
@@ -11,6 +11,14 @@ export { default as useAttachments } from './useAttachments';
 export { default as useSubmitMessage } from './useSubmitMessage';
 export type { ContentMetadataResult } from './useContentMetadata';
 export { default as useExpandCollapse } from './useExpandCollapse';
+export { default as useLazyCollapseBody } from './useLazyCollapseBody';
+export {
+  RowMountProvider,
+  useRowMountWindow,
+  useProgressiveRowMount,
+  completeProgressiveRowMounts,
+} from './useProgressiveRowMount';
+export type { RowMountWindow } from './useProgressiveRowMount';
 export { default as useMessageActions } from './useMessageActions';
 export { useLatestMessage, useLatestMessageId } from './useLatestMessage';
 export { default as useMemoizedChatContext } from './useMemoizedChatContext';
diff --git a/client/src/hooks/Messages/useLazyCollapseBody.ts b/client/src/hooks/Messages/useLazyCollapseBody.ts
new file mode 100644
index 0000000000..ef00dae75d
--- /dev/null
+++ b/client/src/hooks/Messages/useLazyCollapseBody.ts
@@ -0,0 +1,59 @@
+import { useRef, useState, useEffect, useCallback } from 'react';
+import type { TransitionEvent } from 'react';
+
+/**
+ * Defers a disclosure panel's body: collapsed-by-default content stays
+ * unmounted until its first expansion and unmounts again after the collapse
+ * transition completes (`useExpandCollapse` keeps `transitionend` firing even
+ * under reduced motion, so the release always arrives). The expansion-flag
+ * effect mounts one commit after programmatic expands; toggle handlers should
+ * call `mountBody` so user-driven expands mount in the same commit the
+ * height transition measures.
+ *
+ * `retainBody` keeps an already-mounted body across collapses while true —
+ * for descendants that own unsent local form state (pending tool approvals) —
+ * and releases it once the flag clears while collapsed.
+ */
+export default function useLazyCollapseBody(
+  isExpanded: boolean,
+  retainBody = false,
+): {
+  shouldRenderBody: boolean;
+  mountBody: () => void;
+  handleTransitionEnd: (event: TransitionEvent<HTMLElement>) => void;
+} {
+  const [shouldRenderBody, setShouldRenderBody] = useState(isExpanded);
+  const retainedRef = useRef(false);
+  const mountBody = useCallback(() => setShouldRenderBody(true), []);
+
+  useEffect(() => {
+    if (isExpanded) {
+      retainedRef.current = false;
+      setShouldRenderBody(true);
+    }
+  }, [isExpanded]);
+
+  useEffect(() => {
+    if (!isExpanded && !retainBody && retainedRef.current) {
+      retainedRef.current = false;
+      setShouldRenderBody(false);
+    }
+  }, [isExpanded, retainBody]);
+
+  const handleTransitionEnd = useCallback(
+    (event: TransitionEvent<HTMLElement>) => {
+      if (event.target !== event.currentTarget || isExpanded) {
+        return;
+      }
+      if (retainBody) {
+        retainedRef.current = true;
+        return;
+      }
+      retainedRef.current = false;
+      setShouldRenderBody(false);
+    },
+    [isExpanded, retainBody],
+  );
+
+  return { shouldRenderBody, mountBody, handleTransitionEnd };
+}
diff --git a/client/src/hooks/Messages/useProgressiveRowMount.tsx b/client/src/hooks/Messages/useProgressiveRowMount.tsx
new file mode 100644
index 0000000000..57335b51b9
--- /dev/null
+++ b/client/src/hooks/Messages/useProgressiveRowMount.tsx
@@ -0,0 +1,202 @@
+import {
+  useRef,
+  useState,
+  useEffect,
+  useContext,
+  useCallback,
+  createContext,
+  useLayoutEffect,
+  startTransition,
+} from 'react';
+import type { ReactNode, RefObject } from 'react';
+
+/**
+ * Depth range (inclusive) of visible-path rows allowed to mount; `null` means
+ * no restriction. `MultiMessage` reads this to gate each row while always
+ * continuing its recursion, so the tree's structure, sibling state, and
+ * streaming spine are identical whether or not a window is active.
+ */
+export type RowMountWindow = { start: number; end: number } | null;
+
+const RowMountContext = createContext<RowMountWindow>(null);
+
+export function RowMountProvider({
+  mountWindow,
+  children,
+}: {
+  mountWindow: RowMountWindow;
+  children: ReactNode;
+}) {
+  return <RowMountContext.Provider value={mountWindow}>{children}</RowMountContext.Provider>;
+}
+
+export function useRowMountWindow(): RowMountWindow {
+  return useContext(RowMountContext);
+}
+
+/** Below this path length every row mounts in one commit, exactly as before. */
+const MIN_PROGRESSIVE_ROWS = 40;
+/** Rows in the first anchored commit — about one viewport plus overscan. */
+const INITIAL_ROWS = 16;
+/** Rows added per expansion step until the window covers the whole path. */
+const CHUNK_ROWS = 32;
+
+type ProgressiveRowMountOptions = {
+  /** Depth of the active branch tail (`latestMessageDepth` from ChatContext). */
+  tailDepth: number | undefined;
+  /** True anchors the first commit at the newest rows (auto-scroll lands
+   *  there); false anchors at the conversation start, which is where a
+   *  default-settings load rests. */
+  anchorBottom: boolean;
+  isSubmitting: boolean;
+  conversationId: string | null | undefined;
+  scrollableRef: RefObject<HTMLDivElement | null>;
+};
+
+function initialWindow(
+  tailDepth: number | undefined,
+  anchorBottom: boolean,
+  isSubmitting: boolean,
+): RowMountWindow {
+  if (isSubmitting || tailDepth == null || tailDepth + 1 <= MIN_PROGRESSIVE_ROWS) {
+    return null;
+  }
+  if (anchorBottom) {
+    return { start: Math.max(0, tailDepth - INITIAL_ROWS + 1), end: Number.POSITIVE_INFINITY };
+  }
+  return { start: 0, end: INITIAL_ROWS - 1 };
+}
+
+/**
+ * Windowed first commit for long threads: mount only the rows around the
+ * scroll anchor, then widen the window in transition-wrapped chunks until
+ * every row is mounted, then drop the restriction entirely. The DOM converges
+ * to the exact full structure — nothing ever unmounts — so message counts,
+ * screenshot export, and the nav rail see the same document they always have,
+ * just a few frames later.
+ *
+ * Bottom-anchored expansion inserts rows above the viewport; the layout
+ * effect re-pins the previously first-mounted row to its pre-commit viewport
+ * offset by measuring its actual shift, which also degrades to a no-op
+ * wherever native scroll anchoring already compensated.
+ */
+export function useProgressiveRowMount({
+  tailDepth,
+  anchorBottom,
+  isSubmitting,
+  conversationId,
+  scrollableRef,
+}: ProgressiveRowMountOptions): RowMountWindow {
+  const [mountWindow, setMountWindow] = useState<RowMountWindow>(() =>
+    initialWindow(tailDepth, anchorBottom, isSubmitting),
+  );
+  const anchorRef = useRef<{ element: Element; documentOffset: number } | null>(null);
+
+  /** Re-arm per conversation so every navigation gets the anchored fast
+   *  first commit (state adjustment during render, per React's guidance,
+   *  so the old conversation's window never gates the new tree). */
+  const [prevConversationId, setPrevConversationId] = useState(conversationId);
+  if (prevConversationId !== conversationId) {
+    setPrevConversationId(conversationId);
+    setMountWindow(initialWindow(tailDepth, anchorBottom, isSubmitting));
+    anchorRef.current = null;
+  }
+
+  useEffect(() => {
+    if (isSubmitting && mountWindow != null) {
+      setMountWindow(null);
+    }
+  }, [isSubmitting, mountWindow]);
+
+  const captureAnchor = useCallback(() => {
+    const container = scrollableRef.current;
+    if (!container || !anchorBottom) {
+      anchorRef.current = null;
+      return;
+    }
+    const element = container.querySelector('.message-render');
+    /** Document-space offset (viewport top + scrollTop): the widening commit
+     *  is transition-deferred, so the user may scroll between capture and
+     *  commit. User scrolling moves viewport coordinates but not document
+     *  ones, so measuring here isolates the inserted-row shift and never
+     *  folds the user's own movement into the correction. */
+    anchorRef.current = element
+      ? { element, documentOffset: element.getBoundingClientRect().top + container.scrollTop }
+      : null;
+  }, [anchorBottom, scrollableRef]);
+
+  useEffect(() => {
+    if (mountWindow == null || tailDepth == null) {
+      return;
+    }
+    if (mountWindow.start <= 0 && mountWindow.end >= tailDepth) {
+      setMountWindow(null);
+      return;
+    }
+    const frameId = requestAnimationFrame(() => {
+      captureAnchor();
+      startTransition(() => {
+        setMountWindow((current) => {
+          if (current == null) {
+            return current;
+          }
+          return {
+            start: Math.max(0, current.start - CHUNK_ROWS),
+            end: current.end >= tailDepth ? current.end : current.end + CHUNK_ROWS,
+          };
+        });
+      });
+    });
+    return () => cancelAnimationFrame(frameId);
+  }, [mountWindow, tailDepth, captureAnchor]);
+
+  useLayoutEffect(() => {
+    const captured = anchorRef.current;
+    anchorRef.current = null;
+    const container = scrollableRef.current;
+    if (!captured || !container || !captured.element.isConnected) {
+      return;
+    }
+    const shift =
+      captured.element.getBoundingClientRect().top + container.scrollTop - captured.documentOffset;
+    if (shift !== 0) {
+      container.scrollTop += shift;
+    }
+  }, [mountWindow, scrollableRef]);
+
+  /** Registered while a window is active so `completeProgressiveRowMounts`
+   *  (screenshot capture) can force the remaining rows in and wait for the
+   *  commit to paint before cloning the DOM. */
+  const isWindowActive = mountWindow != null;
+  useEffect(() => {
+    if (!isWindowActive) {
+      return;
+    }
+    const complete = () =>
+      new Promise<void>((resolve) => {
+        setMountWindow(null);
+        requestAnimationFrame(() => requestAnimationFrame(() => resolve()));
+      });
+    activeCompleters.add(complete);
+    return () => {
+      activeCompleters.delete(complete);
+    };
+  }, [isWindowActive]);
+
+  return mountWindow;
+}
+
+const activeCompleters = new Set<() => Promise<void>>();
+
+/**
+ * Forces every in-flight progressive mount to completion and resolves after
+ * the resulting commit has painted. DOM consumers that clone the thread
+ * (screenshot export) call this so a capture taken mid-widening cannot
+ * silently truncate the rows still outside the window.
+ */
+export async function completeProgressiveRowMounts(): Promise<void> {
+  if (activeCompleters.size === 0) {
+    return;
+  }
+  await Promise.all([...activeCompleters].map((complete) => complete()));
+}
diff --git a/client/src/hooks/ScreenshotContext.tsx b/client/src/hooks/ScreenshotContext.tsx
index 1e26398d28..5e4418e025 100644
--- a/client/src/hooks/ScreenshotContext.tsx
+++ b/client/src/hooks/ScreenshotContext.tsx
@@ -1,6 +1,7 @@
 import { createContext, useRef, useContext, RefObject, ReactNode } from 'react';
 import { toCanvas } from 'html-to-image';
 import { ThemeContext, isDark } from '@librechat/client';
+import { completeProgressiveRowMounts } from '~/hooks/Messages/useProgressiveRowMount';
 
 type ScreenshotContextType = {
   ref?: RefObject<HTMLDivElement>;
@@ -76,6 +77,9 @@ export const useScreenshot = () => {
     if (ref instanceof Function) {
       throw new Error('Ref callback is not supported.');
     }
+    /** A capture taken while a long thread is still progressively mounting
+     *  would clone a truncated DOM; force the remaining rows in first. */
+    await completeProgressiveRowMounts();
     if (ref?.current) {
       return takeScreenShot(ref.current);
     }
diff --git a/client/src/utils/groupToolCalls.ts b/client/src/utils/groupToolCalls.ts
index 2d6b72e087..f924a84a9e 100644
--- a/client/src/utils/groupToolCalls.ts
+++ b/client/src/utils/groupToolCalls.ts
@@ -7,6 +7,33 @@ export type GroupedPart =
   | { type: 'single'; part: PartWithIndex }
   | { type: 'tool-group'; parts: PartWithIndex[]; labelPart?: PartWithIndex };
 
+type ToolCallWithNestedContent = Agents.ToolCall & {
+  subagent_content?: TMessageContentParts[];
+};
+
+/**
+ * True when the part carries an unresolved tool approval — directly or nested
+ * in subagent content. Collapsed disclosure bodies retain instead of
+ * unmounting while this holds, because `ToolApproval` owns unsent local
+ * edit/respond/reason state that an unmount would discard.
+ */
+export function hasPendingApprovalInPart(part: TMessageContentParts): boolean {
+  if (part.type !== ContentTypes.TOOL_CALL) {
+    return false;
+  }
+  const toolCall = part[ContentTypes.TOOL_CALL] as ToolCallWithNestedContent | undefined;
+  if (!toolCall) {
+    return false;
+  }
+  if (toolCall.approval != null && (toolCall.output?.length ?? 0) === 0) {
+    return true;
+  }
+  return (
+    Array.isArray(toolCall.subagent_content) &&
+    toolCall.subagent_content.some(hasPendingApprovalInPart)
+  );
+}
+
 function isGroupableToolCall(part: TMessageContentParts): boolean {
   if (part.type !== ContentTypes.TOOL_CALL) {
     return false;
diff --git a/e2e/specs/mock/export.spec.ts b/e2e/specs/mock/export.spec.ts
index 515f82d980..bb6482fa48 100644
--- a/e2e/specs/mock/export.spec.ts
+++ b/e2e/specs/mock/export.spec.ts
@@ -177,8 +177,15 @@ test.describe('conversation export', () => {
     });
 
     const target = page.getByTestId('screenshot-target');
-    const area = await target.evaluate((node) => node.scrollWidth * node.scrollHeight);
-    expect(area).toBeGreaterThan(ABORT_CSS_AREA * 1.15);
+    /** Long threads mount progressively from the scroll anchor, so the full
+     *  area lands a few frames after first paint — poll until it converges.
+     *  (The capture path itself force-completes the mount; this precondition
+     *  samples the DOM directly and must wait on its own.) */
+    await expect
+      .poll(() => target.evaluate((node) => node.scrollWidth * node.scrollHeight), {
+        timeout: 60_000,
+      })
+      .toBeGreaterThan(ABORT_CSS_AREA * 1.15);
 
     const dialog = await openExportModal(page);
     await selectExportType(page, dialog, 'screenshot (.png)');
diff --git a/packages/data-provider/src/messages.spec.ts b/packages/data-provider/src/messages.spec.ts
index 1d3aed846b..f08da71286 100644
--- a/packages/data-provider/src/messages.spec.ts
+++ b/packages/data-provider/src/messages.spec.ts
@@ -144,4 +144,55 @@ describe('buildTree', () => {
     expect(tree).toHaveLength(1);
     expect(tree?.[0].files?.[0]).toBe(file);
   });
+
+  describe('memoization', () => {
+    const chain = () => [
+      msg('u1', '00000000-0000-0000-0000-000000000000', { isCreatedByUser: true }),
+      msg('a1', 'u1'),
+    ];
+
+    it('returns the identical tree for the same messages array', () => {
+      const messages = chain();
+      expect(buildTree({ messages })).toBe(buildTree({ messages }));
+    });
+
+    it('keeps one cached tree per fileMap identity', () => {
+      const messages = chain();
+      const fileMap = { f1: { file_id: 'f1' } as TFile };
+
+      const bare = buildTree({ messages });
+      const hydrated = buildTree({ messages, fileMap });
+
+      expect(hydrated).not.toBe(bare);
+      expect(buildTree({ messages })).toBe(bare);
+      expect(buildTree({ messages, fileMap })).toBe(hydrated);
+    });
+
+    it('rebuilds for a new messages array identity', () => {
+      const first = chain();
+      const second = chain();
+      expect(buildTree({ messages: first })).not.toBe(buildTree({ messages: second }));
+    });
+
+    it('rebuilds when the fileMap identity changes', () => {
+      const messages = chain();
+      const treeA = buildTree({ messages, fileMap: {} });
+      const treeB = buildTree({ messages, fileMap: {} });
+      expect(treeB).not.toBe(treeA);
+    });
+
+    it('keeps only the latest hydrated tree, leaving the bare slot intact', () => {
+      const messages = chain();
+      const bare = buildTree({ messages });
+      const fileMapA = { f1: { file_id: 'f1' } as TFile };
+      const fileMapB = { f1: { file_id: 'f1' } as TFile };
+
+      const treeA = buildTree({ messages, fileMap: fileMapA });
+      const treeB = buildTree({ messages, fileMap: fileMapB });
+
+      expect(buildTree({ messages, fileMap: fileMapB })).toBe(treeB);
+      expect(buildTree({ messages, fileMap: fileMapA })).not.toBe(treeA);
+      expect(buildTree({ messages })).toBe(bare);
+    });
+  });
 });
diff --git a/packages/data-provider/src/messages.ts b/packages/data-provider/src/messages.ts
index 518da77e7b..4b50e05952 100644
--- a/packages/data-provider/src/messages.ts
+++ b/packages/data-provider/src/messages.ts
@@ -23,6 +23,22 @@ export function stripReasoningLabelMetadata(part: TMessageContentParts): TMessag
 }
 
 export type ParentMessage = TMessage & { children: TMessage[]; depth: number };
+
+/**
+ * Memoizes built trees per messages-array identity. The same query data feeds
+ * several independent `select`s (ChatView plus the branch-tail helpers), which
+ * used to rebuild the full tree five times per cache write. Exactly two slots
+ * per array — the bare tree and the tree for the LATEST fileMap identity — so
+ * a long-lived cached conversation cannot accumulate a tree per historical
+ * file-map; entries die with the messages array itself.
+ */
+type TreeCacheEntry = {
+  bare?: TMessage[];
+  fileMap?: Record<string, TFile>;
+  hydrated?: TMessage[];
+};
+const treeCache = new WeakMap<(TMessage | undefined)[], TreeCacheEntry>();
+
 /**
  * Builds the render tree from the flat messages array. Order-robust: live
  * stream/steer/preempt cache writes can momentarily place a child before its
@@ -42,6 +58,16 @@ export function buildTree({
     return null;
   }
 
+  const cached = treeCache.get(messages);
+  if (cached) {
+    if (fileMap == null && cached.bare) {
+      return cached.bare;
+    }
+    if (fileMap != null && cached.fileMap === fileMap && cached.hydrated) {
+      return cached.hydrated;
+    }
+  }
+
   const messageMap: Record<string, ParentMessage> = {};
   const orderedMessages: ParentMessage[] = [];
   const rootMessages: ParentMessage[] = [];
@@ -116,5 +142,16 @@ export function buildTree({
     }
   }
 
-  return rootMessages as TMessage[];
+  const tree = rootMessages as TMessage[];
+  const entry = cached ?? {};
+  if (fileMap == null) {
+    entry.bare = tree;
+  } else {
+    entry.fileMap = fileMap;
+    entry.hydrated = tree;
+  }
+  if (!cached) {
+    treeCache.set(messages, entry);
+  }
+  return tree;
 }
diff --git a/packages/data-schemas/src/index.ts b/packages/data-schemas/src/index.ts
index a860a1b682..fdb7fe28d9 100644
--- a/packages/data-schemas/src/index.ts
+++ b/packages/data-schemas/src/index.ts
@@ -7,6 +7,7 @@ export * from './utils';
 export { createModels } from './models';
 export {
   createMethods,
+  CLIENT_MESSAGE_SELECT,
   RoleConflictError,
   DEFAULT_REFRESH_TOKEN_EXPIRY,
   DEFAULT_SESSION_EXPIRY,
diff --git a/packages/data-schemas/src/methods/conversation.spec.ts b/packages/data-schemas/src/methods/conversation.spec.ts
index d83ccb0c8a..b6f42bed2a 100644
--- a/packages/data-schemas/src/methods/conversation.spec.ts
+++ b/packages/data-schemas/src/methods/conversation.spec.ts
@@ -1422,6 +1422,41 @@ describe('Conversation Operations', () => {
     });
   });
 
+  describe('getConvoOwnership', () => {
+    it('resolves only the owning user id, without the preset or message list', async () => {
+      await Conversation.create({
+        conversationId: mockConversationData.conversationId,
+        user: 'user123',
+        title: 'Test Conversation',
+        endpoint: EModelEndpoint.openAI,
+      });
+
+      const result = await methods.getConvoOwnership(
+        'user123',
+        mockConversationData.conversationId,
+      );
+
+      expect(result?.user).toBe('user123');
+      expect(result).not.toHaveProperty('title');
+      expect(result).not.toHaveProperty('messages');
+      expect(result).not.toHaveProperty('endpoint');
+    });
+
+    it('returns null for another user or a missing conversation', async () => {
+      await Conversation.create({
+        conversationId: mockConversationData.conversationId,
+        user: 'user123',
+        title: 'Test Conversation',
+        endpoint: EModelEndpoint.openAI,
+      });
+
+      expect(
+        await methods.getConvoOwnership('someone-else', mockConversationData.conversationId),
+      ).toBeNull();
+      expect(await methods.getConvoOwnership('user123', 'non-existent-id')).toBeNull();
+    });
+  });
+
   describe('getConvoRetention', () => {
     it('should retrieve only retention fields for a user conversation', async () => {
       await Conversation.create({
diff --git a/packages/data-schemas/src/methods/conversation.ts b/packages/data-schemas/src/methods/conversation.ts
index 0cc7093d99..c4a85c2d55 100644
--- a/packages/data-schemas/src/methods/conversation.ts
+++ b/packages/data-schemas/src/methods/conversation.ts
@@ -80,6 +80,10 @@ export interface ConversationMethods {
     convoMap: Record<string, unknown>;
   }>;
   getConvo(user: string, conversationId: string): Promise<IConversation | null>;
+  getConvoOwnership(
+    user: string,
+    conversationId: string,
+  ): Promise<Pick<IConversation, 'user'> | null>;
   getConvoRetention(
     user: string,
     conversationId: string,
@@ -135,6 +139,23 @@ export function createConversationMethods(
     }
   }
 
+  /**
+   * Ownership probe for request validation: resolves only the owning user id
+   * instead of materializing the full conversation document (preset spread +
+   * message ObjectId array).
+   */
+  async function getConvoOwnership(user: string, conversationId: string) {
+    try {
+      const Conversation = mongoose.models.Conversation as Model<IConversation>;
+      return await Conversation.findOne({ user, conversationId }, 'user').lean<
+        Pick<IConversation, 'user'>
+      >();
+    } catch (error) {
+      logger.error('[getConvoOwnership] Error checking conversation ownership', error);
+      throw new Error('Error checking conversation ownership');
+    }
+  }
+
   /**
    * Retrieves only the retention deadline for a conversation.
    */
@@ -1083,6 +1104,7 @@ export function createConversationMethods(
     getConvosByCursor,
     getConvosQueried,
     getConvo,
+    getConvoOwnership,
     getConvoRetention,
     getConvoTitle,
     deleteConvos,
diff --git a/packages/data-schemas/src/methods/index.ts b/packages/data-schemas/src/methods/index.ts
index 1683489a8d..b5b3347bed 100644
--- a/packages/data-schemas/src/methods/index.ts
+++ b/packages/data-schemas/src/methods/index.ts
@@ -44,7 +44,7 @@ import { createCategoriesMethods, type CategoriesMethods } from './categories';
 import { createPresetMethods, type PresetMethods } from './preset';
 /* Tier 2 — Moderate (service deps injected) */
 import { createConversationTagMethods, type ConversationTagMethods } from './conversationTag';
-import { createMessageMethods, type MessageMethods } from './message';
+import { createMessageMethods, CLIENT_MESSAGE_SELECT, type MessageMethods } from './message';
 import { createConversationMethods, type ConversationMethods } from './conversation';
 import { createChatProjectMethods, type ChatProjectMethods } from './chatProject';
 export type {
@@ -132,6 +132,7 @@ export {
 };
 export { tokenValues, cacheTokenValues, premiumTokenValues, defaultRate, createTxMethods };
 export { permissionBitSupersets };
+export { CLIENT_MESSAGE_SELECT };
 export {
   partitionIssues,
   validateSkillName,
diff --git a/packages/data-schemas/src/methods/message.spec.ts b/packages/data-schemas/src/methods/message.spec.ts
index 4b1d5ccd50..dd0922d886 100644
--- a/packages/data-schemas/src/methods/message.spec.ts
+++ b/packages/data-schemas/src/methods/message.spec.ts
@@ -3,8 +3,8 @@ import { v4 as uuidv4 } from 'uuid';
 import { RetentionMode } from 'librechat-data-provider';
 import { MongoMemoryServer } from 'mongodb-memory-server';
 import type { IMessage } from '..';
+import { createMessageMethods, CLIENT_MESSAGE_SELECT } from './message';
 import { tenantStorage, runAsSystem } from '~/config/tenantContext';
-import { createMessageMethods } from './message';
 import { createModels } from '../models';
 import logger from '~/config/winston';
 
@@ -487,6 +487,134 @@ describe('Message Operations', () => {
     });
   });
 
+  describe('CLIENT_MESSAGE_SELECT projection', () => {
+    it('strips server-internal fields and dead SERP verticals, keeping rendered data', async () => {
+      const conversationId = uuidv4();
+      await Message.create({
+        messageId: 'projected-msg',
+        conversationId,
+        user: 'user123',
+        isCreatedByUser: false,
+        sender: 'Agent',
+        text: 'visible text',
+        content: [{ type: 'text', text: 'part text' }],
+        tokenCount: 42,
+        conversationSignature: 'sig',
+        clientId: 'client-1',
+        invocationId: 7,
+        summary: 'legacy summary',
+        summaryTokenCount: 11,
+        contextMeta: { anything: true },
+        langfuseSampled: true,
+        langfuseDestinationIds: ['lf-1'],
+        metadata: {
+          usage: { input: 10, output: 20 },
+          thoughtSignatures: { tool_1: 'opaque' },
+        },
+        attachments: [
+          {
+            type: 'web_search',
+            toolCallId: 'tool_1',
+            web_search: {
+              turn: 0,
+              organic: [
+                {
+                  title: 'Result',
+                  link: 'https://example.com',
+                  snippet: 'snippet',
+                  sitelinks: [{ title: 'sub', link: 'https://example.com/sub' }],
+                  highlights: ['raw scrape'],
+                },
+              ],
+              topStories: [{ title: 'Story', link: 'https://example.com/s', highlights: ['x'] }],
+              references: [{ link: 'https://example.com', title: 'Result', type: 'link' }],
+              images: [{ imageUrl: 'https://example.com/i.png' }],
+              answerBox: { answer: '42' },
+              knowledgeGraph: { title: 'KG' },
+              peopleAlsoAsk: [{ question: 'q' }],
+              relatedSearches: ['related'],
+              news: [{ title: 'n' }],
+              videos: [{ title: 'v' }],
+              places: [{ title: 'p' }],
+              shopping: [{ title: 's' }],
+            },
+          },
+        ],
+      });
+
+      const [message] = await getMessages(
+        { conversationId, user: 'user123' },
+        CLIENT_MESSAGE_SELECT,
+      );
+
+      expect(message.text).toBe('visible text');
+      expect(message.content).toHaveLength(1);
+      expect(message.tokenCount).toBe(42);
+      const metadata = message.metadata as Record<string, unknown>;
+      expect(metadata.usage).toBeDefined();
+      expect(metadata.thoughtSignatures).toBeUndefined();
+
+      const hidden = message as unknown as Record<string, unknown>;
+      for (const field of [
+        '_id',
+        'user',
+        'conversationSignature',
+        'clientId',
+        'invocationId',
+        'summary',
+        'summaryTokenCount',
+        'contextMeta',
+        'langfuseSampled',
+        'langfuseDestinationIds',
+      ]) {
+        expect(hidden[field]).toBeUndefined();
+      }
+
+      type ProjectedWebSearch = {
+        turn: number;
+        organic: Array<Record<string, unknown>>;
+        topStories: Array<Record<string, unknown>>;
+        references: unknown[];
+        images: unknown[];
+      } & Record<string, unknown>;
+      const webSearch = (message.attachments?.[0] as { web_search: ProjectedWebSearch }).web_search;
+      expect(webSearch.turn).toBe(0);
+      expect(webSearch.organic[0].title).toBe('Result');
+      expect(webSearch.organic[0].link).toBe('https://example.com');
+      expect(webSearch.organic[0].snippet).toBe('snippet');
+      expect(webSearch.organic[0].sitelinks).toBeUndefined();
+      expect(webSearch.organic[0].highlights).toBeUndefined();
+      expect(webSearch.topStories[0].title).toBe('Story');
+      expect(webSearch.topStories[0].highlights).toBeUndefined();
+      expect(webSearch.references).toHaveLength(1);
+      expect(webSearch.images).toHaveLength(1);
+      /** `videos` stays: `turn…video…` citation markers resolve against it
+       *  (the clipboard refTypeMap addresses it explicitly). */
+      expect(webSearch.videos).toHaveLength(1);
+      expect(webSearch.answerBox).toBeDefined();
+      for (const vertical of [
+        'knowledgeGraph',
+        'peopleAlsoAsk',
+        'relatedSearches',
+        'news',
+        'places',
+        'shopping',
+      ]) {
+        expect(webSearch[vertical]).toBeUndefined();
+      }
+    });
+  });
+
+  describe('conversation fetch index', () => {
+    it('declares the compound index that serves the conversation fetch and its sort', () => {
+      const indexes = Message.schema.indexes() as Array<[Record<string, number>, unknown]>;
+      expect(indexes).toContainEqual([
+        { conversationId: 1, user: 1, createdAt: 1 },
+        expect.anything(),
+      ]);
+    });
+  });
+
   describe('getMessages', () => {
     it('should retrieve messages with the correct filter', async () => {
       const conversationId = uuidv4();
diff --git a/packages/data-schemas/src/methods/message.ts b/packages/data-schemas/src/methods/message.ts
index ca1928a907..a864acc576 100644
--- a/packages/data-schemas/src/methods/message.ts
+++ b/packages/data-schemas/src/methods/message.ts
@@ -9,6 +9,40 @@ import logger from '~/config/winston';
 /** Simple UUID v4 regex to replace zod validation */
 const UUID_REGEX = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
 
+/**
+ * Exclusion projection for message reads that feed the chat client (the
+ * conversation GET and shared-link reads). Every excluded field is either
+ * server-internal (ids, replay signatures, legacy summarization state) or a
+ * web_search SERP vertical no citation marker or UI can address: markers
+ * resolve `search|image|news|video|ref|file` through organic/images/
+ * topStories/videos/references (all kept — `news` markers read topStories,
+ * never the `news` collection). The JSON export mirrors this cache, so
+ * fields removed here also leave user exports.
+ */
+export const CLIENT_MESSAGE_SELECT: string = [
+  '-_id',
+  '-__v',
+  '-user',
+  '-clientId',
+  '-invocationId',
+  '-conversationSignature',
+  '-summary',
+  '-summaryTokenCount',
+  '-contextMeta',
+  '-langfuseSampled',
+  '-langfuseDestinationIds',
+  '-metadata.thoughtSignatures',
+  '-attachments.web_search.knowledgeGraph',
+  '-attachments.web_search.peopleAlsoAsk',
+  '-attachments.web_search.relatedSearches',
+  '-attachments.web_search.shopping',
+  '-attachments.web_search.places',
+  '-attachments.web_search.news',
+  '-attachments.web_search.organic.sitelinks',
+  '-attachments.web_search.organic.highlights',
+  '-attachments.web_search.topStories.highlights',
+].join(' ');
+
 interface MessageQueryOptions {
   limit?: number;
   sort?: Record<string, 1 | -1> | false;
diff --git a/packages/data-schemas/src/methods/share.ts b/packages/data-schemas/src/methods/share.ts
index 88356114a6..87d470efc1 100644
--- a/packages/data-schemas/src/methods/share.ts
+++ b/packages/data-schemas/src/methods/share.ts
@@ -10,6 +10,7 @@ import {
 } from '~/utils/stripUIResourceMarkers';
 import { activeExpirationFilter } from '~/utils/retention';
 import { isValidObjectIdString } from '~/utils/objectId';
+import { CLIENT_MESSAGE_SELECT } from './message';
 import logger from '~/config/winston';
 
 class ShareServiceError extends Error {
@@ -782,7 +783,7 @@ export function createShareMethods(mongoose: typeof import('mongoose')): {
       const share = (await query
         .populate({
           path: 'messages',
-          select: '-_id -__v -user',
+          select: CLIENT_MESSAGE_SELECT,
         })
         .select('-__v')
         .lean()) as (t.ISharedLink & { messages: t.IMessage[] }) | null;
diff --git a/packages/data-schemas/src/schema/message.ts b/packages/data-schemas/src/schema/message.ts
index 99415cb561..2d74d6b71c 100644
--- a/packages/data-schemas/src/schema/message.ts
+++ b/packages/data-schemas/src/schema/message.ts
@@ -199,6 +199,15 @@ messageSchema.index({ expiredAt: 1 }, { expireAfterSeconds: 0 });
 messageSchema.index({ createdAt: 1 });
 messageSchema.index({ messageId: 1, user: 1, tenantId: 1 }, { unique: true });
 
+/**
+ * Serves the conversation fetch ({conversationId, user} filter + createdAt
+ * sort) from the index alone; without it Mongo fetches every full document in
+ * the conversation and sorts them in memory. tenantId is deliberately not in
+ * the middle: untenanted deployments issue no tenantId predicate, and a gap in
+ * the prefix would push the sort back into memory for them.
+ */
+messageSchema.index({ conversationId: 1, user: 1, createdAt: 1 });
+
 // index for MeiliSearch sync operations
 messageSchema.index({ _meiliIndex: 1, isTemporary: 1, expiredAt: 1 });