🔌 fix: Preserve Ephemeral MCP Selections Across Model Switches (#13697)

The no-spec branch of `useApplyModelSpecEffects` (added in #11796) reset
`ephemeralAgentByConvoId` to null on every `newConversation` call when
model specs are configured. On in-place model/endpoint switches (modular
chat, same conversation or new-chat draft), BadgeRowContext never refills
from localStorage — its init effect only re-runs when the storage suffix
or spec changes — so the MCP selection (and tool toggles) were silently
dropped from subsequent request payloads while the MCP badge kept
displaying them.

Reset now only happens on context transitions (leaving a spec, or moving
to a different conversation key), where a BadgeRowContext refill is
guaranteed; in-place non-spec switches preserve the ephemeral agent.

- Gate the no-spec reset on `prevSpecName` / `prevConvoId`, passed from
  `newConversation` via a snapshot read of the pre-switch conversation
- Add jest coverage for all five branches of the no-spec path
- Add e2e spec asserting `ephemeralAgent.mcp` stays in the chat payload
  after a new-chat model switch and after regenerate on a switched
  conversation (verified failing before the fix, passing after)
- Add non-spec "Mock Provider D" endpoint to the e2e config so tests can
  switch between two real ephemeral endpoints; widen `MockEndpoint` type

e2e/config/librechat.e2e.yaml

@@ -50,6 +50,18 @@ endpoints:
       titleConvo: false
       modelDisplayLabel: 'Mock Provider C'
 
+    # Second non-spec endpoint so e2e tests can switch between two real
+    # ephemeral endpoints (e.g. MCP selection persistence across switches).
+    - name: 'Mock Provider D'
+      apiKey: 'e2e-mock-key-d'
+      baseURL: 'http://127.0.0.1:8889/v1'
+      models:
+        default:
+          - 'mock-model-d'
+        fetch: false
+      titleConvo: false
+      modelDisplayLabel: 'Mock Provider D'
+
 modelSpecs:
   prioritize: true
   # Enforcement would reject sends from the non-spec paths addedEndpoints
@@ -59,6 +71,7 @@ modelSpecs:
   # set) limited to entries that don't collide with the spec labels above.
   addedEndpoints:
     - 'Mock Provider C'
+    - 'Mock Provider D'
     - 'agents'
   list:
     - name: 'e2e-mock-provider-a'

e2e/specs/mock/helpers.ts

@@ -10,7 +10,7 @@ export const MOCK_ENDPOINTS = [
   { label: 'Mock Provider B', model: 'mock-model-b' },
 ] as const;
 
-export type MockEndpoint = (typeof MOCK_ENDPOINTS)[number];
+export type MockEndpoint = { label: string; model: string };
 
 export const NEW_CHAT_PATH = '/c/new';
 

e2e/specs/mock/mcp-ephemeral.spec.ts

@@ -0,0 +1,84 @@
+import { expect, test } from '@playwright/test';
+import type { Page, Response } from '@playwright/test';
+import {
+  NEW_CHAT_PATH,
+  isAgentsStream,
+  mockReply,
+  selectMockEndpoint,
+  sendMessage,
+} from './helpers';
+
+/** Non-spec endpoints from e2e/config/librechat.e2e.yaml — switching between
+ *  them exercises the no-spec `applyModelSpecEffects` path that previously
+ *  wiped the ephemeral agent (MCP selection) for the active conversation. */
+const PROVIDER_C = { label: 'Mock Provider C', model: 'mock-model-c' };
+const PROVIDER_D = { label: 'Mock Provider D', model: 'mock-model-d' };
+
+const MCP_SERVER_NAME = 'e2e-memory';
+const MCP_SERVER_TITLE = 'E2E Memory';
+
+const uniqueText = (prefix: string) => `${prefix} ${Date.now()}-${Math.floor(Math.random() * 1e4)}`;
+
+const mcpBadge = (page: Page) => page.getByRole('button', { name: new RegExp(MCP_SERVER_TITLE) });
+
+/** Select the MCP server from the composer's ephemeral MCP dropdown. */
+async function selectEphemeralMCP(page: Page) {
+  await page.getByRole('button', { name: 'MCP Servers', exact: true }).click();
+  const serverItem = page.getByRole('menuitemcheckbox', { name: new RegExp(MCP_SERVER_TITLE) });
+  await expect(serverItem).toBeVisible();
+  await serverItem.click();
+  await expect(serverItem).toHaveAttribute('aria-checked', 'true');
+  await page.keyboard.press('Escape');
+  await expect(mcpBadge(page)).toBeVisible();
+}
+
+/** The `ephemeralAgent.mcp` array sent with a chat request. */
+function requestMCP(response: Response): string[] | undefined {
+  const body = response.request().postDataJSON() as { ephemeralAgent?: { mcp?: string[] } };
+  return body.ephemeralAgent?.mcp;
+}
+
+test.describe('ephemeral MCP selection persistence', () => {
+  test('keeps the MCP selection when switching models on a new chat', async ({ page }) => {
+    test.setTimeout(120000);
+    await page.goto(NEW_CHAT_PATH, { timeout: 10000 });
+
+    await selectMockEndpoint(page, PROVIDER_C);
+    await selectEphemeralMCP(page);
+
+    await selectMockEndpoint(page, PROVIDER_D);
+    await expect(mcpBadge(page)).toBeVisible();
+
+    const response = await sendMessage(page, uniqueText('mcp new chat switch'));
+    expect(response.ok()).toBeTruthy();
+    expect(requestMCP(response)).toContain(MCP_SERVER_NAME);
+
+    await expect(mockReply(page)).toBeVisible({ timeout: 20000 });
+  });
+
+  test('keeps the MCP selection when regenerating after a model switch', async ({ page }) => {
+    test.setTimeout(120000);
+    await page.goto(NEW_CHAT_PATH, { timeout: 10000 });
+
+    await selectMockEndpoint(page, PROVIDER_C);
+    await selectEphemeralMCP(page);
+
+    const first = await sendMessage(page, uniqueText('mcp regenerate switch'));
+    expect(first.ok()).toBeTruthy();
+    expect(requestMCP(first)).toContain(MCP_SERVER_NAME);
+    await expect(mockReply(page)).toBeVisible({ timeout: 20000 });
+    await expect(page).toHaveURL(/\/c\/(?!new)/, { timeout: 15000 });
+
+    await selectMockEndpoint(page, PROVIDER_D);
+    await expect(mcpBadge(page)).toBeVisible();
+
+    const [regenerated] = await Promise.all([
+      page.waitForResponse(isAgentsStream, { timeout: 30000 }),
+      page.getByRole('button', { name: 'Regenerate', exact: true }).click(),
+    ]);
+    expect(regenerated.ok()).toBeTruthy();
+    expect(requestMCP(regenerated)).toContain(MCP_SERVER_NAME);
+
+    await expect(mockReply(page).first()).toBeVisible({ timeout: 20000 });
+  });
+});