fix: strip legacy MCP tokens on removal, guard action creation, model button spacing

MCP selection accepts every historical token format (server placeholder,
raw server name, mcp_-prefixed, and per-tool ids in prefix/suffix shapes)
but removal only filtered the new placeholder plus the server's current
tool ids, so a legacy token left the server permanently selected and its
tools still expanded after save. Selection and removal now share a
matchesMcpServer predicate.

Creating an action from the marketplace on an unsaved agent opened an
editor whose save was guaranteed to fail; it now surfaces the existing
save-the-agent-first error, matching the action-removal guard.

The model picker button keeps its tight px-1 with a provider icon but gets
px-3 in the empty Select-a-model state so the placeholder is not flush
against the border.

client/src/components/SidePanel/Agents/AgentConfig.tsx

@@ -116,7 +116,10 @@ export default function AgentConfig() {
             type="button"
             onClick={() => setActivePanel(Panel.model)}
             title={model || undefined}
-            className="relative flex h-9 w-full min-w-0 items-center overflow-hidden rounded-lg border border-border-light bg-surface-secondary px-1 text-sm font-medium text-text-primary transition-colors hover:bg-surface-tertiary focus:outline-none focus-visible:ring-2 focus-visible:ring-ring-primary"
+            className={cn(
+              'relative flex h-9 w-full min-w-0 items-center overflow-hidden rounded-lg border border-border-light bg-surface-secondary text-sm font-medium text-text-primary transition-colors hover:bg-surface-tertiary focus:outline-none focus-visible:ring-2 focus-visible:ring-ring-primary',
+              model != null && model ? 'px-1' : 'px-3',
+            )}
           >
             <div className="flex w-full min-w-0 items-center gap-2">
               {Icon && (

client/src/components/SidePanel/Agents/Tools/ToolsMarketplaceDialog.tsx

@@ -7,12 +7,13 @@ import {
   OGDialogTitle,
   OGDialogContent,
   OGDialogDescription,
+  useToastContext,
 } from '@librechat/client';
 import type { AgentItem, AgentItemKind, ItemFilter } from './items/types';
 import type { AgentForm } from '~/common';
+import { itemKey, mcpServerToken, matchesMcpServer } from './items/selectors';
 import { useAgentItems, useUninstallToolCredentials } from './hooks';
 import AddMcpServerDialog from './ItemDialog/AddMcpServerDialog';
-import { itemKey, mcpServerToken } from './items/selectors';
 import { computeToggleAction } from './items/mutations';
 import { useLocalize, useToolFavorites } from '~/hooks';
 import MarketplaceSidebar from './MarketplaceSidebar';
@@ -20,6 +21,7 @@ import MarketplaceCatalog from './MarketplaceCatalog';
 import ItemDialog from './ItemDialog/ItemDialog';
 import { applyFilter } from './items/filtering';
 import { NEW_ACTION_ID } from './items/types';
+import { isEphemeralAgent } from '~/common';
 
 interface ToolsMarketplaceDialogProps {
   open: boolean;
@@ -36,6 +38,7 @@ export default function ToolsMarketplaceDialog({
   agentId,
 }: ToolsMarketplaceDialogProps) {
   const localize = useLocalize();
+  const { showToast } = useToastContext();
   const { getValues, setValue } = useFormContext<AgentForm>();
   const uninstallToolCredentials = useUninstallToolCredentials();
 
@@ -56,6 +59,13 @@ export default function ToolsMarketplaceDialog({
         setAddMcpOpen(true);
         return;
       }
+      /** Actions are persisted against the agent id, so an unsaved agent has
+       * nothing to attach them to — surface the save-first error instead of
+       * letting the editor fail on submit. */
+      if (isEphemeralAgent(agentId)) {
+        showToast({ message: localize('com_agents_no_agent_id_error'), status: 'error' });
+        return;
+      }
       setDetailItem({
         kind: 'action',
         id: NEW_ACTION_ID,
@@ -65,7 +75,7 @@ export default function ToolsMarketplaceDialog({
         endpointCount: 0,
       });
     },
-    [localize],
+    [agentId, localize, showToast],
   );
 
   const selectedIds = useMemo(() => new Set(selectedItems.map(itemKey)), [selectedItems]);
@@ -123,11 +133,10 @@ export default function ToolsMarketplaceDialog({
         case 'mcp-remove': {
           if (item.kind !== 'mcp') break;
           const toolIds = new Set((item.server.tools ?? []).map((t) => t.tool_id));
-          const serverToken = mcpServerToken(item.id);
           const current = (getValues('tools') ?? []) as string[];
           setValue(
             'tools',
-            current.filter((t) => t !== serverToken && !toolIds.has(t)),
+            current.filter((t) => !matchesMcpServer(t, item.id) && !toolIds.has(t)),
             { shouldDirty: true },
           );
           break;

client/src/components/SidePanel/Agents/Tools/items/__tests__/selectors.spec.ts

@@ -1,7 +1,7 @@
 import { AgentCapabilities, Constants } from 'librechat-data-provider';
 import type { AgentItem } from '../types';
 import { makePlugin, makeSkill, makeMcpServer, makeAction } from 'test/itemFactories';
-import { deriveSelectedItems } from '../selectors';
+import { deriveSelectedItems, matchesMcpServer } from '../selectors';
 
 const mcpServerToken = (serverName: string) =>
   `${Constants.mcp_server}${Constants.mcp_delimiter}${serverName}`;
@@ -197,3 +197,23 @@ describe('deriveSelectedItems', () => {
     expect(kindOrder.indexOf('tool')).toBeLessThan(kindOrder.indexOf('skill'));
   });
 });
+
+describe('matchesMcpServer', () => {
+  test('matches every persisted token format for the server', () => {
+    expect(matchesMcpServer(`${Constants.mcp_server}${Constants.mcp_delimiter}srv`, 'srv')).toBe(
+      true,
+    );
+    expect(matchesMcpServer('srv', 'srv')).toBe(true);
+    expect(matchesMcpServer('mcp_srv', 'srv')).toBe(true);
+    expect(matchesMcpServer('mcp_srv_tool', 'srv')).toBe(true);
+    expect(matchesMcpServer('search_mcp_srv', 'srv')).toBe(true);
+    expect(matchesMcpServer(`sys__all__sys${Constants.mcp_delimiter}srv`, 'srv')).toBe(true);
+  });
+
+  test('does not match tokens for other servers or plain tool ids', () => {
+    expect(matchesMcpServer('mcp_other', 'srv')).toBe(false);
+    expect(matchesMcpServer('search_mcp_other', 'srv')).toBe(false);
+    expect(matchesMcpServer('dalle', 'srv')).toBe(false);
+    expect(matchesMcpServer('srv2', 'srv')).toBe(false);
+  });
+});

client/src/components/SidePanel/Agents/Tools/items/selectors.ts

@@ -62,17 +62,28 @@ export function mcpServerToken(serverName: string): string {
   return `${Constants.mcp_server}${Constants.mcp_delimiter}${serverName}`;
 }
 
+/**
+ * Whether a form `tools` token references the given MCP server, across every
+ * format ever persisted: the server placeholder token, the raw server name,
+ * the legacy `mcp_<server>` token, and per-tool ids in both prefix and suffix
+ * shapes. Selection and removal must share this predicate — anything the
+ * selection logic counts as attached, an explicit remove must also strip, or
+ * a legacy token leaves the server permanently selected.
+ */
+export function matchesMcpServer(token: string, serverName: string): boolean {
+  const prefixed = `${MCP_PREFIX}${serverName}`;
+  return (
+    token === mcpServerToken(serverName) ||
+    token === serverName ||
+    token === prefixed ||
+    token.startsWith(`${prefixed}_`) ||
+    token.endsWith(`_${prefixed}`)
+  );
+}
+
 function isMcpSelected(item: AgentItem, form: FormSelection): boolean {
   if (item.kind !== 'mcp') return false;
-  const prefixed = `${MCP_PREFIX}${item.id}`;
-  return form.tools.some(
-    (t) =>
-      t === mcpServerToken(item.id) ||
-      t === item.id ||
-      t === prefixed ||
-      t.startsWith(`${prefixed}_`) ||
-      t.endsWith(`_${prefixed}`),
-  );
+  return form.tools.some((t) => matchesMcpServer(t, item.id));
 }
 
 function isSkillSelected(item: AgentItem, form: FormSelection): boolean {