chore(mcp): align with React Query and design-token best practices

- useForceRefreshMcpTools: onSuccess → onSettled so cache reconciles on error
- useMcpServerTest: replace `instanceof Error` ternaries with `toError().message`
- mcp.tsx: use `--text-error` token (not the unused `--error`) and drop redundant dark variant

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/settings/components/mcp/mcp.tsx

@@ -716,7 +716,7 @@ export function MCP({ initialServerId }: MCPProps) {
         <div className='min-h-0 flex-1 overflow-y-auto'>
           {error ? (
             <div className='flex h-full flex-col items-center justify-center gap-2'>
-              <p className='text-[var(--error)] text-xs leading-tight dark:text-[var(--error)]'>
+              <p className='text-[var(--text-error)] text-xs leading-tight'>
                 {error instanceof Error ? error.message : 'Failed to load MCP servers'}
               </p>
             </div>

apps/sim/hooks/queries/mcp.ts

@@ -1,5 +1,6 @@
 import { useEffect } from 'react'
 import { createLogger } from '@sim/logger'
+import { toError } from '@sim/utils/errors'
 import { keepPreviousData, useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
 import { ApiClientError } from '@/lib/api/client/errors'
 import { requestJson } from '@/lib/api/client/request'
@@ -115,8 +116,9 @@ export function useForceRefreshMcpTools() {
 
   return useMutation({
     mutationFn: (workspaceId: string) => fetchMcpTools(workspaceId, true),
-    onSuccess: (tools, workspaceId) => {
-      queryClient.setQueryData(mcpKeys.toolsList(workspaceId), tools)
+    onSettled: (tools, _error, workspaceId) => {
+      if (tools) queryClient.setQueryData(mcpKeys.toolsList(workspaceId), tools)
+      queryClient.invalidateQueries({ queryKey: mcpKeys.toolsList(workspaceId) })
     },
   })
 }
@@ -455,7 +457,7 @@ export function useMcpServerTest() {
       logger.info(`MCP server test ${result.success ? 'passed' : 'failed'}:`, variables.name)
     },
     onError: (error) => {
-      logger.error('MCP server test failed:', error instanceof Error ? error.message : error)
+      logger.error('MCP server test failed:', toError(error).message)
     },
   })
 
@@ -466,8 +468,7 @@ export function useMcpServerTest() {
         ? ({
             success: false,
             message: 'Connection failed',
-            error:
-              mutation.error instanceof Error ? mutation.error.message : 'Unknown error occurred',
+            error: toError(mutation.error).message,
           } as McpServerTestResult)
         : null),
     isTestingConnection: mutation.isPending,