fix(mcp): make the SSE push subscription intrinsic to the tools query

The 5min stale time assumed push, but useMcpToolsEvents was only mounted in the
settings page and the tool picker — other consumers of the tools query (dynamic
args, tool selector, canvas block via useMcpToolsQuery/useMcpTools) had no
subscription, so list_changed updates could stay invisible for the full window.

Mount useMcpToolsEvents inside useMcpToolsQuery so every tools consumer gets
real-time push from the shared, reference-counted connection — no consumer is
left re-probing. Removed the now-redundant explicit mounts from the settings
page and tool-input.

Author: waleedlatif1

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

@@ -39,7 +39,6 @@ import {
   useDeleteMcpServer,
   useForceRefreshMcpTools,
   useMcpServers,
-  useMcpToolsEvents,
   useMcpToolsQuery,
   useRefreshMcpServer,
   useStoredMcpTools,
@@ -196,9 +195,6 @@ export function MCP() {
   } = useMcpServers(workspaceId)
   const { data: mcpToolsData = [], toolsStateByServer } = useMcpToolsQuery(workspaceId)
   const { data: storedTools = [], refetch: refetchStoredTools } = useStoredMcpTools(workspaceId)
-  // Real-time refresh via the shared list_changed → SSE push (same subscription the workflow
-  // editor uses), so tool changes reflect here without re-probing on every visit.
-  useMcpToolsEvents(workspaceId)
   const forceRefreshToolsMutation = useForceRefreshMcpTools()
   const forceRefreshTools = forceRefreshToolsMutation.mutate
   const createServerMutation = useCreateMcpServer()

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/tool-input/tool-input.tsx

@@ -79,7 +79,6 @@ import {
   useCreateMcpServer,
   useForceRefreshMcpTools,
   useMcpServers,
-  useMcpToolsEvents,
   useStoredMcpTools,
 } from '@/hooks/queries/mcp'
 import { useWorkflowState, useWorkflows } from '@/hooks/queries/workflows'
@@ -570,7 +569,6 @@ export const ToolInput = memo(function ToolInput({
   const { data: mcpServers = [], isLoading: mcpServersLoading } = useMcpServers(workspaceId)
   const { data: storedMcpTools = [] } = useStoredMcpTools(workspaceId)
   const forceRefreshMcpTools = useForceRefreshMcpTools().mutate
-  useMcpToolsEvents(workspaceId)
   const { navigateToSettings } = useSettingsNavigation()
   const createMcpServer = useCreateMcpServer()
   const { startOauthForServer } = useMcpOauthPopup({ workspaceId })

apps/sim/hooks/queries/mcp.test.tsx

@@ -103,13 +103,25 @@ function mockServers(servers: McpServer[]) {
   })
 }
 
+// jsdom has no EventSource; useMcpToolsQuery mounts the shared SSE subscription.
+class FakeEventSource {
+  onopen: (() => void) | null = null
+  onerror: (() => void) | null = null
+  constructor(public url: string) {}
+  addEventListener(): void {}
+  close(): void {}
+}
+
 describe('useMcpToolsQuery', () => {
   beforeEach(() => {
     vi.clearAllMocks()
+    ;(globalThis as unknown as { EventSource: unknown }).EventSource = FakeEventSource
   })
 
   afterEach(() => {
     vi.restoreAllMocks()
+    ;(globalThis as unknown as Record<string, unknown>).__mcp_sse_connections = undefined
+    ;(globalThis as unknown as Record<string, unknown>).__mcp_sse_subscribed = undefined
   })
 
   it('does not auto-discover disconnected or errored OAuth servers', async () => {

apps/sim/hooks/queries/mcp.ts

@@ -146,6 +146,11 @@ function isServerEligibleForDiscovery(server: McpServer, workspaceId: string): b
 export function useMcpToolsQuery(workspaceId: string) {
   const queryClient = useQueryClient()
   const { data: servers, isLoading: serversLoading } = useMcpServers(workspaceId)
+  // Push is intrinsic to consuming the tools query: every surface that reads tools (settings,
+  // tool picker, dynamic args, tool selector, canvas block) gets real-time `list_changed`
+  // refresh via the shared, reference-counted subscription — so the 5-min stale time is always
+  // push-backed and no consumer is left re-probing.
+  useMcpToolsEvents(workspaceId)
 
   /**
    * Skip disabled rows, rows retained from a previous workspace, and OAuth rows