π Bug: [CopilotKit] "Step 'chat_node' is already active for 'STEP_STARTED'" on concurrent users despite unique thread_id isolationΒ #2708
Description
β»οΈ Reproduction Steps
When multiple users (or browser tabs) interact with the CopilotKit chat simultaneously, the frontend throws:
Error: Step "chat_node" is already active for 'STEP_STARTED'
at useChat.useAsyncCallback[runChatCompletion] (http://localhost:3000/_next/static/chunks/52940_%40copilotkit_react-core_dist_56801273._.js:1196:39)
at useChat.useAsyncCallback[runChatCompletion].next (<anonymous>)
at fulfilled (http://localhost:3000/_next/static/chunks/52940_%40copilotkit_react-core_dist_56801273._.js:48:32)
This occurs even when:
- Each frontend instance sends a unique
thread_id. - The FastAPI + LangGraph backend receives it and uses it.
- Postgres checkpointer confirms separate, valid checkpoints per
thread_id.
Reproduction Steps
- Open two browser windows (or incognito tabs).
- Each loads the same CopilotKit app:
const threadId = crypto.randomUUID(); <CopilotKit runtimeUrl="http://localhost:4000/copilotkit" threadId={threadId} />
- Send a message in both tabs at the same time.
- One succeeds (and stops streaming midway and throws a similar error), the other throws the
STEP_STARTEDerror.
Versions
[runtime]
"@copilotkit/runtime": "^1.10.6"
[frontend]
"@ag-ui/langgraph": "0.0.18",
"@copilotkit/react-core": "1.10.6",
"@copilotkit/react-ui": "1.10.6",
"@copilotkit/runtime": "1.10.6",
"next": "15.3.2",
"react": "^19.0.0",
"react-dom": "^19.0.0",
"zod": "^3.24.4"
[python]
langchain = "0.3.13"
langgraph = "^0.3.1"
langchain-postgres = "0.0.12"
langchain-community = "0.3.13"
langserve = "0.3.1"
langchain-openai = "0.2.14"
langchain-aws = "0.2.10"
langchainhub = "0.1.21"
ag-ui-langgraph = "^0.0.18"
copilotkit = "^0.1.70"
My Code:
Frontend
const threadId = useMemo(() => crypto.randomUUID(), []);
<CopilotKit
runtimeUrl="http://localhost:4000/copilotkit"
agent="copilot_agent"
threadId={threadId}
/>Node Runtime
app.use('/copilotkit', (req, res, next) => {
const handler = copilotRuntimeNodeHttpEndpoint({
endpoint: '/copilotkit',
runtime: new CopilotRuntime({
agents: {
'copilot_agent': new LangGraphHttpAgent({
url: process.env.LANGGRAPH_DEPLOYMENT_URL || "http://localhost:8000/copilot-agent/stream",
})
},
}),
serviceAdapter,
});
return handler(req, res, next);
});Backend
add_langgraph_fastapi_endpoint(
app=app,
agent=LangGraphAGUIAgent(
name="copilot_agent",
description="Copilot chat agent for interactions",
graph=copilot_graph,
),
path="/copilot-agent/stream",
)β Expected Behavior
Needs to handle concurrent chat requests.
β Actual Behavior
Throwing an error:
Error: Step "chat_node" is already active for 'STEP_STARTED'
Call Stack
useChat.useAsyncCallback[runChatCompletion]
.next\static\chunks\52940_@copilotkit_react-core_dist_56801273._.js (1196:39)
useChat.useAsyncCallback[runChatCompletion].next
<anonymous> (0:0)
fulfilled
.next\static\chunks\52940_@copilotkit_react-core_dist_56801273._.js (48:32)π CopilotKit Version
βββ @copilotkit/[email protected]
βββ @copilotkit/[email protected] -> .\node_modules\.pnpm\@[email protected]_0bcff3a74d6bfe852236e904d377f3cb\node_modules\@copilotkit\react-core
βββ @copilotkit/[email protected] -> .\node_modules\.pnpm\@[email protected]_c645aa3edf720b751045b826b7930dd6\node_modules\@copilotkit\react-ui
βββ @copilotkit/[email protected] -> .\node_modules\.pnpm\@[email protected]__4ef4253f41ef94dd8014e2bcd0ba1eb0\node_modules\@copilotkit\runtimeπ Logs (Optional)
From Console:
Uncaught (in promise) Error: Cannot send 'STEP_FINISHED' for step "chat_node" that was not started
Runtime error:
ERROR: Error in action execution argument stream
component: "CopilotResolver.generateCopilotResponse"
err: {
"type": "CopilotKitError",
"message": "Unknown error occurred",
"stack":
CopilotError: Unknown error occurred
at new CopilotKitError (C:\work\node_modules\@copilotkit\shared\dist\index.js:349:5)
at C:\work\node_modules\@copilotkit\runtime\dist\index.js:6553:15
at C:\work\node_modules\rxjs\dist\cjs\internal\operators\catchError.js:13:51
at OperatorSubscriber._this._error (C:\work\node_modules\rxjs\dist\cjs\internal\operators\OperatorSubscriber.js:43:21)
at Subscriber.error (C:\work\node_modules\rxjs\dist\cjs\internal\Subscriber.js:60:18)
at Subscriber._error (C:\work\node_modules\rxjs\dist\cjs\internal\Subscriber.js:84:30)
at Subscriber.error (C:\work\node_modules\rxjs\dist\cjs\internal\Subscriber.js:60:18)
at Observable.init [as _subscribe] (C:\work\node_modules\rxjs\dist\cjs\internal\observable\throwError.js:8:58)
at Observable._trySubscribe (C:\work\node_modules\rxjs\dist\cjs\internal\Observable.js:41:25)
at C:\work\node_modules\rxjs\dist\cjs\internal\Observable.js:35:31
"extensions": {
"name": "CopilotError",
"statusCode": 500,
"code": "UNKNOWN",
"visibility": "toast",
"severity": "critical",
"troubleshootingUrl": null,
"originalError": {
"message": "Unknown error occurred",
"stack":
Error
at new CopilotKitError (C:\work\node_modules\@copilotkit\shared\dist\index.js:359:18)
at C:\work\node_modules\@copilotkit\runtime\dist\index.js:6553:15
at C:\work\node_modules\rxjs\dist\cjs\internal\operators\catchError.js:13:51
at OperatorSubscriber._this._error (C:\work\node_modules\rxjs\dist\cjs\internal\operators\OperatorSubscriber.js:43:21)
at Subscriber.error (C:\work\node_modules\rxjs\dist\cjs\internal\Subscriber.js:60:18)
at Subscriber._error (C:\work\node_modules\rxjs\dist\cjs\internal\Subscriber.js:84:30)
at Subscriber.error (C:\work\node_modules\rxjs\dist\cjs\internal\Subscriber.js:60:18)
at Observable.init [as _subscribe] (C:\work\node_modules\rxjs\dist\cjs\internal\observable\throwError.js:8:58)
at Observable._trySubscribe (C:\work\node_modules\rxjs\dist\cjs\internal\Observable.js:41:25)
at C:\work\node_modules\rxjs\dist\cjs\internal\Observable.js:35:31
}
},
"code": "UNKNOWN",
"statusCode": 500,
"severity": "critical",
"visibility": "toast"
}