n8n-io/n8n · error

No transport found for sessionId

Error message

No transport found for sessionId

What it means

Error "No transport found for sessionId" thrown in n8n-io/n8n.

Source

Thrown at packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts:239

				await new Promise<void>((resolve) => {
					this.resolveFunctions[callId] = resolve;
					const requestHandled = transport.handleRequest(req, resp, message as IncomingMessage);
					if (isToolCall && transport.transportType === 'sse') {
						// SSE answers the POST with 202 before the tool has run, so completing the
						// request must not resolve here — the CallTool handler does that once the
						// tool finished. A transport failure still resolves so we never hang.
						void requestHandled.catch(() => resolve());
					} else {
						void requestHandled.finally(resolve);
					}
				});
			} finally {
				delete this.resolveFunctions[callId];
				delete this.pendingGateResults[callId];
			}
		} else {
			this.logger.warn(`No transport found for session ${sessionId}`);
			resp.status(401).send('No transport found for sessionId');
		}

		resp.flush?.();

		// A not-ready gate makes the CallTool handler short-circuit (returning the
		// actionable response over the transport instead of executing). Report it as
		// not a tool call so the node does not also trigger a workflow execution.
		const wasGated = !!gateResult && !gateResult.readyToExecute;

		return {
			wasToolCall: MessageParser.isToolCall(rawBody) && !wasGated,
			toolCallInfo,
			messageId,
		};
	}

	async handleDeleteRequest(req: express.Request, resp: CompressionResponse): Promise<void> {
		const sessionId = this.getSessionId(req);

View on GitHub (pinned to 5ac6606e81)

When it happens

Trigger: Thrown at packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts:239 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/21d204c132bfe5eb. Report an issue: GitHub.