n8n-io/n8n · error

Session not found

Error message

Session not found

What it means

Error "Session not found" thrown in n8n-io/n8n.

Source

Thrown at packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts:178

		if (toolCallInfo) {
			const tool = tools.find((t) => t.name === toolCallInfo!.toolName);
			if (tool?.metadata?.sourceNodeName && typeof tool.metadata.sourceNodeName === 'string') {
				toolCallInfo = { ...toolCallInfo, sourceNodeName: tool.metadata.sourceNodeName };
			}
		}

		if (sessionId && !transport && req.headers['mcp-session-id'] && serverName) {
			this.logger.debug(
				`Recreating StreamableHTTP transport for session ${sessionId} on this main instance`,
			);
			const recreated = await this.recreateStreamableHttpTransport(
				sessionId,
				serverName,
				tools,
				resp,
			);
			if (!recreated) {
				resp.status(404).send('Session not found');
				return { wasToolCall: false };
			}
			transport = this.sessionManager.getTransport(sessionId);
		}

		const isToolCall = MessageParser.isToolCall(rawBody);
		const isListToolsRequest = MessageParser.isListToolsRequest(rawBody);

		if (
			sessionId &&
			!transport &&
			req.query.sessionId &&
			this.executionCoordinator.isQueueMode() &&
			(isToolCall || isListToolsRequest)
		) {
			this.logger.debug(
				`SSE queue mode: forwarding ${isToolCall ? 'tool call' : 'list tools'} for session ${sessionId} via pub/sub`,
			);

View on GitHub (pinned to 5ac6606e81)

When it happens

Trigger: Thrown at packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts:178 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/b19759a319a05cd2. Report an issue: GitHub.