docs: add Docker MCP Gateway streaming transport documentation

- Created comprehensive documentation for Docker MCP Gateway streaming transport configuration
- Clarified that the /mcp path is required when using streaming transport mode
- Added reference in main README.md to guide users to the new documentation
- Addresses issue #6557 where users were experiencing connection errors due to missing /mcp path

Author: roomote

README.md

@@ -97,6 +97,8 @@ Roo Code comes with powerful [tools](https://docs.roocode.com/basic-usage/how-to
 
 MCP extends Roo Code's capabilities by allowing you to add unlimited custom tools. Integrate with external APIs, connect to databases, or create specialized development tools - MCP provides the framework to expand Roo Code's functionality to meet your specific needs.
 
+> **Note:** When using Docker MCP Gateway with streaming transport, see our [Docker MCP Gateway configuration guide](docs/docker-mcp-gateway-streaming.md) for important URL requirements.
+
 ### Customization
 
 Make Roo Code work your way with:

docs/docker-mcp-gateway-streaming.md

@@ -0,0 +1,60 @@
+# Docker MCP Gateway - Streaming Transport Configuration
+
+## Overview
+
+When using the Docker MCP Gateway with the `streaming` transport mode, it's important to understand the correct URL configuration to avoid connection errors.
+
+## Issue
+
+When connecting an MCP client to the Docker MCP Gateway using the `streaming` transport (`docker mcp gateway run --transport streaming`), the connection will fail with errors like "Invalid session ID" if the client is configured to connect to the root URL (e.g., `http://localhost:8080`).
+
+## Root Cause
+
+The Docker MCP Gateway, when running in `streaming` mode, does not serve its MCP functionality from the root path of the server. Instead, it expects all MCP requests to be sent to the `/mcp` endpoint.
+
+## Solution
+
+### Correct Configuration
+
+When configuring your MCP client to connect to a Docker MCP Gateway running with streaming transport, you must include the `/mcp` path in the URL:
+
+```json
+{
+	"mcpServers": {
+		"Docker_MCP_Gateway_streaming": {
+			"type": "streamable-http",
+			"url": "http://localhost:8080/mcp"
+		}
+	}
+}
+```
+
+### Incorrect Configuration (Will Fail)
+
+```json
+{
+	"mcpServers": {
+		"Docker_MCP_Gateway_streaming": {
+			"type": "streamable-http",
+			"url": "http://localhost:8080" // Missing /mcp path
+		}
+	}
+}
+```
+
+## Quick Reference
+
+| Transport Type | Correct URL Format          |
+| -------------- | --------------------------- |
+| Streaming      | `http://localhost:8080/mcp` |
+
+## Additional Notes
+
+- This requirement is specific to the `streaming` transport mode
+- The port number (8080) may vary based on your Docker configuration
+- Always ensure the `/mcp` path is included when using streaming transport
+
+## Related Links
+
+- [MCP Documentation](https://docs.roocode.com/advanced-usage/mcp)
+- [Docker MCP Toolkit Documentation](https://docs.roocode.com/advanced-usage/mcp#docker-mcp-toolkit)