[Bug] Fresh ucode install pulls mcp 2.0 and mcp-proxy crashes on a removed API

[davidnasi]

Summary

A fresh ucode installation resolved mcp 2.0.0 because the package declares mcp>=1.28.0. ucode mcp-proxy then crashed during import because it uses streamablehttp_client, which is no longer available under that name in MCP 2.0.0. Every MCP server configured through the proxy consequently failed to connect.

The same incompatible combination remains possible on current main (5f0d5ecdb8106d20f0d218bdd635b4bf707f4973):

• pyproject.toml permits mcp>=1.28.0
• mcp_proxy.py imports streamablehttp_client

Environment

• ucode 0.0.0+174.g62c5536
• mcp 2.0.0 from the unconstrained dependency resolution
• Python 3.14
• Linux container
• Databricks CLI v1.11.0

Steps to reproduce

uv tool install git+https://github.com/databricks/ucode

ucode mcp-proxy \
  --url https://<workspace>/ai-gateway/mcp-services/<service> \
  --host https://<workspace> \
  --profile <profile>

The failure occurs while importing the proxy, before the upstream MCP connection is established.

Actual result

File "ucode/cli.py", line 1015, in mcp_proxy_cmd
  from ucode.mcp_proxy import serve

File "ucode/mcp_proxy.py", line 33, in <module>
  from mcp.client.streamable_http import streamablehttp_client

ImportError: cannot import name streamablehttp_client from mcp.client.streamable_http

The coding agent reports that the MCP server failed to connect.

Expected result

A clean installation should resolve a supported MCP SDK version and start ucode mcp-proxy successfully.

Workaround

uv tool install --force --with "mcp<2" git+https://github.com/databricks/ucode

This resolved MCP 1.29.0, after which the same proxy and governed GitHub MCP connection started successfully.

Acceptance criteria

• Either constrain the dependency to mcp<2 or support the MCP 2.x client API.
• Add a clean-install integration test that resolves the newest dependency version allowed by package metadata and starts ucode mcp-proxy.
• Surface an actionable compatibility error if an unsupported MCP SDK is installed.

Additional context

This was reproduced during an autonomous end-to-end coding-agent governance test on August 9, 2026. The failure blocked the documented clean-install developer path until the dependency was manually downgraded.

[sunishsheth2009]

PR up: #338

Approach: rather than capping mcp<2, the proxy now supports both mcp 1.x and 2.x and the cap is removed, so a fresh install on either major works. Both versions export streamable_http_client(url, http_client=…); the only differences (httpx vs httpx2, and a 3- vs 2-tuple client yield) are resolved at runtime.

Verified against both mcp 1.28.1 and mcp 2.0.0 in a real venv — the proxy imports (the crash point in this issue), the transport composes, and the proxy test suite + type-check pass on each.

Note: I proved import + transport construction + auth preflight under mcp 2.x, but not a full live-gateway tool call (no live token available in my session). If you can retest a clean uv tool install against your workspace with the PR branch, that confirmation would be helpful.