test(mcp): migrate the mcp test helpers to the mcp 2.x MCPServer API

[yuneng-berri]

TLDR

Problem this solves:

• integration-extensions is red on rc/1.103.0
• Two test helpers still import mcp.server.fastmcp
• pyproject pins mcp>=2.2.0,<3, where that module is gone

How it solves it:

• Ports the helpers verbatim from main
• No product code changes; two test files only

User Flow

Not user-facing. This changes test helpers only; no runtime behavior on any route.

Relevant issues

Affected release

Linear ticket

Pre-Submission checklist

• I have added meaningful tests — not applicable: this repairs existing tests that could not be collected
• The handful of test files covering my change pass locally
• My PR passes all required CI/CD checks
• My PR's scope is as isolated as possible; it only solves 1 specific problem
• I have received a Greptile Confidence Score of at least 4/5

Screenshots / Proof of Fix

Root cause: mcp 2.x renamed FastMCP to MCPServer and moved stateless_http, json_response, transport_security, host and port off the constructor onto streamable_http_app() and run(). pyproject.toml pins mcp>=2.2.0,<3, so the v1 import raises at collection. No product code under litellm/ or enterprise/ uses FastMCP — this is test-support only.

Why main is green and the rc is not: the same migration landed on main in 479360ae87, after rc/1.103.0 was cut at fba00f5084. The rc caught the window where an earlier revert (57c757e9d7) was in effect. Only the two helper files are taken from that commit; the rest of it restores unrelated test surface that does not belong on a release candidate.

Setup, both sides:

PYTHONPATH=$PWD/tests:$PWD .venv/bin/python -m pytest \
  tests/integration/mcp/test_mcp_lifecycle.py \
  tests/integration/mcp/test_mcp_protocol_errors.py \
  tests/integration/mcp/test_oauth_configuration.py \
  tests/integration/compatibility/test_persisted_toolsets.py --collect-only -q

Before (fba00f5)

1. Run the command above
2. ModuleNotFoundError: No module named 'mcp.server.fastmcp' on all 4 modules
3. no tests collected, 4 errors in 0.31s

After (9f79a59)

1. Run the same command
2. Zero mcp.server.fastmcp errors
3. 6 tests collected in 0.23s

Type

✅ Test

Caveats (if any)

Low

• tests/mcp_tests/mcp_server.py still imports FastMCP on main and here
• It is launched as a subprocess, not imported, so it does not break collection
• Left alone to keep this port minimal; worth a separate follow-up

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge because it preserves the existing test-helper contracts while adopting the pinned MCP 2.x API

Summary

Migrates two MCP test helpers from the removed FastMCP module to the MCP 2.x MCPServer API while retaining their existing behavior

• Moves stateless HTTP, JSON response, and transport-security options to streamable_http_app
• Moves host, port, and transport-security options to MCPServer.run
• Preserves tool registration, request capture, and synthetic failure coverage

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