feat(mcp): migrate FlowServer to standalone fastmcp 3.x (#243)#246
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Migrate chainweaver.mcp.FlowServer from the SDK-bundled mcp.server.fastmcp.FastMCP to the standalone fastmcp package. The [mcp] extra now installs fastmcp>=3.4 alongside mcp>=1.0 — the inbound MCPToolAdapter still imports mcp.ClientSession and fastmcp re-uses mcp.types.ToolAnnotations, so adapter.py is untouched. FlowServer's public API is preserved (constructor, serve()/serve_async(), .fastmcp, .registered_tool_names). Internals updated for the 3.x API: tools are built via Tool.from_function(...) then add_tool(tool), and serve()/serve_async() delegate to FastMCP.run/run_async(transport=..., show_banner=False) so stdio framing stays clean. Refresh docs + CHANGELOG and add a migration-guard test. https://claude.ai/code/session_01WgHy1iQwVhRtNDU4DPLPFy
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⚠️ Performance Alert ⚠️
Possible performance regression was detected for benchmark 'ChainWeaver microbenchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.25.
| Benchmark suite | Current: 96c836a | Previous: d266f6f | Ratio |
|---|---|---|---|
compiled_overhead_ms_n10_llm200_tool10 |
0.6568399999196117 ms |
0.3857400000697453 ms |
1.70 |
compiled_overhead_ms_n5_llm500_tool50 |
0.3962240000419115 ms |
0.3162339999107644 ms |
1.25 |
This comment was automatically generated by workflow using github-action-benchmark.
CC: @dgenio
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Pull request overview
Migrates chainweaver.mcp.FlowServer from the MCP SDK-bundled mcp.server.fastmcp.FastMCP to the standalone fastmcp 3.x package while preserving FlowServer’s public API (__init__, serve()/serve_async(), .fastmcp, .registered_tool_names) and keeping stdio output clean for MCP framing.
Changes:
- Switch FlowServer implementation to
fastmcp.FastMCPand register tools viafastmcp.tools.Tool.from_function(...)+add_tool(...). - Update the
[mcp]and[dev]extras to installfastmcp>=3.4alongsidemcp>=1.0. - Refresh docs + changelog and add a test that guards the migration to standalone
fastmcp.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
chainweaver/mcp/server.py |
Migrates FlowServer to standalone fastmcp 3.x tool registration and run APIs (with banner suppressed for stdio framing). |
pyproject.toml |
Adds fastmcp>=3.4 to the mcp and dev optional dependency sets. |
tests/test_mcp_server.py |
Adds a migration-guard test asserting FlowServer is backed by fastmcp.FastMCP. |
docs/mcp-server.md |
Updates outbound MCP server docs to reflect the move to standalone fastmcp while retaining mcp for inbound adapter needs. |
docs/distribution.md |
Updates the verified integration matrix entry for the outbound MCP server to fastmcp 3.4.0 (+ mcp for inbound adapter). |
CHANGELOG.md |
Documents the migration and the [mcp] extra behavior change. |
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Migrate chainweaver.mcp.FlowServer from the SDK-bundled
mcp.server.fastmcp.FastMCP to the standalone fastmcp package. The [mcp]
extra now installs fastmcp>=3.4 alongside mcp>=1.0 — the inbound
MCPToolAdapter still imports mcp.ClientSession and fastmcp re-uses
mcp.types.ToolAnnotations, so adapter.py is untouched.
FlowServer's public API is preserved (constructor, serve()/serve_async(),
.fastmcp, .registered_tool_names). Internals updated for the 3.x API:
tools are built via Tool.from_function(...) then add_tool(tool), and
serve()/serve_async() delegate to FastMCP.run/run_async(transport=...,
show_banner=False) so stdio framing stays clean. Refresh docs +
CHANGELOG and add a migration-guard test.
https://claude.ai/code/session_01WgHy1iQwVhRtNDU4DPLPFy