Fix: Add missing lifespan parameter to StreamableHTTP mounting examples #1494
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Fixes modelcontextprotocol#1484 - Add contextlib import and lifespan function to all mounting examples - Add stateless_http=True parameter to FastMCP constructors - Add lifespan=lifespan parameter to Starlette apps - Update README.md documentation with correct examples - Fixes RuntimeError: Task group is not initialized. Make sure to use run() Resolves the issue where mounting StreamableHTTP servers to existing ASGI applications would fail with RuntimeError due to missing session manager initialization.
Run scripts/update_readme_snippets.py to sync documentation with code changes.
felixweinberger
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felixweinberger
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Oct 23, 2025
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Hi @ranjitodedra thanks for this - looks like you also changed the examples to use stateless_http=True which is more than adding a lifespan param.
That's not covered in the description, was that change intentional? If so why was it changed?
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Fixes #1484
Fixes the RuntimeError that occurs when mounting StreamableHTTP servers to existing ASGI applications. The error "Task group is not initialized. Make sure to use run()" was caused by missing session manager initialization.
Motivation and Context
RuntimeError: Task group is not initialized. Make sure to use run().when trying to mount StreamableHTTP servers to existing ASGI applications (like Starlette). This was caused by missing session manager initialization. The documentation examples were incomplete and didn't show the requiredlifespanparameter needed to properly initialize the session manager.How Has This Been Tested?
Breaking Changes
No breaking changes. This is a documentation fix that provides the correct implementation pattern.
Types of changes
Checklist
Additional context
N/A