[quinnmil]

Summary

• Add Python 3.15 to the CI test matrix (main.yml).
• Add a py315-django52 tox env. Like the older Pythons, it runs pytest with --asyncio-mode=auto, which the fastmcp integration tests rely on.
• Add the Programming Language :: Python :: 3.15 classifier.

The release workflow already builds cp315 wheels: cibuildwheel builds every CPython version that matches python_requires. This PR also cleans up stale labels in release.yml:

• cibuildwheel_py38plus / "Build python 3.8+ … wheels" becomes build_linux_wheels / "Build Linux … wheels". It actually builds 3.10 through 3.15, and the name no longer includes a version that can go stale.
• "Build pure python wheels (3.14)" becomes "Build pure Python wheel". The 3.14 was only the Python used to run the build, and the py3-none-any wheel works on every version.
• The CIBW_SKIP: ${{ matrix.cibw_skip }} line is removed. It referenced a matrix key removed in build with python 3.14 #826, so it was always empty.

Behavior change on Python 3.15: plain @instrument now works on async functions

In Python 3.15, contextlib.ContextDecorator wraps coroutine functions itself (the long-standing bpo-37398, referenced in AsyncDecoratorMixin). So on 3.15+, using instrument, WebTransaction or BackgroundTransaction without .async_ on an async function now keeps the span open while the coroutine runs. Nested spans show up correctly, the same as with .async_. On earlier Pythons the span still closes as soon as the coroutine is created, so .async_ is still needed there.

The three *_async_misconfigured tests in tests/integration/test_api.py asserted the pre-3.15 behavior. They now check the Python version, and the CHANGELOG has an entry about the change.

Related

• Python 3.15 crash - KeyError on distribution.metadata Name access #864 and Fix Python 3.15 crash on malformed distribution metadata #865: a crash that only happened on 3.15, which this matrix would have caught.
• Free-threaded Python (3.14t/3.15t): importing _objtrace re-enables the GIL #867: free-threaded builds (cp314t and cp315t wheels are already shipped, but _objtrace re-enables the GIL). That's tracked separately, so this PR doesn't add t jobs.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NgEia2eCsEQTpSH8BMfR1d

[jrothrock]

Approving — looks good. I left a few nits inline; they're all optional, none change behavior, and none need to be addressed before merging.

• tests/integration/test_api.py:42, 181, 239 — the """Test case where .async_ isn't used…""" docstrings now read as if the result is always wrong, but on 3.15+ the plain decorator is correct. Maybe add "(only misbehaves on Python < 3.15)". (docstring accuracy)

[jrothrock]

nit: this if sys.version_info >= (3, 15): … else: … block (and its comment) is repeated at L194-202 and L252-260. The rest of the suite gates on versions with pytest.mark.skipif markers rather than branching inside a test body (e.g. the shared markers in tests/tools.py, tests/unit/test_fastmcp.py:11). You could add a marker like skip_if_context_decorator_wraps_coroutines to tests/tools.py and split each test into a < 3.15 case and a >= 3.15 case. The 3.15 branch asserts the same thing as the matching .async_ test, so the >= 3.15 case could even be dropped. (sibling convention: no conditional logic in tests)