Pin Cython<3.3 for pyzmq source-build compat (3007.x) - #70119
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What broke
Cython 3.3.0 (published to PyPI 2026-08-22) rejects two variable redeclarations in pyzmq's Cython source:
pyzmq's
[build-system].requirespullscythonunpinned, so every PEP 517 source build of pyzmq (--no-binary=:all:onedir path intools/pkg/build.py) pulls Cython 3.3.0 and fails.PIP_CONSTRAINTis already set torequirements/constraints.txtand (per pip docs) still propagates to PEP 517 build envs on pip <26.2.Fix
Add
Cython < 3.3torequirements/constraints.txt. Build tooling only — no runtime deps or lock files change (Cython is a build-only dep, uv-pip-compile does not record it).Scope
requirements/constraints.txt: +7 lines (comment + pin)changelog/70119.fixed.mdNo runtime code touched.
Cross-branch
Same fix on all active branches: