Say the licence once, so anything can be built at all

[MAXAWER]

Every CI job on main is failing, and every release job would fail the same
way, on a repository nobody had changed. This is a two-line fix and it blocks
the v1.1.0 release.

What happened

setuptools 77 implemented PEP 639: a
project may state its licence as an SPDX expression or as a trove
classifier, and stating it both ways is now an error rather than a redundancy.
pyproject.toml did both:

license = "AGPL-3.0-only"
classifiers = [ ..., "License :: OSI Approved :: GNU Affero General Public License v3", ... ]

setuptools.errors.InvalidConfigError: License classifiers have been superseded
by license expressions (see https://peps.python.org/pep-0639/). Please remove:

Nothing in the repository changed to cause it — the runners' setuptools did. The
failure is in pip install -e, so it takes out every test job on every platform
and both packaging jobs with it.

The fix

The classifier goes and the expression stays, that being the one which is not
deprecated.

The build-system floor moves from setuptools>=68 to >=77 at the same time,
for the other half of the same problem: below 77 that same license line is
read as the legacy licence field, which wants a table rather than a string,
and the build fails from the other direction. Pinning the floor makes which of
the two happens a decision rather than a property of whichever setuptools a
runner happened to cache.

Checked

• pip install -e . succeeds locally against setuptools 80.
• 166 tests pass.
• The v1.1.0 tag has been withdrawn and its release run cancelled, since it
  would only have produced a red build. Once this merges the tag goes back on
  and the release builds for real.

🤖 Generated with Claude Code