How factor environments with TOML (tox.toml, e.g. py313-django52)

[bittner]

I'm trying to migrate from tox.ini to tox.toml, but I don't get the environments listed that are meant to be factored.

tox.ini (relevant portions only)

[tox]
envlist =
    # Python/Django combinations that are officially supported (minus end-of-life Pythons)
    py{39,310,311,312}-django{42}
    py{310,311,312,313}-django{51}
    py{310,311,312,313}-django{52}

[testenv]
description = Unit tests
deps =
    coverage[toml]
    pytest-django
    django42: Django>=4.2,<5.0
    django51: Django>=5.1,<5.2
    django52: Django>=5.2,<6.0
commands =
    coverage run -m pytest {posargs}

[gh-actions]
python =
    3.9: py39
    3.10: py310
    3.11: py311
    3.12: py312
    3.13: py313

[gh-actions:env]
DJANGO =
    4.2: django42
    5.1: django51
    5.2: django52

tox.toml (relevant portions only)

requires = ["tox>=4.22"]
env_list = [
    # Python/Django combinations that are officially supported (minus end-of-life Pythons)
    "py{39,310,311,312}-django{42}",
    "py{310,311,312,313}-django{51}",
    "py{310,311,312,313}-django{52}",
]

[env_run_base]
description = "Unit tests"
deps = [
    "coverage[toml]",
    "pytest-django",
    "django42: Django>=4.2,<5.0",
    "django51: Django>=5.1,<5.2",
    "django52: Django>=5.2,<6.0",
]
commands = [
    ["coverage", "run", "-m", "pytest", "{posargs}"],
]

[gh-actions]
python = """
    3.9: py39
    3.10: py310
    3.11: py311
    3.12: py312
    3.13: py313
    """

["gh-actions:env"]
DJANGO = """
    4.2: django42
    5.1: django51
    5.2: django52
    """

The gh-actions sections are needed for tox-gh-actions. See the django-analytical project for full context.

Environments are not listed

When I run tox list I get a full list of expanded environments for the INI-based configuration...

$ tox list
default environments:
py39-django42  -> Unit tests
py310-django42 -> Unit tests
py311-django42 -> Unit tests
py312-django42 -> Unit tests
py310-django51 -> Unit tests
py311-django51 -> Unit tests
py312-django51 -> Unit tests
py313-django51 -> Unit tests
py310-django52 -> Unit tests
py311-django52 -> Unit tests
py312-django52 -> Unit tests
py313-django52 -> Unit tests

... but for the identical TOML-based setup I only get py as an environment. What do I do wrong?

$ tox list
default environments:
py      -> Unit tests

Additional context

I use uv on NixOS, and Tox is installed via uv tool install tox --with tox-uv. I also tried to install Tox without tox-uv both via uv tool and in a dedicated virtualenv, but couldn't see any change in the problematic behavior.