Python

I have an idea of what this might look like, but do you have any examples I can crib from?

it does, I use it every day

this is the standard https://packaging.python.org/en/latest/specifications/dependency-groups/

UV has a shitload of features. I've only ever really used it for making virtualemvs for easier cross platform compatibility, but even just for that, there's tons of options related to which packages, from where, etc.

tl:dr probably, although differentiating between "deploy" and "dev" installs is the task of the package config which UV doesn't (to my knowledge) replace in any way.

wreck can. It's venv aware. Takes full advantage of hierarchical requirement files. Is intuitive. The learning curve is minimal. Written in Python.

[[tool.wreck.venvs]]
venv_base_path = '.venv'
reqs = [
    'requirements/pip',
    'requirements/pip-tools',
    'requirements/prod',
    'requirements/dev',
    'requirements/manage',
    'requirements/kit',
    'requirements/mypy',
    'requirements/tox',
]
[[tool.wreck.venvs]]
venv_base_path = '.doc/.venv'
reqs = [
    'docs/requirements',
    'docs/pip-tools',
]

[tool.setuptools.dynamic]
dependencies = { file = ['requirements/prod.unlock'] }
optional-dependencies.pip = { file = ['requirements/pip.lock'] }
optional-dependencies.pip_tools = { file = ['requirements/pip-tools.lock'] }
optional-dependencies.dev = { file = ['requirements/dev.lock'] }
optional-dependencies.manage = { file = ['requirements/manage.lock'] }
optional-dependencies.docs = { file = ['docs/requirements.lock'] }

reqs fix --venv-relpath='.venv'

reqs fix --venv-relpath='.doc/.venv'

From *.in requirements files would produce *.unlock and *.lock files for venv .venv. Package versions are sync'ed within all requirements files within that venv.

I know it's not the point of this comment, but I'll check harlequin out