Add configurable permanent packages setting

[jezdez]

Summary

Adds a self_permanent_packages conda plugin setting so users can configure extra packages (and their deps) to survive conda self reset. Uses the conda_settings hook with a SequenceParameter, wired into permanent_dependencies().

Configurable via .condarc:

plugins:
  self_permanent_packages:
    - anaconda-anon-usage

Or via CLI: conda config --add plugins.self_permanent_packages anaconda-anon-usage

Or env var: CONDA_PLUGINS_SELF_PERMANENT_PACKAGES=anaconda-anon-usage

Closes #22

Changes

• constants.py: new SELF_PERMANENT_PACKAGES_SETTING constant
• plugin.py: conda_settings hook yielding the new SequenceParameter
• query.py: permanent_dependencies() reads the setting and includes those packages in the protect list
• tests/test_query.py: tests for the setting with/without condarc config
• README.md: documents the new setting under a Configuration section

Test plan

• test_permanent_dependencies_with_setting — packages from the setting are kept
• test_permanent_dependencies_setting_empty_by_default — defaults to empty
• test_permanent_dependencies_without_setting — existing behavior unchanged
• Manual: set self_permanent_packages in condarc, run conda self reset --snapshot current, verify listed packages survive

[soapy1]

This looks good to me. I was having some issues testing this with the conda self reset command. But it looks like the issue I was running into in testing is solved by #122. I was able to verify that this works as intended by testing with the conda self remove command instead.

[soapy1]

when I run a conda config --add plugins.self_permanent_packages anaconda-anon-usage I can see that the config has been added to my condarc. However, it does not appear when I run conda config --show-sources. Is this a bug in core conda?

[jezdez]

Good catch, this is a bug in conda core. conda config --show-sources calls context.collect_all(), which only iterates over Context.raw_data and never consults context.plugins.collect_all(). So plugin settings under the plugins: key are invisible in the output even though they work correctly at runtime.

Filed upstream: conda/conda#15912

[soapy1]

It looks like this is also affecting the conda self remove command. So, if a user runs

$  pixi run conda config --add plugins.self_permanent_packages anaconda-anon-usage
$ pixi run conda self remove anaconda-anon-usage

They will get an error:

SpecsCanNotBeRemoved: Packages '['anaconda-anon-usage']' can not be removed.

Should conda self remove get a flag like --force that allows a user to override the protection for this setting?

[jezdez]

Good point, this is working as designed (the user explicitly configured the package as permanent, so blocking removal is expected), but the UX could definitely be smoother. Rather than adding scope to this PR, let's track a --force flag separately.

Filed: #127

For now the workaround is to remove the package from plugins.self_permanent_packages in .condarc first, then run conda self remove.