ZHG2017

> Thanks for the PR. Can you only include in this one the relevant files for the bug fix? The documentation related files should be in another PR (I think...

> Thanks for the PR. Can you only include in this one the relevant files for the bug fix? The documentation related files should be in another PR (I think...

> What was the reason the bug is happening, the corresponding [test](https://github.com/mamba-org/mamba/blob/main/micromamba/tests/test_env.py#L159-L175) is supposed to check the `--prune` flag's behavior... Can you add a test reproducing the issue and showing...

> > > Thanks for the PR. Can you only include in this one the relevant files for the bug fix? The documentation related files should be in another PR...

> There is `test_classic_spec` in `test_update.py` failing [here](https://github.com/mamba-org/mamba/actions/runs/8434394421/job/23098036714?pr=3243). The modifications should have broken it. This is due to the solution actions in transaction [not empty](https://github.com/mamba-org/mamba/blob/main/libmamba/src/core/transaction.cpp#L828-L831) and so the ["message" key](https://github.com/mamba-org/mamba/blob/main/libmamba/src/core/transaction.cpp#L374-L378)...