What's the problem this feature will solve?
I want to tell users to run pipx inject mytool mytool[feature] when mytool is installed with pipx, or pip install mytool[feature] otherwise. Currently I tell users to use pip if they are missing an optional dependency required for a particular feature, and this is wrong for pipx users. But I haven't found a non-hacky way to tailor a message for pipx users only.

Describe the solution you'd like
Expose an environment variable or metadata file indicating the tool was installed via pipx, so that my software can determine if it was installed via pipx or not.