Undo interaction result

This is some great work, thanks for sharing this!

​I've been looking at the code and noticed there isn't a direct way to undo the last interaction. Currently, correcting a segmentation seems to require either adding a negative interaction or completely resetting everything.

​There are definitely use cases where a user might want to undo their last action while keeping the previous segmentation results. A possible workaround would be to call add_initial_seg_interaction with the previous segmented image, but that still results in the loss of the interaction tensor.
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Do you think it would be worthwhile to add an undo feature? Perhaps multiplying the interaction vector by the inverse of the decay coefficient and using the previous segmentation in the input tensor could work?

​I'm also curious about the decay mechanism. It only seems to apply to the same interaction type. Is there a specific reason it's not applied across all interaction types?

Start by tracing the interaction handling and decay logic, including the add_initial_seg_interaction entry point, and determine how prior segmentation and interaction state are represented. Clarify the intended undo behavior and cross-type decay semantics with maintainers before implementing; done should preserve the prior segmentation and interaction state after an undo.