Reversion strategies

Instead of always reverting all tasks it would be nice to have a way to associate a policy/strategy with how reverting will be done (likely per flow/engine?) that may involve retrying then reverting or another similar strategy.

For example:

Flow A: revert all tasks after retrying tasks 2-3 (if they fail) two times.
Flow B: never revert.
Flow C: revert using X function instead of reverting individual tasks.
....

I would think that we can provide a pretty minimal way to do this, possibly via a attribute (which may be a object) on a flow that decides if and when the flow (and contained tasks) should be retried and how. This attribute could be a 'retry' object (which would signal to the engine to retry X times), or the attribute could be a 'no-fail' object (which would signal to the engine to silence failures - if they occur in the tasks in the flow - TBD what to do with expected task outputs here).