Migration as a sequence.

Create checkpoints that mean something

I would break a migration into transitions with clear entry and exit conditions. A useful checkpoint answers whether the new path can serve a defined need, how its results compare, and what would trigger a return to the previous path.

That structure makes progress easier to assess than a single percentage complete. Moving code, moving data, validating behavior, and changing who depends on the result are different kinds of work. I want each to have visible evidence. The sequence can then expand deliberately as confidence grows in the parts already moved.