I have an outside door that opens onto a concrete slab. Dirt basement
underneath. The wood lap siding ran right down to the edge of the slab.
Or it did.

How should I fix that? I'm thinking transition to hardie plank and
perhaps some rubber strip caulked in.

I'll need a new threshold over to the slab also. It's about 6" from
the floor edge to the slab. The floor is floating not attached to the wall.

I'm thinking, perhaps, some kind of wood plank (or double plywood),
painted with Dry Lock and setting on something so water doesn't pool
against the edge.

Jeff