How do you envision pushing/reviewing a branch of 3 cleanly separated commits (say: write failing test, fix code, refactor) into a repo with a fast-forward/no-merge policy? The end result should of course be 3 commits, but review history should not be lost.

1) push 3 commits (author)

2) push 3 commits + 1 review commit (reviewer)

or even 2a), + 3 interleaved review commits, might be needed if the final refactor removes something.

then

3a) force-push 3 commits with the review comments applied (you mentioned --force is supported)

3b) or push 3 + 1 + (worst case 3) fixup commits, then a squash later?

If 3a), does pico have the concept of patchsets like gerrit, so the state 2) can be retrieved later?

PS: ... or even 2c, if the line I am commenting on is removed in patch 2 I would need to push a whole "review tree" (or fix conflicts in b and c):

   a -- b -- c -- review-c
    \   \
     \   `-review-b
      `- review-a