I squashed a PR update onto the PR's commit

(Parts of this one are implicit in the Flight Rules, but I didn't recognize them.)
Here is how I got into trouble.
1. Open a PR, last commit A. Get feedback requiring lots of fixes.
2. Add new commits B and C, holding first and second rounds of fixes.
3. `git rebase -i` intending to squash C into B, but with literally one extra keystroke squash both C and B into A. Now your local and remote branches each have a single commit, but they are different.
4. Try to push (thinking that locally you have a second commit, holding C squashed into B) and git correctly says you are trying to destroy remote history.

Solution:

1. `git log -1 origin/YOUR_BRANCH_NAME` to recover the hash pr-hash of A you wrote over locally in step 3. above. (Note that the value of pr-hash is in the output of `git reflog`, but it can be hard to identify especially if you've been thrashing around trying to fix things.)
2. `git reset --hard pr-hash` Now you are back to where you were before you started answering PR feedback
3. `git cherry-pick hash-of-B` Add the first round of fixes
4. `git cherry-pick hash-of-C` Add the second round of fixes
5. `git rebase -i` but this time leave B as a pick when you squash C, so you have the original PR plus a single commit holding fixes
6. `git push origin YOUR_BRANCH_NAME`