The `jj debug` commands are hidden from help and are described as
"Low-level commands not intended for users", but e.g. `jj debug
completion` is intended for users, and should be visible in the help
output.
I broke the commands in a27da7d8d5 and thought I just fixed it in
c7cf914694a8. However, as I added a test, I realized that I made it
only reindex the commits since the previous operation. I meant for the
command to do a full reindexing of th repo. This fixes that.
