Emily Shaffer [off-list ref] writes:
Teach pre-applypatch, post-applypatch, and applypatch-msg to use the
hook.h library instead of the run-command.h library. This enables use of
hooks specified in the config, in addition to those in the hookdir.
These three hooks are called only by builtin/am.c.
I was interested in the applypatch-msg the most; it gets fed the
"final-commit" file as its input and expected to modify it in place,
so if you allow two or more to work in series, you do not have to
anything extra (like swapping the output from the previous step to
the input for the next step), which makes this a relatively easy
conversion.