Here's a quick proposal for a new "notmuch search-messages" command,
from which one can generate a list of Message IDs matching a search
string.

Beyond this, I'd like to add some --format options to both "search"
and "search-messages" so that users can get out the information they
want, (such as thread-id only from a thread search, filenames only
from a message search, etc.).

Any thoughts from others on this kind of thing?

I know people have been talking about doing thing like modifying
message files based on tags, and this seems like the beginnings of
support for doing scripted operations like that.

-Carl