So what if we instead modified the top level binary ("notmuch") to:

* add an option to specify that commands are to be processed from stdin
  (--batch)

* when in batch mode the db is opened once at the beginning and locked

* commands are processed from stdin in the exact same form they are
  specified on the command line ("tag +foo -- from:bar", "search
  tag:foo", etc.).

* db is closed when EOF is reached.

That seems like it would be a generally much cleaner interface, and much
more flexible.

jamie.