If you're the sole copyright owner, you can write an exception text, to be attached to the AGPLv3, similar to the GPL-3.0 Interface Exception, and it may look like this:
Linking [name of library] statically or dynamically with other
modules is making a combined work based on [name of library]. Thus,
the terms and conditions of the GNU Affero General Public License,
version 3 ("AGPLv3") cover the whole combination.
As a special exception, the copyright holders of [name of library]
give you permission to combine [name of library] with
independent modules that communicate with [name of library] solely
through the [name of library's interface] interface, and exclude the
source code of those independent modules from the
Corresponding Source of section 13 of the AGPLv3, provided
that you do not modify the [name of library's interface] interface and provided that those independent modules are themselves not licensed under the AGPLv3.
Note that people who make modified versions of [name of library] are
not obligated to grant this special exception for their modified
versions; it is their choice whether to do so. The AGPLv3 gives
permission to release a modified version without this exception; this
exception also makes it possible to release a modified version which
carries forward this exception. If you modify the [name of library's
interface] interface, this exception does not apply to your modified
version of [name of library], and you must remove this exception
when you distribute your modified version.
This exception is an additional permission under section 7 of the
I am not a lawyer and this is not legal advice.