Directory integration, as in, importing a vcard with everyone's phone number into your device such that you can tap on anyone's name and message them on Signal if they've got Signal installed?
Then what I can recommend is installing the desktop client on a server somewhere and reading its sqlite-like (but with some flaky encryption extension) messages database
Fair warning: It will...bloat. It usually keeps 3-4 copies of most recent backups in the folders you select and if you send a lot of photos, imagine it eating tens of gigabytes of storage just for backup.
(My current backups are 9.75 gigs each, approx 3 of them)