Garneau was actually the first player signed by the Astros this offseason. When Robinson Chirinos and Martin Maldonado both became free agents at the end of the 2019 season, Houston was in dire need of a catcher. They quickly snatched up Garneau from the free-agent list and a month later re-signed Maldonado.
I know a lot of Astros fans were hoping for a Chirinos return, but that would ultimately never take place. He ended up going back to the Texas Rangers where he played for six years before coming down to Houston as a one-year rental.