no pg_hba.conf entry for host "[local]", user "pgadmin", database "postgres", SSL off on OSX local  all  postgres    trust
host  all  all  0.0.0.0/0  trust
hostnossl    all          all            0.0.0.0/0  trust


I would think either the second or the third would match these criteria.

I've restarted my service on brew with brew service restart postgres@9.6

Am I missing some setting here?
First, the meanings of the fields  are:

# local       DATABASE  USER  METHOD  [OPTIONS]
# host        DATABASE  USER  ADDRESS  METHOD  [OPTIONS]
# host[no]ssl DATABASE  USER  ADDRESS  METHOD  [OPTIONS]


The attempt is:

host = “[local]” (meaning through a Unix domain socket)

user = “pgadmin”

database = “postgres”

SSL = off

Now your lines:

local  all  postgres    trust


does not match because the user pgadmin is not postgres

host  all  all  0.0.0.0/0  trust


does not match because host only matches TCP/IP connections and [local] is not a TCP/IP connection.

hostnossl    all          all            0.0.0.0/0  trust


does not match for the same reason than the previous line.

If you want to "trust" everyone locally through the Unix domain socket, you may change the first line to:

local  all  all    trust