Ant update: They are mostly all gone. A left the mailbox open when she came home, and by the time I came home more than an hour later, there were only a few left around from what I could see (I didn’t look very closely). The mail - which was indeed stuffed in there by the mail carrier - is still sitting on the front porch waiting for all the ants to leave, but hopefully we won’t have to do that again tomorrow.
A kitty came into our screened-in back porch today. It looked like Agaricus but wasn’t him - a little less orangey, and much skinnier. It’s almost certainly the cat a neighbor called us for a month ago - she knew we were the neighborhood’s crazy cat ladies, and wondered if we knew who owned it; she said she felt bad that it seemed so thin. When it was on our back porch, we got a bowl of cat food and it ate hungrily. I quickly got the spare break-away collar we had lying around, and taped a note around it saying “do you own me? please call…” so that if the kitty does have a home, we’ll hopefully hear about it. If a month goes by and we still haven’t heard anything, then we’ll probably take it in for alteration, a checkup, and possibly hand it over to a no-kill group.