So... I heard back from the grad chair, and there's nothing to worry about with the TA posting. Which means:
1.) I don't have to worry about my thesis, because it's got departmental approval now, and things are moving;
2.) I have reassurance from the grad studies awards people that I'll be fine;
3.) I have reassurance from the history grad secretary that defending in September isn't a problem;
4.) Even my oversight in missing the TA posting deadline wasn't a problem;
5.) Chris has a possibility with a half-time supervisory position at a prominent Christian school, and definite subbing with them.
This afternoon I had a realisation: I have nothing I can worry about. Nothing. I barely know what to do.
I think I'm going to eat a cookie.