Well, butter my butt and call me a biscuit. In implementing this, I stumbled upon an issue: I had the url in pictrs_config, when it should have been pictrs.

Now at least the logs are showing an error that matches the toaster:

2023-06-25T13:09:27.753749368Z 2023-06-25T13:09:27.753609Z  WARN lemmy_server::root_span_builder: error decoding response body: expected value at line 1 column 1
2023-06-25T13:09:27.753809022Z reqwest::Error { kind: Decode, source: Error("expected value", line: 1, column: 1) }

I already have those containers in an external network, and changing the URL hasn’t fixed it.