I couldn't find a logging library that worked for my library, so I made one

Almost every logger in java operates this way. You set your library logging to debug and the end user and configure if they want debug logs from your library or not. They can even set context variables.

This feels a bit like a pub/sub pattern; I wonder what it would look like with a full pub/sub implementation.

At least you learned something

I really want something like this to be built into the language or runtime, I don't want to juggle configuration for 4 different libraries. Log4j and tracing seem to be well established without being built in, but it feels too late for js.

I'm curious if this is enough https://nodejs.org/api/diagnostics_channel.html

I don't like the js hotel libraries, their docs feel deliberately obtuse

Wasn't OpenTelemetry invented for this purpose?

Did you consider log4js?