This looks awesome, I had two questions:

Is there a structured concurrency library being used to manage the chained promise calls and lazy evaluation (IE when the final promise result is actually awaited) of the chained functions?

If an await call is never added, would function calls continue to build up taking up more and more memory - I imagine the system would return an error and clear out the stack of calls before it became overwhelmed, what would these errors look like if they do indeed exist?

> Is there a structured concurrency library being used to manage the chained promise calls

Cap'n Web has no dependencies at all. All the chaining is implemented internally. Arguably, this is the main thing the library does; without promise chaining you could cut out more than half the code.

> If an await call is never added, would function calls continue to build up taking up more and more memory

Yes. I recommend implementing rate limits and/or per-session limits on expensive operations. This isn't something the library can do automatically since it has no real idea how expensive each thing is. Note you can detect when the client has released things by putting disposers on your return values, so you can keep count of the resources the client is holding.