fix(auto-instrumentation): Fully preserve returned promise in tracing channel hook

[Luca Forstner (lforst)]

Fix the auto-instrumentation node hook so Anthropic messages.stream() keeps working under node --import braintrust/hook.mjs.

• Preserve the original promise-like return value in the hook instead of returning a chained promise
• Keep Anthropic APIPromise helpers like withResponse() intact
• Remove the e2e workaround so the Anthropic node-hook scenario uses messages.stream() again
• Add regression coverage for promise subclass helper preservation

Fixes #1591

[Stephen Belanger (Qard)]

This change would be incorrect though. It also breaks behavioural compatibility with Node.js core.

[Stephen Belanger (Qard)]

The problem with doing this though is that we'd be silencing unhandledRejection events due to branching and ignoring failures rather than passing through and re-raising the error for the downstream consumer.

[Luca Forstner (lforst)]

I had the same thought actually. I am wondering though, is there any way to preserve exact Node.js behavior while also preserving the "extended" promise?

Can we throw inside the error callback?

[Stephen Belanger (Qard)]

It's a bug on their part for not preserving the promise species correctly. Unsure if there's a way we can hack around it as correct species use also requires retaining the constructor signature for it to be able to correctly construct descendants, but Anthropic violated that contract and gave it a different constructor signature which makes species construction crash. 😐

[Stephen Belanger (Qard)]

This is incorrect as if it reaches here it did not run the async portion and so should not produce asyncStart and asyncEnd events.