fix: SettableAsyncResource clear callbacks if closed before set

[clintropolis]

Description

Fixes SettableAsyncResource to adhere to the contract of javadoc of AsyncResource#addReadyCallback where callbacks are not meant to be fired if close is called before set/setException. Not sure if this is causing any bugs, but plausible?

[FrankChen021]

Severity	Findings
P0	0
P1	1
P2	1
P3	0
Total	2

Reviewed 3 of 3 changed files.

The review found one lifecycle hang and one cancellation-log regression.

---

This is an automated review by Codex GPT-5.6-Luna(max)

[FrankChen021]

[P1] Closing can strand await callers

AsyncResource.await() registers a latch callback and blocks. Clearing callbacks on close removes that wake-up path; if close wins before completion, a late set or setException drains nothing, so an unbounded await blocks indefinitely and a timed await waits until its timeout. Add a close-aware wake-up path and a regression test.

[clintropolis]

I think this is ok, the consumer is expected to call close to abandon an acquire, while the producer should only ever call set/setException, meaning that this should only be a problem in cases where there are multiple consumer threads I think? Nothing is using await in production currently, but added some javadoc to try to clear up the usage model.

[FrankChen021]

Reviewed 3 of 3 changed files.

The Javadocs clarify the intended usage model, but the lifecycle race remains: await() relies on a callback that close() now removes. An independent cancellation thread can therefore strand a single consumer in await() indefinitely. Please add a close-aware wake-up path and regression test.

[capistrant]

thanks for adding clarification in javadocs to help potential future callers understand expected use

[FrankChen021]

Reviewed 3 of 3 changed files for this follow-up.

The await lifecycle concern remains and was addressed in an inline reply; the prior logging concern is resolved by debug-only logging. No additional inline findings.

---

This is an automated review by Codex GPT-5.6-Luna(max)