alwaysReplay: run()'s AbortSignal can't observe a sibling fiber's interrupt() within one attempt

[nstandif]

Under alwaysReplay, a fiber parked in ops.run() cannot observe an interrupt() call issued from a sibling fiber that itself needs a durable resume (e.g. sleep) to reach that call, within the same attempt:

• Delivering the sibling's already-ready durable completion requires the attempt to suspend.
• The SDK won't suspend while any run() is still pending.
• The pending run() can only stop being pending via interrupt() (gated behind that same suspend) or its own fallback/rejection.

Closed loop — the run() closure only ever settles via whatever resolves it locally, never via the cross-fiber abort, in that attempt. Once settled, the journal entry is fixed; replays don't re-invoke the closure, they replay the recorded result.

Reproduction:

   httpRequest.on("close", () => {
-    abortController.abort();
+    if (!httpRequest.readableEnded) abortController.abort();
   });

Applying this correct fix (needed independently, see #745) exposes the gap — before it, a spurious abort on every normal half-close happened to overwrite the test's side-channel observation, masking this.

Scope: the fiber-throw interrupt-delivery path (this.wake in fiber.ts) is unaffected and 100% reliable — the worker's catch block and result are correct in every mode. Only the auxiliary run()-scoped AbortSignal firing promptly enough to cancel a real external side effect (e.g. an in-flight fetch) is affected, specifically under alwaysReplay with this exact cross-fiber ordering shape.

Not fixed here — deferred pending a decision on whether alwaysReplay's suspend-gating should special-case this, or whether it's accepted as inherent to the debug mode.