💥 Schedule async markers like regular threads

[Quinn-With-Two-Ns]

What was changed

Added SCHEDULE_ASYNC_STUB_OPERATIONS, which queues detected Async stub calls in command order without allocating a workflow thread. The flag remains disabled by default. Previously async stub were executed inline.

Why?

Changing an Async call between a stub method reference and a lambda can change command order and break replay. The flag provides a way to preserve that order for histories that record it.

In practice this meant that changing workflow code from this:

    @Override
    public String execute() {
      Promise<String> first =  Async.function(activities::first)
      String second = activities.second();
      return first.get() + "," + second;
    }

to this

    @Override
    public String execute() {
      Promise<String> first = Async.function(() -> activities.first())
      String second = activities.second();
      return first.get() + "," + second;
    }

was not deterministic. After this change and the flag is enabled it would be a deterministic change.

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?

---

Note

Medium Risk
Touches core Async/replay command ordering in AsyncInternal; mitigated by default-off flag and replay tests, but enabling it changes scheduling semantics for new runs.

Overview
Introduces versioned SCHEDULE_ASYNC_STUB_OPERATIONS SDK flag (off by default) so that when it is recorded in workflow history, Async.function / Async.procedure on Temporal stubs are dispatched through a workflow thread like generic lambdas, instead of running stub logic inline on the caller thread.

AsyncInternal.execute now checks the flag before branching: legacy behavior keeps immediate invokeTemporalStub; with the flag, stub work is completeFrom(invokeTemporalStub(...)) inside WorkflowThread.newThread, aligning command order between equivalent forms such as activities::first and () -> activities.first() and letting outbound interceptors observe/block around scheduling. Unflagged histories still replay with the old inline-stub path.

CHANGELOG notes the behavior; tests add replay fixtures (method reference ↔ lambda, unflagged), blocking-interceptor and cancellation cases (activities and child workflows).

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[Quinn-With-Two-Ns]

related: #2981

[maciejdudko]

Awesome! The code looks good, just needs rebasing. LGTM!