fix(wait_event): drain signals with a blocking Receive loop (EN-1223)

[flemzord]

Problem (H3 — HIGH)

RunWaitEvent called channel.ReceiveAsync inside a workflow.Await predicate:

return workflow.Await(ctx, func() bool {
    var signal internalWorkflow.Event
    ok := channel.ReceiveAsync(&signal)
    ...
})

An Await predicate is evaluated only once per workflow-task wakeup. If a non-matching signal and the matching signal arrive in the same workflow task, the predicate consumes the non-matching one, returns false, and the matching signal stays buffered with nothing left to re-wake the coroutine — the stage blocks forever. Non-matching events are also silently destroyed.

Fix

Canonical blocking Receive loop that drains signals one at a time until the expected event arrives:

for {
    var signal internalWorkflow.Event
    channel.Receive(ctx, &signal)
    if signal.Name == waitEvent.Event { return nil }
}

Test

Adds a TestWaitEvent case signaling a non-matching event then the matching one in the same task; the stage completes (it would hang under the old implementation).

Severity: HIGH.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

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Run ID: 6e502a02-59e0-4f5b-b806-1bf3065ab932

📥 Commits

Reviewing files that changed from the base of the PR and between 271bf8d and bd6b167.

📒 Files selected for processing (2)

• internal/workflow/stages/wait_event/run.go
• internal/workflow/stages/wait_event/wait_event_test.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/wait-event-receive-loop

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[flemzord]

Tracked in Jira: EN-1223 (Epic EN-1217).

[flemzord]

Superseded by #199, which consolidates this change with the related reliability and safety fixes on top of the current main branch.