runNode

The user-facing implementation of the node's execution logic.

Emits any of:

• A raw output value (e.g. String, Int, a data class, List, Map), which becomes this node's output and is normalized into an Event by the engine.

• An Event, which passes through directly (useful for progress emissions or custom events).

• null or Unit, both of which signify that no output was produced. Unit represents side-effecting Kotlin lambdas/functions that return no value, while null represents the explicit absence of an output.