Return when flow changes during pre_actions

[balalofernandez]

This PR suggests a change in pre-action allowing to call flow_manager.set_node() inside pre-action and perform an early return on the other first set_node call.

Consider this scenario where a pre-action changes the flow to a different node:

async def check_and_redirect_user(action: dict, flow_manager: FlowManager) -> None:
    """Pre-action that checks user state and redirects to a different node if needed."""
    user_state = action.get("user_state", {})
    
    # If the user needs to be redirected to a different flow node
    if user_state.get("needs_onboarding"):
        logger.info("User needs onboarding, redirecting to onboarding node")
        # This call changes the current_node, but the original set_node would continue
        await flow_manager.set_node("onboarding", onboarding_node_config)

Then in a node configuration:

def welcome_node() -> NodeConfig:
    """Welcome node that may redirect to onboarding."""
    return {
        "task_messages": [
            {
                "role": "user",
                "content": "Welcome to our service!"
            }
        ],
        "functions": [...],
        "pre_actions": [
            {
                "type": "check_user_state",
                "handler": check_and_redirect_user,
                "user_state": {"needs_onboarding": True}
            }
        ]
    }

# Usage in main code
await flow_manager.set_node("welcome", welcome_node())

With the fix, when check_and_redirect_user calls set_node("onboarding", ...), the original set_node("welcome", ...) call detects the node change and returns early, preventing it from overwriting the context with the welcome node's configuration.
This ensures that when a pre-action explicitly changes nodes, we respect that decision and don't continue with the original node setup.

I particularly use it to run deterministic functions before, but sometimes I don't want to keep running the original set_node.

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Name	Status	Preview	Updated (UTC)
pipecat-flows	✅ Ready (Inspect)	Visit Preview	Mar 18, 2025 2:26pm