FlowMutator parameter conflicts in multi-level inheritance

[ShantanuKumar]

When using FlowMutator to add parameters to a base flow class with multi-level inheritance (grandchild classes), Metaflow throws an error indicating that the parameter already exists, even though it was added by the mutator on a parent class.

Error Message

Metaflow 2.19.5 executing FlowGrandChild for user:skumar
    Flow failed:
    Flow 'FlowGrandChild' already has a class member 'triggered_by' -- set overwrite=True in add_parameter to overwrite it.

Environment

• Metaflow Version: 2.19.5
• Python Version: 3.11.10

Reproduction Steps

Run this code

from metaflow import (
    FlowMutator,
    Parameter,
    FlowSpec,
    step,
)
from metaflow.user_decorators.mutable_flow import MutableFlow

class TriggeredByParameter(FlowMutator):

    def pre_mutate(self, mutable_flow: MutableFlow):

        mutable_flow.add_parameter(
            "triggered_by",
            Parameter(
                "triggered_by",
                default="ci-cd",
                type=str,
                help="Username of the user triggering the flow",
            ),
        )

@TriggeredByParameter()
class BaseFlow(FlowSpec):

    def dummy_method(self):
        pass

class BaseFlowChild(BaseFlow):

    def child_method(self):
        pass

class FlowGrandChild(BaseFlowChild):
    """Final Flow."""

    msg: str = Parameter(  # type: ignore
        "msg",
        type=str,
        help="Error message to log",
    )

    @step
    def start(self):
        print("BaseFlowError:", self.msg)
        self.next(self.end)

    @step
    def end(self):
        pass

if __name__ == "__main__":
    FlowGrandChild()

[ShantanuKumar]

Should be fixed by #2639