chore(backend): correct node id for metrics reporting

[HumairAK]

Description of your changes:

This fixes metrics reporting for v1 pipeline runs that log metrics. Previously the wrong node id was sent to the api server.

You can verify this with this sample pipeline:

sample.py

from typing import NamedTuple

import kfp
from kfp import dsl
from kfp.components import create_component_from_func


# Step 1: Define a Python function as a component
def train_op() -> NamedTuple('Outputs', [('mlpipeline_metrics', 'Metrics')]):
    import json
    import random
    from pathlib import Path

    # Generate a dummy metric (accuracy)
    accuracy = random.uniform(0.7, 0.99)

    # Write metrics to the designated file
    metrics = {
        "metrics": [
            {
                "name": "accuracy",
                "numberValue": accuracy,
                "format": "PERCENTAGE"
            }
        ]
    }

    # KFP convention: write metrics.json to /mlpipeline-metrics.json
    # Path("/mlpipeline-metrics.json").write_text(json.dumps(metrics))

    return [json.dumps(metrics)]


# Step 2: Convert function to KFP component
train_component = create_component_from_func(
    func=train_op,
    base_image="python:3.9"
)


# Step 3: Define the pipeline
@dsl.pipeline(
    name="Simple Metric Logging Pipeline",
    description="A minimal example that logs a single metric."
)
def simple_pipeline():
    train_task = train_component()


# Step 4: Compile the pipeline
if __name__ == "__main__":
    kfp.compiler.Compiler().compile(
        pipeline_func=simple_pipeline,
        package_path="simple_pipeline.yaml"
    )

Here's the resulting json if you query this run:

sample.json

{
  "run": {
    "id": "aee677a3-c3a1-47a2-bbbb-81821f47c447",
    "name": "Run of simple_pipeline (261da)",
    "pipeline_spec": {}, # omitted
    "resource_references": [
      {
        "key": {
          "type": "EXPERIMENT",
          "id": "fa3653ac-312d-46bc-a67a-a9eaab61c779"
        },
        "relationship": "OWNER"
      },
      {
        "key": {
          "type": "PIPELINE_VERSION",
          "id": "428f5c85-d0c6-4062-b795-76b846272c59"
        },
        "relationship": "CREATOR"
      }
    ],
    "service_account": "pipeline-runner",
    "created_at": "2025-09-03T19:50:04Z",
    "scheduled_at": "2025-09-03T19:50:04Z",
    "finished_at": "2025-09-03T19:50:14Z",
    "status": "Succeeded",
    "metrics": [
      {
        "name": "accuracy",
        "node_id": "simple-metric-logging-pipeline-gxltq-train-op-3397519976",
        "number_value": 0.7160825905928586,
        "format": "PERCENTAGE"
      }
    ]
  },
  "pipeline_runtime": { } # omitted
}

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[mprahl]

/approve
/lgtm

[mprahl]

/approve
/lgtm

[google-oss-prow]

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