Remote trigger should not pass metadata implicitly to downstream pipelines

[y-oksaku]

What happened:

When using the Remote trigger / Remote join feature in Screwdriver, metadata defined in the upstream pipeline is automatically inherited by the downstream pipeline.
This inherited metadata behaves as if it were defined directly in the downstream pipeline, which can cause confusion.
Especially, downstream event cards display the inherited parameters same as own.

This behavior is inconsistent with the meta-cli functionality, which provides an --external option for explicitly referencing metadata from another pipeline.
Since the current inheritance is implicit, the expected behavior is unclear and may lead to unintended dependencies.

What you expected to happen:

Upstream pipeline metadata should not be implicitly inherited by the downstream pipeline.
Instead, downstream pipelines should explicitly retrieve upstream metadata by using the meta-cli --external option.
If necessary, users can explicitly set inherited values by using meta get --external followed by meta set, making metadata dependencies intentional and predictable.

How to reproduce it:

1. Configure an upstream pipeline with metadata values (e.g., build parameters).
2. Trigger a downstream pipeline using Remote trigger / Remote join.
3. Observe that the downstream pipeline’s metadata includes values from the upstream pipeline.
   • In the UI, event cards display upstream metadata as if it were configured by the downstream pipeline itself.

[minghay]

@y-oksaku I think that this should be the correct behavior as implicit inheritance of externally set meta data can be a problem.

For existing pipelines that are inheriting the externally set meta data, is it possible to determine that from the API server? If it is possible, then it would be possible to message those pipelines with a build warning that they need to update the pipeline to use the --external flag to properly inherit the meta data.

[y-oksaku]

Sadly, it’s difficult for the API to determine which pipelines are using the inherited external metadata without --external option.