Story

Modify the current inheritance model of the .spec.osImageStream field. Currently, custom MCPs do not inherit the worker's osImageStream. This leads to unexpected behavior, as custom MCPs are fundamentally designed to inherit all settings from the worker pool.

This story updates the logic so that the custom MCP inherits the osImageStream from the worker pool. If the custom MCP CR explicitly defines an osImageStream, that value takes precedence. If neither the custom MCP nor the worker pool specifies an osImageStream, it must default to the OSImageStream.status.defaultStream value.

Acceptance Criteria

• If a custom MCP does not explicitly set an osImageStream, it successfully inherits the value used by the worker pool.

• If an osImageStream is defined in neither the worker pool nor the custom MCP, the system correctly falls back to using OSImageStream.status.defaultStream.
• QE has verified the previous two points.

Slack context: https://redhat-internal.slack.com/archives/GH7G2MANS/p1771433254621059