Pull request overview

This PR introduces plugin stability levels (Alpha/Beta/Stable) into the EPP plugin registry, adds an experimentalPlugins feature gate to block Alpha plugin initialization by default, and adds stability dependency validation between Consumer/Producer plugins in the data layer.

Changes:

• Extend plugin registration to include stability metadata and expose stability lookup via GetPluginStability.
• Add experimentalPlugins feature-gate enforcement during plugin instantiation (Alpha blocked unless explicitly enabled).
• Add data-layer validation to prevent higher-stability consumers from depending on lower-stability producers.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

		fwkplugin.Register(mockType, fwkplugin.StabilityStable, func(name string, _ *json.Decoder, _ fwkplugin.Handle) (fwkplugin.Plugin, error) {
			return mockDataSource, nil
		})
		defer delete(fwkplugin.Registry, mockType)
	}

One follow-up... the Alpha gate is only enforced in instantiatePlugins, so plugins auto-created via registerDefaultPlugin or CreateMissingDataProducers bypass it. No Alpha default producers exist today, so probably just a TODO.