Add field maturity and remove experimental pipeline

[kgeller]

Summary

• Add alpha as a first-class schema attribute mirroring beta (validation, reuse propagation, doc rendering), with mutual exclusion enforced
• Remove the experimental/ build pipeline, directory, and unused cgroup.* fields — zero adoption, container.* already covers the use case
• Document field stability definitions (alpha, beta, GA) and promotion criteria in ecs-principles-design.md
• Update authoring docs in schemas/README.md, USAGE.md, and internal developer docs

This is the first of three PRs: (1) alpha maturity + remove experimental, (2) streamline RFC process, (3) annotate in-flight RFCs.

Test plan

• make test — 153 tests pass
• make generate — clean build, no diff
• No stale experimental references in .py, .yml, .j2, or Makefile
• Beta fieldset (device) renders correctly — no regression
• Manually added alpha to agent.version, confirmed italic marker renders in generated docs, then reverted

[github-actions]

🤖 GitHub comments

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Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[github-actions]

Documentation changes preview: https://docs-v3-preview.elastic.dev/elastic/ecs/pull/2599/reference/

[trisch-me]

lgtm

[github-actions]

🔍 Preview links for changed docs

• CHANGELOG.next.md
• USAGE.md
• docs/reference/ecs-principles-design.md
• experimental/README.md
• schemas/README.md
• scripts/docs/markdown-generator.md
• scripts/docs/schema-pipeline.md

[github-actions]

Vale Linting Results

Summary: 1 suggestion found

💡 Suggestions (1)

File	Line	Rule	Message
docs/reference/ecs-principles-design.md	60	Elastic.WordChoice	Consider using 'can, might' instead of 'may', unless the term is in the UI.

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[trisch-me]

one thing that came to my mind - in our docs we don’t have a prominent beta (or alpha) sign, we only have This field is beta and subject to change.

Maybe we should add a tag similar to what we do for otel such as related? and put it near the name so that person see at once the maturity status. Or even use a new column for maturity. wdyt?

[kgeller]

one thing that came to my mind - in our docs we don’t have a prominent beta (or alpha) sign, we only have This field is beta and subject to change.

Maybe we should add a tag similar to what we do for otel such as related? and put it near the name so that person see at once the maturity status. Or even use a new column for maturity. wdyt?

@trisch-me we can consult with the docs team on this as a followup? It definitely sounds nice to make it clearer, but I think it would be great to get their take on it to make sure we can match existing / define the convention

[trisch-me]

sure, do you know who is contact person for this? :)

[kgeller]

sure, do you know who is contact person for this? :)

I'm not sure, my plan was to post in their slack channel 😄