Add changelog unpack command

[lcawl]

Summary

Adds a changelog unpack command that derives changelog files from a bundle file.

Rationale

For PRs like elastic/elasticsearch#158728 where a bundle file has been created, but changelogs are not stored locally and have not been uploaded to the CDN.
Perhaps this might be an exceptional situation in the long-term, but IMO it is useful to be able to reverse-engineer changelogs from bundles.

Details

Unpack is implemented as a mapper onto changelog add / changelog note, including amend merge and docs for scrubbed public bundles.

Command: docs-builder changelog unpack <bundle.yaml> [--output] [--config] [--concise]

• PR-anchored entries go through CreatePreparedChangelog (same writer as add, no GitHub fetch, no one-file-per-PR split).
• Entries with no PRs or with product versions go through CreateNote.
• # PRIVATE: sentinels are unwrapped to the underlying URL.
• Parent bundles merge sibling .amend-* files like render. Amend inputs unpack entries only and skip exclude-entries.
• Filenames follow add/note rules; a warning is emitted if that differs from file.name. Checksums are not restored.
• Scrubbed public bundles that lost PRs and have no product versions fail with an error that tells you to unpack the private-side YAML.

Tests

I used this command to successfully generate changelog files from the bundles like this:

/path/to/docs-builder/.artifacts/publish/docs-builder/release/docs-builder changelog unpack ./docs/releases/elasticsearch-serverless-2026-09-08.yaml --concise

/path/to/docs-builder/.artifacts/publish/docs-builder/release/docs-builder changelog unpack ./docs/releases/cloud-serverless/elasticsearch-2026-09-08.yaml --output ./docs/changelog-temp --concise

I was then able to successfully make some edits to the changelogs, upload the changelogs to S3, and re-generate the bundles.

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

2. If you answered "Yes" to the previous question, please specify the tool(s) and model(s) used (e.g., Google Gemini, OpenAI ChatGPT-4, etc.).

Tool(s) and model(s) used: Cursor Grok 4.6

[github-actions]

Docs preview (local build)

Handbook preview: https://docs-v3-preview.elastic.dev/elastic/docs-builder/pull/4059/

Sample changed pages:

• docs/cli/changelog/cmd-unpack.md
• docs/cli/changelog/cmd-bundle.md
• docs/cli/changelog/cmd-upload.md
• docs/cli/changelog/index.md
• docs/data/release-notes/create.md