docs(cli-generator): document group help derivation from OpenAPI tags

[devin-ai-integration]

Summary

Generated CLIs no longer show Operations on '<group>' for every command group: group --help text is now derived from the OpenAPI document, using root-level tags[].description and overridable per group with x-fern-groups. This matters because API authors get useful CLI help for free from spec prose they already maintain, and x-fern-groups was previously undocumented anywhere in the docs.

Implements docs for: feat(cli-generator): derive CLI group help from OpenAPI tags and keep help lines concise (fern-api/fern#17476)

Pages changed

• fern/products/cli-generator/openapi-extensions.mdx — new Command group help section: tag-derived help with a plants example, the tag attribution rules (name match, or exclusive to the group and covering at least half its operations; colon-scoped tags excluded; ambiguous tags fall back), and an x-fern-groups subsection covering summary/description, the short-line resolution order (summary → first sentence of description → first sentence of an attributed tag description → Operations on '<name>'), the name-restating summary rule, long help, and the 80-character short-line cap.
• fern/products/cli-generator/quickstart.mdx — one sentence cross-referencing the new section from the --help walkthrough.

Behavior documented was verified against the merged implementation in generators/cli/sdk/src/openapi/commands.rs (group_about_text_for_group, find_tag_description) and the x-fern-groups schema in getFernGroups.ts.

Lint (pre-commit, Vale: 0 errors/warnings/suggestions) and fern check --warnings (0 errors; the 8 warnings are preexisting and unrelated) both pass.

Link to Devin session: https://app.devin.ai/sessions/005b2ff9125446bea0fb18372b62f433

[devin-ai-integration]

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1787505230-cli-group-help-docs.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/cli-generator/get-started/openapi-extensions
• learn/cli-generator/get-started/quickstart