Document allowed version values in fern.config.json

[devin-ai-integration]

Summary

The Fern CLI now accepts only an exact semver version, "latest", or "*" for version in fern.config.json. It used to accept any string. This change matters for security, because the CLI installs and runs whatever version that field names. Customers who pin the CLI version can now see which values are valid, so a v-prefixed version or a range like ^5.40.0 won't surprise them with a validation error.

Implements docs for: fix(cli): reject non-semver versions in fern.config.json (fern-api/fern#17945)

Pages changed

• fern/products/docs/pages/getting-started/project-structure.mdx and fern/products/sdks/project-structure.mdx (both have the same fern.config.json section): added one paragraph covering:
  • accepted values: exact semver (prereleases allowed), "latest", "*"
  • rejected forms: v prefix, ranges, dist-tags, surrounding whitespace, and file:/npm:/git/URL specs
• fern/products/cli-api-reference/pages/general-commands.mdx: one sentence each under fern upgrade --version and fern downgrade. Both commands now check the version the same way before they write fern.config.json (isValidProjectConfigVersion).

fern check --warnings reports 0 errors. The only Vale error is at sdks/project-structure.mdx:51 ("that is"). It's in an unchanged line and was already there.

Link to Devin session: https://app.devin.ai/sessions/76bd1188a1734b9fac32e42fd2efeec8
Open in Devin Desktop: https://app.devin.ai/desktop/session/76bd1188a1734b9fac32e42fd2efeec8?variant=devin

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1790960968-fern-config-version-values.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/cli-api-reference/cli-reference/general-commands
• learn/docs/getting-started/project-structure
• learn/sdks/overview/project-structure