Read the Docs pull request previews and the project visibility boundary

Read the Docs can build documentation for pull requests so reviewers can inspect rendered changes before a merge. The unresolved point is how those preview builds relate to the project's visibility setting: whether the preview URL inherits the project's public or private state, or is reachable by anyone holding the link.

Visibility is configured at the project level, but individual versions — branches, tags, and pull request builds — are managed separately and can be active or inactive, public or private, on their own. On the community site (readthedocs.org), private project support has historically been limited and imported repositories default to public visibility, while the commercial platform (readthedocs.com) gates private docs behind authenticated access such as organization or team membership. Because of that split, the default exposure of a pull request preview build is not obvious from the main visibility setting, and the exact behavior may vary by platform and plan.

Questions to resolve:

1. Do pull request preview builds inherit the parent project's visibility, or are they served as link-public URLs by default?
2. Where is per-version privacy configured so an active pull request version matches the intended project-level boundary?
3. How does this behavior differ between readthedocs.org and readthedocs.com, and has it changed in recent releases?