Stable vs internal

Stable means you expect downstream breakage to hurt real users and you will update platform-spec / semver policy before changing behavior. Internal means “I can rename this Tuesday.”

Corelib documents stability tiers under Stability and API shape. Your application packages should copy the discipline, not necessarily the same tier names.

API checklist

• Export only symbols you want to support long-term.
• Keep internal modules private unless they are intended extension points.
• Prefer one public boundary file per subsystem.