## What changed
- Require each `ContextualUserFragment` to provide a stable `<feature>.<name>`
`ContentItemKind`.
- Add `AnnotatedContent` and `RenderedFragment` so rendered text, its role, and
its classification can travel together to API boundaries.
- Derive extension-owned world-state classifications from the extension ID and
keep the skills catalog classification with its fragment implementation.
## Testing
- Verify that an extension-owned world-state section renders with an
`<extension-id>.instructions` content kind.
GitOrigin-RevId: e46b74a0bb41e0b6112667c9d36bc9e7f2714451
