Enable full TypeScript `strict` mode and fix issues discovered during
this refactor. Introduced a `errorMessage` helper function to cleanly
extract a error messages from the `unknown` type.
Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (claude-opus-4-7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>