The .gitmodules was updated in d22593d53 to point at
apps/backend/src/private/implementation, but the gitlink entry (mode
160000) was never added to the tree. This caused
`git clone --recurse-submodules` to silently skip the private submodule.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>