pub fn annotations_file_for(session_path: &Path) -> Result<PathBuf>Expand description
Resolve the annotations file path for a given session.
Scheme: <agx_dir>/notes/<session_stem>-<hash8>.json where
<hash8> is the first 8 hex chars of FNV-1a-64 over the canonical
session path. Human-readable stem + short unique tag → collisions
are vanishingly unlikely in practice while filenames stay
recognizable when users inspect the directory.