Function upsert_note_for 

pub fn upsert_note_for(
    git_dir: &Path,
    format: ObjectFormat,
    store: &FileRefStore,
    notes_ref: &NotesRef,
    annotated: &ObjectId,
    blob: ObjectId,
    message: &str,
    identity: &NotesCommitIdentity,
    ref_expected: Option<RefTarget>,
) -> Result<UpsertNoteOutcome>

Incrementally upsert a single note, reading any fanout layout and writing a flat sorted tree. Returns UpsertNoteOutcome::Unchanged when annotated already maps to blob.