Function add 

pub async fn add(
    pool: &PgPool,
    actor: &Actor,
    version_id: Uuid,
    new: NewAnnotation,
) -> AppResult<Annotation>

Pins a note to a point of a file version.

Invariants

• Permission: the version is readable (“not found” otherwise).
• Limits: text 1–2000 characters, finite coordinates (400), at most MAX_PER_VERSION notes per version (409).
• Audit: annotation.add on the revision.