pub fn append(card_id: &str, fields: Value) -> Result<Value, String>Expand description
Append new top-level fields to an existing Card.
Semantics: additive only. If any top-level key in fields already
exists in the Card, the call fails — Cards are immutable w.r.t. existing
data. New top-level keys are inserted and the Card file is rewritten
atomically.
Returns the merged Card JSON.