Action-Bound Injective Authorization under Signer Harvesting

This preprint defines Action-Bound Injective Authorization (ABIA) for an authorization collector that may solicit genuine signatures on many semantic contexts and later choose which artifacts to present. The experiment records semantic signing events, not only raw byte queries, so a non-injective context transplant remains visible even when the accepted bytes were previously signed. A game-based reduction separates exact-context authenticity and 2-of-2 quorum binding from stateful, completely mediated single-use admission. Four necessity propositions and nine deliberately weakened symbolic variants identify the load-bearing assumptions. Four Tamarin models check the corresponding symbolic properties. The paper states a narrow trace-prefix authenticity result across later key reveal and proves that ordinary signatures alone do not provide offline anti-backdating. It does not claim a new signature primitive, trusted rendering, human identity, exactly-once physical execution, or security of a particular deployment. This is an unrefereed technical preprint.