AGORA: Interface Irreducibility in Human-Agent Software

Artificial intelligence turns every serious product into a three-body system: user, agent, and interface. Products that let the interface dissolve into user habit or agent optimization may work briefly, but they become replaceable; products that conserve an irreducible interface become places people return to, recognize, and trust. AGORA formalizes a design hypothesis for this new class of software: a durable human-agent interface should preserve an independent mode basis under simultaneous pressure from user habit and agent optimization; this paper proposes and preregisters rhythm, friction, and style as a risky, testable candidate basis. We formalize the claim as the Three-Eigenmode Stability Lemma , introduce the Interface Autonomy Index for public measurement, and preregister Crest alongside external comparison systems as falsifiable tests. The deposit of this paper is the opening lab notebook: if the named invariants do not predict persistence, recognition, and resistance to absorption, AGORA is weakened by the evidence that should have tested it.