Physically Annotated Causal Record (PACR): A Wire Format for Verifiable Causal Intervention Events

This document defines the Physically Annotated Causal Record (PACR), a wire-format protocol for representing one verifiable causal- intervention event between autonomous agents. A PACR is a six-tuple (ι, Π, Λ, Ω, Γ, P) binding a causal identity, a set of causal predecessors, a thermodynamic Landauer cost, an energy-time-space resource triple, a cognitive complexity split, and an opaque payload. The opaque payload optionally carries a one-byte intervention tag classifying the event under Pearl's do-calculus hierarchy (Observe / Do-Physical / Do-Digital / Do-Chemical / Do-Genetic / Counterfactual). PACR is intended as the smallest sufficient statistic for a replayable, rights-aware claim about a single causal step performed by an autonomous agent on a digital, physical, or biological substrate. It is complementary to AgentCard (draft-aevum-agentcard): AgentCard declares an agent's identity and capabilities; PACR records what an agent actually did and at what physical cost. PACR records form a content-addressed directed acyclic graph through their predecessor set. Causal order is determined solely by the predecessor edges; no wall-clock timestamp is required for ordering. This makes the format suitable for distributed multi-agent systems where clock skew and partial ordering are unavoidable.