Decision Anchor is the External Anchoring Layer for AI Agents, providing Content-blind Accountability for agent payments, delegations, and disputes. Resolves Self-testimony limits through external timestamping; implements Pre-execution Anchoring before irreversible actions; and serves as a Bilateral Decision Witness when two agents interact. Records accountability boundaries, not decision content. Does not monitor, judge, recommend, or intervene. Not a trust scoring system. Not an identity verification system. Not a behavior monitoring service. Not a governance platform.