Decision lineage is the complete, traceable path of a decision: backward from the action to the reasoning, policy, and source signals that produced it, and forward from the action to its downstream outcome. A decision with lineage can be audited, replayed, and defended; a decision without it can only be remembered.
Lineage is what separates an explainable system from an explained one. Post-hoc explanations are reconstructions; lineage is the original chain of custody, captured at the moment each link was formed.
In regulated environments, lineage is rapidly becoming the procurement requirement behind the word 'traceability': every automated determination must cite the provision, the data, and the approver that stand behind it.
This vocabulary is implemented, not aspirational — it describes how the MAIA substrate actually runs. See the platform or read the research.