Use when the user expresses a commitment with rationale that the team is making — "we'll go with…", "let's use X", "we decided to…", "I'm going to switch to…". Records the decision via the `add_decision` MCP tool (or `cairn decision add` CLI), attributed to the appropriate collaborator. Distinct from a *finding* (an observed fact), an *open question* (uncertainty awaiting resolution), and an *action item* (assigned pending work).
