principle-single-source-of-truthlisted

# Single Source of Truth Every rule, constant, and schema is defined in exactly one place, and every other surface consults it rather than restating it. Where a copy must exist, one side is canon and a deterministic check pins the other to it. **Why:** The second copy is the one that drifts. Two authorities that disagree are worse than none, because each reader picks one and both believe they followed the rule. **Pattern:** - Name the owner at the point of deference: "the schema is canonical in <path> — consult that skill rather than restating it." - Constants live where they execute (the script, the table, the skill that runs them), and prose points at them instead of repeating values. - A deliberate duplication — a template block, a byte-identical fragment — gets a consistency gate so the copies cannot drift, and a comment naming the canon. - When a summary and its source disagree, the source wins. State which surface is authoritative where both exist. - Restate at most one line inline for readability; anything longer than a line belongs to the owner, cited.