Exactly — and "decision receipt" is the better name. A log answers what happened. A receipt answers was this admissible, by which rule, at the moment it crossed into execution — and only the gate that made the allow/deny call can emit that, because it's the one thing holding the inputs, the active policy, and the verdict at decision time.

Post-hoc reconstruction can't recover that even in principle: the policy may have changed since, and the counterfactual ("checked against rule X v3, denied") was never captured unless something recorded it at the boundary. Your field list is the right schema — inputs observed, rule applied, authority boundary, allow/deny, accountable gate.

That maps almost 1:1 onto what a PreToolUse gate can write per decision (rule + version, timestamp, verdict, reviewer path). The two I'd push to make first-class are the two you named that systems usually drop: the explicit authority boundary and a named accountable gate — not just "denied," but "denied by gate G under boundary B." Those are the fields a reviewer always wishes existed six weeks later.

Are you building toward this? I'd genuinely like to compare notes on the receipt schema.