Resolve one pending tool approval on a suspended run.

Delivers the verdict through the task workflow's resolve_approval update — an acknowledged RPC whose result is the truth about what the workflow recorded. The handler runs atomically with respect to batch settlement, so a 200 here always means the decision applied to the exact call the caller saw in pending_approvals; verdicts racing the 4h timeout or a concurrent decision come back not_pending/superseded and map to 409 instead of a false accept. Retrying the same verdict is idempotent (first decision wins). Authorization mirrors check/await (uniform 404 outside the caller's read scope) — whoever can see a run can decide its approvals, matching the a2a trust model where the caller agent is the approver.