Stop an active run: cancels the Laravel batch (in-flight steps finish their current step, remaining jobs no-op), reverts still-queued cells, stamps finished_at, emits playtable-runs.cancelled (reason=user). Spent credits are NOT refunded - receipts stand; result carries spent_credits so far (may still grow from in-flight steps) and reverted_cells_count. Idempotent on an already-cancelled run (already_cancelled:true); a normally finished run → 409 conflict.

Contract:

• MCP tool cancel_playtable_run, registry package mcp.playtables/playtable_runs, mount playtables.columns.
• Operation action, response envelope action.
• Flags: dangerous: the MCP layer gates it behind a preview/commit token, and the effect cannot be undone through this API.