Invalid Action Budget Accounting

Count malformed or unknown commands against the episode action budget even when they are ignored, so format failure cannot be free.

When an agent emits text that is not a valid command, WebGPT ignores the action for environment effect but still charges it against the maximum action budget. Combined with action format enforcement (error templates and early exit on streaks), this prevents infinite free retries that never move state.

Use the same rule in any discrete-action ACI (browser tool action inventory, shell/tool enums): invalid turns are expensive observations, not no-ops. Report invalid-action rate next to agent episode termination modes — rising invalid spend is a harness health signal before resolve rate collapses.

---

Sources

• WebGPT (Nakano et al.), §2