Read an action definition

Use for an action's current input schema and configuration availability. Historical captured inputs/results are in get_action_execution; this definition does not reconstruct the configuration at execution time. Requires actions:read. Use the receipt actionId, including custom:, sheets: or http: prefixes. Integration instances share actionId; specify integrationId when ambiguous (409 ACTION_AMBIGUOUS). Returns operation input schemas, including separate Sheets read/write operations. No credentials, destination URLs or internal configuration. This read does not authorize execution. Sheets v2 exposes enabled read/update/create operations; legacy definitions retain read/write.