output_config.effort 400 errors on a message now go to the output_config fallback path

Claude Code sorts API errors that mention output_config, which carries the effort option. A 400 error is the API rejecting a request as invalid. Before, any 400 error saying effort is not supported when thinking is disabled was left alone.

Now that error is left alone only if it does not also point at a specific message's effort, in the form messages.N: output_config.effort. An error that does point there is treated as "effort unsupported", and the usual fallback of sending the request without effort applies.