Replace ErrorResponse with SlurmAPIError that extracts structured errors/warnings from JSON body when Slurm returns non-2xx (e.g. 404 with valid JSON). Add IsNotFound helper for fallback logic.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>