fix(slurm): parse structured errors from non-2xx Slurm API responses

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>

internal/slurm/errors.go

@@ -1,38 +1,85 @@
 package slurm
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
 )
 
-// ErrorResponse represents an error returned by the Slurm REST API.
-type ErrorResponse struct {
-	Response *http.Response
-	Message  string
+// errorResponseFields is used to parse errors/warnings from a Slurm API error body.
+type errorResponseFields struct {
+	Errors   OpenapiErrors   `json:"errors,omitempty"`
+	Warnings OpenapiWarnings `json:"warnings,omitempty"`
 }
 
-func (r *ErrorResponse) Error() string {
+// SlurmAPIError represents a structured error returned by the Slurm REST API.
+// It captures both the HTTP details and the parsed Slurm error array when available.
+type SlurmAPIError struct {
+	Response   *http.Response
+	StatusCode int
+	Errors     OpenapiErrors
+	Warnings   OpenapiWarnings
+	Message    string // raw body fallback when JSON parsing fails
+}
+
+func (e *SlurmAPIError) Error() string {
+	if len(e.Errors) > 0 {
+		first := e.Errors[0]
+		detail := ""
+		if first.Error != nil {
+			detail = *first.Error
+		} else if first.Description != nil {
+			detail = *first.Description
+		}
+		if detail != "" {
+			return fmt.Sprintf("%v %v: %d %s",
+				e.Response.Request.Method, e.Response.Request.URL,
+				e.StatusCode, detail)
+		}
+	}
 	return fmt.Sprintf("%v %v: %d %s",
-		r.Response.Request.Method, r.Response.Request.URL,
-		r.Response.StatusCode, r.Message)
+		e.Response.Request.Method, e.Response.Request.URL,
+		e.StatusCode, e.Message)
+}
+
+// IsNotFound reports whether err is a SlurmAPIError with HTTP 404 status.
+func IsNotFound(err error) bool {
+	if apiErr, ok := err.(*SlurmAPIError); ok {
+		return apiErr.StatusCode == http.StatusNotFound
+	}
+	return false
 }
 
 // CheckResponse checks the API response for errors. It returns nil if the
 // response is a 2xx status code. For non-2xx codes, it reads the response
-// body and returns an ErrorResponse.
+// body, attempts to parse structured Slurm errors, and returns a SlurmAPIError.
 func CheckResponse(r *http.Response) error {
 	if c := r.StatusCode; c >= 200 && c <= 299 {
 		return nil
 	}
 
-	errorResponse := &ErrorResponse{Response: r}
 	data, err := io.ReadAll(r.Body)
 	if err != nil || len(data) == 0 {
-		errorResponse.Message = r.Status
-		return errorResponse
+		return &SlurmAPIError{
+			Response:   r,
+			StatusCode: r.StatusCode,
+			Message:    r.Status,
+		}
 	}
 
-	errorResponse.Message = string(data)
-	return errorResponse
+	apiErr := &SlurmAPIError{
+		Response:   r,
+		StatusCode: r.StatusCode,
+		Message:    string(data),
+	}
+
+	// Try to extract structured errors/warnings from JSON body.
+	var fields errorResponseFields
+	if json.Unmarshal(data, &fields) == nil {
+		apiErr.Errors = fields.Errors
+		apiErr.Warnings = fields.Warnings
+	}
+
+	return apiErr
 }