Classify PromptKit generation errors safely

internal/framework/contracts/errors.go

@@ -9,3 +9,31 @@ var ErrInvalidStructuredOutput = errors.New("invalid structured output")
 // ErrLLMCapacityExceeded identifies backend admission exhaustion before model
 // generation begins.
 var ErrLLMCapacityExceeded = errors.New("LLM capacity exceeded")
+
+// ErrLLMGeneration identifies a provider generation failure.
+var ErrLLMGeneration = errors.New("LLM generation failed")
+
+type LLMGenerationError struct {
+	status     int
+	diagnostic string
+}
+
+func NewLLMGenerationError(status int, diagnostic string) *LLMGenerationError {
+	if status < 0 {
+		status = 0
+	}
+	return &LLMGenerationError{status: status, diagnostic: diagnostic}
+}
+func (e *LLMGenerationError) Error() string {
+	if e == nil || e.diagnostic == "" {
+		return ErrLLMGeneration.Error()
+	}
+	return e.diagnostic
+}
+func (e *LLMGenerationError) Unwrap() error { return ErrLLMGeneration }
+func (e *LLMGenerationError) StatusCode() int {
+	if e == nil {
+		return 0
+	}
+	return e.status
+}