Isolate execution observations and preserve injected error categories

llm_adapter.go

@@ -2,9 +2,11 @@ package promptkit
 
 import (
 	"context"
+	"errors"
 	"fmt"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
 )
 
 type publicLLMClientAdapter struct {
@@ -13,11 +15,28 @@ type publicLLMClientAdapter struct {
 
 func (a publicLLMClientAdapter) Generate(ctx context.Context, req domain.GenerateRequest) (*domain.GenerateResponse, error) {
 	resp, err := a.client.Generate(ctx, fromDomainGenerateRequest(req))
-	if err != nil {
-		return nil, err
+	if err == nil && resp == nil {
+		err = fmt.Errorf("%w: %w: llm client returned nil response", ErrLLMGenerate, ErrMalformedResponse)
 	}
-	if resp == nil {
-		return nil, fmt.Errorf("%w: %w: llm client returned nil response", ErrLLMGenerate, ErrMalformedResponse)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrTransport):
+			return nil, classifiedClientError{cause: err, category: llm.ErrTransport}
+		case errors.Is(err, ErrMalformedResponse):
+			return nil, classifiedClientError{cause: err, category: llm.ErrMalformedResponse}
+		}
+		return nil, err
 	}
 	return toDomainGenerateResponse(resp), nil
 }
+
+// classifiedClientError makes an explicit public category available internally
+// without replacing the client's diagnostic or original error chain.
+type classifiedClientError struct {
+	cause    error
+	category error
+}
+
+func (e classifiedClientError) Error() string        { return e.cause.Error() }
+func (e classifiedClientError) Unwrap() error        { return e.cause }
+func (e classifiedClientError) Is(target error) bool { return target == e.category }