Retain injected client diagnostic evidence

llm_adapter_internal_test.go

@@ -2,6 +2,7 @@ package promptkit
 
 import (
 	"context"
+	"errors"
 	"reflect"
 	"strconv"
 	"sync"
@@ -65,12 +66,42 @@ func TestPublicLLMClientAdapterCopiesUsagePresence(t *testing.T) {
 	}
 }
 
+func TestPublicLLMClientAdapterPreservesOwnedResponseAlongsideError(t *testing.T) {
+	presence := &TokenUsagePresence{PromptTokens: true}
+	source := &GenerateResponse{
+		Content:       "returned with error",
+		Usage:         TokenUsage{PromptTokens: 6},
+		UsagePresence: presence,
+	}
+	marker := errors.New("injected failure")
+	adapter := publicLLMClientAdapter{client: responseAndErrorClient{response: source, err: marker}}
+
+	got, err := adapter.Generate(context.Background(), domain.GenerateRequest{})
+	if got == nil || !errors.Is(err, marker) {
+		t.Fatalf("response=%+v error=%v", got, err)
+	}
+	source.Content = "mutated after return"
+	presence.PromptTokens = false
+	if got.Content != "returned with error" || got.UsagePresence == nil || !got.UsagePresence.PromptTokens {
+		t.Fatalf("adapter response was not owned: %+v", got)
+	}
+}
+
 type usagePresenceClient struct{ response *GenerateResponse }
 
 func (c *usagePresenceClient) Generate(context.Context, GenerateRequest) (*GenerateResponse, error) {
 	return c.response, nil
 }
 
+type responseAndErrorClient struct {
+	response *GenerateResponse
+	err      error
+}
+
+func (c responseAndErrorClient) Generate(context.Context, GenerateRequest) (*GenerateResponse, error) {
+	return c.response, c.err
+}
+
 type retainingMutatingLLMClient struct {
 	retained GenerateRequest
 }