1 files changed, 50 insertions, 0 deletions
diff --git a/internal/image/gemini_test.go b/internal/image/gemini_test.go
index aae8014..91e0ce4 100644
--- a/internal/image/gemini_test.go
+++ b/internal/image/gemini_test.go
@@ -9,6 +9,7 @@ import (
 	"net/http/httptest"
 	"strings"
 	"testing"
+	"unicode/utf8"
 
 	"google.golang.org/genai"
 )
@@ -189,6 +190,55 @@ func TestGeminiProvider_Search_CustomPromptIsTruncated(t *testing.T) {
 	}
 }
 
+func TestGeminiProvider_Search_CustomPromptTruncatesUTF8Safely(t *testing.T) {
+	originalText := geminiGenerateText
+	originalImage := geminiGenerateImage
+	t.Cleanup(func() {
+		geminiGenerateText = originalText
+		geminiGenerateImage = originalImage
+	})
+
+	geminiGenerateText = func(context.Context, *GeminiProvider, string, string, string, float32, int32) (string, error) {
+		t.Fatal("unexpected text generation for truncated custom prompt")
+		return "", nil
+	}
+
+	var gotPrompt string
+	geminiGenerateImage = func(_ context.Context, _ *GeminiProvider, prompt, _ string) ([]byte, string, error) {
+		gotPrompt = prompt
+		return mustJPEGBytes(t), "image/jpeg", nil
+	}
+
+	client := NewGeminiProvider(&GeminiConfig{APIKey: "test-key"})
+	longPrompt := strings.Repeat("яa", 2500)
+	if len(longPrompt) <= maxCustomPrompt {
+		t.Fatal("test prompt did not exceed truncation limit")
+	}
+
+	results, err := client.Search(context.Background(), &SearchOptions{
+		Query:        "ябълка",
+		CustomPrompt: longPrompt,
+	})
+	if err != nil {
+		t.Fatalf("Search() unexpected error: %v", err)
+	}
+	if !utf8.ValidString(gotPrompt) {
+		t.Fatalf("Search() returned invalid UTF-8 prompt: %q", gotPrompt)
+	}
+	if len(gotPrompt) > maxCustomPrompt {
+		t.Fatalf("prompt length = %d, want <= %d", len(gotPrompt), maxCustomPrompt)
+	}
+	if !strings.HasSuffix(gotPrompt, "...") {
+		t.Fatalf("prompt = %q, want ellipsis suffix", gotPrompt)
+	}
+	if client.LastPrompt() != gotPrompt {
+		t.Fatalf("LastPrompt() = %q, want %q", client.LastPrompt(), gotPrompt)
+	}
+	if len(results) != 1 {
+		t.Fatalf("expected 1 result, got %d", len(results))
+	}
+}
+
 func TestGeminiProvider_GenerateImage_UsesCustomPrompt(t *testing.T) {
 	originalText := geminiGenerateText
 	originalImage := geminiGenerateImage