Add prompt-based picture command

internal/telegram/render_test.go

@@ -90,6 +90,20 @@ func TestParseCommand(t *testing.T) {
 	}
 }
 
+func TestPictureGenerationInstruction(t *testing.T) {
+	instruction := pictureGenerationInstruction("generate a blue cube")
+	for _, want := range []string{"Telegram /pic command", "built-in image generation", "generate a blue cube"} {
+		if !strings.Contains(instruction, want) {
+			t.Fatalf("instruction missing %q in %q", want, instruction)
+		}
+	}
+	for _, unwanted := range []string{"/home", "repo/playground"} {
+		if strings.Contains(instruction, unwanted) {
+			t.Fatalf("instruction contains non-portable text %q: %q", unwanted, instruction)
+		}
+	}
+}
+
 func TestSplitAssistantMessageSegmentsWithPhotoDirective(t *testing.T) {
 	photoPath := filepath.Join(string(filepath.Separator), "workspace", "photo.jpg")
 	text := fmt.Sprintf("before\n<!-- telegram-photo {\"path\":%q,\"caption\":\"hello\"} -->\nafter", photoPath)