fix(image): don't block the main loop with exec in the multiple-image path

MultipleImageStrategy::update() and handleClick() ran util::command::exec
(a blocking fork+exec+read) on the GTK main thread, so the whole bar froze
for the script's duration on every interval and on every click.

Move the exec into a new IStrategy::fetch() hook that the SleeperThread
worker runs before dp.emit(); update() now only parses the cached output
and draws on the main thread (mirroring how custom.cpp separates exec from
formatting). handleClick() uses forkExec() so clicks fire-and-forget instead
of blocking on the command's output. The entries and single-image paths are
unchanged.

src/modules/image.cpp

@@ -45,6 +45,9 @@ auto waybar::modules::Image::getStrategy(const std::string& id, const Json::Valu
 
 void waybar::modules::Image::delayWorker() {
   thread_ = [this] {
+    // Do the blocking work (e.g. running a user script) here on the worker
+    // thread; update() then only parses the result and draws on the main thread.
+    strategy_->fetch();
     dp.emit();
     thread_.sleep_for(interval_);
   };
@@ -82,6 +85,15 @@ MultipleImageStrategy::MultipleImageStrategy(const std::string& id, const Json::
   }
 }
 
+void MultipleImageStrategy::fetch() {
+  // Run the (blocking) user script off the GTK main thread so the bar doesn't
+  // freeze for the script's duration on every interval. update() consumes the
+  // captured output. The static "entries" path takes priority and needs no exec.
+  if (config_["entries"].empty() && !config_["exec"].empty()) {
+    exec_output_ = util::command::exec(config_["exec"].asString(), "").out;
+  }
+}
+
 void MultipleImageStrategy::update() {
   // spdlog::info("update function run");
 
@@ -94,12 +106,12 @@ void MultipleImageStrategy::update() {
   if (!config_["entries"].empty()) {
     setImagesData(config_["entries"]);
   } else if (!config_["exec"].empty()) {
-    auto exec = util::command::exec(config_["exec"].asString(), "");
+    // exec output was captured by fetch() on the worker thread
     Json::Value as_json;
     Json::Reader reader;
 
-    if (!reader.parse(exec.out, as_json)) {
-      spdlog::error("invalid json from exec {}", exec.out);
+    if (!reader.parse(exec_output_, as_json)) {
+      spdlog::error("invalid json from exec {}", exec_output_);
       return;
     }
 
@@ -211,9 +223,8 @@ void MultipleImageStrategy::resetBoxAndMemory() {
 }
 
 void MultipleImageStrategy::handleClick(const Glib::ustring& data) {
-  auto msg = std::string(data);
-
-  auto exec = util::command::exec(data, "");
+  // Fire-and-forget: don't block the main loop waiting on the command's output.
+  util::command::forkExec(data);
 }
 
 SingleImageStrategy::SingleImageStrategy(const std::string& id, const Json::Value& config,