[core] Freshen loop_component_start_time_ before scheduler dispatch (#16064)

esphome/core/application.h

@@ -377,12 +377,16 @@ class Application {
 
  protected:
   friend Component;
+  friend class Scheduler;
 #ifdef USE_RUNTIME_STATS
   friend class runtime_stats::RuntimeStatsCollector;
 #endif
   friend void ::setup();
   friend void ::original_setup();
 
+  /// Freshen the cached loop component start time. Called by Scheduler before each dispatch.
+  void set_loop_component_start_time_(uint32_t now) { this->loop_component_start_time_ = now; }
+
   /// Walk all registered components looking for any whose component_state_
   /// has the given flag set. Used by Component::status_clear_*_slow_path_()
   /// (which is a friend) to decide whether to clear the corresponding bit on

esphome/core/scheduler.cpp

@@ -772,6 +772,8 @@ Scheduler::SchedulerItem *HOT Scheduler::pop_raw_locked_() {
 // Helper to execute a scheduler item
 uint32_t HOT Scheduler::execute_item_(SchedulerItem *item, uint32_t now) {
   App.set_current_component(item->component);
+  // Freshen so callbacks reading App.get_loop_component_start_time() see this item's dispatch time.
+  App.set_loop_component_start_time_(now);
   WarnIfComponentBlockingGuard guard{item->component, now};
   item->callback();
   uint32_t end = guard.finish();