Fix: Update runtime last-epoch-reached before resuming from sync

This race was likely inconsequential for the runtime correctness, but
was observable through the unit test "reaching an epoch will prune
all nodes of the preceding task graph".

src/dry_run_executor.cc

@@ -45,8 +45,10 @@ void dry_run_executor::thread_main(executor::delegate* const dlg) {
 			    host_object_instances.erase(dhoinstr.get_host_object_id());
 		    },
 		    [&](const epoch_instruction& einstr) {
-			    if(einstr.get_promise() != nullptr) { einstr.get_promise()->fulfill(); }
+			    // Update the runtime last-epoch *before* fulfilling the promise to ensure that the new state can be observed as soon as runtime::sync returns.
+			    // This in turn allows the TDAG to be pruned before any new work is submitted after the epoch.
 			    if(dlg != nullptr) { dlg->epoch_reached(einstr.get_epoch_task_id()); }
+			    if(einstr.get_promise() != nullptr) { einstr.get_promise()->fulfill(); }
 			    shutdown |= einstr.get_epoch_action() == epoch_action::shutdown;
 		    },
 		    [&](const fence_instruction& finstr) {

src/live_executor.cc

@@ -696,8 +696,12 @@ void executor_impl::issue(const epoch_instruction& einstr) {
 		expecting_more_submissions = false;
 		break;
 	}
-	if(einstr.get_promise() != nullptr) { einstr.get_promise()->fulfill(); }
+
+	// Update the runtime last-epoch *before* fulfilling the promise to ensure that the new state can be observed as soon as runtime::sync returns.
+	// This in turn allows the TDAG to be pruned before any new work is submitted after the epoch.
 	if(delegate != nullptr) { delegate->epoch_reached(einstr.get_epoch_task_id()); }
+
+	if(einstr.get_promise() != nullptr) { einstr.get_promise()->fulfill(); }
 	collect(einstr.get_garbage());
 
 	CELERITY_DETAIL_IF_TRACY_ENABLED(FrameMarkNamed("Horizon"));