Add printer-agent and plugin status tests

Ports the agent lifecycle, duplicate
agent-id, built-in-id clash and
status-resolution tests. The loader
runs on a detached worker thread, so
the lifecycle tests live in their own
executable. Tests install the
production unload-side registry
wiring themselves (no GUI in the
test binary) and register agents
manually so concurrent loads stay
deterministic.

tests/slic3rutils/test_plugin_status.cpp

@@ -0,0 +1,23 @@
+#include <catch2/catch_all.hpp>
+
+#include <slic3r/GUI/PluginStatus.hpp>
+
+using Slic3r::GUI::PluginStatus;
+using Slic3r::GUI::resolve_plugin_status;
+
+TEST_CASE("resolve_plugin_status precedence", "[plugin][status]") {
+    // the new branch: loaded module + error -> runtime fault, not a load failure.
+    REQUIRE(resolve_plugin_status(/*loading*/ false, /*has_error*/ true, /*is_loaded*/ true) == PluginStatus::RuntimeError);
+
+    // error without a live module is a load-time Error.
+    REQUIRE(resolve_plugin_status(false, true, false) == PluginStatus::Error);
+
+    // loading wins over a pending error so a reload never flashes red.
+    REQUIRE(resolve_plugin_status(true, true, true) == PluginStatus::Loading);
+
+    // healthy loaded plugin.
+    REQUIRE(resolve_plugin_status(false, false, true) == PluginStatus::Activated);
+
+    // nothing loaded, no error.
+    REQUIRE(resolve_plugin_status(false, false, false) == PluginStatus::Inactive);
+}