fix: initialize embedded python from bundled runtime

tests/slic3rutils/python_test_support.hpp

@@ -2,7 +2,10 @@
 
 // Shared embedded-interpreter bootstrap for slic3rutils tests that need a live Python
 // interpreter (test_plugin_host_api.cpp, test_slicing_pipeline_bindings.cpp, ...).
-
+#include <boost/dll/runtime_symbol_info.hpp>
+#include <boost/filesystem.hpp>
+#include <memory.h>
+#include <stdexcept>
 #include <pybind11/embed.h>
 #include <pybind11/pybind11.h>
 
@@ -12,17 +15,29 @@ namespace {
 
 void ensure_python_initialized()
 {
-    // Deliberately a bare scoped_interpreter rather than Slic3r::PythonInterpreter:
-    // `orca` is a PYBIND11_EMBEDDED_MODULE compiled into this test binary, so importing
-    // it needs no bundled stdlib/sys.path, and the deterministic assertions are
-    // independent of the host's Python. PythonInterpreter::initialize() expects the
-    // bundled Python home laid out next to the app bundle (lib/python3.12/encodings),
-    // which is not deployed beside the test binary, so using it here would fail to find
-    // a home on macOS/Linux. The optional numpy-backed assertions are guarded at runtime.
-    if (!Py_IsInitialized()) {
-        static pybind11::scoped_interpreter interpreter;
-        (void) interpreter;
+    if (Py_IsInitialized())
+        return;
+
+    static std::unique_ptr<pybind11::scoped_interpreter> interpreter;
+
+    PyConfig config;
+    PyConfig_InitPythonConfig(&config);
+    config.parse_argv = 0;
+
+    const auto python_home = boost::dll::program_location().parent_path() / "python";
+
+    if (boost::filesystem::exists(python_home)) {
+        const std::string home = python_home.string();
+        const PyStatus status  = PyConfig_SetBytesString(&config, &config.home, home.c_str());
+
+        if (PyStatus_Exception(status)) {
+            const char* message = status.err_msg ? status.err_msg : "Failed to set Python home";
+            PyConfig_Clear(&config);
+            throw std::runtime_error(message);
+        }
     }
+
+    interpreter = std::make_unique<pybind11::scoped_interpreter>(&config);
 }
 
 pybind11::module_ import_orca_module()