feat: add configurable UCE error pages

src/lib/sys.cpp

@@ -348,6 +348,15 @@ String cwd_get()
 	return(std::filesystem::current_path());
 }
 
+String process_start_directory()
+{
+	// Primed in main() before any unit handler can chdir; fault recovery and
+	// config-relative path resolution anchor to this instead of the volatile
+	// per-unit working directory.
+	static String start_directory = cwd_get();
+	return(start_directory);
+}
+
 void cwd_set(String path)
 {
 	chdir(path.c_str());