Function pick_at_dir

src/builtin/module_jit.cpp:1310–1323

Try a candidate dir / rel_path; if it (or its _debug variant in debug builds, gated on DAS_NO_ASSERTIONS to match register_dynamic_module's rewrite at module_builtin_fio.cpp:1099) exists, return the path to load. Empty string = miss. Returns the non-_debug name even when the _debug variant is what exists — register_dynamic_module applies the _debug rewrite itself in debug builds, so we mustn't do

// trailing-separator and root cases correctly (POSIX `/` + `modules/X` →
// `/modules/X`, not `//modules/X`).
static das::string pick_at_dir ( const std::filesystem::path & dir, const char * rel_path ) {
    namespace fs = std::filesystem;
    if ( dir.empty() || !rel_path || !*rel_path ) return "";
    fs::path candidate = dir / rel_path;
    das::string candidate_str = candidate.string().c_str();
    if ( jit_path_exists(candidate_str.c_str()) ) return candidate_str;
#ifndef DAS_NO_ASSERTIONS
    if ( candidate.extension() == ".shared_module" ) {
        fs::path dbg = candidate.parent_path() / (candidate.stem().string() + "_debug" + candidate.extension().string());
        if ( jit_path_exists(dbg.string().c_str()) ) return candidate_str;
    }
#endif
    return "";
}

// Pure resolution: pick the path to load, in priority order:
//   1. <exe_dir>/<rel_path>   — daspkg release bundle layout (modules sit next to the exe)