Can Lua safely unload a required module for zero‑downtime updates?

Goal

Enable a small Lua application to migrate to new code without stopping the process, by reloading modules at runtime.

Constraints and uncertainty

• require caches modules in package.loaded, so subsequent calls return the original instance even after source changes.
• Setting package.loaded[mod] = nil forces a reload, but this technique is undocumented and may interfere with LuaJIT’s JIT compilation.
• The debug.reload function exists only in some distributions and is not part of the core API, limiting portability.
• No standard mechanism exists to unload a module that holds global resources or participates in circular dependencies.

Which approach guarantees that all references to the old module are released? Does clearing package.loaded suffice on LuaJIT without leaving stale JIT code? What portable pattern can be used across Lua 5.4 and LuaJIT?