[AlphaWeaver]

Erlang does have a mechanism that allows a module to control when it moves from the "old version" to the "new version" of its own code. Calls to the module with the fully qualified name (e.g. `module:function()`) will invoke the "new code" once it's loaded, but calls within that module using only function names (just `function()`) will continue to invoke the "old code".

If the portion of the app you were hot upgrading was an OTP process like a GenServer, you could theoretically wait for some sort of atomic coordination mechanism to make that fully qualified function call after the new code has loaded, at least in theory.

We use hot code reloading at my work, but haven't had a reason to atomically sync the reload. Most of the time it's a tmux session with `synchronize-panes` and that suffices. If your application can handle upgrades within a module smoothly, it's rare to have a need for some sort of cluster-level coordination of a code change, at least one that's atomic.