An approach I've seen many projects (such as rofi) take for plugins, which I'm a huge fan of, is loading dynamic libraries in a certain directory (could be the config dir for example).
Ghostty could utilize this as a way for advanced users to configure their terminal.

Why this makes sense

1. Ghostty already has many of its types being C-compatible (for libghostty and the macOS apprt). This would mean that this is pretty low-effort to implement.
2. Users may be more comfortable writing Zig or C than Ghostty's own configuration format. I myself had trouble staring at configuration lines that were giving me an error, unable to figure out why (yes, that's a separate problem, but the general point still holds :D).
3. Keybinds could be given custom callbacks (function pointers) to do essentially anything.
4. This would elegantly fix API for managing windows / tabs / splits #601 — such a config, or perhaps plugin is a better word, could implement some wire protocol, but that might not even be necessary depending on the use case.
5. Microoptimization nuts like me will get a kick out of it :P

How to implement this

1. Export relevant symbols and create headers (this is probably done already). A Zig client library could also be considered, but this isn't really a must.
2. Discover plugins: search for dynamic library files (Linux: .so, Windows: .dll, macOS: no idea). This could just be the config directory, but also a subdirectory or somewhere entirely different.
3. For each library - note that Zig has abstractions for both dlopen and dlsym (see: std.DynLib):
   • dlopen it (need to dlclose on shutdown)
   • Load and call some well-defined entry point symbol from it using dlsym. This could be ghostty_plugin_open, for example.
   • Plugins can now call into ghostty's API to do whatever.