Extension hook registration is stubbed out.

[python-processing-unit]

According to the specification section 8.2:

Extensions MUST be able to register handlers for REPL, event, and periodic hook callbacks during initialization.

In the implementation, however, the extension context registration functions in extensions.c (ctx_register_event_handler, ctx_register_periodic_hook, and ctx_register_repl_handler) are implemented as no-ops. They return immediately without storing the callbacks, preventing extensions from registering REPL commands, event handlers, or periodic hooks. As a result, those handlers are never invoked.