NOTE
Netty Server Startup: Registering with the EventLoop
Assigning the server channel to an event loop and transport selector before binding.
This is a historical learning note and may contain outdated or incomplete understanding.
Before binding, the server channel is registered with an event loop. For NIO transports this includes selector registration/setup so readiness events can later be processed on that event-loop thread.
Registration establishes the thread-confinement relationship between channel and event loop. Operations invoked externally are commonly queued to that loop when required.
Do not depend on exact selector attachment/key internals outside source analysis.