NOTE
Netty Pipeline: Adding and Removing ChannelHandlers
Dynamic pipeline modification, handler lifecycle callbacks, event-loop serialization, and sharability constraints.
This is a historical learning note and may contain outdated or incomplete understanding.
Handlers can be added, replaced, or removed from a channel pipeline. Netty maintains handler contexts and invokes lifecycle callbacks such as handler-added/removed as appropriate.
Pipeline mutations from outside the event-loop thread are coordinated/scheduled so channel processing remains correctly serialized.
A handler instance is not automatically safe to share between channels. Only share stateless/thread-safe handlers with the documented sharability semantics; otherwise create one instance per pipeline/channel.