asyncio's Server.wait_closed() waits for live connections, not just the listener

Fact

Since Python 3.12, Server.wait_closed() returns only once the listening sockets are closed and every connection handler has finished. Before 3.12 it returned as soon as the server itself was closed, however many clients were still connected. async with server: exits through the same call.

So a shutdown written as "close the server, await wait_closed(), then tell the clients to leave" never reaches step three. The handlers are parked in a read that ends only when their peer goes away, and the peers are waiting to be told.

Why it matters

Shutdown is the least exercised path in a server, and this failure has no traceback: the loop sits in select() forever. The same code was correct on 3.11, so it reads as a hang introduced by the runtime rather than by the order of two lines.

How to apply

• Order shutdown: server.close() (stop accepting) → tell connected clients to go → await the handler tasks with a timeout, cancelling stragglers → wait_closed() last, when it is guaranteed to return promptly.
• Keep your own set of handler tasks. The Server object does not expose them, and shutdown needs to wait on them deliberately rather than blindly.
• Do not use async with server: when handlers can outlive the listener; its __aexit__ awaits wait_closed() with no timeout.
• Bound the final wait_closed() in wait_for() anyway — a client that has stopped reading can otherwise keep a handler alive.