ws echo round-trip hangs (server + client in one program) — on main #11309

Found by tokio lane L2 (#11277). It fails identically on main.

A minimal ws echo program (ws server + client, send one message, echo it back, close) hangs under Perry, while Node completes. Needs a package-free-where-possible repro and bisect; check both the default turnloop ws route and PERRY_DISABLE_WELL_KNOWN=1.