The resumption module (SessionTicket/TicketValidator) was never wired into
the client or server — nothing issued or validated tickets, and no Resume
frame was ever sent. But it "encrypted" tickets by XOR-ing them with a
single static keystream SHA256(psk || const) and had no MAC (despite a doc
comment claiming HMAC): a textbook many-time-pad, trivially broken from a
couple of captured tickets, and malleable. Leaving it in-tree invited
someone to wire up a broken 0-RTT path later.
Removed the module, its FrameKind::Resume wire variant, and the protocol
handler for it. 0-RTT can be reintroduced later on a real AEAD-sealed
ticket if desired.
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