DealSession

Drives a cryptographically fair card deal over a Seam, as an op-based CRDT.

Each card is a CardState; players sequentially encrypt the deck (SRA layers compose because the cipher is commutative), then non-quorum players strip their layer so only the visibility quorum can read each card. A partial multi-member quorum (1 < |quorum| < N) additionally runs per-member reveal tracks (QuorumTrack) so each member — and no one else — ends up able to decrypt (see strip). State converges via the CardOp stream broadcast over the seam: each op carries the base sets it was computed against and is folded in via CardState.merge, so convergence holds under per-sender FIFO delivery even when ops from different senders interleave differently at different peers (cross-sender transport reorder).

Single-local-writer assumption. The shuffle and strip helpers read the base ciphertext from state outside the _state.update block, run crypto, then commit. If the incoming-op collector races to apply a remote op to the same card in that window, the local op was computed against a stale base and its merged ciphertext can lose the remote layer while the metadata claims it. This is safe under the current model where writes to a card are serialized by the protocol (one shuffler/stripper at a time); concurrent local shuffle/strip while remote ops mutate the same card is a production hazard that needs an "await my turn" gate (deferred).