Foundation for messages too large for a single transaction (tier 2's 16-output
ceiling, ~4000 chars). A long message is now split across SEVERAL transactions
that share a random message id; each carries a slice of the one ciphertext with
GLOBAL chunk indices, and the receiver reassembles across the siblings.
Protocol: the Message header gains an optional "mid" (message id); "n" is reused
as the TOTAL chunk count and its bound raised to kHushChatMaxMessageChunks (64 ⇒
up to ~16 KB / 4 txs, tunable, ≤256 for the 2-hex index). The grouper, when a
tx's header carries "mid", emits a PARTIAL (its global-indexed chunks + message
id + total) instead of reassembling in-place; HushChatTransactionMetadata
carries those partials through. Crypto is untouched — one secretstream session
for the whole message, chunking is transport-only.
Compose: splitOutgoingMessage() returns one OutgoingChatMemos per transaction
(one element = the classic tier-1/2 single tx, byte-identical; several = tier 3).
buildOutgoingMessage (single-tx) is unchanged. Old clients bound "n" to 16 so a
tier-3 header fails to parse and its memos are dropped — graceful degradation.
Unit-tested (testHushChatLargeMessageTier3): a ~9000-char message splits into 3
txs, every output shuffled, slices gathered across siblings, reassembled and
decrypted back to the original; short message stays single-tx (no mid); the
total-chunk cap is enforced. The stateful accumulator (persisted, confirm-gated),
sequential broadcast, and progressive/incomplete UI follow in later commits.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
DanSandClaude Opus 4.8
cc08854237