feat(spec-msg): add Speculative Messaging primitives#12676
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Introduce the parachain-side and relay-visible primitives for Speculative Messaging v0.5 (per PR paritytech#12659 design). Relay-visible (polkadot-primitives::v9): - StreamsRoot newtype and RequiresSet (canonical sorted (ParaId, StreamsRoot) set, strictly-increasing ParaId enforced at decode; MAX_SOURCES_PER_BLOCK). - UMPSignal::Provides/Requires + CandidateUMPSignals; MAX_UMP_SIGNALS=4 bounds ump_signals(); NodeFeature::SpeculativeMessaging=5. Parachain-side (cumulus-primitives-spec-messaging): - StreamId: frozen 8-byte big-endian canonical encoding, reserved-kind rejection. - mmr: domain-tagged SpecMerge (blake2), peaks-only accumulator matching mmr-lib. - streams_root: keyed binary Patricia trie over (StreamId, stream root); keyed membership proofs bind the StreamId. - lift: ConsumptionRecord / RequiresLift / MMRExtensionProof and build_requires synthesis (trusted record + untrusted POV lifts, forward-chain stitch). - message: fetch protocol (MessagesRequest/Response) + verify_messages_response, leaf_hash, SpecHasher. - cumulus-primitives-core: re-exports + SpeculativeOutbox/InboxApi. Hardening: - Frozen consensus vectors for the StreamsRoot trie root and MMR root. - verify_messages_response rejects malformed (start_peaks, base) frontiers instead of panicking in Mmr::append; guards base+len overflow. - Bound StreamProof depth (<= KEY_BITS) and MMRExtensionProof connecting nodes.
Extend the requires-lift PoV harness to cover the design's "Proof Size Considerations" worst case alongside the empirical measurements, as two distinct angles: - Angle 1 (empirical share): a full-source candidate with real measured proofs (deepest 100k-message extension + 1024-stream tree_proof) — 3.44% of MAX_POV_SIZE, guarded <10%. - Angle 2 (day-scale worst case): a synthetic ~30-node extension (log2(1e9)) + one advance-proof gap + tree_proof, per the design's ~4KB/stream + ~2KB/gap ceiling. Guards one worst lift <8KB and reframes headroom as the authoring-time budget (how many touched streams fit vs the source cap). Also note in-code that each connecting node is (u64 position, Hash) = 40 B, ~25% above the design's hash-only 32 B count (positions are derivable from prev_size + new_mmr_size; stripping them is a deferred, consensus-critical optimization).
Add the wire/encoding types of the v0.5 channel protocol (type primitives
only; pallet logic stays deferred to integration):
- SpecMsgKind { Signal(SpecMsgSignal), Data(Vec<u8>) } — channel-stream leaf
payload (fills leaf_hash's opaque `payload`; Data bound is the STF constant,
not a type bound, matching the design's Vec<u8>).
- SpecMsgSignal { OpenChannel{version}, CloseChannel, Upgrade{version} } —
sender channel lifecycle; OpenChannel is variant index 0 (frozen core).
- Register { version, up_to: MessagePosition, grant: WindowGrant, closed } —
the receiver's ack-stream leaf payload, read out-of-band.
- WindowGrant { max_messages, max_bytes, max_message_size } — advisory credit.
Frozen-core encoding vectors pin OpenChannel=index 0 and the Register byte
layout (consensus-critical, read cross-chain). MessagePosition gains
MaxEncodedLen + Default (needed by Register). Re-exported via lib.rs and
cumulus-primitives-core.
Deferred to the pallet: ChannelId, OutChannels/InChannels storage, send()
API, window accounting, version enforcement, accept extrinsic.
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Introduce the parachain-side and relay-visible primitives for Speculative Messaging v0.5 (per PR #12659 design).
Relay-visible (polkadot-primitives::v9):
Parachain-side (cumulus-primitives-spec-messaging):
Resolves #12346 and #12347