igneum/docs/fork-divergence.md

Igneum fork divergence from rusty-kaspa

Fork: vendor/igneum-node, a git clone of vendor/rusty-kaspa at v2.1.0 commit 01b532e8 (22 Sep 2026). Every Igneum change is a commit on top of that base, one per subject, so git log 01b532e8..HEAD in the fork is the full list. This file is the reading guide: what each change touched, why, how risky it is, and what to do when upstream moves. docs/fork-map.md is the plan this implements; row ids there (a1 to f2) are cited below.

Status: devnet v0, mining layer only (3 Oct 2026). Finality, VDF seeds, the zkEVM and the proving layer are not in the fork yet.

The table

File (vendor/igneum-node/)	What changed	Why	Risk	Upstream-merge note
consensus/core/src/header.rs, consensus/core/src/hashing/header.rs	Header gains vote_key_hash: Hash (32 bytes) as the last field; new_finalized takes it; hash_override_nonce_time writes it after pruning_point so the header hash and the PoW commit to it	Finality rule v2: vote weight is blue blocks per BLS vote key. The hash of the key rides in every header now so the weight table can be built from headers alone later (fork-map d)	Low by depth, high by spread: every header hash and every genesis hash moved	Any upstream change to Header or to the hashing order conflicts here. Re-derive the four genesis hashes after merging (consensus/core/src/config/genesis.rs tests print them).
consensus/core/src/config/genesis.rs	All four genesis hashes recomputed; devnet genesis has payload igneum-devnet, timestamp 2026-10-03T00:00Z, bits 0x1e020000 (2^23 expected hashes per block, approximate), nonce 0	Hash field change above; a devnet that three CPU miners on one Mac can hold at about 1 block per second	Low	Mainnet, testnet and simnet genesis blocks are still Kaspa's content with new hashes. Replace them with Igneum genesis blocks before any public network.
consensus/core/src/errors/block.rs, consensus/src/pipeline/header_processor/pre_ghostdag_validation.rs	RuleError::MissingVoteKeyHash; check_vote_key_hash_present rejects an all-zero vote_key_hash	Nodes only check presence until the finality layer exists	Low	Keep. The presence check becomes a key-registry check later.
protocol/p2p/proto/p2p.proto, protocol/p2p/src/convert/{header,block,messages}.rs, protocol/flows/src/v10/request_headers.rs	BlockHeader wire message gains Hash voteKeyHash = 15; converters copy it both ways	p2p round trip of the field	Low	Field number 15 must stay unique if upstream adds header fields. Protocol version is still Kaspa's 11; bump it when the fork gets its own peers.
rpc/grpc/core/proto/rpc.proto, rpc/core/src/model/header.rs, rpc/core/src/model/optional/header.rs, rpc/core/src/model/verbosity.rs, rpc/core/src/convert/verbosity.rs, rpc/grpc/core/src/convert/{header,optional/header}.rs, rpc/service/src/converter/consensus.rs, consensus/client/src/header.rs	RpcHeader and RpcOptionalHeader carry vote_key_hash; gRPC proto fields (string voteKeyHash = 16 on the header, optional string voteKeyHash = 15 on the optional header) and converters; wasm client header	RPC round trip, template to miner and block back	Low	Mechanical. Borsh wire for wRPC changed shape: old wRPC clients cannot decode headers.
consensus/src/model/stores/headers.rs, consensus/src/test_helpers.rs, mining/src/testutils/consensus_mock.rs, mining/src/template_limits_tests.rs, consensus/src/pipeline/virtual_processor/processor.rs, consensus/src/pipeline/body_processor/body_validation_in_isolation.rs	Header store serde includes the field; template builder passes the field through; tests construct it	Storage and mining paths	Low	Database format changed: a node from before this commit must resync from scratch.
consensus/core/src/network.rs	Network name prefix igneum- (was kaspa-); devnet ports gRPC 26610, wRPC borsh 27610, wRPC json 28610, P2P 26611 (Kaspa devnet: 166xx to 186xx); error text	The prefixed name is the p2p handshake magic (FlowContext::handshake rejects a Version.network mismatch), so igneum-devnet never completes a handshake with kaspa-devnet. Distinct ports stop a Kaspa node on the same host from being dialled by mistake	Low	Mainnet, testnet and simnet ports are still Kaspa's. Change them before any public network.
crypto/addresses/src/lib.rs, bridge/src/default_client.rs, bridge/src/tests.rs	Devnet address prefix igneumdev (was kaspadev)	A devnet address can never parse as a Kaspa devnet address	Low	The bech32 prefix is only the devnet one so far.
consensus/core/src/config/bps.rs, consensus/core/src/config/params.rs	OneBps = Bps<1>; DEVNET_PARAMS uses BlockrateParams::new::<1>(): 1,000 ms blocks, GHOSTDAG k 18 (calculate_ghostdag_k(2 x 5 x 1, 0.01)), 10 max parents, mergeset limit 180, merge depth 3,600 blocks, finality depth 43,200 blocks, pruning depth 108,000 blocks, coinbase maturity 100; crescendo_activation: always(); doc table and a test pinning every value	1 block per second at launch (fork-map f1, f2, e1). Finality and pruning depths are upper bounds only: live finality will be the certified checkpoint	Low; this is Kaspa mainnet's pre-Crescendo path	The ForkedParam and bps_history plumbing is still present for the other networks. Strip it in one pass when mainnet params are written.
consensus/core/src/igneum.rs (new), consensus/core/src/lib.rs, consensus/core/src/constants.rs	Emission constants and functions: 1,000,000,000 coins in year one, per-second rate halving every two years (SUBSIDY_PER_SECOND_BY_PERIOD[i] = 3,168,808,781 >> i, 33 periods), block_subsidy(daa_score, bps), 30-day linear launch ramp from 10%, proving_pool_share 20% and producer_share 80%, proving_pool_script_public_key (OP_RETURN tagged igneum-proving-pool-v0), POW_EPOCH_BLOCKS = 3,600	The design's schedule, hard cap 4,000,000,000 (the geometric series sums to it; rounding leaves under 100 coins unminted), no emission treasury (fork-map b1, b2)	Medium: consensus money	Pure addition. Keep as the one source of the schedule.
consensus/src/processes/coinbase.rs	Kaspa's pre-deflationary phase, 426-month table and Crescendo rescaling removed; CoinbaseManager::new(max_spk_len, max_payload_len, bps); calc_block_subsidy reads the period table; expected_coinbase_transaction pays 80% plus fees per rewarded block to its declared script and pools 20% of every subsidy (blues and reds) into one output to the proving pool script, placed after the blue outputs and before any red reward; tests rewritten	80/20 split in consensus; the 20% is burned on devnet v0 and becomes the prover payout when the proving layer records prover sets (fork-map b3)	High: changes what every node accepts as a valid coinbase	Upstream edits to coinbase.rs will conflict. The payload format is unchanged (full subsidy in the payload, split derived from it), so Kaspa's payload parsing merges cleanly.
consensus/src/consensus/services.rs, consensus/src/consensus/test_consensus.rs, consensus/src/pipeline/body_processor/body_validation_in_context.rs, consensus/src/processes/parents_builder.rs, consensus/src/processes/transaction_validator/tx_validation_in_isolation.rs	Call sites of the new CoinbaseManager constructor; subsidy expectations in tests use igneum::block_subsidy	Wiring	Low	Mechanical.
consensus/pow/src/igneum.rs (new), consensus/pow/src/lib.rs, consensus/pow/Cargo.toml, Cargo.lock	PowEngine trait (check_header(header, &EpochSeeds) -> (passed, pow)), HeavyHashEngine stub (default), IgneumEngine behind feature igneum-pow calling the igneum-pow crate (Epoch::memory_hard, Epoch::hash), caching three (epoch seed, day seed) entries of program plus 256 MiB cache; igneum-pow as an optional path dependency ../../../../igneum-pow; doc note on the existing calc_block_level (pruning proofs still use the stub for block levels)	The hash swap behind a trait so the devnet runs on the stub while the real path is wired (fork-map a1 to a3)	Medium	Pure addition in the pow crate. State (kHeavyHash) is untouched, so upstream pow changes merge. The path dependency must become a workspace or git dependency when the fork gets its own repository.
consensus/src/pipeline/header_processor/processor.rs, consensus/src/pipeline/header_processor/pre_ghostdag_validation.rs	PoW check moved from validate_header_in_isolation to after GHOSTDAG (check_pow_and_calc_block_level(header, selected_parent)); epoch_seed walks the selected-parent chain to the last block below the epoch's start DAA score (genesis for epoch 0) with a memo; pow_engine: Arc<dyn PowEngine> on the processor	The epoch seed is chain state, so PoW cannot be checked in isolation any more (fork-map a4). Temporary seed rule until the 10-minute VDF over a certified checkpoint exists	High: a header now reaches GHOSTDAG before its PoW is checked, so an attacker can make a node run GHOSTDAG on headers with bad nonces (bounded by the per-peer header rate; the stub engine ignores the seeds so devnet v0 is not exposed)	Upstream rarely touches this ordering, but any refactor of process_header conflicts. Pruning-proof validation (processes/pruning_proof/validate.rs) still uses the stub for block levels; thread seeds through it before enabling the real engine on a pruning network.
consensus/Cargo.toml, kaspad/Cargo.toml	Feature igneum-pow forwarded (kaspad -> kaspa-consensus -> kaspa-pow)	cargo build -p kaspad --features igneum-pow selects the real engine	Low	Keep.
consensus/core/src/config/constants.rs	Comment block only: the DAA constants kept at 1 BPS (sample every 4 blocks, 661 samples, 2,644-block window, min window 150 samples) and the two timestamp rules kept (132 s future tolerance in isolation, strictly above the sampled past median time of 27 samples in context)	Difficulty step verified rather than changed (fork-map c1, c2); the known gap (per-epoch hash-speed step vs a 44-minute window) is recorded there	None	Comment only.
igneum/miner/ (new crate igneum-miner), Cargo.toml (workspace member), Cargo.lock	CPU devnet miner on kaspa_pow::State (the stub), sets vote_key_hash from a label; watch prints block counts, DAA, tips, peers, difficulty and sink per node and a blocks-per-second summary; inspect walks the selected chain and checks vote_key_hash equality across nodes and the 80/20 coinbase split	Kaspa ships no miner; the devnet needs one that follows the fork's own PoW crate	None to consensus	Internal tool. Switch it to PowEngine when the real engine is the default.

Decisions recorded as open

Decision	v0 choice	Why it is open
8 or 18 decimals	Kaspa's 8 (SOMPI_PER_KASPA), so one coin is 100,000,000 units and the cap is 4e17 units, inside u64	The zkEVM side expects 18 decimals (wei). 18 decimals put the cap at 4e27, which does not fit u64, so the UTXO amount type, mass rules and every RPC amount would change. Decide with the execution engineer before the EVM bridge; a fixed 1e10 scaling at the bridge is the alternative.
Epoch seed	Hash of the last selected-chain block of the previous 3,600-block epoch; genesis for epoch 0	The design uses a 10-minute class-group VDF over a certified checkpoint (bench-log, proto-vdf). The v0 rule is grindable in principle (a miner choosing which block ends an epoch) and needs the VDF and checkpoints to close.
Day seed for the 256 MiB cache	header.timestamp / 86,400,000	Timestamps are miner-chosen inside the two timestamp rules, so a day boundary can be straddled by a few blocks; harmless for a cache seed, but the exact rule is not final.
Lane hash to 256-bit target	Lane hash (64 bits) in the top 64 bits, cSHAKE of the header folded with the lane in the low 192 bits	The lane hash does not absorb the header (see the TODO in consensus/pow/src/igneum.rs): a miner could tabulate an epoch's 2^32 lane hashes once. The cryptographer owns the fix before the real engine is the default.
Proving pool payee	OP_RETURN burn tagged igneum-proving-pool-v0	Becomes a payout to the prover set of the proven block once the proving layer records prover sets (20 to 60 s behind the tip).
Finality and pruning depths	Kaspa's 12 h and 30 h at 1 BPS	Upper bounds. Live finality is the 30-s certified checkpoint; pruning depth must stay above the longest checkpoint gap.
PoW before or after GHOSTDAG	After	Needed for the chain-derived seed; costs GHOSTDAG work on invalid headers. A header-only seed (for example the VDF output carried in the header and verified against the checkpoint) would move it back.

Per-second subsidy numbers (8 decimals, 1 BPS)

Period	Years	Per second (units)	Per second (coins)	Per block at 1 BPS
0	0 to 2	3,168,808,781	31.68808781	same
0, day 0 of the ramp (10%)		316,880,878	3.16880878	same
0, day 15 of the ramp (55%)		1,742,844,829	17.42844829	same
1	2 to 4	1,584,404,390	15.84404390	same
2	4 to 6	792,202,195	7.92202195	same
31	62 to 64	1	0.00000001	same
32 and after	64 on	0	0	0

Split of 3,168,808,781: producer 2,535,047,025 (80%, plus the rounding remainder), proving pool 633,761,756 (20%). Total over the schedule: under the 4,000,000,000-coin cap by less than 100 coins (test total_emission_stays_under_the_cap).