feat: Multi-Worker Support — PR 3: Per-Worker `LocalNetwork`

[grantkee]

Problem

The node currently hardcodes a single worker per validator (worker_id = 0). The EpochManager, network layer, and several initialization paths assume exactly one worker. This blocks the ability to run independent fee markets, specialized transaction pools, or any form of worker-level parallelism.

Goal

Refactor the node to support N independent workers per validator. Each worker operates as a standalone unit with its own:

• libp2p swarm (dedicated gossip topics, listen address, network key)
• RPC server (unique port)
• Transaction pool
• Batch builder + batch validator
• LocalNetwork instance for primary communication

Workers share only the Primary (consensus) and the execution engine (block production). The num_workers count is a consensus-level parameter — all validators must agree on it.

Why

The immediate motivation is multiple fee markets. Once multi-worker is in place, a follow-up (Phase 2) spawns 2 workers by default:

• Worker 0 (General): accepts all transactions, standard EIP-1559 fee market
• Worker 1 (Whitelisted Transfers): accepts only whitelisted ERC-20 transfer/transferFrom calls, operates with a reduced base fee

This architecture also enables future process separation — workers can be extracted into standalone processes communicating with the primary over RPC.

Design Constraints

1. Workers are fully independent — no cross-worker shared state. Each worker has its own network identity, pool, and gossip topics.
2. Per-worker gossip topics — tn-worker-{id} and tn-txn-{id} replace the current global tn-worker and tn-txn topics. This provides network-level isolation.
3. Per-worker LocalNetwork — each worker gets its own LocalNetwork instance for primary communication. The primary registers as the handler on every worker's LocalNetwork. This is the seam for future process separation.
4. num_workers is a consensus parameter — changing it requires a coordinated upgrade across all validators. Defaults to 1 for backward compatibility.
5. Execution engine is shared — batches from all workers are processed sequentially by the same engine. Worker ID is already encoded in the block difficulty field.
6. Faucet on worker 0 only — the testnet faucet attaches to the general-purpose worker.

Current State

Much of the infrastructure already supports N workers but is only called with worker_id = 0:

• ExecutionNodeInner.workers: Vec<WorkerComponents> — vec exists, only 1 element
• GasAccumulator — supports N workers internally, but initialized with new(1)
• BatchValidator — already stores worker_id and rejects mismatched batches
• adjust_base_fees() — loops over num_workers() but is a no-op
• Block difficulty field — already encodes batch_index << 16 | worker_id

Hardcoded locations that block multi-worker:

Location	Current	Fix
manager.rs spawn_worker_node_components()	let worker_id = 0;	Loop over 0..num_workers
manager.rs GasAccumulator::new(1)	Hardcoded 1 worker	Use num_workers
manager.rs catchup_accumulator()	gas_accumulator.base_fee(0)	Restore per-worker base fees
manager.rs EpochManager struct	Singular worker_network_handle	Vec<WorkerNetworkHandle>
manager.rs create_consensus()	Returns (PrimaryNode, WorkerNode)	Returns (PrimaryNode, Vec<WorkerNode>)
config/genesis.rs NodeP2pInfo	Single worker: NetworkInfo	workers: Vec<NetworkInfo>
config/node.rs Parameters	No num_workers field	Add num_workers: u16 (default 1)
config/network.rs	Global topics tn-worker, tn-txn	Per-worker tn-worker-{id}, tn-txn-{id}
config/consensus.rs	Single LocalNetwork	Vec<LocalNetwork>

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This PR: Per-Worker LocalNetwork

Each worker gets its own LocalNetwork instance for communicating with the primary. This is the seam for future process separation — today these are in-process channels, but they can be replaced with remote RPC clients without changing the worker or primary code. With num_workers = 1, there is exactly one LocalNetwork and behavior is identical to today.

Scope

crates/config/src/consensus.rs — ConsensusConfig:

• Change the LocalNetwork field from a single instance to local_networks: Vec<LocalNetwork> (indexed by WorkerId)
• Add local_network(worker_id: WorkerId) -> &LocalNetwork accessor

crates/network-types/src/local.rs — LocalNetwork:

• No structural changes needed — each instance is already self-contained
• Each worker creates its own LocalNetwork and registers its own handlers
• The primary-side handler (WorkerReceiverHandler) accepts WorkerOwnBatchMessage which already contains worker_id

crates/consensus/primary/src/ — Primary receiver:

• WorkerReceiverHandler already handles WorkerOwnBatchMessage with worker_id — no handler change needed
• The primary must register as the worker_to_primary_handler on each worker's LocalNetwork instance

crates/consensus/worker/src/worker.rs — Worker:

• Currently receives LocalNetwork from ConsensusConfig
• Change to receive its specific LocalNetwork instance by worker_id index

blocked by #554