Constants & types

Constants — @tezosx/relayer/constants

The kernel-level facts, exported so nothing gets hardcoded downstream:

Constant	Value	What it is
TEZLINK_EVM_RPC	https://evm.previewnet.tezosx.nomadic-labs.com	The EVM runtime JSON-RPC node
TEZOS_L1_RPC	https://michelson.previewnet.tezosx.nomadic-labs.com	The Michelson runtime node (signing / injection)
NAC_CONTRACT	KT18oDJJKXMKhfE1bSuAPGp92pYcwVDiqsPw	The NAC gateway contract (Michelson side)
NAC_ENTRYPOINT	call_evm	The gateway's ABI-call entrypoint name
NAC_PRECOMPILE_ADDR	0xff00000000000000000000000000000000000007	The NAC precompile (EVM side)
NAC_RECOMMENDED_GAS	{ call: 3_000_000n, callMichelson: 5_000_000n }	Gas budgets for precompile sub-calls
NAC_HTTP_POST	1	The HTTP-method enum value for the generic call
NAC_TEZOS_RUNTIME_URL	http://tezos/	URL prefix crediting a tz1/KT1 (EVM → Michelson)
NAC_ETHEREUM_RUNTIME_URL	http://ethereum/	URL prefix crediting a 0x (Michelson → EVM)
RPC_TIMEOUT_MS	15_000	The read deadline (behavior)

There is no chain-id constant here. The chain id (128064 / 0x1f440) is fetched at runtime via eth_chainId; as a product-level constant it lives in @tezosx/wallet-core, alongside the explorer URLs, the TzKT API base and the USDC address.

Types — @tezosx/relayer/types

The shared vocabulary, grouped by what you're doing:

Talking EIP-1193 — EIP1193Provider (EventEmitter-based, request() + on() overloads), RequestArguments, ProviderRpcError ({ code: number; data?: unknown } on Error), ProviderConnectInfo.

Building cross-runtime calls — CrossRuntimeIntent (the three-kind union), GatewayCall / PrecompileCall / CrossRuntimeCall, CrossRuntimeDirection ('michelson-to-evm' | 'evm-to-michelson'), EthTransactionRequest, EthTransactionReceipt.

Tracking — CrossTxStatus (the six-stage union yielded by trackCrossRuntimeStatus), PendingOpView (an unresolved op: l1OpHash, evmAlias, to, fromBlock, broadcastedAt), PendingOp.

Implementing a wallet client — ITezosWalletClient, WalletPermissions, JsonRpcTransport / TransportPort.

Two caveats worth knowing:

• PendingOpsStore / PendingOpsSnapshot are NOT in /types — import them from @tezosx/relayer/tezos. PendingOp itself is best treated as an opaque persistence payload, not a consumer type.
• The NacHttpHeader shape ({ key, value }) taken by encodeNacCall's headers parameter is not currently re-exported — pass [] or shape the objects inline.

Error classes

Two separate hierarchies:

• RelayerError (base, carries code + optional data) with subclasses GatewayError and PrecompileError — exported from /types. In practice only PrecompileError is thrown today (by the EVM-side builder on a call-evm intent, and by the tracker on a wrong direction).
• The three build errors — UnknownSelectorError, SubMutezPrecisionError, InvalidDestinationError — extend plain Error (not RelayerError) and are exported from @tezosx/relayer/tezos. Catch them by instanceof; the provider translates all three to JSON-RPC -32602 (details).