[codex] add evm-only giga executor path

giga/evmonly/README.md

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+# EVM-only giga execution
+
+This package contains the EVM-only execution boundary for the final-form giga
+path. It is intentionally separate from the current Cosmos-backed giga wiring in
+`app/app.go`.
+
+The target execution model is based on the `sei-v3` executor:
+
+- raw transaction bytes are Ethereum RLP transactions, not Cosmos SDK txs
+- state layout is EVM-native: balance, storage, code, and nonce are keyed by
+  EVM addresses and hashes
+- block execution can overlap with parsing or persistence work for nearby blocks
+- hot execution should not allocate `sdk.Context`, `sdk.Tx`,
+  `MsgEVMTransaction`, Cosmos messages, or Cosmos coins
+
+The current implementation executes raw RLP transactions with go-ethereum
+against an EVM-native state backend, then returns a changeset plus Ethereum
+receipts. Custom precompiles are still placeholders. The open work is to port
+them behind an EVM-native context that is visible to the executor's conflict
+tracking without reintroducing Cosmos keeper dependencies.
+
+## Current implementation
+
+The `evmonly` package currently provides:
+
+- sequential execution of the ordered block transaction list
+- RLP decoding and sender recovery through go-ethereum signers
+- go-ethereum `core.ApplyMessage` execution against an SDK-free `vm.StateDB`
+- key-addressable state reads for balance, nonce, code, and storage
+- deterministic post-block `StateChangeSet` construction
+- Ethereum receipt construction with logs, bloom, gas, tx hash, block metadata,
+  contract address, and effective gas price
+- a map-backed `MemoryState` for tests and early integration
+- fail-closed custom precompile placeholders
+
+The executor accepts config for nonce checks, gas-price checks, minimum gas
+price, chain config, and the custom precompile registry.
+
+## Executor interface
+
+The boundary is:
+
+```go
+ExecuteBlock(context.Context, BlockRequest) (*BlockResult, error)
+```
+
+The executor should be commit-neutral. It executes an ordered EVM block and
+returns the state writes and receipts produced by that block. The caller owns
+durable persistence, state commitment, block indexing, and receipt publication.
+The concrete `Executor` accepts a `StateReader` backend through `WithState(...)`;
+callers can persist the returned `ChangeSet` with a matching `StateWriter`.
+
+A non-nil `error` means block validation failed and the caller must not commit a
+partial output. EVM call failures inside an otherwise valid transaction are
+represented in `Receipts` and `Txs` with failed status.
+
+## Input block format
+
+`BlockRequest` is the expected input:
+
+- `Context` contains block-constant EVM fields:
+  - block number
+  - timestamp
+  - block gas limit
+  - chain ID
+  - base fee
+  - blob base fee, when enabled
+  - coinbase
+  - parent hash
+  - current block hash
+  - prevRandao
+- `Txs` is the canonical, already-ordered transaction list for the block.
+- Each tx is raw Ethereum transaction RLP bytes.
+- There is no Cosmos SDK tx envelope, `MsgEVMTransaction`, ante wrapper, memo,
+  fee object, account address mapping object, or Cosmos gas meter in the input.
+
+The runtime or consensus layer is responsible for choosing the block order and
+providing the block context. The executor is responsible for parsing tx RLP,
+recovering senders, validating EVM nonce/fee/intrinsic-gas rules, executing EVM
+state transitions, and producing deterministic outputs.
+
+`BlockHash` is used for receipts and log metadata. The current `BLOCKHASH`
+opcode callback only exposes `ParentHash`; older historical hashes require a
+runtime-provided hash source in a later integration step.
+
+## Output format
+
+`BlockResult` contains two primary outputs:
+
+- `ChangeSet`: the EVM-native state writes produced by the block.
+- `Receipts`: Ethereum receipts for the executed transactions.
+
+`ChangeSet` is expressed as post-block values, not deltas:
+
+- `Balances`: final balance for each changed EVM address
+- `Nonces`: final nonce for each changed EVM address
+- `Code`: final bytecode updates or deletions
+- `Storage`: final storage slot updates or deletions
+
+The changeset should be deterministic and serializable by the runtime layer.
+The executor should not require `sdk.Context` or Cosmos stores to build it.
+
+`Receipts` are emitted in transaction order and should contain the Ethereum
+receipt fields needed by RPC and indexing: status, cumulative gas used, bloom,
+logs, tx hash, contract address, and effective gas price metadata where needed.
+
+`Txs` carries per-transaction execution metadata used to build or enrich
+receipts and RPC responses. `GasUsed` is the total EVM gas consumed by the block.
+
+## Open precompile work
+
+Native custom precompiles still need a separate design. If they introduce state
+outside balance, nonce, code, and storage, that state must either become part of
+the EVM-native changeset or be represented through an explicit extension that is
+visible to the OCC conflict tracker.
+
+The intended direction is to treat each custom precompile's migrated module
+state as contract storage owned by that precompile address. With no range reads
+and no side state, precompile reads and writes can then flow through ordinary
+`(address, slot)` storage tracking.
+
+Until that design is implemented, the `evmonly` executor accepts a custom
+precompile registry only as a fail-closed placeholder. Calls to registered
+custom precompile addresses return `ErrCustomPrecompilesOpen`.
+
+## Current limitations
+
+- The current port is sequential. The EVM-native state boundary and changeset
+  shape are intended to be replaceable with the sei-v3 OCC scheduler/store.
+- State input is key-addressable only. The executor lazily reads storage slots
+  by `(address, slot)` and does not require or expose range iteration.
+- The map-backed `MemoryState` is for tests and early integration; production
+  should provide a durable native state backend.
+- Historical `BLOCKHASH` lookups beyond the parent block are not wired yet.

giga/evmonly/config.go

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+package evmonly
+
+import (
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/params"
+
+	"github.com/sei-protocol/sei-chain/giga/evmonly/precompiles"
+)
+
+// Config captures the sei-v3 executor knobs needed by the EVM-only path.
+type Config struct {
+	DisableNonceCheck    bool
+	DisableGasPriceCheck bool
+	MinGasPrice          *big.Int
+	ChainConfig          *params.ChainConfig
+	CustomPrecompiles    precompiles.Registry
+}
+
+func DefaultConfig() Config {
+	return Config{
+		MinGasPrice: big.NewInt(1_000_000_000),
+	}
+}
+
+func (c Config) WithDefaults() Config {
+	defaults := DefaultConfig()
+	if c.MinGasPrice == nil {
+		c.MinGasPrice = new(big.Int).Set(defaults.MinGasPrice)
+	}
+	return c
+}