Feat(chainspec): adding xlayer-devnet chainspec

[dloghin]

Description

Adding xlayer-devnet chainspec to chainspec crate. This helps in running devnet with testnet/mainnet data by making the process of starting op-reth-seq (sequencer) and op-reth-rpc (RPC) much faster compared to starting with genesis. Since devnet genesis changes every time we create a devnet, we need to inject genesis hash into chainspec, so we do this by writing the hash into res/genesis/xlayer-devnet-genesis-hash.txt and reading it into XLAYER_DEVNET_GENESIS_HASH.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Other (please describe):

Code Guidelines

Before submitting your PR, please review the relevant code guidelines in the docs/ folder:

• Building on Reth Guide - Comprehensive guide for building on top of Reth

Specific Guidelines by Component:

• Chainspec & EVM Guide - For changes to chainspec or EVM configuration
• Database Guide - For changes to database tables or storage
• Engine & Consensus Guide - For changes to consensus or engine API
• Extension Guide - For adding extensions or plugins
• Node Builder Guide - For changes to node initialization
• Payload Builder Guide - For changes to block building logic

Checklist

• I have reviewed the relevant code guidelines in the docs/ folder
• My code follows the coding standards of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Testing

cargo test --package xlayer-chainspec --lib -- xlayer_devnet::tests --nocapture

[Vui-Chee]

Review Summary

4 new findings not covered by existing discussion:

1. Inconsistent 0x prefix in fallback hash values (xlayer_devnet.rs)

The genesis hash fallback (line ~28) uses "0xc5d2..." (with 0x prefix), but the state root fallback (line ~53) uses "c5d2..." (without prefix). Both are parsed with .parse::<B256>(). Pick one format — preferably bare hex without 0x to match the b256!() convention used in mainnet/testnet.

2. Doc comment says "testnet" instead of "devnet" (lib.rs line 118)

XLAYER_DEVNET_HARDFORKS has doc comment /// X Layer testnet list of hardforks. — copy-paste error, should say "devnet".

3. Filesystem writes during Lazy static initialization (xlayer_devnet.rs)

XLAYER_DEVNET_GENESIS_HASH and XLAYER_DEVNET_STATE_ROOT create files on disk via std::fs::write if they do not exist. Concerns:

• Read-only environments (Docker, CI, production): will panic! on first access
• Silent incorrect state: a fresh clone runs with keccak256("") as genesis hash with no warning to the operator

Consider failing with a clear error when the file is missing (forcing operator to provide the correct hash), or at minimum logging a warning when falling back to the placeholder. The mainnet/testnet equivalents are const values with zero I/O.

4. terminalTotalDifficultyPassed: false in genesis JSON (xlayer-devnet.json line 24)

Both mainnet and testnet genesis files set this to true. With terminalTotalDifficulty: 0, having Passed: false is contradictory. While the programmatic hardfork config likely overrides this, other tooling consuming the raw JSON could be confused. Should this be true?

[dloghin]

1. Fixed.
2. Fixed.
3. Using empty hash is as intended: devnet chainspec should be used only in conjunction with xlayer-toolkit devnet scripts since devnet genesis modifies each time a devnet is set up. Hence, we do not have a consistent pre-defined hash.
4. terminalTotalDifficulty: 0 is consistent with the genesis files generated during devnet setup.

[Vui-Chee]

All 4 previous review comments have been addressed:

1. 0x prefix consistency — Both fallback hashes now consistently use the 0x prefix. ✔
2. Doc comment fix — XLAYER_DEVNET_HARDFORKS doc now correctly says "devnet". ✔
3. Filesystem writes during Lazy init — Explanation accepted: devnet chainspec is intended to be used with xlayer-toolkit devnet scripts where genesis changes each time, so the file-creation fallback is by design.
4. terminalTotalDifficultyPassed: false — Acceptable since Paris is explicitly configured in XLAYER_DEVNET_HARDFORKS via ForkCondition::TTD, overriding the JSON value at runtime.

LGTM.

[Vui-Chee]

LGTM — all 4 previous review comments have been addressed.