Evm block hash history contract

[mpapierski]

Summary

This PR adds EIP-2935 block hash history support for Prague-mode Casper EVM.

It installs the standard EIP-2935 block-hash-history predeploy and updates it once per block with the parent Casper block hash. This gives EVM contracts the expected Prague system-contract interface while keeping the existing BLOCKHASH opcode behavior unchanged.

The important Casper-specific semantic is:

stored block hash := parent Casper block hash

So the interface matches EIP-2935, but the stored values are Casper block hashes, not Ethereum L1 execution block hashes.

What Changed

• Added EIP-2935 constants under casper_types::evm:

  • standard predeploy address
  • exact 83-byte runtime bytecode
  • code-hash helper

• Generalized Prague EVM predeploy setup so genesis and protocol upgrade install both:

  • EIP-4788 beacon roots
  • EIP-2935 block hash history

• Preserved the existing idempotent predeploy behavior:

  • create missing entries
  • repair missing or empty code hashes
  • repair missing bytecode
  • reject conflicting non-empty code or bytecode

• Added a pre-block EIP-2935 system call:

  • skipped at block height 0
  • runs after the EIP-4788 update
  • runs before user transactions
  • fails block execution if the system call does not succeed

• Updated EVM documentation to mark EIP-2935 as implemented and clarify that BLOCKHASH remains separate.

Semantics

For each non-genesis Prague EVM block, Casper calls the EIP-2935 contract with the parent Casper block hash as calldata. The contract stores that hash in the standard 8191-slot history ring buffer.

Contracts can then call the EIP-2935 predeploy at:

0x0000F90827F1C53a10cb7A02335B175320002935

to retrieve recent stored Casper block hashes through the standard EIP-2935 lookup interface.

This does not change the BLOCKHASH opcode. BLOCKHASH still uses Casper’s existing node-supplied block hash provider.