Implement set-code transactions (EIP-7702)

[mw2000]

Summary

Implement EIP-7702 set-code transactions (type 0x04), introduced in Prague. This allows EOAs to temporarily delegate their execution to contract code by setting a delegation indicator 0xef0100 ++ target_address as their code.

Specification

Transaction Type 0x04

New fields beyond EIP-1559:

• authorization_list: list of (chain_id, address, nonce, y_parity, r, s) tuples
• Each authorization allows setting the signer's code to a delegation designator

Delegation Designator

• Code: 0xef0100 ++ 20-byte-address (23 bytes total)
• When any CALL-family opcode targets an address with this designator, execution follows the pointer and runs the target contract's code in the EOA's context

Gas

• PER_AUTH_BASE_COST = 2500 gas per authorization tuple in the list
• Authorizations are processed before execution begins
• Invalid authorizations are skipped (not failure)

Authorization Processing

For each (chain_id, address, nonce, y_parity, r, s):

1. Recover signer from signature
2. Verify chain_id matches (or is 0 for any chain)
3. Verify nonce matches signer's current nonce
4. Set signer's code to 0xef0100 ++ address
5. Increment signer's nonce

CALL Dispatch Change

When CALL/CALLCODE/DELEGATECALL/STATICCALL targets an address whose code starts with 0xef0100:

• Read the 20-byte target address from bytes 3–22
• Load code from that target address
• Execute in the context of the original (delegating) address

Implementation Guide

1. Add EEVM.Transaction.SetCode struct for type 0x04 with authorization_list field
2. Update EEVM.Transaction.Envelope to encode/decode type 0x04
3. Update EEVM.Transaction.Signer for type 0x04 signing hash
4. Add authorization processing — new module EEVM.Transaction.Authorization
5. Update CALL dispatch in calls.ex — detect 0xef0100 prefix and follow delegation
6. Update EXTCODESIZE/EXTCODECOPY/EXTCODEHASH for delegated accounts
7. Tests: authorization processing, CALL delegation, gas costs, invalid auth skipping

Acceptance Criteria

• Type 0x04 transaction struct, encoding, and signing
• Authorization list processing with signature recovery
• Code delegation designator set correctly
• CALL-family opcodes follow delegation pointer
• Invalid authorizations skipped without tx failure
• Gas: 2500 per authorization tuple
• EXTCODE* opcodes handle delegated accounts
• Tests pass

Reference

• EIP-7702: https://eips.ethereum.org/EIPS/eip-7702