fix(levm): install the specified EIP-8272 RECENT_ROOT_CODE instead of a native write

[AnkushinDaniil]

Stacked on #7086; review the last commit only.

Motivation

RECENT_ROOT_CODE was TBD in EIP-8272, so the predeploy carried no bytecode and the 64-byte salt ‖ root write was a VM-level special case on four paths: the top-level entry, the CALL family, the frame default-code path, and a carve-out in the simple-transfer fast path. The write cost a flat RECENT_ROOT_WRITE_GAS.

ethereum/EIPs#12131 specifies the bytecode, assembled verbatim from the spec's write operation. With it installed the write is ordinary EVM execution, so the entry a caller commits and the gas it pays for committing it are both what the code does, and none of the interception points are needed.

This also removes a consensus divergence. The native write bypassed the EIP-8037 state-gas charge for the created storage slot, so the same transaction cost 38 064 here and 127 196 on a client that executes the predeploy, and the two forked on the first block carrying a root write. An isolated contract doing one fresh SSTORE costs the same on both, so the general 8037 path already agrees — it was only the predeploy that did not.

Description

• RECENT_ROOT_RUNTIME_BYTECODE: the 144 bytes from EIPs#12131, with the derivation and the two prohibitions the spec says need no explicit check documented on the constant.
• install_recent_root_code now installs code, matching install_nonce_manager_code: idempotent on code equality, nonce converges to max(existing, 1), balance preserved.
• Removed run_top_level_recent_root_write, recent_root_native_write, execute_recent_root_frame, the generic_call interception, the fast-path carve-out and RECENT_ROOT_WRITE_GAS.
• Updated the EIP-8272 notes: divergences 4, 6, 7, 8 and 9 no longer exist.

The read side is untouched: reference validity, the hash derivations and the mempool policy are unchanged, and a root written through the predeploy still validates its own reference because both sides derive keys from the same helpers.

How to test

cargo test -p ethrex-vm --lib and cargo test -p ethrex-common recent_root pass; cargo check --workspace is clean.

[greptile-apps]

Greptile Summary

The PR replaces EIP-8272’s VM-native recent-root write with an installed 144-byte runtime contract, allowing ordinary EVM execution and EIP-8037 state-gas accounting.

• Installs the runtime at Hegota activation while preserving balance and converging the nonce.
• Removes top-level, frame, CALL-family, fast-path, and flat-gas special cases.
• Updates EIP-8272 implementation notes for bytecode-driven write semantics.
• Existing integration fixtures still need to install the new runtime.

Confidence Score: 4/5

The PR appears safe to merge after the non-blocking EIP-8272 integration fixtures are updated to execute the newly installed runtime.

The runtime’s derivations and generic EVM behavior match the removed native implementation, but two existing regression tests still construct an empty-code predeploy and will no longer validate or complete the intended write.

Files Needing Attention: crates/vm/system_contracts.rs and test/tests/levm/eip8272_tests.rs

Important Files Changed

Filename	Overview
crates/vm/system_contracts.rs	Adds the EIP-8272 runtime bytecode; its decoded hash and storage layouts match the read-side helpers, but existing integration fixtures do not install it.
crates/vm/backends/levm/mod.rs	Installs recent-root code and nonce on both L1 activation paths while preserving account balance and recording BAL changes.
crates/vm/levm/src/opcode_handlers/frame_tx.rs	Removes frame-specific native writes so frames rely on installed bytecode; stale empty-code test fixtures now silently execute default EOA behavior.
crates/vm/levm/src/opcode_handlers/system.rs	Removes CALL-family interception and delegates write behavior, gas, and rollback to ordinary EVM execution.
crates/vm/levm/src/vm.rs	Removes native and top-level recent-root handling while retaining generic execution and unrelated frame receipt cleanup.
docs/eip-8272.md	Documents the transition from native writes to bytecode execution and the resulting gas and call-path semantics.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Hegota activation] --> B[Install RECENT_ROOT runtime]
  C[Top-level tx / Frame / CALL] --> D[Ordinary EVM execution]
  B --> D
  D --> E[Validate calldata and value]
  E --> F[Derive source ID and slot key]
  F --> G[SSTORE through standard gas and journaling]

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Prompt To Fix All With AI

### Issue 1
crates/vm/system_contracts.rs:164
**Update empty-code write fixtures**

The existing EIP-8272 write tests still seed `RECENT_ROOT_ADDRESS` with empty code, so after removal of the native frame interception they execute EOA default behavior and fail to populate the expected storage slot. Install `RECENT_ROOT_RUNTIME_BYTECODE` in those fixtures so the write and BAL regression cases exercise the new consensus path.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "fix(levm): install the specified EIP-827..." | Re-trigger Greptile}

[greptile-apps]

Update empty-code write fixtures

The existing EIP-8272 write tests still seed RECENT_ROOT_ADDRESS with empty code, so after removal of the native frame interception they execute EOA default behavior and fail to populate the expected storage slot. Install RECENT_ROOT_RUNTIME_BYTECODE in those fixtures so the write and BAL regression cases exercise the new consensus path.

Knowledge Base Used: VM: LEVM Execution and the Database Glue

Prompt To Fix With AI

This is a comment left during a code review.
Path: crates/vm/system_contracts.rs
Line: 164

Comment:
**Update empty-code write fixtures**

The existing EIP-8272 write tests still seed `RECENT_ROOT_ADDRESS` with empty code, so after removal of the native frame interception they execute EOA default behavior and fail to populate the expected storage slot. Install `RECENT_ROOT_RUNTIME_BYTECODE` in those fixtures so the write and BAL regression cases exercise the new consensus path.

**Knowledge Base Used:** [VM: LEVM Execution and the Database Glue](https://app.greptile.com/lambdaclass/-/custom-context/knowledge-base/lambdaclass/ethrex/-/docs/vm-levm.md)

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.