docs: add Kroma MPT migration upgrade

specs/SUMMARY.md

@@ -31,6 +31,9 @@
     - [Ecotone](./protocol/ecotone/overview.md)
       - [Derivation](./protocol/ecotone/derivation.md)
       - [L1 attributes](./protocol/ecotone/l1-attributes.md)
+    - [Kroma MPT Migration](./protocol/mpt-migration/overview.md)
+      - [Execution Engine](./protocol/mpt-migration/exec-engine.md)
+      - [Predeploys](./protocol/mpt-migration/predeploys.md)
 - [Fault Proof]()
   - [Challenge](zk-fault-proof/challenge.md)
   - [zkVM Prover](zk-fault-proof/zkvm-prover.md)

specs/protocol/mpt-migration/exec-engine.md

@@ -0,0 +1,75 @@
+# L2 Execution Engine
+
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+**Table of Contents**
+
+- [Overview](#overview)
+- [Timestamp Activation](#timestamp-activation)
+- [EVM Changes](#evm-changes)
+  - [Transition from ZK Trie to MPT](#transition-from-zk-trie-to-mpt)
+  - [`SELFDESTRUCT` opcode](#selfdestruct-opcode)
+  - [`isSystemTransaction` boolean at transaction struct](#issystemtransaction-boolean-at-transaction-struct)
+- [Fee Distribution Process](#fee-distribution-process)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+[g-zktrie]: ../../glossary.md#zk-trie
+[g-mpt]: ../../glossary.md#merkle-patricia-trie
+[validator-system]: ../validator-v2/overview.md
+
+## Overview
+
+This upgrade changes the underlying trie structure of the execution client from the [ZK Trie][g-zktrie] to the
+[Merkle Patricia Trie][g-mpt]. There are also subsequent changes to the EVM to enhance the compatibility with
+Vanilla OP Stack.
+
+## Timestamp Activation
+
+Kroma MPT Migration upgrade, like other network upgrades, is activated at a timestamp. Changes to the L2 Block execution
+rules are applied when the `L2 Timestamp >= activation time`.
+
+## EVM Changes
+
+### Transition from ZK Trie to MPT
+
+The underlying trie structure of the execution client is changed from the ZK Trie to the Merkle Patricia Trie. This
+enhances the performance of the execution client, and reduces the operational cost of maintaining zkEVM circuits by
+enabling the proving scheme transition to zkVM.
+
+### `SELFDESTRUCT` opcode
+
+The `SELFDESTRUCT` opcode was regarded as invalid opcode, since zkEVM proving system used in ZK fault proof cannot prove
+the self-destruct operation. However, with the transition to zkVM, the `SELFDESTRUCT` opcode is now enabled, following
+rules that are defined at [EIP-6780].
+
+[EIP-6780]: https://eips.ethereum.org/EIPS/eip-6780
+
+### `isSystemTransaction` boolean at transaction struct
+
+In the previous version of the protocol, the `isSystemTransaction` boolean was removed. To enhance the compatibility
+with vanilla OP Stack, the `isSystemTransaction` boolean is re-enabled.
+
+However, since `isSystemTransaction` was disabled as in the [Regolith upgrade](../regolith/overview.md), system
+transactions remain to use the same gas accounting rules as regular deposits.
+
+## Fee Distribution Process
+
+The fee distribution process is updated to be compatible with OP Stack. Previously, the fee distribution process was
+defined to support robustness of validator system.
+
+| Vault                  | Address                                      | Amount                                                                |
+|------------------------|----------------------------------------------|-----------------------------------------------------------------------|
+| `ProtocolVault`        | `0x4200000000000000000000000000000000000006` | `(base_fee + priority_fee) * (10000 - validatorRewardScalar) / 10000` |
+| `L1FeeVault`           | `0x4200000000000000000000000000000000000007` | `l1_cost`                                                             |
+| `ValidatorRewardVault` | `0x4200000000000000000000000000000000000008` | `(base_fee + priority_fee) * validatorRewardScalar / 10000`           |
+
+However, with transition to [KRO-based validator system][validator-system], validators are now getting KRO rewards,
+and `validatorRewardScalar` was set to 0. After Kroma MPT Migration upgrade, the fee distribution process is updated
+as follows:
+
+| Vault               | Address                                      | Amount         |
+|---------------------|----------------------------------------------|----------------|
+| `SequencerFeeVault` | `0x4200000000000000000000000000000000000011` | `priority_fee` |
+| `BaseFeeVault`      | `0x4200000000000000000000000000000000000019` | `base_fee`     |
+| `L1FeeVault`        | `0x420000000000000000000000000000000000001a` | `l1_cost`      |

specs/protocol/mpt-migration/overview.md

@@ -0,0 +1,16 @@
+# Kroma MPT Migration
+
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+**Table of Contents**
+
+- [Execution Layer](#execution-layer)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+## Execution Layer
+
+- [Transition from ZK Trie to MPT](./exec-engine.md#transition-from-zk-trie-to-mpt)
+- [`SELFDESTRUCT` opcode](./exec-engine.md#selfdestruct-opcode)
+- [`isSystemTransaction` boolean at transaction struct](./exec-engine.md#issystemtransaction-boolean)
+- [Fee distribution process](./exec-engine.md#fee-distribution-process)