interop: Specify deposit handling

specs/interop/derivation.md

@@ -0,0 +1,22 @@
+<!-- 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)
+ - [Deposit Context](#deposit-context)
+- [Security Considerations](#security-considerations)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+## Overview 
+
+This is an experimental section and may be changed in the future. It is not required
+for the initial release.
+
+### Deposit Context
+
+Derivation is extended to create **deposit contexts**, which signifies the execution of a depositing transaction. A deposit context is scoped to a single block, commencing with the execution of the first deposited transaction and concluding immediately after the execution of the final deposited transaction within that block. As such, there is exactly one deposit context per block.
+
+## Security Considerations
+
+TODO

specs/interop/predeploys.md

@@ -11,6 +11,7 @@
  - [`_target`](#_target)
  - [`ExecutingMessage` Event](#executingmessage-event)
  - [Reference implementation](#reference-implementation)
+ - [Deposit Handling](#deposit-handling)
  - [`Identifier` Getters](#identifier-getters)
 - [L2ToL2CrossDomainMessenger](#l2tol2crossdomainmessenger)
  - [`relayMessage` Invariants](#relaymessage-invariants)
@@ -26,6 +27,9 @@
 - [L1Block](#l1block)
  - [Static Configuration](#static-configuration)
  - [Dependency Set](#dependency-set)
+ - [Deposit Context](#deposit-context)
+ - [`isDeposit`](#isdeposit)
+ - [`setDepositing`](#setdepositing)
 - [Security Considerations](#security-considerations)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -139,6 +143,12 @@ function executeMessage(Identifier calldata _id, address _target, bytes calldata
 
 Note that the `executeMessage` function is `payable` to enable relayers to earn in the gas paying asset.
 
+### Deposit Handling
+
+A call to `executeMessage` reverts if the call is made in a [deposit context](./derivation.md#deposit-context). The deposit context status can be determined by callling `isDeposit` on the `L1Block` contract.
+
+In the future, deposit handling will be modified to be more permissive. It will revert only in specific cases where interop dependency resolution is not feasible.
+
 ### `Identifier` Getters
 
 The `Identifier` MUST be exposed via `public` getters so that contracts can call back to authenticate
@@ -416,6 +426,30 @@ dependency set called `dependencySet()`. This function MUST return the array of
 `L1Block` MUST also provide a public getter to get the dependency set size called `dependencySetSize()`. This function
 MUST return the length of the dependency set array.
 
+### Deposit Context
+
+The `L1Block` contract is updated with the following methods to support [deposit contexts](./derivation.md#deposit-context).
+
+#### `isDeposit`
+
+```solidity
+function isDeposit() (return bool)
+```
+
+A new method added to `L1Block` indicating whether the current execution is in a [deposit context](./derivation.md#deposit-context). The method has the following signature:
+
+
+Only the `CrossL2Inbox` is authorized to call `isDeposit`.
+
+#### `setDepositing`
+
+```solidity
+function setDepositing(bool _isDepositing)
+```
+A new method added to indicate whether the current execution is in a deposit context.
+
+Only the `DEPOSITOR_ACCOUNT` is authorized to call `setDepositing`.
+
 ## Security Considerations
 
 TODO

specs/interop/upgrade.md

@@ -5,6 +5,7 @@
 **Table of Contents**
 
 - [Security Considerations](#security-considerations)
+ - [Deposit Transactions During Upgrades](#deposit-transactions-during-upgrades)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
@@ -29,3 +30,7 @@ The exact definitions for these upgrade transactions are still to be defined.
 ## Security Considerations
 
 TODO
+
+### Deposit Transactions During Upgrades
+
+TODO