---
eip: 8141
title: Frame Transaction
description: Add frame abstraction for transaction validation, execution, and gas payment
author: Vitalik Buterin (@vbuterin), lightclient (@lightclient), Felix Lange (@fjl), Yoav Weiss (@yoavw), Alex Forshtat (@forshtat), Dror Tirosh (@drortirosh), Shahaf Nacson (@shahafn), Derek Chiang (@derekchiang), Toni Wahrstätter (@nerolation)
discussions-to: https://ethereum-magicians.org/t/frame-transaction/27617
status: Draft
type: Standards Track
category: Core
created: 2026-01-29
requires: 1559, 2718, 3607, 4844, 7623, 7702
---

## Abstract

Adds a new transaction whose validity and gas payment can be defined abstractly. This is achieved by decomposing the transaction into a sequence of *frames* which are contract calls that validate the transaction, approve gas payment, and execute standard user operations.

## Motivation

The frame transaction type offers UX and security benefits across many areas:

- it provides a native off-ramp from the elliptic curve based cryptographic system used to authenticate transactions today, to post-quantum (PQ) secure systems.
- accounts are unlinked from their ECDSA keys, allowing native key rotation
- smart accounts become simpler and therefore safer by natively providing batch call processing
- alternative fee payment schemes are supported without centralized, third party relayers
- the default account gives the protocol an even stronger guarantee on the lowest common denominator of account functionality
 
Ultimately, frame transactions realize the original vision of account abstraction: an account simply becomes an address with code. It leverages the EVM to support arbitrary *user-defined* definitions of validation and gas payment.

## Specification

### Constants

| Name                      | Value           |
|---------------------------|-----------------|
| `FRAME_TX_TYPE`           | `0x06`          |
| `FRAME_TX_INTRINSIC_COST` | `15000`         |
| `FRAME_TX_PER_FRAME_COST` | `475`           |
| `ENTRY_POINT`             | `address(0xaa)` |
| `EXPIRY_VERIFIER`         | `address(0x8141)` |
| `EXPIRY_DATA_LENGTH`      | `8`             |
| `MAX_FRAMES`              | `64`            |

### Frame Transaction

A new [EIP-2718](./eip-2718.md) transaction with type `FRAME_TX_TYPE` is introduced. Transactions of this type are referred to as **frame transactions**.

#### Payload Encoding

The payload is defined as the RLP serialization of the following:

```
[chain_id, nonce, sender, frames, max_priority_fee_per_gas, max_fee_per_gas, max_fee_per_blob_gas, blob_versioned_hashes]

frames = [[mode, flags, target, gas_limit, value, data], ...]
```

#### Field Definitions

Below are high-level definitions of each field in the transaction definition. Detailed behavior is defined in subsequent sections.

##### Outer transaction payload

- `chain_id` -- the chain ID in which the transaction is valid.
- `nonce` -- nonce of the sender to prevent replays.
- `sender` -- the address of the intended sender of the transaction.
- `frames` -- list of frames to execute.
- `max_priority_fee_per_gas` -- the EIP-1559 priority fee per gas the transaction will pay.
- `max_fee_per_gas` -- the maximum EIP-1559 fee the transaction is willing to pay, per gas.
- `max_fee_per_blob_gas` -- the maximum EIP-4844 fee per blob gas the transaction is willing to pay. Must be `0` if `blob_versioned_hashes` is empty.
- `blob_versioned_hashes` -- list of EIP-4844 blob versioned hashes.

##### Frame object

- `mode` -- the mode specifies the specific execution semantics the frame will execute with.
- `flags` -- specifies optional frame / mode features.
- `target` -- the destination or `to` address for the frame.
- `gas_limit` -- the maximum gas allowed to be execute in pursuit of the frame.
- `value` -- the amount in wei that should transferred from the `sender` as part of the frame execution.
- `data` -- the calldata provided to the top level call frame.

The `mode` of each frame sets the context of execution. It allows the protocol to identify
the purpose of the frame within the execution loop.

| `mode`  | Name           | Summary                                    |
|---------|----------------|--------------------------------------------|
| 0       | `DEFAULT` mode | Execute frame as `ENTRY_POINT`             |
| 1       | `VERIFY` mode  | Frame identifies as transaction validation |
| 2       | `SENDER` mode  | Execute frame as `sender`                  |


The `flags` field configures additional execution constraints. Bit positions are zero-based, with the least significant bit numbered `0`.

| Flag bits | Meaning                      | Valid with  |
|-----------|------------------------------| ----------- |
| 0-1       | Approval scope               | Any mode    |
| 2         | Atomic batch                 | Any mode    |

The `Valid with` column indicates the mode under which the flag is valid. If a flag is not valid under the current mode, the transaction is invalid.

#### Constraints

Some validity constraints can be determined statically. They are outlined below:

```python
assert tx.chain_id < 2**256
assert tx.nonce < 2**64
assert len(tx.frames) > 0 and len(tx.frames) <= MAX_FRAMES
assert len(tx.sender) == 20

total_frame_gas = 0
for frame in tx.frames:
    assert frame.mode < 3
    assert frame.flags < 8
    assert frame.target is None or len(frame.target) == 20
    assert frame.gas_limit <= 2**64 - 1
    assert frame.value < 2**256
    assert frame.mode == SENDER or frame.value == 0
    total_frame_gas += frame.gas_limit
    assert total_frame_gas <= 2**64 - 1

    # Atomic batch flag (bit 2 of flags) requires a subsequent frame to batch with.
    if frame.flags & ATOMIC_BATCH_FLAG:
        assert i + 1 < len(tx.frames)                  # must not be last frame
```

#### Receipt Encoding

The `ReceiptPayload` is defined as:

```
[cumulative_gas_used, payer, [frame_receipt, ...]]
frame_receipt = [status, gas_used, logs]
```

`payer` is the address of the account that paid the fees for the transaction. `status` is the return code of the top-level call. A new code `0x3` is introduced for frames which are skipped due to failed atomic batch.

#### Signature Hash

With the frame transaction, the signature may be at an arbitrary location in the frame list. In the canonical signature hash any frame with mode `VERIFY` will have its data elided, except for [expiry verifier frames](#expiry-verifier-frame), whose `data` is the deadline and is covered by the signature:

```python
def compute_sig_hash(tx: FrameTx) -> Hash:
    for i, frame in enumerate(tx.frames):
        if frame.mode == VERIFY and frame.target != EXPIRY_VERIFIER:
            tx.frames[i].data = Bytes()
    return keccak(bytes([FRAME_TX_TYPE]) + rlp(tx))
```

#### Expiry Verifier Frame

A `VERIFY` frame whose `frame.target` equals `EXPIRY_VERIFIER` is an **expiry verifier frame**. It calls the expiry verifier contract deployed at `EXPIRY_VERIFIER` with `frame.data` as calldata. The calldata is interpreted as an 8-byte unsigned big-endian expiry timestamp. The call reverts unless `block.timestamp <= expiry_timestamp`.

An expiry verifier frame is invalid unless all of the following hold:

- `frame.flags == 0`,
- `frame.value == 0`, and
- `len(frame.data) == EXPIRY_DATA_LENGTH`.

A transaction can contain at most one expiry verifier frame.

At activation, clients must install the following expiry verifier contract runtime code at `EXPIRY_VERIFIER`. The expiry verifier contract's runtime code must be:

```asm
push1 0x08
calldatasize
eq
push1 0x0a
jumpi
push0
push0
revert

jumpdest
push0
calldataload
push1 0xc0
shr
timestamp
gt
push1 0x16
jumpi
stop

jumpdest
push0
push0
revert
```

The runtime bytecode is:

```text
0x60083614600a575f5ffd5b5f3560c01c4211601657005b5f5ffd
```

Equivalently, the runtime behavior is:

```python
if len(evm.calldata) != EXPIRY_DATA_LENGTH:
    revert()

expiry_timestamp = int.from_bytes(evm.calldata, "big")
if evm.timestamp > expiry_timestamp:
    revert()

stop()
```

If the check passes, the frame succeeds with no return data and no logs. The frame consumes gas according to normal EVM execution rules. Although `TIMESTAMP` is generally banned during validation-prefix execution, it is permitted in this special `VERIFY` frame when executing the canonical expiry verifier runtime code at `EXPIRY_VERIFIER`.

Clients may omit the explicit EVM execution and directly perform the expiry check above, provided the externally observable result is identical to executing the canonical contract. Note: While this is a valid optimization for Ethereum mainnet, it could be problematic on non-mainnet situations in case a different contract is used.

#### Behavior

When processing a frame transaction, perform the following steps.

To begin processing a frame transaction:

1. Ensure `tx.nonce == state[tx.sender].nonce`
1. Initialize transaction-scoped variables:
    - `payer = None`
    - `sender_approved = false`
1. Let `resolved_target = frame.target if frame.target is not None else tx.sender`
    - Unless otherwise stated, checks that refer to the target account during execution use the resolved target.

Then for each frame:

1. Execute a call with the specified `mode`, `flags`, `resolved_target`, `gas_limit`, `value`, and `data`.
   - If mode is `SENDER`:
       - `sender_approved` must be `true`. If not, the transaction is invalid.
       - Set `caller` as `tx.sender`.
   - If mode is `DEFAULT` or `VERIFY`:
       - Set the `caller` to `ENTRY_POINT`.
   - In the top-level frame call, `CALLVALUE` is `frame.value`.
   - As with an ordinary `CALL`, if the caller does not have sufficient balance to transfer `frame.value`, the frame reverts.
   - If `resolved_target` code hash is empty, i.e. `0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470`, execute the logic described in [default code](#default-code).
   - Otherwise, if `resolved_target` uses an [EIP-7702](./eip-7702.md) delegation indicator, execute according to [EIP-7702](./eip-7702.md)'s delegated-code semantics.
   - The `ORIGIN` opcode returns frame `caller` throughout all call depths.
   - If a frame's execution reverts, its state changes are discarded. Additionally, if this frame has the atomic batch flag set, mark all subsequent frames in the same atomic group as skipped.
2. If frame has mode `VERIFY` the following additional requirements are imposed:
    - Execute the frame as a `STATICCALL`, disallowing state manipulation.
      - Only `APPROVE` can modify the state or transaction context in `VERIFY`.
    - If the frame reverts, the transaction is invalid.
3. If a frame is part of an atomic batch and it fails, unroll the associated atomic batch.
    - An **atomic batch** is a maximal contiguous sequence of frames `[i, j]` where `j > i`, frames `i` through `j - 1` have `ATOMIC_BATCH_FLAG` set, and frame `j` does not have `ATOMIC_BATCH_FLAG` set.
    - When a frame in the batch fails, the state must be rolled back to the condition it was immediately before the atomic batch began. All remaining frames in the atomic batch are skipped.
    - Since skipped frames are not executed, the gas value allotted to them is refunded at the end of the transaction.
    - If the frame does not have an associated atomic batch, further special
      handling is not needed, simple revert the individual frame.

After executing all frames, verify that `payer` has been set (i.e. `payer != None`). If `payer` is set, refund any unpaid gas to the payer. If it is not, the whole transaction is invalid.

##### Cross-frame interactions

A few cross-frame interactions to note:

- For the purposes of gas accounting of warm / cold state status, the journal of such touches is shared across frames.
- Discard the `TSTORE` and `TLOAD` transient storage between frames.

##### Gas Accounting

The total gas limit of the transaction is:

```
tx_gas_limit = FRAME_TX_INTRINSIC_COST + len(tx.frames) * FRAME_TX_PER_FRAME_COST + calldata_cost(rlp(tx.frames)) + sum(frame.gas_limit for all frames)
```

Where `calldata_cost` is calculated per standard [EIP-7623](./eip-7623.md) rules.

The total fee is defined as:

```
tx_fee = tx_gas_limit * effective_gas_price + blob_fees
blob_fees = len(blob_versioned_hashes) * GAS_PER_BLOB * blob_base_fee
```

The `effective_gas_price` is calculated per [EIP-1559](./eip-1559.md) and `blob_fees` is calculated as per [EIP-4844](./eip-4844.md).

Any `frame.value` transferred by `SENDER` frames is separate from `tx_fee` and follows ordinary `CALL` value-transfer semantics. The gas cost of sending `frame.value` is the same as for any `CALL` instruction.

Each frame has its own `gas_limit` allocation. Unused gas from a frame is **not** available to subsequent frames. After all frames execute, the gas refund is calculated as:

```
refund = sum(frame.gas_limit for all frames) - total_gas_used
```

This refund is returned to the gas payer (the `resolved_target` that called `APPROVE(APPROVE_PAYMENT)` or `APPROVE(APPROVE_EXECUTION_AND_PAYMENT)`) and added back to the block gas pool.

##### Default code

Frame transactions can be used by accounts who do not have deployed code, nor an [EIP-7702](./eip-7702.md) delegation indicator via the "default code" mechanism. The behavior of the default code is defined below:

- If `mode` is `VERIFY`:
  - Read the allowed approval scope from the flags field: `allowed_scope = frame.flags & APPROVE_SCOPE_MASK`. If `allowed_scope == APPROVE_SCOPE_NONE`, revert.
  - If `allowed_scope & APPROVE_EXECUTION != 0` and `resolved_target != tx.sender`, revert.
  - Read the first byte of `frame.data` as `signature_type`.
  - If `signature_type` is:
    - `0x0`:
      - Read the rest of `frame.data` as `(v, r, s)`.
      - If `s > secp256k1n / 2`, revert.
      - Let `recovered = ecrecover(sig_hash, v, r, s)`, where `sig_hash = compute_sig_hash(tx)`.
      - If `recovered == address(0)` or `resolved_target != recovered`, revert.
    - Otherwise revert.
  - Call `APPROVE(allowed_scope)`.
- If `mode` is `SENDER` or `DEFAULT`:
  - Return successfully as if calling empty code.

### `APPROVE` Instruction (`0xaa`)

The `APPROVE` instruction exits the current EVM call frame successfully and updates the transaction-scoped approval context based on the `scope` operand.

#### Stack

| Stack      | Value        |
| ---------- | ------------ |
| `top - 0`  | `offset`     |
| `top - 1`  | `length`     |
| `top - 2`  | `scope`      |

#### Scope Operand

The `scope` operand is a bitmask. Define the following constants:

- `APPROVE_NONE` (`0x0`): No approval scope allowed - the current frame is not allowed to approve any scope.
- `APPROVE_PAYMENT` (`0x1`): Approval of payment - the contract approves paying the total gas cost for the transaction.
- `APPROVE_EXECUTION` (`0x2`): Approval of execution - the sender contract approves future frames calling on its behalf.
   - Note this is only valid when `resolved_target` equals `tx.sender`.
- `APPROVE_EXECUTION_AND_PAYMENT` (`0x3`): Approval of payment and execution.

`APPROVE_SCOPE_MASK` is defined as an alias for `APPROVE_EXECUTION_AND_PAYMENT`.

### Introspection

The instructions in this section provide the needed introspection capabilities of the new frame transaction type and the frame objects themselves, including some runtime information like the execution result status.

#### `TXPARAM` Instruction `(0xb0)`

This instruction gives access to transaction-scoped information. The gas cost of this operation is `2`. It takes one value from the stack, `param`, and returns the associated transaction value to the stack. See the table for the full mapping.

| `param` | Return value                                                                |
|---------|-----------------------------------------------------------------------------|
| 0x00    | current transaction type                                                    |
| 0x01    | `nonce`                                                                     |
| 0x02    | `sender`                                                                    |
| 0x03    | `max_priority_fee_per_gas`                                                  |
| 0x04    | `max_fee_per_gas`                                                           |
| 0x05    | `max_fee_per_blob_gas`                                                      |
| 0x06    | max cost (basefee=max, all gas used, includes blob cost, and intrinsic cost) |
| 0x07    | `len(blob_versioned_hashes)`                                                |
| 0x08    | `compute_sig_hash(tx)`                                                      |
| 0x09    | `len(frames)`                                                               |
| 0x0A    | currently executing frame index                                             |


Undefined `param` values result in an exceptional halt.

#### `FRAMEDATALOAD` Instruction `0xb1`

This opcode loads one 32-byte word of data from frame input. Gas cost: 3 (matches CALLDATALOAD).

It takes two values from the stack, an `offset` and `frameIndex`.
It places the retrieved data on the stack.

When the `frameIndex` is out-of-bounds, an exceptional halt occurs.

The operation semantics match CALLDATALOAD, returning a word of data from the chosen
frame's `data`, starting at the given byte `offset`. When targeting a frame in `VERIFY`
mode, the returned data is always zero.

#### `FRAMEDATACOPY` Instruction (`0xb2`)

This opcode copies data frame input into the contract's memory. Its gas cost is calculated
exactly as for `CALLDATACOPY`, including the fixed cost of 3, the per-word copy cost, and
the standard EVM memory expansion cost.

It takes four values from the stack: `memOffset`, `dataOffset`, `length` and `frameIndex`.
No stack output value is produced.

When the `frameIndex` is out-of-bounds, an exceptional halt occurs.

The operation semantics match CALLDATACOPY, copying `length` bytes from the chosen frame's
`data`, starting at the given byte `dataOffset`, into a memory region starting at
`memOffset`. When targeting a frame in `VERIFY` mode, no data is copied.

#### `FRAMEPARAM` Instruction (`0xb3`)

This instruction gives access to frame-scoped information. The gas cost of this operation is `2`. It takes two values from the stack, `frameIndex` on top and `param` second from top.

| `param` | `frameIndex` | Return value                                              |
|---------|--------------|-----------------------------------------------------------|
| 0x00    | frameIndex   | `resolved_target`                                         |
| 0x01    | frameIndex   | `gas_limit`                                               |
| 0x02    | frameIndex   | `mode`                                                    |
| 0x03    | frameIndex   | `flags`                                                   |
| 0x04    | frameIndex   | `len(data)`                                               |
| 0x05    | frameIndex   | `status` (exceptional halt if current/future)             |
| 0x06    | frameIndex   | `allowed_scope` (`frame.flags & APPROVE_SCOPE_MASK`)      |
| 0x07    | frameIndex   | `atomic_batch` (`(frame.flags >> 2) & 0x01`, returns 0/1) |
| 0x08    | frameIndex   | `value`                                                   |

Notes:

- The `status` field (0x05) returns `0` for failure or `1` for success.
- Undefined `param` values result in an exceptional halt.
- Out-of-bounds access for `frameIndex` results in an exceptional halt.
- Attempting to access the return `status` of the current frame or a subsequent frame results in an exceptional halt.
- `len(data)` returns size 0 when called on a frame with `VERIFY` set.

### Mempool

The transaction mempool must carefully handle frame transactions, as a naive implementation could introduce denial-of-service vulnerabilities. The fundamental goal of the public mempool rules is to avoid allowing an arbitrary number of transactions to be invalidated by a single environmental change or state modification. Beyond this, the rules also aim to minimize the amount of work needed to complete the initial validation phase of a transaction before an acceptance decision can be made.

This policy is inspired by [ERC-7562](./eip-7562.md), but removes staking and reputation entirely. Any behavior that ERC-7562 would admit only for a staked or reputable third party is rejected here for the public mempool. Transactions outside these rules may be accepted into a local or private mempool, but must not be propagated through the public mempool.

#### Constants

| Name  | Value  | Description  |
|---|---|---|
| `MAX_VERIFY_GAS`   | `100_000`  | Maximum amount of gas a node should expend simulating the validation prefix |
| `MAX_PENDING_TXS_USING_NON_CANONICAL_PAYMASTER`   | `1`  | Maximum amount of pending transactions that can be using any given non-canonical paymaster |

#### Validation Prefix

The **validation prefix** of a frame transaction is the shortest prefix of frames whose successful execution sets `payer`.

Public mempool rules apply only to the validation prefix. Once `payer` has been set, subsequent frames are outside public mempool validation and may be arbitrary. In particular, `user_op` and `post_op` occur after payment approval and are therefore not subject to the public mempool restrictions below.

#### Policy Summary

A frame transaction is eligible for public mempool propagation only if its validation prefix depends exclusively on:

1. transaction fields, including the canonical signature hash,
2. the block timestamp as read by an expiry verifier frame,
3. the sender's nonce, code, and storage,
4. if a deploy frame is present, the code of the factory targeted by that frame (subject to the deploy-frame trace rules below),
5. if a paymaster frame is present, either a canonical paymaster instance together with explicit paymaster balance reservation, or a non-canonical paymaster being used by less than `MAX_PENDING_TXS_USING_NON_CANONICAL_PAYMASTER` pending transactions,
6. the code of any other existing non-delegated contracts reached during validation via `CALL*` or `EXTCODE*`, provided the resulting trace does not access disallowed mutable state.

Any dependency on third-party mutable state outside these categories must result in rejection by the public mempool.

#### Mode Subclassifications

While the frames are designed to be generic, we refine some frame modes for the purpose of specifying public mempool handling clearly.

| Name  | Mode  | Description  |
|---|---|---|
| `self_verify`   | VERIFY  | Validates the transaction and approves both sender and payer |
| `deploy`  | DEFAULT | Deploys a new smart account, typically via a deterministic factory such as the [EIP-7997](./eip-7997.md) predeploy |
| `only_verify`  | VERIFY  | Validates the transaction and approves only the sender |
| `pay`  | VERIFY | Validates the transaction and approves only the payer |
| `expiry_verify` | VERIFY | Calls the expiry verifier contract (target = `EXPIRY_VERIFIER`) |
| `user_op` | SENDER | Executes the intended user operation |
| `post_op` | DEFAULT | Executes an optional post-op action as needed by the paymaster |


#### Public Mempool-recognized Validation Prefixes

The public mempool recognizes four validation prefixes. Structural rules are enforced only up to and including the frame that sets `payer`.

##### Self Relay

###### Basic Transaction

```
+-------------+
| self_verify |
+-------------+
```

###### Deploy New Account

```
+--------+-------------+
| deploy | self_verify |
+--------+-------------+
```

##### Canonical Paymaster

###### Basic Transaction

```
+-------------+-----+
| only_verify | pay |
+-------------+-----+
```

###### Deploy New Account

```
+--------+-------------+-----+
| deploy | only_verify | pay |
+--------+-------------+-----+
```

Frames after these prefixes are outside public mempool validation. For example, a transaction may continue with any number of `user_op`s and/or `post_op`s.

#### Structural Rules

To be accepted into the public mempool, a frame transaction must satisfy the following:

1. Its validation prefix must match one of the four recognized prefixes above.
2. If present, `deploy` must be the first frame. This implies there can be at most one `deploy` frame in the validation prefix.
3. `self_verify` and `only_verify` must execute in `VERIFY` mode, target `tx.sender` (either explicitly or via a null target), and must successfully call `APPROVE`.
    - `self_verify` must call `APPROVE(APPROVE_EXECUTION_AND_PAYMENT)`.
    - `only_verify` must call `APPROVE(APPROVE_EXECUTION)`.
4. `pay` must execute in `VERIFY` mode and successfully call `APPROVE(APPROVE_PAYMENT)`.
5. No frame in the validation prefix may have the `ATOMIC_BATCH_FLAG` set.
6. The sum of `gas_limit` values across the validation prefix must not exceed `MAX_VERIFY_GAS`.
7. Nodes should stop simulation immediately once `payer` has been set.

#### Expiry Verifier Frame

An `expiry_verify` frame MAY appear at any position in the frame list. For the purposes of matching the recognized validation-prefix shapes above, expiry verifier frames are skipped (e.g., `[expiry_verify, self_verify]` is recognized as `[self_verify]`).

A node MUST drop a frame transaction from the public mempool if it contains an `expiry_verify` frame whose deadline is less than the node's view of the current block timestamp at any point.

Expiry verifier frames are not subject to the validation trace rules, storage-dependency tracking, or `MAX_VERIFY_GAS`. The `TIMESTAMP` opcode is permitted only for the canonical expiry verifier runtime code at `EXPIRY_VERIFIER`; clients may optimize the frame by performing the same deadline check without explicit EVM execution.

#### Canonical Paymaster Exception

The generic validation trace and opcode rules below apply to all frames in the validation prefix except a `pay` frame whose target runtime code exactly matches the canonical paymaster implementation. The canonical paymaster implementation is explicitly designed to be safe for public mempool use and is therefore admitted by code match, successful `APPROVE(APPROVE_PAYMENT)`, and the paymaster accounting rules in this section, rather than by requiring it to satisfy each generic validation rule individually.

#### Validation Trace Rules

A public mempool node must simulate the validation prefix and reject the transaction if any of the following occurs before `payer` has been set:

- a frame in the validation prefix reverts
- a `self_verify`, `only_verify`, or `pay` frame exits without its required `APPROVE`
- execution exceeds `MAX_VERIFY_GAS`
- execution uses a banned opcode
- execution performs a state write, except inside the first `deploy` frame for (a) `CREATE`, `CREATE2`, or `SETDELEGATE` operations that install code at `tx.sender`, or (b) `SSTORE`s to `tx.sender`'s storage
- execution reads storage outside `tx.sender`
- execution performs `CALL*` or `EXTCODE*` to an address that is neither an existing contract nor a precompile, or to an address that uses an EIP-7702 delegation, except for `tx.sender` default-code behavior
- if a `deploy` frame is present, its execution does not result in non-empty code being installed at `tx.sender` (either conventional contract code or an EIP-7702 delegation indicator)

##### Banned Opcodes

For `VERIFY` frames, the usual `STATICCALL` restrictions apply except for the protocol-defined effects of `APPROVE`. In addition, the following opcodes are banned during the validation prefix, with a few caveats:

- ORIGIN (0x32)
- GASPRICE (0x3A)
- BLOCKHASH (0x40)
- COINBASE (0x41)
- TIMESTAMP (0x42)
    - Except in an expiry verifier frame executing the canonical runtime code at `EXPIRY_VERIFIER`.
- NUMBER (0x43)
- PREVRANDAO/DIFFICULTY (0x44)
- GASLIMIT (0x45)
- BASEFEE (0x48)
- BLOBHASH (0x49)
- BLOBBASEFEE (0x4A)
- GAS (0x5A)
    - Except when followed immediately by a `*CALL` instruction. This is the standard method of passing gas to a child call and does not create an additional public mempool dependency.
- CREATE (0xF0)
    - Except inside the first `deploy` frame.
- CREATE2 (0xF5)
    - Except inside the first `deploy` frame.
- SETDELEGATE (0xF6, [EIP-7819](./eip-7819.md))
    - Except inside the first `deploy` frame.
- INVALID (0xFE)
- SELFDESTRUCT (0xFF)
- BALANCE (0x31)
- SELFBALANCE (0x47)
- SSTORE (0x55)
- TLOAD (0x5C)
- TSTORE (0x5D)

`SLOAD` can be used only to access `tx.sender` storage, including when reached transitively via `CALL*` or `DELEGATECALL`.

`CALL*` and `EXTCODE*` may target any existing contract or precompile, provided the resulting trace still satisfies the storage, opcode, and EIP-7702 restrictions above. This permits helper contracts and libraries during validation, including via `DELEGATECALL`, so long as they do not introduce additional mutable-state dependencies.

#### Paymasters

A paymaster can choose to sponsor a transaction's gas. Generally the relationship is one paymaster to many transaction senders, however, this is in direct conflict with the goal of not predicating the validity of many transactions on the value of one account or storage element.

We address this conflict in two ways:

1. If a paymaster sponsors gas for a large number of accounts simultaneously, it must be a safe, standardized paymaster contract. It is designed such that ether which enters it cannot leave except:
  a. in the form of payment for a transaction, or
  b. after a delay period.
2. If a paymaster sponsors gas for a small number of accounts simultaneously (no more than `MAX_PENDING_TXS_USING_NON_CANONICAL_PAYMASTER`), it may be any paymaster contract.

##### Canonical paymaster

The canonical paymaster is not a singleton deployment. Many instances may be deployed. For public mempool purposes, a paymaster instance is considered canonical if and only if the runtime code at the `pay` frame target exactly matches the canonical paymaster implementation.

The canonical paymaster in this draft authorizes with a single secp256k1 signer via `ecrecover`, does not support contract-signature schemes, and may change in later specifications, in which case a new canonical implementation version would be required.

Because the canonical paymaster implementation is explicitly standardized to be safe for public mempool use, nodes do not need to apply the generic validation trace and opcode rules to that `pay` frame. Instead, they identify it by runtime code match and apply the paymaster-specific accounting and revalidation rules in this section.

A transaction using a paymaster is eligible for public mempool propagation only if the `pay` frame targets a canonical paymaster instance and the node can reserve the maximum transaction cost against that paymaster.

For public mempool purposes, each node maintains a local accounting value `reserved_pending_cost(paymaster)` and computes:

```python
available_paymaster_balance = state.balance(paymaster) - reserved_pending_cost(paymaster) - pending_withdrawal_amount(paymaster)
```

Where `pending_withdrawal_amount(paymaster)` is the currently pending delayed withdrawal amount of the canonical paymaster instance, or zero if no delayed withdrawal is pending.

A node must reject a paymaster transaction if `available_paymaster_balance` is less than the transaction's maximum cost (`TXPARAM(0x06)`).

On admission, the node increments `reserved_pending_cost(paymaster)` by the transaction's maximum cost (`TXPARAM(0x06)`). On eviction, replacement, inclusion, or reorg removal, the node decrements it accordingly.

##### Non-canonical paymaster

For non-canonical paymasters, `pending_withdrawal_amount` is not meaningful since they may not support timelocked withdrawals.  Instead, we keep the mempool safe by enforcing that each non-canonical paymaster can only be used with no more than `MAX_PENDING_TXS_USING_NON_CANONICAL_PAYMASTER` pending transactions.

Therefore we perform two checks:

- For balance, `available_paymaster_balance` must not be less than the transaction cost, where:

```python
available_paymaster_balance = state.balance(paymaster) - reserved_pending_cost(paymaster)
```

- The number of pending transactions in the mempool that uses this paymaster must be less than `MAX_PENDING_TXS_USING_NON_CANONICAL_PAYMASTER`.

[See here for rationale](#non-canonical-paymasters-in-the-mempool) for enabling non-canonical paymasters in the mempool.

#### Acceptance Algorithm

1. A transaction is received over the wire and the node decides whether to accept or reject it.
2. The node analyzes the frame structure and determines the validation prefix. If the prefix is not one of the recognized prefixes, reject.
3. The node simulates the validation prefix and enforces the structural and trace rules above, except that a `pay` frame whose target runtime code exactly matches the canonical paymaster implementation is handled via the canonical paymaster exception and the paymaster-specific rules below.
4. The node records the sender storage slots read during validation. Calls into helper contracts do not create additional mutable-state dependencies unless they cause disallowed storage access under the trace rules above.
5. If a canonical paymaster instance is used, the node verifies paymaster solvency using the reservation rule above.
6. A node should keep at most one pending frame transaction per sender in the public mempool. A new transaction from the same sender MAY replace the existing one only if it uses the same nonce and satisfies the node's fee bump rules.
7. If all checks pass, the transaction may be accepted into the public mempool and propagated to peers.

#### Revalidation

When a new canonical block is accepted, the node removes any included frame transactions from the public mempool, updates paymaster reservations accordingly, and identifies the remaining pending transactions whose tracked dependencies were touched by the block. This includes at least transactions for the same sender, transactions whose recorded sender storage slots changed, and transactions that reference a canonical paymaster instance whose balance, code, or delayed-withdrawal state changed. The node then re-simulates the validation prefix of only those affected transactions against the new head and evicts any transaction that no longer satisfies the public mempool rules.

#### Transaction origination

Do not apply the restriction put in place by [EIP-3607](./eip-3607.md) to frame transactions.
Specifically, `SENDER` frames originate calls where `tx.sender` is a contract account.
Validation logic for other transaction types remains unchanged, i.e. the transaction is only valid if the sender account's code is either empty or a valid delegation indicator.

## Rationale

### Canonical signature hash

The canonical signature hash is provided in `TXPARAM` to simplify the development of smart accounts.

Computing the signature hash in EVM is complicated and expensive. While using the canonical signature hash is not mandatory, it is strongly recommended. Creating a bespoke signature requires precise commitment to the underlying transaction data. Without this, it's possible that some elements can be manipulated in-the-air while the transaction is pending and have unexpected effects. This is known as transaction malleability. Using the canonical signature hash avoids malleability of the frames other than `VERIFY`.

The `frame.data` of `VERIFY` frames is elided from the signature hash. This is done for three reasons:

1. It contains the signature so by definition it cannot be part of the signature hash.
2. In the future it may be desired to aggregate the cryptographic operations for data and compute efficiency reasons. If the data was introspectable, it would not be possible to aggregate the verify frames in the future.
3. For gas sponsoring workflows, we also recommend using a `VERIFY` frame to approve the gas payment. Here, the input data to the sponsor is intentionally left malleable so it can be added onto the transaction after the `sender` has made its signature. Notably, the raw `frame.target` field of `VERIFY` frames is covered by the signature hash, i.e. the `sender` chooses the sponsor address explicitly.

[Expiry verifier frames](#expiry-verifier-frame) are an exception: their `data` is the deadline, a sender-authored commitment that must not be malleable in transit, so it is included in the signature hash.

Implementations MUST NOT treat `VERIFY` frame `data` as sender-authenticated by the canonical signature hash. Any verifier or paymaster that depends on its input data, including sponsor parameters, exchange rates, fee terms, or custom account context, MUST authenticate that data independently. Replacing or mutating `VERIFY` frame `data` does not change the canonical signature hash.

By contrast, non-`VERIFY` frame metadata, including a `SENDER` frame's `value`, remains covered by the canonical signature hash.

Verification logic MUST NOT assign policy meaning to signature encodings or adjacent `VERIFY` frame data unless that meaning is independently authenticated.

### `APPROVE` calling convention

Originally `APPROVE` was meant to extend the space of return statuses from 0 and 1 today to 0 to 4. However, this would mean smart accounts deployed today would not be able to modify their contract code to return with a different value at the top level. For this reason, we've chosen behavior above: `APPROVE` terminates the executing frame successfully like `RETURN`, but it actually updates the transaction scoped values `sender_approved` and `payer` during execution. It is still required that only the sender can toggle the `sender_approved` to `true`. Only the frame's resolved target can call `APPROVE` generally, because it can allow the transaction pool and other frames to better reason about `VERIFY` mode frames.

Because `DELEGATECALL` preserves `ADDRESS`, code executed via `DELEGATECALL` from the resolved target may also execute `APPROVE` successfully. Contracts that rely on `APPROVE` should therefore treat delegatecalled libraries as fully trusted.

### Payer in receipt

The payer cannot be determined statically from a frame transaction and is relevant to users. The only way to provide this information safely and efficiently over the JSON-RPC is to record this data in the receipt object.

### No authorization list

The EIP-7702 authorization list heavily relies on ECDSA cryptography to determine the authority of accounts to delegate code. While delegations could be used in other manners later, it does not satisfy the PQ goals of the frame transaction.

### No access list

The access list was introduced to address a particular backwards compatibility issue that was caused by EIP-2929. The risk-reward of using an access list successfully is high. A single miss, paying to warm a storage slot that does not end up getting used, causes the overall transaction cost to be greater than had it not been included at all.

Future optimizations based on pre-announcing state elements a transaction will touch will be covered by block level access lists.

### Atomic batching

Atomic batching allows multiple frames to be grouped into a single all-or-nothing unit. This is useful when a sequence of calls is only meaningful if all succeed together, such as an approval followed by a swap, or a series of interdependent state changes. Without this feature, a revert in one frame would leave the preceding frames' state changes applied, potentially leaving the account in an undesirable intermediate state.

Using a flag to indicate atomic batches saves us from having to introduce a new mode. Batches are identified purely by consecutive frames with the flag set, terminated by a frame without it. This design enables consecutive atomic batches since the batch boundary is clearly indicated by the frame without the flag.

### Per-frame cost

Each frame incurs a fixed CALL execution-context overhead (100) plus `G_log` (375) for the receipt sub-entry it produces, giving `FRAME_TX_PER_FRAME_COST = 475`. The execution-context component covers context setup, mode dispatch, and gas accounting at the frame boundary, analogous to the fixed overhead of a CALL. The `G_log` component covers the `[status, gas_used, logs]` receipt sub-entry that each frame adds to the transaction receipt, which must be serialized, hashed into the receipt trie, and proven by ZK-EVM implementations. Cold/warm access costs for the frame's target account are charged within the frame's own `gas_limit` through the normal EVM warm/cold accounting, not through the per-frame cost.

### Per-frame value

A design goal of the frame transaction is to provide a good experience out-of-the-box for users and to reduce the threat surface of smart contract wallets. Like batching, sending native value is a part of achieving that.

Restricting non-zero `value` to `SENDER` frames keeps `VERIFY` and `DEFAULT` frames side-effect-free with respect to ETH transfer semantics, preserves the intended `STATICCALL`-like behavior of `VERIFY`, and avoids requiring the protocol-defined `ENTRY_POINT` caller to fund top-level ETH transfers.

### Externally Owned Account (EOA) support

While we expect EOA users to migrate to smart accounts eventually, we recognize that most Ethereum users today are using EOAs, so we want to improve UX for them where we can.

Thanks to the default code, EOAs today can use frame transactions to reap many benefits of account abstraction, including sending sponsored transactions, paying gas in ERC-20 tokens, batch transactions, and more.

### Non-canonical paymasters in the mempool

The primary use case for non-canonical paymasters is to enable users to pay gas with a dedicated "gas account," so that their other accounts can transact without holding any ETH. For example, a user might have a single account that holds some ETH, while other accounts only hold stablecoins and NFTs, and they can transact freely with these other accounts while using the gas account as the paymaster.

Note that users can use any EOA as a paymaster thanks to the [default code](#default-code).

### Examples

#### Example 1: Simple Transaction

| Frame | Caller      | Target        | Value | Flags                         | Data      | Mode   |
| ----- | ----------- | ------------- | ----- | ----------------------------- | --------- | ------ |
| 0     | ENTRY_POINT | Null (sender) | 0     | APPROVE_EXECUTION_AND_PAYMENT | Signature | VERIFY |
| 1     | Sender      | Target        | 0     | APPROVE_SCOPE_NONE            | Call data | SENDER |

Frame 0 verifies the signature and calls `APPROVE(APPROVE_EXECUTION_AND_PAYMENT)` to approve both payment and execution. Frame 1 executes and exits normally via `RETURN`.

The mempool can process this transaction with the following static validation and call:

- Verify that the first frame is a `VERIFY` frame.
- Verify that the call of frame 0 succeeds, and does not violate the mempool rules (similar to [ERC-7562](./eip-7562.md)).

#### Example 1a: Simple ETH transfer

| Frame | Caller      | Target        | Value  | Flags                         | Data      | Mode   |
| ----- | ----------- | ------------- | ------ | ----------------------------- | --------- | ------ |
| 0     | ENTRY_POINT | Null (sender) | 0      | APPROVE_EXECUTION_AND_PAYMENT | Signature | VERIFY |
| 1     | Sender      | Destination   | Amount | APPROVE_SCOPE_NONE            | Empty     | SENDER |

A simple transfer is performed by setting the `SENDER` frame target to the destination account and the frame `value` to the transfer amount. This requires two frames for mempool compatibility, since the validation phase of the transaction has to be static.

#### Example 1b: Simple account deployment

| Frame | Caller      | Target        | Value  | Flags                         | Data           | Mode    |
| ----- | ----------- | ------------- | ------ | ----------------------------- | -------------- | ------- |
| 0     | ENTRY_POINT | Deployer      | 0      | APPROVE_SCOPE_NONE            | Initcode, Salt | DEFAULT |
| 1     | ENTRY_POINT | Null (sender) | 0      | APPROVE_EXECUTION_AND_PAYMENT | Signature      | VERIFY  |
| 2     | Sender      | Destination   | Amount | APPROVE_SCOPE_NONE            | Empty          | SENDER  |

This example illustrates the initial deployment flow for a smart account at the `sender` address. Since the address needs to have code in order to validate the transaction, the transaction must deploy the code before verification.

The first frame would call the [EIP-7997](./eip-7997.md) deterministic factory predeploy. The deployer determines the address in a deterministic way from the salt and initcode. However, since the transaction sender is not authenticated at this point, the user must choose an initcode which is safe to deploy by anyone.

#### Example 2: Atomic Approve + Swap

| Frame | Caller      | Target        | Value | Flags                         | Data                 | Mode   |
| ----- | ----------- | ------------- | ----- | ----------------------------- | -------------------- | ------ |
| 0     | ENTRY_POINT | Null (sender) | 0     | APPROVE_EXECUTION_AND_PAYMENT | Signature            | VERIFY |
| 1     | Sender      | ERC-20        | 0     | ATOMIC_BATCH_FLAG            | approve(DEX, amount) | SENDER |
| 2     | Sender      | DEX           | 0     | APPROVE_SCOPE_NONE           | swap(...)            | SENDER |

Frame 0 verifies the signature and calls `APPROVE(APPROVE_EXECUTION_AND_PAYMENT)`. Frames 1 and 2 form an atomic batch: if the swap in frame 2 reverts, the ERC-20 approval from frame 1 is also reverted, preventing the account from being left with a dangling approval.

#### Example 3: Sponsored Transaction (Fee Payment in ERC-20)

| Frame | Caller      | Target        | Value | Flags              | Data                   | Mode    |
| ----- | ----------- | ------------- | ----- | ------------------ | ---------------------- | ------- |
| 0     | ENTRY_POINT | Null (sender) | 0     | APPROVE_EXECUTION  | Signature              | VERIFY  |
| 1     | ENTRY_POINT | Sponsor       | 0     | APPROVE_PAYMENT    | Sponsor data           | VERIFY  |
| 2     | Sender      | ERC-20        | 0     | APPROVE_SCOPE_NONE | transfer(Sponsor,fees) | SENDER  |
| 3     | Sender      | Target addr   | 0     | APPROVE_SCOPE_NONE | Call data              | SENDER  |
| 4     | ENTRY_POINT | Sponsor       | 0     | APPROVE_SCOPE_NONE | Post op call           | DEFAULT |

- Frame 0: Verifies signature and calls `APPROVE(APPROVE_EXECUTION)` to authorize execution from sender.
- Frame 1: Checks that the user has enough ERC-20 tokens, and that the next frame is an ERC-20 send of the right size to the sponsor. Calls `APPROVE(APPROVE_PAYMENT)` to authorize payment.
- Frame 2: Sends tokens to sponsor.
- Frame 3: User's intended call.
- Frame 4 (optional): Check unpaid gas, refund tokens, possibly convert tokens to ETH on an AMM.

### Data Efficiency

**Basic transaction sending ETH from a smart account:**

| Field                             | Bytes |
| --------------------------------- | ----- |
| Tx wrapper                        | 1     |
| Chain ID                          | 1     |
| Nonce                             | 2     |
| Sender                            | 20    |
| Max priority fee                  | 5     |
| Max fee                           | 5     |
| Max fee per blob gas              | 1     |
| Blob versioned hashes (empty)     | 1     |
| Frames wrapper                    | 1     |
| Sender validation frame: mode     | 1     |
| Sender validation frame: flags    | 1     |
| Sender validation frame: target   | 1     |
| Sender validation frame: gas      | 2     |
| Sender validation frame: value    | 1     |
| Sender validation frame: data     | 65    |
| Execution frame: mode             | 1     |
| Execution frame: flags            | 1     |
| Execution frame: target           | 20    |
| Execution frame: gas              | 1     |
| Execution frame: value            | 5     |
| Execution frame: data             | 0     |
| **Total**                         | 136   |

Notes: Nonce assumes < 65536 prior sends. Fees assume < 1099 gwei. Validation frame target is 1 byte because target is `tx.sender`. Validation gas assumes <= 65,536 gas. Validation frame value is zero. Execution frame target is encoded directly as the destination address. Execution frame value assumes a compact 5-byte encoding. The execution frame data is empty for a plain ETH transfer. Validation data is 65 bytes for an ECDSA signature. Blob fields assume no blobs (empty list, zero max fee).

This is not much larger than an EIP-1559 transaction; the extra overhead is mainly the need to specify the sender and the per-frame wrapper explicitly.

**First transaction from an account (add deployment frame):**

| Field                      | Bytes |
| -------------------------- | ----- |
| Deployment frame: mode     | 1     |
| Deployment frame: flags    | 1     |
| Deployment frame: target   | 20    |
| Deployment frame: gas      | 3     |
| Deployment frame: value    | 1     |
| Deployment frame: data     | 100   |
| **Total additional**       | 126   |

Notes: Gas assumes cost < 2^24. Calldata assumes small proxy.

**Trustless pay-with-ERC-20 sponsor (add these frames):**

| Field                                | Bytes |
| ------------------------------------ | ----- |
| Sponsor validation frame: mode       | 1     |
| Sponsor validation frame: flags      | 1     |
| Sponsor validation frame: target     | 20    |
| Sponsor validation frame: gas        | 3     |
| Sponsor validation frame: value      | 1     |
| Sponsor validation frame: calldata   | 0     |
| Send to sponsor frame: mode          | 1     |
| Send to sponsor frame: flags         | 1     |
| Send to sponsor frame: target        | 20    |
| Send to sponsor frame: gas           | 3     |
| Send to sponsor frame: value         | 1     |
| Send to sponsor frame: calldata      | 68    |
| Sponsor post op frame: mode          | 2     |
| Sponsor post op frame: flags         | 1     |
| Sponsor post op frame: target        | 20    |
| Sponsor post op frame: gas           | 3     |
| Sponsor post op frame: value         | 1     |
| Sponsor post op frame: calldata      | 0     |
| **Total additional**                 | 147   |

Notes: Sponsor can read info from other fields. ERC-20 transfer call is 68 bytes.

There is some inefficiency in the sponsor case, because the same sponsor address must appear in three places (sponsor validation, send to sponsor inside ERC-20 calldata, post op frame), and the ABI is inefficient (~12 + 24 bytes wasted on zeroes). This is difficult to mitigate in a "clean" way, because one of the duplicates is inside the ERC-20 call, "opaque" to the protocol. However, it is much less inefficient than ERC-4337, because not all of the data takes the hit of the 32-byte-per-field ABI overhead.


## Backwards Compatibility

The `ORIGIN` opcode behavior changes for frame transactions, returning the frame's caller rather than the traditional transaction origin. This is consistent with the precedent set by EIP-7702, which already modified `ORIGIN` semantics. Contracts that rely on `ORIGIN = CALLER` for security checks (a discouraged pattern) may behave differently under frame transactions.

## Security Considerations

### Transaction Propagation

Frame transactions introduce new denial-of-service vectors for transaction pools that node operators must mitigate. Because validation logic is arbitrary EVM code, attackers can craft transactions that appear valid during initial validation but become invalid later. Without any additional policies, an attacker could submit many transactions whose validity depends on some shared state, then submit one transaction that modifies that state, and cause all other transactions to become invalid simultaneously. This wastes the computational resources nodes spent validating and storing these transactions.

#### Example Attack

A simple example is transactions that check `block.timestamp`:

```solidity
function validateTransaction() external {
    require(block.timestamp < SOME_DEADLINE, "expired");
    // ... rest of validation
    APPROVE(APPROVE_EXECUTION_AND_PAYMENT);
}
```

Such transactions are valid when submitted but become invalid once the deadline passes, without any on-chain action required from the attacker.

#### Deploy Frame Front-Running

If a transaction uses a `deploy` frame, that frame executes before the sender is authenticated. An observer can front-run the same deterministic deployment and cause the `deploy` frame to fail because code is already present at `tx.sender`. Accordingly, the deploy frame's calldata (and any initcode it carries) must be safe to submit by any party, and wallets should expect resubmission without the `deploy` frame once deployment has already occurred.

#### Explicit Sender State-Read Amplification

Because `tx.sender` is explicit in the transaction envelope, an attacker can submit many invalid frame transactions that name arbitrary sender addresses and force nodes to read sender state, including the nonce check required before execution. Public mempool implementations should therefore perform all available structural and stateless checks before sender-state access and should consider peer-level rate limiting or other DoS mitigations for repeated invalid transactions that vary `tx.sender`.

#### Cross-frame Data Visibility During Validation

`FRAMEPARAM`, `FRAMEDATALOAD`, and `FRAMEDATACOPY` allow validation code to inspect other frames, including later `SENDER` frames and their `value`s. As a result, paymasters and other `VERIFY` frames can observe user operation parameters before approval and may condition their behavior on that information. Users should therefore treat non-`VERIFY` frame parameters and data as visible to validation logic and should not rely on untrusted paymasters or verifiers to keep such information private.

##### Mitigations

Node implementations should consider restricting which opcodes and storage slots validation frames can access, similar to ERC-7562. This isolates transactions from each other and limits mass invalidation vectors.

It's recommended that to *validate* the transaction, a specific frame structure is enforced and the amount of gas that is expended executing the validation phase must be limited. Once the validation prefix reaches payer approval via `APPROVE(APPROVE_PAYMENT)` or `APPROVE(APPROVE_EXECUTION_AND_PAYMENT)`, the transaction can be included in the mempool and propagated to peers safely.

For deployment of the sender account in the first frame, the mempool enforces deploy-frame determinism via the validation trace rules. Any contract may be used as `frame.target`, provided the frame's execution satisfies those rules — notably, it must not read mutable state outside `tx.sender` or maintain per-deploy factory storage (counters, reentrancy flags, etc.), so that the deployment result is independent of chain state. Factories deployed via the [EIP-7997](./eip-7997.md) deterministic factory predeploy are the canonical choice for acquiring a cross-chain-stable factory address.

In general, it can be assumed that handling of frame transactions imposes similar restrictions as EIP-7702 on mempool relay, i.e. only a single transaction can be pending for an account that uses frame transactions.

## Copyright

Copyright and related rights waived via [CC0](../LICENSE.md).