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chore: add crosschain desc #421

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8a7bf2c
chore: upload dao deployed safe addresses
gabririgo Oct 15, 2025
538f6d5
add sepolia safe
gabririgo Oct 15, 2025
496695f
use null on non-supported chain
gabririgo Oct 21, 2025
45950b7
fix typo
gabririgo Oct 21, 2025
67e5d8e
chore: cross-chain intent settler initial description
gabririgo Oct 21, 2025
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72 changes: 48 additions & 24 deletions chain_config.json
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,8 @@
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Expand Down Expand Up @@ -50,7 +51,8 @@
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Expand Down Expand Up @@ -81,7 +83,8 @@
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Expand Down Expand Up @@ -112,7 +115,8 @@
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Expand Down Expand Up @@ -143,7 +147,8 @@
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Expand Down Expand Up @@ -174,7 +179,8 @@
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Expand Down Expand Up @@ -205,7 +211,8 @@
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Expand Down Expand Up @@ -236,7 +243,8 @@
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Expand Down Expand Up @@ -267,7 +275,8 @@
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Expand Down Expand Up @@ -297,7 +306,8 @@
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Expand Down Expand Up @@ -328,7 +338,8 @@
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Expand Down Expand Up @@ -359,7 +370,8 @@
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Expand Down Expand Up @@ -390,7 +402,8 @@
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Expand Down Expand Up @@ -421,7 +434,8 @@
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Expand Down Expand Up @@ -451,7 +465,8 @@
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Expand Down Expand Up @@ -482,7 +497,8 @@
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Expand Down Expand Up @@ -513,7 +529,8 @@
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Expand Down Expand Up @@ -543,7 +560,8 @@
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Expand Down Expand Up @@ -573,7 +591,8 @@
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Expand Down
105 changes: 105 additions & 0 deletions sh/initial_description_crosschain_intent.md
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# 0x Cross-chain Intent Settler

[0x](https://0x.org/)'s settlement contracts for cross-chain intents
utilising [Permit2](https://github.com/Uniswap/permit2) to perform swaps
without any passive allowance. Full source code and audits are found at
[0xProject/0x-settler](https://github.com/0xProject/0x-settler).

## Bug Bounty

If you've found a bug, you may be eligible for a bounty under the 0x [bug bounty
program](https://0x.org/docs/developer-resources/bounties). Please see that link
for eligibility requirements as well as the advertised payout tiers. If you have
any findings, send an email to [mailto:[email protected]]([email protected]) with
the subject line "BUG BOUNTY". Please describe the bug that you've found **in
detail** and ideally provide a proof-of-concept exploit.

## Architecture

### Allowances

`CrossChainIntentSettler` does not hold allowances, nor does it hold token
balances between swaps. This provides an enhanced security posture.
`CrossChainIntentSettler` relies on the aforementioned `Permit2` contract to
hold allowances.

`CrossChainIntentSettler` allows arbitrary calls to other contracts.
Therefore it is of the utmost importance that _**settler does not hold token
balances or allowances**_.

### `ISignatureTransfer` vs `IAllowanceTransfer`

In order to remove the risk that passive allowances could be exploited, 0x
Settler **does not** support the typical `Permit2` pattern of time-bound,
value-bound allowances set via an ECDSA or
[ERC1271](https://eips.ethereum.org/EIPS/eip-1271) signature. This is the
`IAllowanceTransfer` half of `Permit2`. Instead, 0x Settler only supports the
`ISignatureTransfer` interface, which requires a single-use signature (called a
coupon) be submitted with every transaction.

This provides enhanced security at the cost of some gas and inconvenience.

### Actions

0x Cross Chain Intent Settler settles swaps by performing a sequence of actions
encoded in calldata. Actions are ABIEncoded with a selector. See
`ICrossChainIntentSettlerActions` for the available options. Typically, actions
are parametrized by the `recipient` where tokens are sent after the trade and
the `bps` specifying a proportion of the `Settler` contract's token balance to
be liquidated in the action.

## Action encoding

The action encoding is not stable. Do not rely on the action encoding being
preserved between 0x Settler instances. See [0x's developer
documentation](https://0x.org/docs/developer-resources/settler) for a detailed
explanation.

Typically, actions are only added to `ICrossChainIntentSettlerActions` for 2
reasons: 1) to gas-optimize a high-volume settlement path; 2) to provide
compatibility with a liquidity source that does not support typical
`ERC20.approve`...`ERC20.transferFrom` flows.

## Cross-chain Intents

This instance of `Settler` supports swaps where the received token may be
located on a different network than the sent token. Furthermore, the execution
path is not dictated in the encoded calldata, and is instead decided by the
solver. A solver may decide to use other instances of `Settler`, or any other
way. It also supports swaps where the tokens are located on the same network.
This instance of `Settler` supports swaps where the submitting address is not
the taker. This means that we must provide an alternative mechanism for
authorizing a swap that ensures the signed-over swap is not
malleable. Settlement of intents is facilitated by the `executeMetaTxn` entry
point and uses the "witness" functionality of `Permit2` to ensure that the
taker's signature is over the tokens being sent and the tokens being
received. In contrast to the "metatransaction" flow, the taker *ONLY* signs the
tokens to be sent and the tokens to be received. In a way, settling an intent is
analogous to a short-lived limit order. Settlement of cross-chain intents is
permissioned, as it requires the action of a new actor, i.e. permissioned
`relayers`. These relayers have the task of verifying the intent is executable,
and monitoring onchain (i.e. by monitoring of `CrossChainIntentSettler` events)
or offchain (i.e. signed intents via API) user-generated intents, and prompting
an auction to notify the solvers, and are compensated by a relayer-pre-set
`amount` or `bpsAmount`. The `Settler` instance will initially retain 0% of this
fee, but may activate a 30% fee share. Integrating frontends may act as a
`relayer`. Furthermore, they also have the task of moving the source token to the
destination chain, and are encouraged to use the `BridgeSettler` instance.
The list of active `relayers` is updated by the 0x DAO, and is adjusted based
on, in order of importance, 1. delegated ZRX/WZRX stake and 2. speed in relaying
orders. Intents shall go through an auction for the winning solver to be able
to fill the order. An intent may specify a selected `solver`, thus giving
priority to a particular solver to execute the swap (i.e. a prearranged agreement
between the user and the solver).
Once an intent is filled on the destination chain, source tokens are sent to the
`relayers` by submitting a ZK proof. Proofs are submitted in batches, but a
relayer may decide to self-generate and submit it to unlock the tokens faster.
The restriction of participants to relayers and the winning solver avoids leakage
of surplus value to MEV. Obviously, the settlement of the order for *at least*
the specified amount to be received is guaranteed by the contracts. Cross-chain
intent settlement is permissioned so that in the case that it is possible, the
taker receives more than the minimum specified in the signature, up to the value
that the market supports. `Permit2` allows the combination of the authorization
of the token transfer as well as confirming the user's intention to receive the
specified amount of the other token. This results in the taker signing a single
[EIP712](https://eips.ethereum.org/EIPS/eip-712) struct.