Intent Settlement Layers: Designing Solvers That Don’t Rug Your UX

A practical field guide to building and buying intent settlement layers—how to structure auctions, constrain solvers, and integrate shared sequencing and OFAs so users get faster, fairer, MEV-safe execution without trust trade‑offs.

If you’re evaluating CoW‑style batch auctions, UniswapX RFQ/Dutch auctions, or shared sequencers like Astria (and even SUAVE‑style orderflow), this post gives the concrete design patterns, APIs, SLAs, and governance controls to ship an intent stack that scales and doesn’t break your product’s UX.

TL;DR

Intents move execution complexity from users to a market of “solvers” competing to complete goals under constraints you define; good UX depends on auction design, fairness guarantees, and solver accountability, not just price. (anoma.net)
CoW Protocol’s fair combinatorial batch auctions and bonding/slashing give a working template for MEV‑resilient price discovery and solver accountability at production scale. (docs.cow.fi)
UniswapX RFQ v2 + Dutch auctions use a cosigner and hard quotes to minimize “quote fade” and ensure users don’t get the worst price in their signed range—an actionable pattern for any intent layer. (docs.uniswap.org)
Shared sequencers (e.g., Astria mainnet alpha, Oct 28, 2024) enable cross‑rollup atomicity and censorship resistance—key for multi‑chain intent completion without centralizing orderflow. (astria.org)
Order Flow Auctions (OFAs) like Flashbots MEV‑Share and MEV Blocker are gaining market share and can be composed with intent layers for faster inclusion and user rebates. (writings.flashbots.net)
Standards to watch: ERC‑7521 (generalized intents for smart contract wallets) and EIP‑7702 (EOAs delegating to code, proposed for Pectra), which unlock safer, more universal intent execution. (eips.ethereum.org)

What decision‑makers actually need from an intent layer

For enterprise and consumer products, the right intent abstraction produces:

Reliable fill >99% at target price constraints (not just “best effort”).
Predictable inclusion latency (P50/P90) with explicit failover when quotes fade.
MEV‑aware routing that returns value to the user or app, not third‑party builders.
Accountability: bonding/slashing, KYC where needed, clear dispute rules.
Multi‑domain optionality: settlement on your preferred L1/L2 today; shared sequencer or cross‑domain tomorrow.

The rest of this post maps those UX goals to concrete mechanisms you can deploy now.

Primer: intent settlement layers (ISLs) in practice

An ISL is the infrastructure that takes user‑signed “what I want” expressions and turns them into on‑chain state changes, safely and competitively. Designing one means choosing:

Expression format: how intents are signed, constraints encoded, how gas/payment works.
Counterparty discovery: who sees intents and when (public/private/permissioned).
Solving and auctions: how competition happens and how fairness is enforced.
Settlement: how constraints are enforced on‑chain and who bears MEV/gas risk.

Anoma frames the stack as generalized intents → discovery → solving → settlement, and that framing is useful well beyond its own chain. (anoma.net)

Auction mechanics that won’t rug your users

Fair batch auctions with EBBO/UCP guardrails

Pattern: CoW Protocol groups intents, runs a solver competition, and chooses the solution that maximizes user surplus with fairness checks. The system enforces Uniform Clearing Prices and “Ethereum Best Bid/Offer” floors so users can’t be settled worse than on‑chain AMMs. (docs.cow.fi)
Why it matters: UCP reduces ordering games; EBBO guarantees baseline fairness; batch combinatorics let solvers exploit “coincidence of wants” without LP fees. (docs.cow.fi)

RFQ v2 + cosigner to stop “range‑rugging”

Pattern: UniswapX’s RFQ v2 splits indicative vs hard quotes; after the user signs, quoters provide hard quotes with minimal time gap. A cosigner (currently Uniswap Labs in their interface) ensures the auctioneer can’t pick the worst price within the user’s signed range. Fallback to Dutch if exclusivity fails or fades. (docs.uniswap.org)
Why it matters: Near‑instant fills with near‑100% fill rates on mainnet RFQ and no “got the bottom of your slippage range” outcomes. (docs.uniswap.org)

Dutch auctions for fast chains

Pattern: On Arbitrum (0.25s blocks), UniswapX runs direct Dutch without RFQ—the chain’s block cadence gives better price discovery fast enough that exclusivity is unnecessary. (docs.uniswap.org)

Meta‑aggregation without batching

Pattern: UniswapX positions itself as a meta‑aggregator—every trade is executed individually and MEV‑protected by design; fillers source private/public liquidity and return MEV as price improvement. If you don’t need batching, mimic this execution race while keeping strong protections. (x.uniswap.org)

Decision takeaway: If your users value strict fairness guarantees and sandwich immunity, prefer batch auctions with EBBO/UCP. If speed and single‑order latency dominate, RFQ v2 + Dutch with a cosigner is a robust template.

Solvers: make them compete—and make them accountable

You’re trusting solvers with delegated execution. Give them a way to win fairly and a way to lose dearly.

Bonding and slashing. CoW requires solver bonding via pools (historically $500k stables + 1.5M COW; now a reduced path exists: $50k + 500k COW with growth targets). Misbehavior (surplus shifts, overbidding/pennying, hook omission) can be slashed via DAO process; there are real, executed slashes. (docs.cow.fi)
Shadow competitions. Let new solvers simulate against production orderflow before touching funds. Promote on measurable wins. (docs.cow.fi)
Private order submission. Require MEV‑safe relays and OFAs for settlement transactions to minimize exposure and deliver rebates to users or integrators where applicable. (docs.cow.fi)
Transparency. Publish competition rules, unfair‑bid filters, and consequences. The existence of Local Token Conservation rules and explicit penalties discourages “free option” behavior. (docs.cow.fi)

Checklist for procurement: bond size; slashing precedents; audit coverage; KYC; private RPCs used; quote fade rate; solver’s internal risk limits; offtime procedures.

Shared sequencing and OFAs: faster inclusion, better UX

Shared sequencers for multi‑rollup intents
Astria launched mainnet alpha on Oct 25, 2024, providing a decentralized shared sequencing layer: fast pre‑confirmations, censorship resistance, and atomic cross‑rollup inclusion guarantees. If your product needs cross‑rollup intents (swap on L2 A that depends on transfer on L2 B), shared sequencing reduces “stuck leg” risk without collapsing everything onto one chain. (astria.org)
Order Flow Auctions (OFA) as a complement
Flashbots MEV‑Share specifies an open OFA so wallets and dapps can redistribute backrun value; CoW’s MEV Blocker RPC adds fast inclusion and rebates with multiple endpoints for different privacy/rebate profiles. Integrate your ISL’s settlement transactions with an OFA by default and pass rebates to users or your product’s fee engine. (docs.flashbots.net)
Why now
Flashbots’ 2024 State of Wallets shows OFAs (CoWSwap‑style batch, UniswapX‑style RFQ/Dutch, MEV‑Blocker execution auctions) taking volume share—users vote with flow when the UX is faster and safer. (writings.flashbots.net)

Standards to future‑proof your stack

ERC‑7521 (draft): generalized intents for smart contract wallets with a single entry point that routes to various intent standards solvers can compose. If you’re designing an in‑house intent format, align with 7521 to avoid stranding your users. (eips.ethereum.org)
EIP‑7702 (Pectra scope): lets EOAs “delegate” to contract code via a new tx type, bringing batching/sponsorship UX to EOAs without new opcodes; notable security/phishing considerations apply. Track this for wallet support and user education if you accept EOAs. (eips.ethereum.org)

A reference architecture we deploy for clients

Intent expression and signing

Use an ERC‑7521‑compatible schema for forward interoperability; support (a) price bounds, (b) time‑in‑force, (c) hook permissions, (d) MEV policy (e.g., “private only”), (e) payout token for gas/fees. (eips.ethereum.org)

Example (simplified):

{
  "version": "1.0",
  "sender": "0xUser",
  "chainId": 1,
  "constraints": {
    "want": [{"token":"ETH","amount":"1.0"}],
    "give": [{"token":"USDC","amount":"<=2000"}],
    "minFill": "0.99",
    "ebbo": true,
    "deadline": 1732752000,
    "hooks": {"pre": [], "post": ["rebate", "notify"]},
    "mevPolicy": "private-only"
  },
  "signature": "0x..."
}

Discovery and privacy

Default: private submission to your intent gateway with opt‑in gossip to solver allowlist; publish minimal fields to prevent exploitation, similar in spirit to MEV‑Share’s selective disclosure. (docs.flashbots.net)

Auction policy

If multi‑order flow and fairness matter: batch auction with EBBO/UCP filters. If single‑order low‑latency matters: RFQ v2 design with cosigner and hard quotes; Dutch fallback on fade. (docs.cow.fi)

Solver integration

Onboard via shadow competition; production requires bonding + private submission; enforce competition rules; require MEV‑safe builders and OFA endpoints; programmatic penalties for fade, illegal surplus shifts, or hook omission. (docs.cow.fi)

Settlement and inclusion

Route the winning solution through MEV Blocker or your OFA partners to minimize latency and leak‑free inclusion; if cross‑rollup dependencies exist, integrate a shared sequencer (Astria) for atomic inclusion guarantees or fast pre‑confirmations. (docs.cow.fi)

Governance and risk

DAO or board‑controlled slashing, transparent incident response (precedent: CoW slashing events), independent monitoring, and on‑chain telemetry for price improvement vs EBBO. (forum.cow.fi)

Two concrete patterns you can adopt this quarter

Pattern A: “Fair‑price batching” for larger trades

Who: OTC‑ish consumer apps, treasuries, aggregators.
How: CoW‑style batch auction with EBBO guardrail and UCP; solver bonding + slashing; private settlement via MEV Blocker; publish weekly scorecards: median price improvement, P90 fill latency, fade rate, and slashing incidents. (docs.cow.fi)
Why: Maximum “can’t be worse than AMM” assurance and strong MEV shielding; great for trust‑sensitive users.

Pattern B: “RFQ v2 + Dutch fallback” for latency‑sensitive retail

Who: Mobile wallets, retail dapp frontends.
How: Use cosigner to enforce best executable price within the user’s signed range; demand hard quotes post‑signature; if fade, auto‑descend Dutch auction; on fast L2s, skip RFQ entirely and rely on Dutch with priority gas auctions. (docs.uniswap.org)
Why: Near‑instant fills and robust against quote gaming; UX is “tap and done” with MEV protection and zero failed tx cost.

Cross‑rollup intents: design for atomicity now

If your roadmap includes “swap on Rollup A, deliver on Rollup B,” plan now for sequencing:

Shared sequencer integration (Astria): one temporal domain across multiple rollups, enabling atomic (or near‑atomic with pre‑confirmations) inclusion; improves UX vs. multi‑hop relays with probabilistic finality. Astria mainnet alpha has been live since Oct 2024 and is designed for censorship resistance and fast confirmations. (astria.org)
Backstop path: If shared sequencing isn’t available on all domains you target, encode fallback branches in the intent (e.g., “settle on A only” or “refund”), and price the risk into the auction parameters.

SLAs, SLOs, and the scorecard you should demand

Fill SLOs
- P50 inclusion < 2 blocks; P90 < 6 (mainnet), or chain‑specific targets on L2s.
- RFQ hard‑quote fill rate ≥ 99%; Dutch fallback success ≥ 99.5% within TTF ≤ 30s on fast L2s. (docs.uniswap.org)
Price SLOs
- EBBO floor enforced 100% on batch auctions; report median price improvement vs on‑chain AMM. (docs.cow.fi)
Integrity SLOs
- Zero unfair batched bids selected; zero illegal surplus shifts; slashing within 7 days for proven violations; publish incident postmortems (precedent exists). (docs.cow.fi)
Inclusion and rebates
- ≥ X% of settlement txs via OFA/private relays with observed rebates returned; publish monthly rebate stats. (docs.flashbots.net)

Implementation notes your engineering team will thank you for

Don’t reinvent signatures. If possible, align your intent signing with ERC‑7521 patterns; you’ll reduce wallet‑side lift later and make it easier for third‑party solvers to integrate. (eips.ethereum.org)
Sandbox solvers. Run shadow comps against production orderflow; require reproducible sim pipelines; set per‑solver risk budgets; throttle order types during probation. (docs.cow.fi)
Enforce privacy by default. Integrate MEV‑Share‑style selective disclosure; publish which fields are visible at which phase (pre‑ vs post‑signature). (docs.flashbots.net)
Add a cosigner if you run the auctioneer. This removes the “auctioneer picks worst price in range” class of abuse entirely. (docs.uniswap.org)
Publish competition rules—and enforce them. Illegal surplus shift detection and overbidding penalties should be in code and governance. (docs.cow.fi)
Choose your settlement lane wisely. On mainnet, RFQ v2 + hard quotes are excellent; on fast L2s, Dutch auctions compete naturally through PGAs; route settlement via private builders/OFA endpoints. (docs.uniswap.org)
Plan for Pectra/7702. If users remain EOAs, EIP‑7702 may unlock smoother UX (batching, sponsorship). Track the phishing risks and restrict delegations to audited, immutable code paths. (ethereum.org)

Brief, in‑depth examples

Example 1: Treasury rebalancing, large tickets

Constraints: “Buy 1,200 ETH with USDC at or better than EBBO; complete within 5 minutes; MEV private; allow pre/post hooks for reporting.”
Execution: Batch auction with EBBO/UCP; solvers access private MM inventory and on‑chain liquidity; submit via private RPC (MEV Blocker) to minimize leakage; publish post‑trade surplus vs AMM baseline. (docs.cow.fi)

Example 2: Retail swap on mainnet, instant feel

Constraints: “Swap 2 ETH to USDC; accept outputs within signed range.”
Execution: RFQ v2 with cosigner; user signs range; hard quotes arrive post‑signature; the winner fills near‑instantly; if it fades, order auto‑enters Dutch and settles permissionlessly; no failed‑tx gas. (docs.uniswap.org)

Example 3: Cross‑rollup “pay on A, deliver on B”

Constraints: “Pay stablecoin on L2‑A; receive NFT on L2‑B; atomic or refund.”
Execution: Shared sequencer coordinates inclusion across A and B; solver composes bridge/DEX legs as needed; user sees fast pre‑confirmation and final settlement when DA finalizes; fallback refunds if cross‑domain leg fails. (astria.org)

Emerging best practices (2025)

Cosigned auctions: adopt a neutral cosigner role even if you don’t run a UniswapX‑style RFQ; it’s the simplest way to bound auctioneer discretion. (docs.uniswap.org)
Solver bonding tiers: mirror CoW’s reduced bonding path to expand competition while maintaining slashing recourse; require private submission until full bond reached. (forum.cow.fi)
OFA‑first routing: default settlement via MEV Blocker/MEV‑Share to reduce latency and share backrun value with users; tune builder bids for any per‑block fees these RPCs charge. (docs.cow.fi)
Shared sequencing pilots: if you rely on multiple L2s, run a pilot with Astria to measure inclusion latency and atomicity benefits before wiring your core flows. (astria.org)
Standards alignment: shape your intent schema toward ERC‑7521 and monitor Pectra/7702 wallet roadmaps for smoother EOA onboarding. (eips.ethereum.org)

The 7Block Labs checklist for an ISL that won’t rug UX

Expression: ERC‑7521‑aligned schema; explicit EBBO/UCP or cosigner requirement; MEV policy field. (eips.ethereum.org)
Discovery: private by default; selective disclosure; audit your gossip. (docs.flashbots.net)
Auction: pick batch vs RFQ/Dutch by user need; publish rules; simulate before production. (docs.cow.fi)
Solvers: bonding/slashing with historical precedent; shadow comp; private settlement; KYC if required. (docs.cow.fi)
Settlement: OFA integration for rebates and inclusion; shared sequencer for atomic cross‑rollup legs. (docs.cow.fi)
Governance: incident response runbook; 7‑day slashing window; quarterly public scorecard. (forum.cow.fi)

Bottom line

If you’re at the “build or buy” decision, start with RFQ v2 + cosigner (single‑order UX) or fair batch auctions with EBBO/UCP (portfolio/OTC) and layer in OFA/private settlement. Use bonding + slashing to keep solvers honest; pilot shared sequencing for your cross‑rollup roadmap; and align with ERC‑7521 while tracking Pectra/7702. Your users will feel the difference in fills, latency, and trust—without you hand‑waving MEV or auction fairness.

7Block Labs helps teams ship these systems end‑to‑end: schema design, solver onboarding, auction rules, OFA routing, shared sequencing pilots, and the governance scaffolding that keeps it all honest.