Summary: Strategy contracts are where your yield aggregator actually makes or loses money; the wrong patterns bleed APY through MEV, gas waste, brittle adapters, and unsafe harvests. Below is a pragmatic blueprint we use at 7Block Labs to ship ERC‑4626/7540/7575‑native strategies that are audit‑ready, MEV‑aware, gas‑optimized, and tied to clear GTM metrics.

Audience: DeFi protocol teams (keywords: Gas optimization, ERC‑4626, MEV protection, Uniswap v3 TWAP, Chainlink Automation, EigenLayer/LRT, ERC‑7702)

Title: Building a Yield Aggregator: Strategy Contracts Explained

Pain (specific technical headache)

• Your vaults expose deposit/withdraw but “strategy” code is fork‑and‑pray. Each new farm needs bespoke glue: swap routers, chef interfaces, debt accounting, and off‑by‑one share math. Integration teams then spend weeks writing adapters and still miss edge cases on redemption rounding and asynchronous exits.
• Harvest scheduling is naïve. Public harvests get sandwiched, you leak basis points to MEV, and fees spike. Worse, a poorly timed harvest can let new depositors “steal” accrued yield from incumbents if you don’t lock profits correctly.
• Oracle and liquidity assumptions rot. A 10‑minute TWAP on a pool with cardinality=1 is not a TWAP; your price protection reverts in volatility, or worse, passes manipulation because the pool never grew its observation buffer. (docs.uniswap.org)
• Composability debt. Not implementing ERC‑4626 (and its async/multi‑asset extensions) forces partners to maintain one‑off adapters and limits listings across integrators. In 2025–2026, vault ecosystems standardized on ERC‑4626 with ERC‑7540 for async flows (LSTs/LRTs/RWAs) and ERC‑7575 for multi‑asset entry points. (ethereum.org)
• Roadmap drift. Ops want Chainlink Automation or Gelato; product wants Permit2 for approvals; infra wants Flashbots/MEV‑Blocker; security wants Yearn‑style tokenized strategies with immutable logic. Coordination breaks, deadlines slip, and audits become re‑writes instead of confirmations. (docs.chain.link)

Agitation (why this risk is expensive)

• Missed integrations = missed TVL. The post‑ERC‑4626 world expects plug‑and‑play vaults; teams deploy dozens of tokenized vaults weekly, and allocators shortlist standards‑compliant implementations first. If your vaults aren’t 4626‑native, you’re invisible in aggregator listings. (blockworks.co)
• Gas drag kills competitive APY. Storage writes, unbounded loops, and redundant approvals routinely waste 60–100k gas per user flow; harvests burn even more. Over a quarter, that can erase 20–40 bps of net APY on L2s with heavy usage—while your competitors pocket the spread. (alchemy.com)
• MEV and failed harvests create negative carry. Public mempool harvests get sandwiched or reverted under congestion; you pay for failed tries and suffer stale compounding. MEV‑aware flows using private builders and refunds change the unit economics of harvesting. (docs.flashbots.net)
• Async exits (LST/LRT or EigenLayer strategies) without ERC‑7540 semantics lead to stuck claims and UX escalations. As slashing goes live across AVSs, risk accounting must reflect layered penalties and delayed redemptions. Your “simple” exit queue is not enough. (eips.ethereum.org)
• Oracle misconfiguration is a latent incident. If you don’t grow Uniswap v3 observation cardinality and compute TWAP/TWAL correctly, one whale can push your rebalancer into toxic fills or freeze redemptions. Security reviewers flag this instantly; shipping slips. (docs.uniswap.org)

Solution (7Block’s methodology that ties code to ROI) We build strategy systems that are standards‑first, MEV‑aware, and automation‑ready—then prove value with GTM metrics. The playbook:

1. Architecture: vaults and strategies the market can integrate

• ERC‑4626 Vaults with Strategy Debt Allocation. Allocator vaults mint shares and allocate debt ceilings across strategies. Strategies themselves are ERC‑4626 “tokenized strategies” à la Yearn V3, enabling isolated logic, multiple attach points, and composability. This reduces adapter surface, makes strategies independently testable, and standardizes accounting. (docs.yearn.fi)
• Async and Multi‑Asset Support by Design. For LST/LRT and RWA flows, implement ERC‑7540 request/claim lifecycles (pending/claimable) and optionally ERC‑7887 cancelation if your UX mandates it. For LP tokens or multi‑entry assets, adopt ERC‑7575 so one share token fronts multiple asset entry points (“pipes”). This keeps integrators happy and exits debuggable. (eips.ethereum.org)
• Permit‑aware UX. Integrate Uniswap Permit2 for capped, time‑boxed approvals, minimizing on‑chain approval friction while supporting revocation tooling. For power users and routers (Universal Router), Permit2 reduces clicks and failures—raising first‑deposit conversion. (docs.uniswap.org)

1. Strategy contract patterns that don’t leak value

• Profit Locking and Harvest‑on‑Deposit. Borrow from Beefy/Yearn patterns: lock reported profits over N blocks or harvest on deposit to remove yield theft by late entrants. Keep allowance hygiene and “panic” hooks to yank funds from third‑party farms instantly. (docs.beefy.finance)
• Deterministic Accounting. Use convertToAssets/convertToShares consistently; never mix shadow accounting with ERC‑4626 math. Always implement preview and max functions to make routing predictable for integrators. When async, follow ERC‑7540 overrides and revert previews as specified. (eips.ethereum.org)
• Oracle Discipline. Programmatically increase Uniswap v3 observation cardinality on attach (e.g., +50 slots) and compute TWAP/TWAL via observe(), not by reading single observations. Fail closed under manipulations. Document parameters per pool. (docs.uniswap.org)

1. MEV‑aware execution and automation

• Private Order Flow for Harvests and Large Rebalances. Route harvest transactions via Flashbots Protect RPC (fast mode for multi‑builder distribution) or MEV Blocker to avoid sandwiches and capture backrun rebates when possible. This directly reduces “MEV leakage” and failed‑tx gas burn. (docs.flashbots.net)
• Deterministic Schedulers. Use Chainlink Automation v2.1+ for time‑based or custom logic upkeeps with sane LINK buffers and non‑flickering checkUpkeep conditions; use Gelato Functions where off‑chain conditions (subgraphs, LRT APYs) are required. We document OPEX: fee schedules, gas limits, and funding runways. (docs.chain.link)

1. Gas optimization where it actually pays

• Reduce storage writes, pack flags, use immutables/constant addresses, prefer mappings, and cache frequently used values; only “unchecked” in mathematically bounded loops; reserve Yul for tight inner loops with tests and comments. We baseline with solc IR optimizer and budget code size vs runtime gas. (alchemy.com)
• Track compiler features. Use Solidity ≥0.8.28 for transient storage support (useful for intra‑tx flags) and align with optimizer improvements; evaluate 0.8.29’s experimental EOF backend in staging—don’t ship to mainnet until the target EVM version is live. (soliditylang.org)

1. Security process aligned to DeFi reality

• Guard rails: CEI pattern, ReentrancyGuard where invariants are fragile, pull‑payments for fees, access control via roles instead of tx.origin, and explicit pause/panic paths on strategies. (docs.openzeppelin.com)
• Testing stack: Foundry unit + invariants, Echidna property fuzzing (including ERC‑4626 properties), Slither CI with upgradeability checks; GitHub Actions for continuous findings. This converts security work from “event” to “process.” (github.com)
• Audit‑ready documentation: State diagrams for ERC‑7540 flows, oracle cardinality settings, MEV routing configs, and keeper funding runbooks. This reduces audit time and de‑risks mainnet day‑1. (learn.openzeppelin.com)

Practical example: a tokenized strategy that won’t bite you later Below is a minimal, production‑leaning skeleton for an ERC‑4626 “strategy vault” that deploys a single asset into an external farm and harvests via private flow. It assumes an Allocator Vault controls debt ceilings and calls deposit/withdraw on the strategy. Highlights: 4626 math only; harvest‑on‑deposit option; Uniswap v3 TWAP guard; Chainlink Automation compatibility.

// SPDX-License-Identifier: AGPL-3.0
pragma solidity ^0.8.28;

import {ERC4626, ERC20, Math} from "solmate/mixins/ERC4626.sol";
import {ReentrancyGuard} from "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import {AccessControl} from "@openzeppelin/contracts/access/AccessControl.sol";

interface IChef { function deposit(uint256 pid, uint256 amt) external; function withdraw(uint256 pid, uint256 amt) external; function pendingReward(uint256 pid, address user) external view returns (uint256); }
interface IRouter { function swapExactTokensForTokens(uint amtIn, uint amtOutMin, address[] calldata path, address to, uint deadline) external returns (uint[] memory); }
interface IUniswapV3Oracle { function observe(uint32[] calldata secondsAgos) external view returns (int56[] memory, uint160[] memory); }

contract TokenizedStrategy is ERC4626, AccessControl, ReentrancyGuard {
    bytes32 public constant ALLOCATOR_ROLE = keccak256("ALLOCATOR_ROLE");
    bytes32 public constant KEEPER_ROLE    = keccak256("KEEPER_ROLE");

    IChef   public immutable chef;
    IRouter public immutable router;
    IUniswapV3Oracle public immutable oracle;
    uint256 public immutable pid;

    // Config
    bool    public harvestOnDeposit;
    uint32  public twapWindow = 600; // seconds
    uint16  public minCardinality = 50; // grow target for v3 oracle ring buffer
    uint256 public slippageBps = 50; // 0.5%

    // Accounting — no shadow balances; rely on ERC4626’s totalAssets()
    constructor(
        ERC20 asset_,
        address chef_,
        uint256 pid_,
        address router_,
        address oracle_
    ) ERC4626(asset_, string(abi.encodePacked("strat-", asset_.symbol())), string(abi.encodePacked("s", asset_.symbol()))) {
        chef = IChef(chef_); pid = pid_;
        router = IRouter(router_); oracle = IUniswapV3Oracle(oracle_);
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
        _grantRole(ALLOCATOR_ROLE, msg.sender);
        _grantRole(KEEPER_ROLE, msg.sender);
        asset_.approve(address(chef), type(uint256).max);
    }

    // Vault-facing
    function beforeDeposit() external nonReentrant onlyRole(ALLOCATOR_ROLE) {
        if (harvestOnDeposit) _harvestInternal();
    }

    function afterDeposit(uint256 assets, uint256) internal override nonReentrant {
        // push funds to farm
        chef.deposit(pid, assets);
    }

    function beforeWithdraw(uint256 assets, uint256) internal override nonReentrant {
        // pull from farm just-in-time
        chef.withdraw(pid, assets);
    }

    // Keeper harvest; route privately off-chain via Protect/MEV Blocker when sending the tx
    function harvest() external nonReentrant onlyRole(KEEPER_ROLE) {
        _harvestInternal();
    }

    function _harvestInternal() internal {
        // 1) claim rewards (chef.deposit(pid, 0) or dedicated method, omitted)
        // 2) price sanity using v3 TWAP over twapWindow
        _sanityCheckTWAP();
        // 3) swap rewards->asset via router with slippage guard
        // 4) re-deposit to compound
        // NOTE: all approvals granted at deploy; keep allowances minimal in prod if protocol risk
    }

    function _sanityCheckTWAP() internal view {
        // Minimal TWAP example; production should check cardinality and use TWAL as well
        uint32[] memory secs = new uint32[](2); secs[0] = 0; secs[1] = twapWindow;
        (int56[] memory ticks,) = oracle.observe(secs);
        int56 diff = ticks[0] - ticks[1];
        require(diff != 0, "TWAP/STALE");
        // additional checks omitted; wire into price limits
    }

    // Admin ops
    function setHarvestOnDeposit(bool on) external onlyRole(DEFAULT_ADMIN_ROLE) { harvestOnDeposit = on; }
    function setParams(uint32 twapSec, uint16 minCard, uint256 slipBps) external onlyRole(DEFAULT_ADMIN_ROLE) {
        require(twapSec >= 60 && slipBps <= 200, "bad-params");
        twapWindow = twapSec; minCardinality = minCard; slippageBps = slipBps;
    }

    // ERC‑4626 overrides
    function totalAssets() public view override returns (uint256) {
        // read farm balance + idle (example: call into chef userInfo)
        // return wantInChef + asset.balanceOf(address(this));
        return asset.balanceOf(address(this)); // stub
    }
}

Why this works in practice

• Allocator controls debt via ERC‑4626; strategies never keep their own parallel accounting.
• Harvest-on-deposit option prevents value drift for incumbents.
• TWAP sanity ensures swaps occur only under predictable prices; in production we also bump Uniswap v3 cardinality on attach to guarantee enough history for your twapWindow. (docs.uniswap.org)
• Keeper calls are stateless and safe to batch. In production, keepers submit via Flashbots Protect or MEV Blocker; you document RPC parameters (fast mode vs. max privacy) in runbooks for SRE. (docs.flashbots.net)
• Chainlink Automation or Gelato can own harvest cadence; we size performGasLimit and LINK/OPEX budgets to avoid flicker and underfunding halts. (docs.chain.link)

Emerging practices to fold into your 2026 roadmap

• Async exits with ERC‑7540 are table stakes for LST/LRT and RWAs. Implement requestDeposit/requestRedeem + claim lifecycles, and publish dashboards for pending vs. claimable. Keep an eye on ERC‑7887 (cancelation) if your UX demands it. (eips.ethereum.org)
• ERC‑7575 for multi‑asset entry. LP strategies and cross‑asset pipes should share a single share token with multiple deposit endpoints—no more wrapper sprawl. (eips.ethereum.org)
• Account abstraction touchpoints. With EIP‑7702 live (Pectra, May 7, 2025), you can batch deposit+permit in one smart‑account transaction and sponsor gas selectively—useful for onboarding campaigns without compromising custody. (blog.ethereum.org)
• Compiler realities. Adopt solc >=0.8.28 for transient storage and optimizer improvements; trial 0.8.29’s EOF only in testnets until the EVM target is live. This avoids brittle assembly and “stack too deep” rewrites while preserving gas gains. (soliditylang.org)
• Formalized testing. Encode ERC‑4626 invariants and strategy‑specific safety properties (e.g., “no share price decrease absent external loss”) in Echidna; run Slither in CI; publish coverage/props in your audit folder. (github.com)

GTM metrics you should demand (and what we measure in pilots)

• Integration velocity: Time from “new farm spec” to a new live strategy with 4626 interface and docs. Target: ≤10 business days after adapter template, because no off‑standard glue is needed. Proxy: number of new listings on aggregators per quarter. Backed by ecosystem standardization around ERC‑4626/7540/7575. (ethereum.org)
• Gas optimization:
  • User flows: −60k to −120k gas per deposit/withdraw vs. baseline via storage minimization, caching, and immutables.
  • Harvest: −10–25% by netting swaps, profit‑locking, and avoiding failed public‑mempool attempts. We validate using solc IR optimizer profiles and live tx traces. (alchemy.com)
• MEV‑aware performance:
  • Failed harvest rate: target <1% (vs. public mempool baseline) using Protect fast mode;
  • MEV refunds: non‑zero refunds on eligible backrun‑friendly flows. We track builder set, hints, and refunds per epoch. (docs.flashbots.net)
• Oracle reliability: Uniswap v3 cardinality grown to ≥50 on attach; TWAP window ≥10m with consistent observe() reads; zero manipulation incidents in chaos tests. Publish cardinality growth txids and parameters. (docs.uniswap.org)
• Automation OPEX: Monthly LINK spend with Chainlink Automation v2.1+ at target cadence; eliminate flicker by keeping checkUpkeep true until execute and maintaining ≥3–5× minimum LINK balance. Report runbook and alerts. (docs.chain.link)
• Compliance for integrations: Strategies and vaults pass 4626 conformance tests; async flows pass 7540 interface checks; multi‑asset entries pass 7575 interface checks. Publish interface support via ERC‑165. (eips.ethereum.org)

Implementation checklist (what we actually ship)

• Standards‑first vault/strategy set with docs and diagrams, plus adapters only where absolutely necessary.
• MEV‑protected operational runbooks (Flashbots/MEV‑Blocker configurations; builder lists; privacy/refund hints).
• Chainlink/Gelato automation with documented OPEX, alerting, and emergency pause.
• Oracle initialization scripts that grow cardinality and set sanity bounds per pair.
• Foundry + Echidna + Slither CI, with a dedicated “audit folder” containing invariants, params, and deployment playbooks.
• Procurement‑ready artifacts: secure development lifecycle, audit scope, and test evidence for exchanges/aggregators.

Where 7Block fits

• If you’re starting fresh or refactoring, we deliver strategy systems as part of our custom smart contract development and end‑to‑end DeFi development services, wire them into MEV‑aware ops, and hand off a GTM metrics dashboard.
• Already live? We run a targeted security audit focusing on strategy‑specific failure modes (oracle drift, async redemption bugs, harvest griefing) and a “gas/MEV” remediation sprint.
• Scaling to multi‑chain or cross‑asset? We design the vault topology and cross‑chain adapters through our cross‑chain solutions development and extend your dApp UX with our dApp development practice.

Appendix: configuration snippets you’ll actually use

• Flashbots Protect (fast, multi‑builder; for harvests)
  • RPC: rpc.flashbots.net/fast with appropriate hints for refund/privacy; use useMempool=true fallback only if landing times are unacceptable. Maintain consistent RPCs during confirmation to avoid mempool exposure. (docs.flashbots.net)
• Chainlink Automation (custom logic)
  • Keep performGasLimit aligned to worst‑case harvest; fund ERC‑677 LINK with ≥3–5× minimum; avoid flickering predicates in checkUpkeep. Upgrade time‑based upkeeps if pre‑Dec 11, 2025. (docs.chain.link)
• Uniswap v3 oracle growth
  • On strategy attach, call Oracle.grow() (or use a helper) to reach target cardinality (e.g., 50–144) based on your TWAP window and chain block time. Validate via observe(). (docs.uniswap.org)
• Permit2 onboarding
  • One‑time max approval to Permit2; then use time‑boxed, amount‑capped signatures in frontends/routers to remove redundant approvals and reduce support tickets. (docs.uniswap.org)

Proof points (external signals you can rely on)

• ERC‑4626/7540/7575 are now documented and maintained across ethereum.org, EIPs, and the Tokenized Vault Foundation; Yearn V3 popularized tokenized strategies with immutable logic sharing. This is the ecosystem’s lingua franca for yield vaults. (ethereum.org)
• Pectra’s EIP‑7702 unlocked “smart EOA” affordances that materially improve conversion for first‑time depositors via batched flows and sponsored gas where appropriate. (blog.ethereum.org)
• Flashbots Protect/MEV‑Blocker provide private orderflow and configurable privacy/refund settings—deployed in production by many DeFi teams—to reduce harmful MEV exposure in harvests and rebalance ops. (docs.flashbots.net)
• Chainlink Automation v2.1+ standardizes keeper economics and mitigates common failure modes (deprecated registries, underfunding, flicker), making scheduled compounding a solved problem operationally. (docs.chain.link)

The business outcome

• You ship faster (no bespoke adapters), earn more (less gas drag, fewer failed harvests), and expand listings (standards‑native). More importantly, your ops burden drops: private order flow + deterministic automation removes “harvest roulette,” while robust oracle params prevent costly incidents.

Call to action (DeFi) Book a Strategy Architecture Review.