6.1. 0.5% Auction Success Fee

The 0.5% Auction Success Fee is the foundational revenue stream of the Fhenix-FairMarket protocol. Designed to align protocol sustainability with user success, this flat-rate fee is levied exclusively on the winning bid upon successful settlement. It replaces opaque, recurring subscription models or extractive gas markup schemes with a transparent, mathematically enforced deduction that activates only when economic value is successfully transferred.

By strictly coupling fee collection to the FINALIZED state, the protocol guarantees that no participant incurs protocol costs during failed, cancelled, or emergency-voided auctions. This design enforces a “profit on success, zero cost on failure” economic model, fostering trust and long-term market participation.

Core Mechanism & Trigger Conditions

Parameter	Specification
Fee Rate	Exactly `0.5%` of the final winning bid value
Trigger State	`FINALIZED` (via valid `submitResolution()` + AVS proof)
Payer	Winning bidder only
Exempt States	`CREATED`, `ACTIVE`, `RESOLVING`, `CANCELLED`, `VOIDED`
Mathematical Precision	Deterministic integer division: `(winningBid * 50) / 10000`
Vickrey Mode Compatibility	Applied to the second-price value (encrypted & decrypted off-chain)

️ Execution Flow

Auction reaches endTime → triggerFinalize() transitions state to RESOLVING.
Off-chain FHEOS computes winner → EigenLayer AVS validates result.
submitResolution() verifies proof → state transitions to FINALIZED.
Settlement engine calculates 0.5% of winning bid → routes 0.2% to keeper, 0.3% to treasury distribution.
Winner claims NFT + pays success fee; losers execute claimRefund() fee-free.

Algorithmic Distribution Architecture

The 0.5% fee is not held as a monolithic pool. It is algorithmically partitioned at the contract level to guarantee decentralized liveness and economic resilience:

Allocation	Percentage	Destination	Purpose
Keeper Bounty	`0.2%` (40% of fee)	First valid `triggerFinalize()` executor	Incentivizes self-sustaining automation & network uptime
Net Distribution	`0.3%` (60% of fee)	`Treasury Router Contract`	Funds protocol development, insurance, grants, and bug bounties

Economic Note: The 0.3% net portion is further split deterministically: 60% Treasury, 20% Insurance Fund, 15% Developer Grants, 5% Immunefi Bug Bounty. No administrative discretion or manual overrides are permitted.

️ Technical Implementation

The fee logic is integrated into the settlement routing layer to maintain gas efficiency and state isolation. It executes only after cryptographic finality is achieved.

// packages/contracts/settlement/SettlementEngine.sol (Conceptual Routing)
function _distributeSuccessFees(uint256 auctionId, uint256 winningBidAmount) internal {
 require(auctions[auctionId].state == AuctionState.FINALIZED, "Not finalized");
 
 // Deterministic 0.5% calculation with safe integer math
 uint256 successFee = (winningBidAmount * 50) / 10000;
 uint256 keeperBounty = (successFee * 40) / 100; // 0.2%
 uint256 netProtocolFee = successFee - keeperBounty; // 0.3%
 
 // Route Keeper Bounty (0.2%)
 address finalizer = auctions[auctionId].finalizer;
 _safeTransfer(finalizer, keeperBounty);
 
 // Route Net Distribution (0.3%)
 treasuryRouter.allocate(netProtocolFee);
 
 emit SuccessFeeCollected(auctionId, winningBidAmount, successFee);
 emit KeeperBountyPaid(finalizer, keeperBounty);
}

️ Economic Guarantees & User Alignment

Outcome-Based Pricing: The protocol only profits when a trade successfully completes. Users are never penalized for market exploration, seller cancellations, or infrastructure failures.
Predictable Cost Structure: A flat 0.5% rate eliminates gas volatility surprises or hidden scaling fees. Bidders can precisely calculate net acquisition costs upfront.
Decentralized Liveness Funding: By allocating 0.2% directly to the first valid closure executor, the protocol creates a competitive, self-sustaining automation market. External keepers are economically incentivized to maintain uptime even if internal infrastructure experiences downtime.
State-Gated Capital Protection: The fee collection path is strictly guarded by AuctionState.FINALIZED. Attempts to extract fees during CANCELLED or VOIDED states revert instantly, preserving 100% of user capital during disruptions.
Transparent On-Chain Accounting: Every fee allocation emits indexed events (SuccessFeeCollected, KeeperBountyPaid, TreasuryAllocated), enabling permissionless auditing by users, DAOs, and external security firms.

Audit Gate Compliance (P0)

Progression through Phase 6 and final mainnet readiness is strictly blocked until all fee-related P0 criteria pass:

[] Deterministic Math: Fee calculation uses safe integer arithmetic (amount * 50 / 10000) to prevent rounding exploits or precision loss.
[] State Enforcement: Fees are only routed when state == FINALIZED. Unit tests confirm zero extraction in CANCELLED/VOIDED/RESOLVING states.
[] Exact Split Verification: On-chain logic guarantees 0.2% → Keeper, 0.3% → Net Distribution. No leakage or discretionary routing exists.
[] Event Transparency: All fee transfers emit indexed, auditable events with exact amounts and recipient addresses.
[] Immutable Rate Governance: The 0.5% rate is hardcoded or timelock-governed. No onlyOwner function can modify it without a 48h delay and multisig approval.
[] Zero Hidden Fees: CI lint rules and gas reporters confirm no secondary tolls, gas markups, or withdrawal penalties are applied alongside the success fee.

Next Steps

Proceed to 6.2. 0.2% Keeper Bounty for liveness incentives, race-condition resistance, and decentralized automation economics.

Review 6.3. Net Fee Distribution for the 60/20/15/5 treasury split and insurance fund mechanics.

Explore Security Model → Audit Readiness Matrix for P0 economic verification standards.

Economic Model 6.2 Keeper Bounty (0.2%)