feat: fastswap sweep redesign

[owen-eth]

Describe your changes

Full info on changes: https://www.notion.so/primev/SWEEP_IMPROVEMENTS_PLAN-V2-1-35d6865efd6f809785b9e4d2088ef085?source=copy_link

What this PR does

• Decouples user miles from sweep timing — users see miles in minutes instead of waiting for sweep settlement
• Sweeps run on per-token cadence, optimized for protocol P&L

Backtest result

• ~+18% total miles vs current design, no bleed cases
• USDC +51%, WBTC +48%, USDT +13%, DAI +21%

Two commits for staged deploy

1. Foundation utilities — adds new files + helpers, nothing calls them yet → no-op deploy
2. Wire it up — main.go instantiation + miles.go refactor → behavior change

Plan: deploy commit 1's image, verify pod healthy, then deploy commit 2's image, merge after stable.

New components

• chainlink_oracle.go — Chainlink Feed Registry for ERC20→ERC20 pricing
• cost_estimator.go — per-token p25 of realized sweep overhead (refreshed every 30min)
• gas_buffer.go — in-memory L1 gas observations, persisted for restart
• sweep_scheduler.go — decideSweep decision logic + sweepClock with persistence
• sweep_loop.go — per-token cadence-based sweep iterator with volume-based override
• reconciliation.go — hourly miles-paid vs realized-profit ratio, with per-token breakdown

Security: attacker-token defense

• Risk: malicious actor mints worthless token + controls liquidity + fastswaps to extract fake-surplus miles
• Defense: whitelist-only upfront miles (only tokens in tokenConfigs)
• Unknown tokens defer to sweep — attacker tokens never sweep (Barter can't quote, profitability blocks)

Pricing by swap shape (verified live on mainnet)

• Output is ETH/WETH → surplus is already wei
• ETH/WETH-input + whitelisted output → event-derived from trade execution rate
• Whitelisted ERC20→ERC20 with Chainlink coverage → Feed Registry
• WBTC/ARB/PEPE as output of ERC20-input → defer (no Registry feed, reverts handled)
• Non-whitelisted output → defer

Chainlink Registry coverage

• ✓ Covered: USDC, USDT, DAI, LINK, COMP, UNI, SUSHI, 1INCH, YFI
• ✗ Not in Registry: WBTC, ARB, PEPE (defer to sweep)

Cadence config

• Stables (USDC 24h, USDT/DAI 48h) — gas cap at p25 of recent
• Blue chips (24h) — gas cap at p50
• Volatile (no cadence, every cycle eligible) — gas cap at p75
• Force-sweep at 1.5× cadence (6h for volatile)
• Volume override: bypass cadence when accumulated rows × per-row-estimate ≥ 1.2 × sweep gas

Observability

• erc20_cycle_summary — per-cycle counts: upfront_awarded, no_profit, deferred breakdown, orphaned
• awarding upfront erc20 miles — per row: surplus_eth, overhead_eth, net_profit_eth, pricing source
• sweep_executed + sweep_vs_obligation — per-sweep realized profit vs accrued miles obligation
• reconciliation_metric — hourly aggregate ratio; warn at >1.05 or <0.75
• reconciliation_per_token — per-token miles obligation
• cadence_override_triggered — when high-volume override fires
• chainlink registry lookup failed — once per unsupported token

What's preserved

• ETH/WETH-output path unchanged
• Non-eligible rows still get miles via legacy sweep path (no regression)
• 4-layer idempotency defense from prior PR intact

Out of scope (follow-ups)

• Frontend miles estimator changes
• Direct Chainlink feed addresses for WBTC/ARB/PEPE
• Uniswap V3 TWAP fallback for tokens without Chainlink

Issue ticket number and link

Fixes # (issue)

Checklist before requesting a review

• I have added tests that prove my fix is effective or that my feature works
• I have made corresponding changes to the documentation