feat: swap USDFC back to FIL

AGENTS.md

@@ -20,19 +20,13 @@ npm run test:unit       # Run only unit tests
 - **JSDoc + TypeScript** - Type annotations in comments, TypeScript only for type checking
 - **Node.js native test runner** - Uses `node:test` module
 
-## Architecture
-
-### Two-Layer Design
-
-1. **Library Layer** ([index.js](index.js)) - Pure functions, all exported for testing
-2. **Application Layer** ([bin/bot.js](bin/bot.js)) - Event loop with error handling
-
 ### Key Design Decisions
 
 - **Stateless** - No database, queries contract fresh each iteration
 - **Direct wallet bidding** - No account deposit needed
 - **Deterministic auction selection** - Always picks first auction with available fees
 - **100% bids** - Always bids for all available fees if balance is sufficient
+- **Auto-refuel** - Swaps acquired USDFC back to FIL after successful bids (mainnet only)
 
 ## Coding Conventions
 
@@ -90,13 +84,26 @@ The `createClient` function supports both networks: `mainnet` and `calibration`.
 
 ### Sushiswap Integration
 
-The bot uses Sushiswap's REST API for price checking:
+The bot uses Sushiswap's SDK for swap quoting.
+
+#### Frontrunning Protection (Nonce+1)
+
+To reduce the frontrunning window, both `burnForFees` and swap transactions are submitted simultaneously:
+
+1. Get current nonce N
+2. Submit `burnForFees` with nonce N
+3. Immediately submit swap with nonce N+1 (don't wait for bid confirmation)
+4. Wait for both receipts in parallel
+
+This ensures both transactions hit the mempool together. If `burnForFees` fails, the swap should also fail due to nonce ordering.
+
+#### Flow on Mainnet
+
+1. At startup: Discover Sushiswap router → Approve USDFC for router
+2. Each iteration: Get balances → Get auction info → Get swap quote → Check profitability → Submit bid+swap simultaneously (nonce+1)
+
+#### Error Handling
 
-- **API endpoint**: `https://api.sushi.com/quote/v7/{chainId}`
-- **Quote pair**: USDFC → native FIL
-- **Quote network**: Always queries mainnet (chain ID 314) for accurate pricing
-- **Quote function**: REST API with `tokenIn`, `tokenOut`, `amount`, `maxSlippage`
-- **Max slippage**: Default 0.005 (0.5%)
-- **Profitability logic**: Bot bids only if market price >= auction price
-- **Error handling**: Quote failures skip auction and log warning, continue monitoring
-- **Implementation**: Uses Sushi's EVM SDK `getQuote` function from `sushi/evm`
+- If bid+swap both fail, USDFC (if any) is held for next iteration
+- Quote failures skip the auction (no bid placed)
+- If bid succeeds but swap fails, USDFC held for next iteration

bin/bot.js

@@ -1,14 +1,44 @@
 import 'dotenv/config'
 import { setTimeout } from 'node:timers/promises'
-import { initializeConfig, processAuctions } from '../index.js'
+import { discoverSushiswapRouter } from '../lib/swap.js'
+import { initializeConfig, ensureApproval } from '../lib/config.js'
+import { processAuctions } from '../lib/auction.js'
 
 const config = await initializeConfig(process.env)
+const sushiswapRouterAddress = await discoverSushiswapRouter({
+  chainId: config.chainId,
+  tokenIn: config.usdfcAddress,
+  sender: config.account.address,
+})
+
+if (!sushiswapRouterAddress && config.chainId === 314) {
+  console.error(
+    'Error: Could not discover Sushiswap router address on Filecoin mainnet.',
+  )
+  process.exit(1)
+}
+
+if (sushiswapRouterAddress) {
+  await ensureApproval({
+    publicClient: config.publicClient,
+    walletClient: config.walletClient,
+    account: config.account,
+    tokenAddress: config.usdfcAddress,
+    spenderAddress: /** @type {import('viem').Address} */ (
+      sushiswapRouterAddress
+    ),
+  })
+}
+
+console.log()
+console.log('Starting auction monitoring...')
+console.log()
 
 while (true) {
   console.log(`Starting auction check...`)
 
   try {
-    await processAuctions(config)
+    await processAuctions({ ...config, sushiswapRouterAddress })
   } catch (error) {
     const err = /** @type {Error} */ (error)
     console.log()