Add ALEX STX/ALEX arb receiver

Flash-borrows STX, swaps wSTX->ALEX->wSTX on ALEX amm-pool-v2-01
(pool factor u100000000), repays FlashStack with spread as profit.

Contracts verified from live mainnet swap transactions 2026-05-12.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mattglory

contracts/alex-arb-receiver.clar

@@ -0,0 +1,158 @@
+;; FlashStack - ALEX STX/ALEX Arbitrage Receiver
+;;
+;; Borrows STX from flashstack-stx-core, executes a STX -> ALEX -> STX
+;; round-trip on ALEX's AMM pool, repays FlashStack, keeps the spread.
+;;
+;; Live contracts verified from mainnet transactions 2026-05-12:
+;;   ALEX AMM:    SP102V8P0F7JX67ARQ77WEA3D3CFB5XW39REDT0AM.amm-pool-v2-01
+;;   wSTX token:  SP102V8P0F7JX67ARQ77WEA3D3CFB5XW39REDT0AM.token-wstx-v2
+;;   ALEX token:  SP102V8P0F7JX67ARQ77WEA3D3CFB5XW39REDT0AM.token-alex
+;;   Pool factor: u100000000 (wSTX/ALEX pool)
+;;
+;; Amount conversion:
+;;   ALEX uses 8-decimal fixed-point (ONE_8 = 10^8). STX has 6 decimals.
+;;   1 microSTX = 100 wSTX-v2 units. So: dx = amount_microstx * 100.
+;;
+;; Arb opportunity:
+;;   ALEX token accrues protocol revenue. When buy pressure builds before
+;;   emissions or governance events, ALEX briefly trades above fair value.
+;;   Flash-borrow STX, buy ALEX cheap, sell back for more STX, repay.
+;;
+;; Note: ALEX AMM has a blocklist check (is-blocklisted-or-default).
+;;   New contracts are NOT blocked by default. If a runtime u403 error
+;;   occurs, contact ALEX team to confirm the contract is permitted.
+
+(impl-trait 'SP3TGRVG7DKGFVRTTVGGS60S59R916FWB4DAB9STZ.stx-flash-receiver-trait.stx-flash-receiver-trait)
+
+;; =============================================
+;; Constants
+;; =============================================
+
+(define-constant CONTRACT-OWNER tx-sender)
+
+(define-constant ERR-NOT-OWNER    (err u500))
+(define-constant ERR-SWAP-FAILED  (err u501))
+(define-constant ERR-NO-PROFIT    (err u502))
+(define-constant ERR-REPAY-FAILED (err u503))
+
+;; ALEX AMM pool v2
+(define-constant ALEX-POOL   'SP102V8P0F7JX67ARQ77WEA3D3CFB5XW39REDT0AM.amm-pool-v2-01)
+;; wSTX-v2: STX wrapper used as token-x in the ALEX pool
+(define-constant WSTX        'SP102V8P0F7JX67ARQ77WEA3D3CFB5XW39REDT0AM.token-wstx-v2)
+;; ALEX governance token: token-y in the pool
+(define-constant ALEX-TOKEN  'SP102V8P0F7JX67ARQ77WEA3D3CFB5XW39REDT0AM.token-alex)
+;; Pool factor identifying the wSTX/ALEX pool (confirmed from live swap txs)
+(define-constant ALEX-FACTOR u100000000)
+;; Conversion: 1 microSTX = 100 wSTX-v2 fixed-point units
+(define-constant WSTX-SCALE  u100)
+
+;; =============================================
+;; Flash Loan Callback
+;; =============================================
+
+;; Called by flashstack-stx-core after sending (amount) microSTX to this contract.
+;; Executes STX -> ALEX -> STX round-trip and repays principal + fee.
+(define-public (execute-stx-flash (amount uint) (core principal))
+  (let (
+    (fee-bp      (unwrap! (contract-call? 'SP20XD46NGAX05ZQZDKFYCCX49A3852BQABNP0VG5.flashstack-stx-core
+                    get-fee-basis-points) ERR-REPAY-FAILED))
+    (raw-fee     (/ (* amount fee-bp) u10000))
+    (fee         (if (> raw-fee u0) raw-fee u1))
+    (total-owed  (+ amount fee))
+    ;; Convert microSTX to wSTX-v2 fixed-point for ALEX pool input
+    (dx          (* amount WSTX-SCALE))
+  )
+    ;; Leg 1: wSTX -> ALEX
+    ;; The pool calls wSTX.transfer-fixed(dx, us, vault) which moves (amount) microSTX from us.
+    ;; as-contract required: STX is held by this contract, not by the external caller.
+    (unwrap! (as-contract (contract-call? ALEX-POOL swap-x-for-y
+      WSTX         ;; token-x: wSTX-v2 (STX wrapper)
+      ALEX-TOKEN   ;; token-y: ALEX governance token
+      ALEX-FACTOR  ;; pool factor (wSTX/ALEX pool identifier)
+      dx           ;; dx in wSTX-v2 fixed-point (= amount * 100)
+      none         ;; min-dy: no slippage floor; repay check below is the safety gate
+    )) ERR-SWAP-FAILED)
+
+    ;; Read ALEX balance received from leg 1
+    (let ((alex-bal (unwrap!
+            (as-contract (contract-call? ALEX-TOKEN get-balance tx-sender))
+            ERR-SWAP-FAILED)))
+      (asserts! (> alex-bal u0) ERR-SWAP-FAILED)
+
+      ;; Leg 2: ALEX -> wSTX (back to STX)
+      ;; Pool calls ALEX.transfer-fixed(alex-bal, us, vault) and sends us wSTX (= STX).
+      (unwrap! (as-contract (contract-call? ALEX-POOL swap-y-for-x
+        WSTX         ;; token-x: wSTX-v2 (what we receive)
+        ALEX-TOKEN   ;; token-y: ALEX (what we spend)
+        ALEX-FACTOR  ;; pool factor
+        alex-bal     ;; dy: all ALEX we hold from leg 1
+        none         ;; min-dx: no slippage floor; repay check enforces the minimum
+      )) ERR-SWAP-FAILED)
+
+      ;; Verify we received enough STX to cover repayment
+      (let ((stx-bal (stx-get-balance (as-contract tx-sender))))
+        (asserts! (>= stx-bal total-owed) ERR-REPAY-FAILED)
+        ;; Repay FlashStack: principal + fee
+        (unwrap! (as-contract (stx-transfer? total-owed tx-sender core)) ERR-REPAY-FAILED)
+        (ok true)
+      )
+    )
+  )
+)
+
+;; =============================================
+;; Admin
+;; =============================================
+
+(define-public (rescue-stx (amount uint) (to principal))
+  (begin
+    (asserts! (is-eq tx-sender CONTRACT-OWNER) ERR-NOT-OWNER)
+    (unwrap! (as-contract (stx-transfer? amount tx-sender to)) ERR-REPAY-FAILED)
+    (ok true)
+  )
+)
+
+(define-public (rescue-alex (amount uint) (to principal))
+  (begin
+    (asserts! (is-eq tx-sender CONTRACT-OWNER) ERR-NOT-OWNER)
+    (unwrap!
+      (as-contract (contract-call? ALEX-TOKEN transfer amount tx-sender to none))
+      ERR-REPAY-FAILED)
+    (ok true)
+  )
+)
+
+;; =============================================
+;; Read-only
+;; =============================================
+
+;; Pre-flight profit estimate.
+;; This is a rough estimate based only on fee arithmetic -- actual profit
+;; depends on the pool price at execution time. Use as a sanity check only.
+;; bonus-bp: expected spread capture in basis points (e.g. u100 = 1%)
+(define-read-only (simulate (loan-amount uint) (spread-bp uint))
+  (let (
+    (raw-fee (/ (* loan-amount u5) u10000))
+    (fee     (if (> raw-fee u0) raw-fee u1))
+    (spread  (/ (* loan-amount spread-bp) u10000))
+    (profit  (if (> spread fee) (- spread fee) u0))
+  )
+    {
+      loan-amount:  loan-amount,
+      spread-bp:    spread-bp,
+      spread:       spread,
+      flash-fee:    fee,
+      net-profit:   profit,
+      profitable:   (> spread fee),
+      owed-to-core: (+ loan-amount fee),
+    }
+  )
+)
+
+(define-read-only (get-stx-balance)
+  (stx-get-balance (as-contract tx-sender))
+)
+
+(define-read-only (get-alex-balance)
+  (as-contract (contract-call? ALEX-TOKEN get-balance tx-sender))
+)