Round down availableBalance to prevent health violation on max withdrawal

cadence/contracts/FlowALPv0.cdc

@@ -430,7 +430,7 @@ access(all) contract FlowALPv0 {
                 withdrawBal: withdrawBal,
                 targetHealth: view.minHealth
             )
-            return FlowALPMath.toUFix64Round(uintMax)
+            return FlowALPMath.toUFix64RoundDown(uintMax)
         }
 
         /// Returns the health of the given position, which is the ratio of the position's effective collateral

cadence/tests/available_balance_rounding_test.cdc

@@ -0,0 +1,128 @@
+import Test
+import BlockchainHelpers
+
+import "MOET"
+import "FlowALPModels"
+import "test_helpers.cdc"
+
+// Tests that availableBalance rounds DOWN when converting from UFix128 to UFix64.
+// Rounding up could return a value that, if withdrawn/borrowed, would violate the position's minimum health factor.
+//
+// Token setup:
+//   FLOW: collateralFactor=0.8, borrowFactor=1.0, price=1.0
+//   MOET: collateralFactor=1.0, borrowFactor=1.0, price=1.0  (default token)
+//
+// Scenario:
+//   Deposit 100 FLOW (no debt). Available MOET borrow = 80 / 1.1 = 72.72727272727...
+//   UFix64 round-down:    72.72727272
+//   UFix64 round-half-up: 72.72727273  (incorrect — would breach minHealth)
+
+access(all) let user = Test.createAccount()
+access(all) let lp = Test.createAccount()
+
+access(all) var snapshot: UInt64 = 0
+
+access(all)
+fun setup() {
+    deployContracts()
+
+    setMockOraclePrice(signer: PROTOCOL_ACCOUNT, forTokenIdentifier: FLOW_TOKEN_IDENTIFIER, price: 1.0)
+    setMockOraclePrice(signer: PROTOCOL_ACCOUNT, forTokenIdentifier: MOET_TOKEN_IDENTIFIER, price: 1.0)
+
+    createAndStorePool(signer: PROTOCOL_ACCOUNT, defaultTokenIdentifier: MOET_TOKEN_IDENTIFIER, beFailed: false)
+    addSupportedTokenZeroRateCurve(
+        signer: PROTOCOL_ACCOUNT,
+        tokenTypeIdentifier: FLOW_TOKEN_IDENTIFIER,
+        collateralFactor: 0.8,
+        borrowFactor: 1.0,
+        depositRate: 1_000_000.0,
+        depositCapacityCap: 1_000_000.0
+    )
+
+    // Setup LP with MOET liquidity so the user can borrow
+    setupMoetVault(lp, beFailed: false)
+    mintMoet(signer: PROTOCOL_ACCOUNT, to: lp.address, amount: 10_000.0, beFailed: false)
+    grantBetaPoolParticipantAccess(PROTOCOL_ACCOUNT, lp)
+    createPosition(admin: PROTOCOL_ACCOUNT, signer: lp, amount: 10_000.0, vaultStoragePath: MOET.VaultStoragePath, pushToDrawDownSink: false)
+
+    // Setup user with FLOW
+    setupMoetVault(user, beFailed: false)
+    transferFlowTokens(to: user, amount: 1_000.0)
+    grantBetaPoolParticipantAccess(PROTOCOL_ACCOUNT, user)
+
+    snapshot = getCurrentBlockHeight()
+}
+
+access(all)
+fun beforeEach() {
+    if getCurrentBlockHeight() > snapshot {
+        Test.reset(to: snapshot)
+    }
+}
+
+// ---------------------------------------------------------------------------
+// availableBalance should round down, not up, so the returned amount is always
+// safe to withdraw without breaching minHealth.
+//
+// 100 FLOW deposited, no debt:
+//   effectiveCollateral = 100 * 1.0 * 0.8 = 80
+//   maxWithdraw(MOET) = 80 / minHealth(1.1) = 72.727272727272... (UFix128)
+//
+//   Round-down to UFix64: 72.72727272
+//   Round-half-up to UFix64: 72.72727273
+//
+// The test asserts the round-down value, which fails with toUFix64Round and
+// passes with toUFix64RoundDown.
+// ---------------------------------------------------------------------------
+access(all)
+fun test_availableBalance_rounds_down() {
+    // Open position: deposit 100 FLOW, no auto-borrow
+    createPosition(admin: PROTOCOL_ACCOUNT, signer: user, amount: 100.0, vaultStoragePath: FLOW_VAULT_STORAGE_PATH, pushToDrawDownSink: false)
+    let pid = getLastPositionId()
+
+    // availableBalance for MOET (no MOET credit, so this is the pure borrow path)
+    let available = getAvailableBalance(
+        pid: pid,
+        vaultIdentifier: MOET_TOKEN_IDENTIFIER,
+        pullFromTopUpSource: false,
+        beFailed: false
+    )
+
+    // 80 / 1.1 = 72.72727272727... → round-down = 72.72727272
+    let expectedRoundDown: UFix64 = 72.72727272
+    Test.assert(available == expectedRoundDown,
+        message: "availableBalance should round down: expected \(expectedRoundDown), got \(available)")
+}
+
+// ---------------------------------------------------------------------------
+// Verify the safety property: borrowing the full availableBalance amount must
+// succeed without breaching minHealth.
+// ---------------------------------------------------------------------------
+access(all)
+fun test_borrowing_full_availableBalance_succeeds() {
+    createPosition(admin: PROTOCOL_ACCOUNT, signer: user, amount: 100.0, vaultStoragePath: FLOW_VAULT_STORAGE_PATH, pushToDrawDownSink: false)
+    let pid = getLastPositionId()
+
+    let available = getAvailableBalance(
+        pid: pid,
+        vaultIdentifier: MOET_TOKEN_IDENTIFIER,
+        pullFromTopUpSource: false,
+        beFailed: false
+    )
+
+    // Borrow the exact amount returned by availableBalance
+    borrowFromPosition(
+        signer: user,
+        positionId: pid,
+        tokenTypeIdentifier: MOET_TOKEN_IDENTIFIER,
+        vaultStoragePath: MOET.VaultStoragePath,
+        amount: available,
+        beFailed: false
+    )
+
+    // Health should be >= minHealth (1.1)
+    let health = getPositionHealth(pid: pid, beFailed: false)
+    Test.assert(health >= 1.1,
+        message: "Health after borrowing full availableBalance should be >= 1.1, got \(health)")
+}
+