fix(wallet): correct Platform-to-Shielded Max calculation

DashWallet/Sources/Infrastructure/SwiftDashSDK/PlatformAddressSyncCoordinator.swift

@@ -406,6 +406,26 @@ public final class PlatformAddressSyncCoordinator: NSObject, ObservableObject {
 
     // MARK: - Core ↔ Platform balance movement
 
+    /// SDK-owned affordability preflight for Platform Payment → Shielded.
+    ///
+    /// The Platform balance shown by this coordinator is the sum of every
+    /// derived address, but the shield transition can only spend the suffix
+    /// selected by the Rust wallet. Keep that selection rule in the SDK and
+    /// expose its exact result to the internal-transfer UI instead of
+    /// reimplementing it from `derivedAddresses` here.
+    public func preflightShield(
+        paymentAccount: UInt32 = 0
+    ) async throws -> PlatformWalletManager.ShieldedShieldPreflight {
+        guard isRunning,
+              let manager = walletManager,
+              let walletId = wallet?.walletId
+        else { throw SendError.coordinatorNotReady }
+
+        return try await manager.shieldedShieldPreflight(
+            walletId: walletId,
+            paymentAccount: paymentAccount)
+    }
+
     /// Preflight of the full-balance Platform → Core withdrawal for the
     /// account holding the highest Platform address balance (the same
     /// account `transfer` spends from). See `withdrawAllToCore` for why

DashWallet/Sources/UI/Payments/InternalTransfer/InternalTransferConfirmSheet.swift

@@ -40,10 +40,15 @@ struct InternalTransferConfirmSheet: View {
     /// Shielded reverse routes only: execute the note-aware Max plan and
     /// revalidate it immediately before proving.
     var isFullShieldedSweep: Bool = false
+    /// Frozen with the submitted amount so a capacity refresh can update only
+    /// a value the user explicitly derived via Platform Shield Max.
+    var platformShieldAmountWasMax: Bool = false
     var onCancel: () -> Void
     var onCompleted: () -> Void
+    var onPlatformShieldCapacityChanged: (UInt64?, Bool) -> Void
 
     @StateObject private var coordinator = ShieldedTransferCoordinator()
+    @State private var handledPlatformShieldCapacityChange = false
 
     var body: some View {
         VStack(spacing: 0) {
@@ -67,6 +72,9 @@ struct InternalTransferConfirmSheet: View {
         }
         .background(Color.dash.primaryBackground)
         .interactiveDismissDisabled(isInFlight)
+        .onChange(of: coordinator.phase) { phase in
+            handlePlatformShieldCapacityChange(phase)
+        }
     }
 
     private var isInFlight: Bool {
@@ -483,6 +491,21 @@ struct InternalTransferConfirmSheet: View {
         coordinator.reset()
         confirm()
     }
+
+    private func handlePlatformShieldCapacityChange(
+        _ phase: ShieldedTransferCoordinator.Phase
+    ) {
+        guard !handledPlatformShieldCapacityChange,
+              case .failed = phase,
+              let error = coordinator.lastFailure as? ShieldedTransferCoordinator.CoordinatorError,
+              case .platformShieldCapacityChanged(let maxShieldableCredits) = error
+        else { return }
+
+        handledPlatformShieldCapacityChange = true
+        onPlatformShieldCapacityChanged(
+            maxShieldableCredits,
+            platformShieldAmountWasMax)
+    }
 }
 
 /// Recovery sheet for a stuck "to Shielded" transfer (Core→Shielded). The

DashWallet/Sources/UI/Payments/InternalTransfer/InternalTransferScreen.swift

@@ -6,6 +6,22 @@
 import SwiftUI
 import DashUIKit
 
+/// Immutable values the user saw when tapping Continue. Async balance/preflight
+/// refreshes may keep updating the form underneath the sheet, but they must not
+/// rewrite the amount already presented for confirmation.
+private struct InternalTransferConfirmation: Identifiable {
+    let id = UUID()
+    let route: InternalTransferRoute
+    let dashDuffs: Int64
+    let amountDuffsUnsigned: UInt64
+    let creditsAmount: UInt64
+    let fiatText: String
+    let withdrawalFeeCredits: UInt64?
+    let isFullPlatformWithdrawal: Bool
+    let isFullShieldedSweep: Bool
+    let platformShieldAmountWasMax: Bool
+}
+
 struct InternalTransferScreen: View {
     @ObservedObject var viewModel: InternalTransferViewModel
 
@@ -30,7 +46,7 @@ struct InternalTransferScreen: View {
     /// precedence over `receiveInto`.
     var sendFrom: ChainNetwork? = nil
 
-    @State private var showConfirm: Bool = false
+    @State private var confirmation: InternalTransferConfirmation?
 
     var body: some View {
         VStack(spacing: 0) {
@@ -77,20 +93,27 @@ struct InternalTransferScreen: View {
             keyboardSection
         }
         .background(Color.dash.primaryBackground)
-        .sheet(isPresented: $showConfirm) {
+        .sheet(item: $confirmation) { submission in
             InternalTransferConfirmSheet(
-                route: viewModel.route,
-                dashDuffs: viewModel.dashDuffs,
-                amountDuffsUnsigned: viewModel.dashDuffsUnsigned,
-                creditsAmount: viewModel.creditsPreview,
-                fiatText: viewModel.fiatAmountString,
-                withdrawalFeeCredits: viewModel.withdrawalPreflight?.estimatedFee,
-                isFullPlatformWithdrawal: viewModel.isFullPlatformWithdrawal,
-                isFullShieldedSweep: viewModel.isFullShieldedSweep,
-                onCancel: { showConfirm = false },
+                route: submission.route,
+                dashDuffs: submission.dashDuffs,
+                amountDuffsUnsigned: submission.amountDuffsUnsigned,
+                creditsAmount: submission.creditsAmount,
+                fiatText: submission.fiatText,
+                withdrawalFeeCredits: submission.withdrawalFeeCredits,
+                isFullPlatformWithdrawal: submission.isFullPlatformWithdrawal,
+                isFullShieldedSweep: submission.isFullShieldedSweep,
+                platformShieldAmountWasMax: submission.platformShieldAmountWasMax,
+                onCancel: { confirmation = nil },
                 onCompleted: {
-                    showConfirm = false
+                    confirmation = nil
                     onCompleted()
+                },
+                onPlatformShieldCapacityChanged: { maxCredits, amountWasMax in
+                    confirmation = nil
+                    viewModel.handlePlatformShieldCapacityChanged(
+                        maxShieldableCredits: maxCredits,
+                        submittedAmountWasMax: amountWasMax)
                 })
                 .presentationDetents([.large])
                 .presentationDragIndicator(.hidden)
@@ -133,7 +156,7 @@ struct InternalTransferScreen: View {
             actionButtonText: NSLocalizedString("Continue", comment: ""),
             actionEnabled: viewModel.canContinue,
             inProgress: false,
-            actionHandler: { showConfirm = true }
+            actionHandler: presentConfirmation
         )
         .padding(.top, 12)
         .padding(.horizontal, 16)
@@ -143,6 +166,20 @@ struct InternalTransferScreen: View {
         .background(Color.dash.secondaryBackground, ignoresSafeAreaEdges: .bottom)
     }
 
+    private func presentConfirmation() {
+        guard viewModel.canContinue else { return }
+        confirmation = InternalTransferConfirmation(
+            route: viewModel.route,
+            dashDuffs: viewModel.dashDuffs,
+            amountDuffsUnsigned: viewModel.dashDuffsUnsigned,
+            creditsAmount: viewModel.creditsPreview,
+            fiatText: viewModel.fiatAmountString,
+            withdrawalFeeCredits: viewModel.withdrawalPreflight?.estimatedFee,
+            isFullPlatformWithdrawal: viewModel.isFullPlatformWithdrawal,
+            isFullShieldedSweep: viewModel.isFullShieldedSweep,
+            platformShieldAmountWasMax: viewModel.platformShieldAmountWasMax)
+    }
+
     // MARK: - From / To cards
 
     @ViewBuilder