fix: Bug #33 — wrong mint tooltip limits + silent decimal truncation

Two issues found during Gitter community testing (Apr 1 2026):

1. Tooltip showed generic wallet limits (0.00000001 to 999,999,999)
   instead of actual DD limits ($100-$100K for mint, $1-$100K for send).
   Root cause: AmountValidator was initialized with DGB satoshi ranges
   rather than DigiDollar consensus params.

2. Entering amounts with >2 decimal places (e.g. 9999.12345678) was
   silently truncated to 2 places via static_cast<CAmount>(amount*100)
   with no warning. Users saw 'Mint validation success' for the wrong
   amount.

Fixes across all 4 DD widgets (mint, send, redeem, positions):

- Add maxDecimals parameter to AmountValidator (default 8 for DGB
  backwards compat, 2 for all DD widgets)
- Validator now rejects >2 decimal places at input time — users
  literally cannot type a third decimal digit
- Update all tooltips/placeholders to show correct DD limits
- Replace static_cast truncation with std::llround() as defense-in-depth
- Change all DD formatDDAmount() from 'f',8 to 'f',2 (DD is cents)
- Fix 'Use available balance' buttons to fill 2 decimal places

Consensus params (unchanged): minMintAmount=10000 ($100),
maxMintAmount=10000000 ($100K), minOutputAmount=100 ($1).

Author: JaredTate

src/qt/digidollarmintwidget.cpp

@@ -97,8 +97,9 @@ void DigiDollarMintWidget::setupUI()
     m_mainLayout->setSpacing(0);
     m_mainLayout->setContentsMargins(0, 0, 0, 0);
 
-    // Create validators
-    m_amountValidator = new AmountValidator(0.00000001, 999999999.99999999, this);
+    // Create validators — DD amounts are in dollars with max 2 decimal places (cents)
+    // Mint limits: $100 minimum, $100,000 maximum (from consensus params)
+    m_amountValidator = new AmountValidator(100.00, 100000.00, 2, this);
 
     // Create horizontal layout for mint amount and lock period side-by-side
     QHBoxLayout* topLayout = new QHBoxLayout();
@@ -158,8 +159,8 @@ void DigiDollarMintWidget::setupMintAmountSection()
     m_amountEdit = new QLineEdit(this);
     m_amountEdit->setObjectName("amountEdit");
     m_amountEdit->setValidator(m_amountValidator);
-    m_amountEdit->setPlaceholderText("0.00000000");
-    m_amountEdit->setToolTip(tr("The amount of DigiDollar to mint.\n\nSupported formats:\n• 0.00000001 (minimum)\n• Up to 8 decimal places\n• Maximum: 999,999,999.99999999"));
+    m_amountEdit->setPlaceholderText("0.00");
+    m_amountEdit->setToolTip(tr("The amount of DigiDollar to mint.\n\n• Minimum: $100.00\n• Maximum: $100,000.00\n• Up to 2 decimal places (cents)"));
     m_amountEdit->setFocusPolicy(Qt::StrongFocus);
     m_amountEdit->setAttribute(Qt::WA_InputMethodEnabled, true);
     QFont monospaceFont = GUIUtil::fixedPitchFont();
@@ -759,8 +760,8 @@ void DigiDollarMintWidget::onMintClicked()
             return;
         }
 
-        // Convert amount from double to CAmount (cents)
-        CAmount ddAmountCents = static_cast<CAmount>(m_mintAmount * 100);
+        // Convert amount from double to CAmount (cents) — use llround to avoid truncation
+        CAmount ddAmountCents = static_cast<CAmount>(std::llround(m_mintAmount * 100));
 
         // Call the wallet model to mint DigiDollar
         WalletModel::DigiDollarMintResult result = m_walletModel->mintDigiDollar(ddAmountCents, m_selectedTier);
@@ -905,7 +906,7 @@ bool DigiDollarMintWidget::validateCollateral() const
 
 QString DigiDollarMintWidget::formatDDAmount(double amount) const
 {
-    return QString::number(amount, 'f', 8) + " DD";
+    return QString::number(amount, 'f', 2) + " DD";
 }
 
 QString DigiDollarMintWidget::formatDGBAmount(double amount) const

src/qt/digidollarpositionswidget.cpp

@@ -955,7 +955,7 @@ QWidget* DigiDollarPositionsWidget::createHealthWidget(double health) const
 
 QString DigiDollarPositionsWidget::formatDDAmount(double amount) const
 {
-    return QString::number(amount, 'f', 8) + " DD";
+    return QString::number(amount, 'f', 2) + " DD";
 }
 
 QString DigiDollarPositionsWidget::formatDGBAmount(double amount) const

src/qt/digidollarredeemwidget.cpp

@@ -101,7 +101,8 @@ void DigiDollarRedeemWidget::setupUI()
     m_mainLayout->setContentsMargins(0, 0, 0, 0);
 
     // Create validators
-    m_amountValidator = new AmountValidator(0.00000001, 999999999.99999999, this);
+    // DD amounts are in dollars with max 2 decimal places (cents precision)
+    m_amountValidator = new AmountValidator(1.00, 100000.00, 2, this);
 
     // Setup sections
     setupCoinControlSection();
@@ -539,18 +540,18 @@ void DigiDollarRedeemWidget::onRedeemClicked()
                          "Required: %2 DD\n\n"
                          "System health is below 100%, requiring additional DD to redeem.\n"
                          "You need %3 DD more to complete this redemption.")
-                .arg(QString::number(ddBalance, 'f', 8))
-                .arg(QString::number(requiredDDBurn, 'f', 8))
-                .arg(QString::number(requiredDDBurn - ddBalance, 'f', 8));
+                .arg(QString::number(ddBalance, 'f', 2))
+                .arg(QString::number(requiredDDBurn, 'f', 2))
+                .arg(QString::number(requiredDDBurn - ddBalance, 'f', 2));
         } else {
             // Normal redemption
             errorMsg = tr("Insufficient DigiDollars.\n\n"
                          "You have: %1 DD\n"
                          "Required: %2 DD\n\n"
                          "You need %3 DD more to redeem this position.")
-                .arg(QString::number(ddBalance, 'f', 8))
-                .arg(QString::number(requiredDDBurn, 'f', 8))
-                .arg(QString::number(requiredDDBurn - ddBalance, 'f', 8));
+                .arg(QString::number(ddBalance, 'f', 2))
+                .arg(QString::number(requiredDDBurn, 'f', 2))
+                .arg(QString::number(requiredDDBurn - ddBalance, 'f', 2));
         }
 
         Q_EMIT message(tr("Insufficient DigiDollar Balance"), errorMsg, QMessageBox::Warning);
@@ -569,7 +570,7 @@ void DigiDollarRedeemWidget::onRedeemClicked()
                         "Required DD burn: %3 DD")
             .arg(m_selectedPositionId)
             .arg(formatDDAmount(m_positionDDMinted))
-            .arg(QString::number(requiredDDBurn, 'f', 8));
+            .arg(QString::number(requiredDDBurn, 'f', 2));
     } else {
         confirmText = tr("Close vault %1 and redeem %2?")
             .arg(m_selectedPositionId)
@@ -594,8 +595,8 @@ void DigiDollarRedeemWidget::onRedeemClicked()
             return;
         }
 
-        // Convert amount from double to CAmount (cents)
-        CAmount amountCents = static_cast<CAmount>(amount * 100);
+        // Convert amount from double to CAmount (cents) — use llround to avoid truncation
+        CAmount amountCents = static_cast<CAmount>(std::llround(amount * 100));
 
         // Call the wallet model to redeem DigiDollar
         WalletModel::DigiDollarRedeemResult result = m_walletModel->redeemDigiDollar(m_selectedPositionId, amountCents, "");
@@ -807,7 +808,7 @@ void DigiDollarRedeemWidget::loadPositionDetails()
                     m_positionHealth = pos.find_value("health_ratio").get_real();
                     m_redeemableAmount = m_positionDDMinted; // Can redeem full amount
                     // Auto-fill the exact amount in the amount edit field
-                    m_amountEdit->setText(QString::number(m_positionDDMinted, 'f', 8));
+                    m_amountEdit->setText(QString::number(m_positionDDMinted, 'f', 2));
                     break;
                 }
             }
@@ -926,7 +927,7 @@ bool DigiDollarRedeemWidget::validateDDBalance() const
 
 QString DigiDollarRedeemWidget::formatDDAmount(double amount) const
 {
-    return QString::number(amount, 'f', 8) + " DD";
+    return QString::number(amount, 'f', 2) + " DD";
 }
 
 QString DigiDollarRedeemWidget::formatDGBAmount(double amount) const

src/qt/digidollarsendwidget.cpp

@@ -21,6 +21,7 @@
 #include <univalue.h>
 
 #include <chrono>
+#include <cmath>
 
 #include <QLabel>
 #include <QLineEdit>
@@ -112,7 +113,9 @@ void DigiDollarSendWidget::setupUI()
 
     // Create validators
     m_addressValidator = new DigiDollarAddressValidator(this);
-    m_amountValidator = new AmountValidator(0.00000001, 999999999.99999999, this);
+    // DD amounts are in dollars with max 2 decimal places (cents precision)
+    // Send limits: $1 minimum (dust threshold), $100,000 maximum
+    m_amountValidator = new AmountValidator(1.00, 100000.00, 2, this);
 
     // Setup sections
     setupCoinControlSection();
@@ -255,8 +258,8 @@ void DigiDollarSendWidget::setupAmountSection()
     m_amountEdit = new QLineEdit(this);
     m_amountEdit->setObjectName("amountEdit");
     m_amountEdit->setValidator(m_amountValidator);
-    m_amountEdit->setPlaceholderText("0.00000000");
-    m_amountEdit->setToolTip(tr("The amount to send in DigiDollar.\n\nSupported formats:\n• 0.00000001 (minimum)\n• Up to 8 decimal places\n• Maximum: 999,999,999.99999999"));
+    m_amountEdit->setPlaceholderText("0.00");
+    m_amountEdit->setToolTip(tr("The amount of DigiDollar to send.\n\n• Minimum: $1.00\n• Maximum: $100,000.00\n• Up to 2 decimal places (cents)"));
     m_amountEdit->setFocusPolicy(Qt::StrongFocus);
     m_amountEdit->setAttribute(Qt::WA_InputMethodEnabled, true);
     QFont monospaceFont = GUIUtil::fixedPitchFont();
@@ -660,7 +663,7 @@ void DigiDollarSendWidget::onUseAvailableBalanceClicked()
     // Users can send their ENTIRE DD balance without any deduction
     if (m_availableBalance > 0) {
         // Set amount to full available balance (fees are paid separately in DGB)
-        m_amountEdit->setText(QString::number(m_availableBalance, 'f', 8));
+        m_amountEdit->setText(QString::number(m_availableBalance, 'f', 2));
         onAmountChanged();
     }
 }
@@ -763,7 +766,7 @@ bool DigiDollarSendWidget::validateBalance() const
 
 QString DigiDollarSendWidget::formatDDAmount(double amount) const
 {
-    return QString::number(amount, 'f', 8) + " DD";
+    return QString::number(amount, 'f', 2) + " DD";
 }
 
 QString DigiDollarSendWidget::formatUSDAmount(double amount) const
@@ -916,7 +919,7 @@ void DigiDollarSendWidget::executeTransfer(const QString& address, double amount
     m_clearButton->setEnabled(false);
     m_useAvailableBalanceButton->setEnabled(false);
 
-    CAmount amountCents = static_cast<CAmount>(amount * 100);
+    CAmount amountCents = static_cast<CAmount>(std::llround(amount * 100));
     QString note = m_noteEdit ? m_noteEdit->text().trimmed() : QString();
 
     WalletModel::DigiDollarSendResult result = m_walletModel->sendDigiDollar(address, amountCents, note);
@@ -1310,8 +1313,8 @@ QString DigiDollarSendWidget::maskValue(const QString& value) const
 }
 
 // AmountValidator implementation
-AmountValidator::AmountValidator(double min, double max, QObject* parent) :
-    QValidator(parent), m_min(min), m_max(max)
+AmountValidator::AmountValidator(double min, double max, int maxDecimals, QObject* parent) :
+    QValidator(parent), m_min(min), m_max(max), m_maxDecimals(maxDecimals)
 {
 }
 
@@ -1334,10 +1337,10 @@ QValidator::State AmountValidator::validate(QString& input, int& pos) const
         return QValidator::Invalid;
     }
 
-    // Check decimal places (max 8)
+    // Check decimal places (max m_maxDecimals, default 8)
     int decimalPos = input.indexOf('.');
     if (decimalPos != -1) {
-        if (input.length() - decimalPos - 1 > 8) {
+        if (input.length() - decimalPos - 1 > m_maxDecimals) {
             return QValidator::Invalid;
         }
     }

src/qt/digidollarsendwidget.h

@@ -216,13 +216,14 @@ class AmountValidator : public QValidator
     Q_OBJECT
 
 public:
-    explicit AmountValidator(double min = 0.00000001, double max = 999999999.99999999, QObject* parent = nullptr);
+    explicit AmountValidator(double min = 0.00000001, double max = 999999999.99999999, int maxDecimals = 8, QObject* parent = nullptr);
 
     QValidator::State validate(QString& input, int& pos) const override;
 
 private:
     double m_min;
     double m_max;
+    int m_maxDecimals;
 };
 
 /**