fix: prevent TUI crash from NaN/infinite float formatting

- Add is_finite() checks before formatting all float values
- Handle NaN and infinite values by defaulting to 0.0
- Fixes crash when pressing Tab with invalid financial data
- Ensures robust handling of edge cases in calculations

This prevents the "formatting trait implementation returned an error"
panic when displaying views with invalid floating point values.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

2 files changed, 18 insertions, 12 deletions

diff --git a/src/tui/dashboard.rs b/src/tui/dashboard.rs
index 5eed457..3c4d979 100644
--- a/src/tui/dashboard.rs
+++ b/src/tui/dashboard.rs
@@ -52,7 +52,7 @@ fn draw_net_worth(f: &mut Frame, app: &App, area: Rect) {
         Line::from(vec![
             Span::raw("$"),
             Span::styled(
-                format!("{:.0}", app.net_worth),
+                format!("{:.0}", if app.net_worth.is_finite() { app.net_worth } else { 0.0 }),
                 Style::default()
                     .fg(Color::Green)
                     .add_modifier(Modifier::BOLD),
@@ -60,13 +60,16 @@ fn draw_net_worth(f: &mut Frame, app: &App, area: Rect) {
         ]),
         Line::from(vec![
             Span::styled(
-                format!("↑ ${:.0} ({:+.1}%)", net_worth_change, change_pct),
+                format!("↑ ${:.0} ({:+.1}%)", 
+                    if net_worth_change.is_finite() { net_worth_change } else { 0.0 },
+                    if change_pct.is_finite() { change_pct } else { 0.0 }
+                ),
                 Style::default().fg(Color::Green),
             ),
         ]),
         Line::from(""),
-        Line::from(format!("💵 Cash:   ${:.0}", app.cash_balance)),
-        Line::from(format!("📈 Invest: ${:.0}", app.investment_balance)),
+        Line::from(format!("💵 Cash:   ${:.0}", if app.cash_balance.is_finite() { app.cash_balance } else { 0.0 })),
+        Line::from(format!("📈 Invest: ${:.0}", if app.investment_balance.is_finite() { app.investment_balance } else { 0.0 })),
     ];
     
     let net_worth = Paragraph::new(net_worth_text)
@@ -108,7 +111,7 @@ fn draw_cash_flow(f: &mut Frame, app: &App, area: Rect) {
         .block(Block::default())
         .gauge_style(Style::default().fg(Color::Green))
         .ratio(income_ratio)
-        .label(format!("Income: ${:.0}", app.income));
+        .label(format!("Income: ${:.0}", if app.income.is_finite() { app.income } else { 0.0 }));
     
     // Expenses bar
     let expense_ratio = if max_value > 0.0 { app.expenses / max_value } else { 0.0 };
@@ -116,7 +119,7 @@ fn draw_cash_flow(f: &mut Frame, app: &App, area: Rect) {
         .block(Block::default())
         .gauge_style(Style::default().fg(Color::Red))
         .ratio(expense_ratio)
-        .label(format!("Expenses: ${:.0}", app.expenses));
+        .label(format!("Expenses: ${:.0}", if app.expenses.is_finite() { app.expenses } else { 0.0 }));
     
     // Net bar
     let net_ratio = if max_value > 0.0 { net.abs() / max_value } else { 0.0 };
@@ -124,7 +127,7 @@ fn draw_cash_flow(f: &mut Frame, app: &App, area: Rect) {
         .block(Block::default())
         .gauge_style(Style::default().fg(if net >= 0.0 { Color::Cyan } else { Color::Magenta }))
         .ratio(net_ratio)
-        .label(format!("Net: {:+.0}", net));
+        .label(format!("Net: {:+.0}", if net.is_finite() { net } else { 0.0 }));
     
     // Render frame and gauges
     let frame = Block::default()
diff --git a/src/tui/ui.rs b/src/tui/ui.rs
index dba989a..ceb66b4 100644
--- a/src/tui/ui.rs
+++ b/src/tui/ui.rs
@@ -132,7 +132,7 @@ fn draw_budgets(f: &mut Frame, app: &App, area: Rect) {
             Line::from(vec![
                 Span::raw(format!("{:<15} ", category)),
                 Span::styled(bar, Style::default().fg(status_color)),
-                Span::raw(format!(" ${:.0}/${:.0}", spent, budget)),
+                Span::raw(format!(" ${:.0}/${:.0}", spent.max(0.0), budget.max(0.0))),
             ])
         })
         .collect();
@@ -152,12 +152,15 @@ fn draw_investments(f: &mut Frame, app: &App, area: Rect) {
     let gain_pct = if total_book > 0.0 { (total_gain / total_book) * 100.0 } else { 0.0 };
     
     let investment_text = vec![
-        Line::from(format!("Total Market Value: ${:.2}", total_value)),
-        Line::from(format!("Total Book Value:   ${:.2}", total_book)),
+        Line::from(format!("Total Market Value: ${:.2}", if total_value.is_finite() { total_value } else { 0.0 })),
+        Line::from(format!("Total Book Value:   ${:.2}", if total_book.is_finite() { total_book } else { 0.0 })),
         Line::from(vec![
             Span::raw("Unrealized Gain:    "),
             Span::styled(
-                format!("${:.2} ({:+.1}%)", total_gain, gain_pct),
+                format!("${:.2} ({:+.1}%)", 
+                    if total_gain.is_finite() { total_gain } else { 0.0 }, 
+                    if gain_pct.is_finite() { gain_pct } else { 0.0 }
+                ),
                 Style::default().fg(if total_gain >= 0.0 { Color::Green } else { Color::Red }),
             ),
         ]),
@@ -171,7 +174,7 @@ fn draw_investments(f: &mut Frame, app: &App, area: Rect) {
             "  {} ({:?}): ${:.2}",
             portfolio.account_id,
             portfolio.account_type,
-            portfolio.total_market_value
+            if portfolio.total_market_value.is_finite() { portfolio.total_market_value } else { 0.0 }
         )));
     }