Add wait stats benefit scoring (Stage 2)

src/PlanViewer.App/Controls/PlanViewerControl.axaml.cs

@@ -377,7 +377,7 @@ private void RenderStatement(PlanStatement statement)
         // Update banners
         ShowMissingIndexes(statement.MissingIndexes);
         ShowParameters(statement);
-        ShowWaitStats(statement.WaitStats, statement.QueryTimeStats != null);
+        ShowWaitStats(statement.WaitStats, statement.WaitBenefits, statement.QueryTimeStats != null);
         ShowRuntimeSummary(statement);
         UpdateInsightsHeader();
 
@@ -2635,7 +2635,7 @@ private static long GetChildElapsedMsSum(PlanNode node)
         return sum;
     }
 
-    private void ShowWaitStats(List<WaitStatInfo> waits, bool isActualPlan)
+    private void ShowWaitStats(List<WaitStatInfo> waits, List<WaitBenefit> benefits, bool isActualPlan)
     {
         WaitStatsContent.Children.Clear();
 
@@ -2651,6 +2651,11 @@ private void ShowWaitStats(List<WaitStatInfo> waits, bool isActualPlan)
 
         WaitStatsEmpty.IsVisible = false;
 
+        // Build benefit lookup
+        var benefitLookup = new Dictionary<string, double>(StringComparer.OrdinalIgnoreCase);
+        foreach (var wb in benefits)
+            benefitLookup[wb.WaitType] = wb.MaxBenefitPercent;
+
         var sorted = waits.OrderByDescending(w => w.WaitTimeMs).ToList();
         var maxWait = sorted[0].WaitTimeMs;
         var totalWait = sorted.Sum(w => w.WaitTimeMs);
@@ -2659,10 +2664,10 @@ private void ShowWaitStats(List<WaitStatInfo> waits, bool isActualPlan)
         WaitStatsHeader.Text = $"  Wait Stats \u2014 {totalWait:N0}ms total";
 
         // Build a single Grid for all rows so columns align
-        // Name and duration auto-size; bar fills remaining space
+        // Name, bar, duration, and benefit columns
         var grid = new Grid
         {
-            ColumnDefinitions = new ColumnDefinitions("Auto,*,Auto")
+            ColumnDefinitions = new ColumnDefinitions("Auto,*,Auto,Auto")
         };
         for (int i = 0; i < sorted.Count; i++)
             grid.RowDefinitions.Add(new RowDefinition(GridLength.Auto));
@@ -2709,11 +2714,27 @@ private void ShowWaitStats(List<WaitStatInfo> waits, bool isActualPlan)
                 FontSize = 12,
                 Foreground = new SolidColorBrush(Color.Parse("#E4E6EB")),
                 VerticalAlignment = VerticalAlignment.Center,
-                Margin = new Thickness(0, 2, 0, 2)
+                Margin = new Thickness(0, 2, 8, 2)
             };
             Grid.SetRow(durationText, i);
             Grid.SetColumn(durationText, 2);
             grid.Children.Add(durationText);
+
+            // Benefit % (if available)
+            if (benefitLookup.TryGetValue(w.WaitType, out var benefitPct) && benefitPct > 0)
+            {
+                var benefitText = new TextBlock
+                {
+                    Text = $"up to {benefitPct:N0}%",
+                    FontSize = 11,
+                    Foreground = new SolidColorBrush(Color.Parse("#8b949e")),
+                    VerticalAlignment = VerticalAlignment.Center,
+                    Margin = new Thickness(0, 2, 0, 2)
+                };
+                Grid.SetRow(benefitText, i);
+                Grid.SetColumn(benefitText, 3);
+                grid.Children.Add(benefitText);
+            }
         }
 
         WaitStatsContent.Children.Add(grid);

src/PlanViewer.Core/Models/PlanModels.cs

@@ -62,6 +62,7 @@ public class PlanStatement
     public SetOptionsInfo? SetOptions { get; set; }
     public List<PlanParameter> Parameters { get; set; } = new();
     public List<WaitStatInfo> WaitStats { get; set; } = new();
+    public List<WaitBenefit> WaitBenefits { get; set; } = new();
     public QueryTimeInfo? QueryTimeStats { get; set; }
 
     // MaxQueryMemory + QueryPlan-level warnings
@@ -447,6 +448,13 @@ public class PlanParameter
     public string? RuntimeValue { get; set; }
 }
 
+public class WaitBenefit
+{
+    public string WaitType { get; set; } = "";
+    public double MaxBenefitPercent { get; set; }
+    public string Category { get; set; } = "";
+}
+
 public class WaitStatInfo
 {
     public string WaitType { get; set; } = "";

src/PlanViewer.Core/Output/AnalysisResult.cs

@@ -139,6 +139,10 @@ public class StatementResult
     [JsonPropertyName("wait_stats")]
     public List<WaitStatResult> WaitStats { get; set; } = new();
 
+    // Wait stats benefit analysis
+    [JsonPropertyName("wait_benefits")]
+    public List<WaitBenefitResult> WaitBenefits { get; set; } = new();
+
     // Cursor metadata
     [JsonPropertyName("cursor")]
     public CursorResult? Cursor { get; set; }
@@ -353,6 +357,18 @@ public class WaitStatResult
     public long WaitCount { get; set; }
 }
 
+public class WaitBenefitResult
+{
+    [JsonPropertyName("wait_type")]
+    public string WaitType { get; set; } = "";
+
+    [JsonPropertyName("max_benefit_percent")]
+    public double MaxBenefitPercent { get; set; }
+
+    [JsonPropertyName("category")]
+    public string Category { get; set; } = "";
+}
+
 public class CursorResult
 {
     [JsonPropertyName("name")]

src/PlanViewer.Core/Output/HtmlExporter.cs

@@ -391,14 +391,22 @@ private static void WriteWaitStatsCard(StringBuilder sb, StatementResult stmt, b
         sb.AppendLine("<div class=\"card-body\">");
         if (stmt.WaitStats.Count > 0)
         {
+            // Build benefit lookup
+            var benefitLookup = new Dictionary<string, double>(StringComparer.OrdinalIgnoreCase);
+            foreach (var wb in stmt.WaitBenefits)
+                benefitLookup[wb.WaitType] = wb.MaxBenefitPercent;
+
             var maxWait = stmt.WaitStats.Max(w => w.WaitTimeMs);
             foreach (var w in stmt.WaitStats.OrderByDescending(w => w.WaitTimeMs))
             {
                 var barPct = maxWait > 0 ? (double)w.WaitTimeMs / maxWait * 100 : 0;
+                var benefitTag = benefitLookup.TryGetValue(w.WaitType, out var pct)
+                    ? $" <span class=\"warn-benefit\">up to {pct:N0}%</span>"
+                    : "";
                 sb.AppendLine("<div class=\"wait-row\">");
                 sb.AppendLine($"<span class=\"wait-type\">{Encode(w.WaitType)}</span>");
                 sb.AppendLine($"<div class=\"wait-bar-container\"><div class=\"wait-bar\" style=\"width:{barPct:F0}%\"></div></div>");
-                sb.AppendLine($"<span class=\"wait-ms\">{w.WaitTimeMs:N0} ms</span>");
+                sb.AppendLine($"<span class=\"wait-ms\">{w.WaitTimeMs:N0} ms{benefitTag}</span>");
                 sb.AppendLine("</div>");
             }
         }

src/PlanViewer.Core/Output/ResultMapper.cs

@@ -129,6 +129,17 @@ private static StatementResult MapStatement(PlanStatement stmt)
             });
         }
 
+        // Wait stat benefits
+        foreach (var wb in stmt.WaitBenefits)
+        {
+            result.WaitBenefits.Add(new WaitBenefitResult
+            {
+                WaitType = wb.WaitType,
+                MaxBenefitPercent = wb.MaxBenefitPercent,
+                Category = wb.Category
+            });
+        }
+
         // Parameters — flag potential sniffing issues
         foreach (var p in stmt.Parameters)
         {

src/PlanViewer.Core/Output/TextFormatter.cs

@@ -131,8 +131,18 @@ public static void WriteText(AnalysisResult result, TextWriter writer)
             if (stmt.WaitStats.Count > 0)
             {
                 writer.WriteLine("Wait stats:");
+                // Build a lookup from wait type to benefit %
+                var benefitLookup = new Dictionary<string, double>(StringComparer.OrdinalIgnoreCase);
+                foreach (var wb in stmt.WaitBenefits)
+                    benefitLookup[wb.WaitType] = wb.MaxBenefitPercent;
+
                 foreach (var w in stmt.WaitStats.OrderByDescending(w => w.WaitTimeMs))
-                    writer.WriteLine($"  {w.WaitType}: {w.WaitTimeMs:N0}ms");
+                {
+                    var benefitTag = benefitLookup.TryGetValue(w.WaitType, out var pct)
+                        ? $" (up to {pct:N0}% benefit)"
+                        : "";
+                    writer.WriteLine($"  {w.WaitType}: {w.WaitTimeMs:N0}ms{benefitTag}");
+                }
             }
 
             if (stmt.Parameters.Count > 0)