refactor(dedup): extract self-duplicated helpers in three src/ files

Tackles the in-file copy-paste duplications SonarQube flagged on
`sql-utilities`, narrowing the dedup target to the cases where the
extraction is a clear readability win.

- `LinqToSql.Converters.ReverseConverterExtensions`: the three
  `ToLinqQueryBreakdown` overloads (SqlServer / PostgreSql / Snowflake)
  had identical 26-line bodies. Routes all three through a single
  `BuildLinqBreakdownFrom(QueryBreakdown)` private helper — works
  because Snowflake/PostgreSql `QueryBreakdown` derive from the
  SqlServer one, so the parameter type accepts all three. Public API
  preserved.

- `Markdown.Expressions.ExpressionGenerator`: `VisitInExpression` and
  `VisitNotInExpression` had identical 18-line bodies differing only in
  the "IN"/"NOT IN" label. Both now delegate to a new private
  `RenderInList(label, searchExpression, values)`.

- `PostgreSql.Statements.StatementExpressionParser`: the qualified-
  column-name building loop and the column-id switch were duplicated
  across `HandleStringToken` (qualified-column branch) and
  `GrabColumnExpression`. Extracted to a shared
  `BuildQualifiedColumnExpression(seededBuilder, reader)` private helper.

Deliberately *not* refactored: `PostgreSql.Statements.StatementReader`'s
`<` / `>` operator handlers, which Sonar also flags as duplicate. The
shared pattern there is a structural sequence of "MovePosition;
character check; emit Token; return" repeated across single-/two-char
operator variants; folding it into a helper would replace four short,
self-explanatory inline checks with `TryMatchTwoCharOperator('=', ...)`
indirection that obscures what each branch actually emits. The dedup
isn't worth the readability tax.

All 1180 tests stay green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Strata.SqlTools.LinqToSql/Converters/ReverseConverterExtensions.cs

@@ -19,29 +19,7 @@ public static class ReverseConverterExtensions
     public static LinqQueryBreakdown ToLinqQueryBreakdown(this QueryBreakdown breakdown)
     {
         ArgumentNullException.ThrowIfNull(breakdown);
-
+        return BuildLinqBreakdownFrom(breakdown);
-        var linq = new LinqQueryBreakdown(
-            breakdown.SelectClause?.Clause ?? "*",
-            breakdown.FromClause?.Clause ?? string.Empty,
-            breakdown.WhereClause?.Clause ?? string.Empty
-        );
-
-        if (!string.IsNullOrWhiteSpace(breakdown.GroupByClause?.Clause))
-        {
-            linq.GroupByClause.Clause = breakdown.GroupByClause.Clause;
-        }
-
-        if (!string.IsNullOrWhiteSpace(breakdown.HavingClause?.Clause))
-        {
-            linq.HavingClause.Clause = breakdown.HavingClause.Clause;
-        }
-
-        if (!string.IsNullOrWhiteSpace(breakdown.OrderByClause?.Clause))
-        {
-            linq.OrderByClause.Clause = breakdown.OrderByClause.Clause;
-        }
-
-        return linq;
     }
 
     /// <summary>
@@ -52,29 +30,7 @@ public static class ReverseConverterExtensions
     public static LinqQueryBreakdown ToLinqQueryBreakdown(this PostgreSqlBreakdown breakdown)
     {
         ArgumentNullException.ThrowIfNull(breakdown);
-
+        return BuildLinqBreakdownFrom(breakdown);
-        var linq = new LinqQueryBreakdown(
-            breakdown.SelectClause?.Clause ?? "*",
-            breakdown.FromClause?.Clause ?? string.Empty,
-            breakdown.WhereClause?.Clause ?? string.Empty
-        );
-
-        if (!string.IsNullOrWhiteSpace(breakdown.GroupByClause?.Clause))
-        {
-            linq.GroupByClause.Clause = breakdown.GroupByClause.Clause;
-        }
-
-        if (!string.IsNullOrWhiteSpace(breakdown.HavingClause?.Clause))
-        {
-            linq.HavingClause.Clause = breakdown.HavingClause.Clause;
-        }
-
-        if (!string.IsNullOrWhiteSpace(breakdown.OrderByClause?.Clause))
-        {
-            linq.OrderByClause.Clause = breakdown.OrderByClause.Clause;
-        }
-
-        return linq;
     }
 
     /// <summary>
@@ -85,7 +41,13 @@ public static class ReverseConverterExtensions
     public static LinqQueryBreakdown ToLinqQueryBreakdown(this SnowflakeBreakdown breakdown)
     {
         ArgumentNullException.ThrowIfNull(breakdown);
+        return BuildLinqBreakdownFrom(breakdown);
+    }
 
+    // Shared body — PostgreSql/Snowflake QueryBreakdown derive from SqlServer.QueryBreakdown,
+    // so all three public overloads can flow through this single helper.
+    private static LinqQueryBreakdown BuildLinqBreakdownFrom(QueryBreakdown breakdown)
+    {
         var linq = new LinqQueryBreakdown(
             breakdown.SelectClause?.Clause ?? "*",
             breakdown.FromClause?.Clause ?? string.Empty,

src/Strata.SqlTools.Markdown/Expressions/ExpressionGenerator.cs

@@ -485,37 +485,23 @@ public class ExpressionGenerator : IVisitor<string>
     }
 
     public string VisitInExpression(InExpression inExpression)
-    {
+        => RenderInList("IN", inExpression.SearchExpression, inExpression.ValuesToCompare);
-        var sb = new StringBuilder();
-        sb.AppendLine($"{Indent()}IN:");
-        _indentLevel++;
-        sb.AppendLine($"{Indent()}Search Expression:");
-        _indentLevel++;
-        sb.AppendLine(inExpression.SearchExpression.Accept(this));
-        _indentLevel--;
-        sb.AppendLine($"{Indent()}Values:");
-        _indentLevel++;
-        foreach (var value in inExpression.ValuesToCompare)
-        {
-            sb.AppendLine(value.Accept(this));
-        }
-        _indentLevel--;
-        _indentLevel--;
-        return sb.ToString();
-    }
 
     public string VisitNotInExpression(NotInExpression inExpression)
+        => RenderInList("NOT IN", inExpression.SearchExpression, inExpression.ValuesToCompare);
+
+    private string RenderInList(string label, Expression searchExpression, IEnumerable<Expression> values)
     {
         var sb = new StringBuilder();
-        sb.AppendLine($"{Indent()}NOT IN:");
+        sb.AppendLine($"{Indent()}{label}:");
         _indentLevel++;
         sb.AppendLine($"{Indent()}Search Expression:");
         _indentLevel++;
-        sb.AppendLine(inExpression.SearchExpression.Accept(this));
+        sb.AppendLine(searchExpression.Accept(this));
         _indentLevel--;
         sb.AppendLine($"{Indent()}Values:");
         _indentLevel++;
-        foreach (var value in inExpression.ValuesToCompare)
+        foreach (var value in values)
         {
             sb.AppendLine(value.Accept(this));
         }

src/Strata.SqlTools.PostgreSql/Statements/StatementExpressionParser.cs

@@ -121,39 +121,7 @@ public class StatementExpressionParser : SqlServerStatementExpressionParser
         // Check if this is a qualified column name (e.g., users.id)
         if (reader.TokenType == TokenType.Operator && reader.TokenValue == ".")
         {
-            // Build a qualified column expression using StringBuilder for performance
+            return BuildQualifiedColumnExpression(new System.Text.StringBuilder(startingToken), reader);
-            var columnBuilder = new System.Text.StringBuilder(startingToken);
-            while (reader.TokenType == TokenType.Operator && reader.TokenValue == ".")
-            {
-                reader.Read(); // Skip the dot
-
-                if (reader.TokenType == TokenType.String || reader.TokenType == TokenType.ColumnIdentifier)
-                {
-                    columnBuilder.Append('.').Append(reader.TokenValue);
-                    reader.Read();
-                }
-                else
-                {
-                    throw new InvalidSyntaxException(
-                        $"Invalid syntax at position {reader.Position}. Expected column identifier after dot.");
-                }
-            }
-
-            var columnToken = columnBuilder.ToString();
-
-            // Return a column expression for the qualified name
-            var dataColumnId = GetColumnIdFromToken(columnToken);
-            var tableSource = new RegisteredTableSource(1001, "FW", "DEPARTMENT", "DEPT");
-            return dataColumnId switch
-            {
-                1 => new RegisteredTableColumnExpression(dataColumnId, "DEPARTMENT_ID", tableSource),
-                2 => new RegisteredTableColumnExpression(dataColumnId, "NAME", tableSource),
-                3 => new RegisteredTableColumnExpression(dataColumnId, "REVENUE", tableSource),
-                4 => new RegisteredTableColumnExpression(dataColumnId, "DISCHARGE_DATE", tableSource),
-                586883 => new RegisteredTableColumnExpression(dataColumnId, "FIXED_COST", tableSource),
-                586664 => new RegisteredTableColumnExpression(dataColumnId, "VARIABLE_COST", tableSource),
-                _ => new RegisteredTableColumnExpression(dataColumnId, GetDefaultColumnName(columnToken), tableSource)
-            };
         }
 
         // Not a qualified column, treat as a string expression
@@ -182,9 +150,14 @@ public class StatementExpressionParser : SqlServerStatementExpressionParser
     {
         var columnBuilder = new System.Text.StringBuilder(reader.TokenValue);
         reader.Read();
+        return BuildQualifiedColumnExpression(columnBuilder, reader);
+    }
 
-        // Handle qualified names: table.column, "Table"."Column", etc.
+    // Consumes dot-separated identifier segments from the reader, appending each to the seeded builder,
-        // Keep reading while we see dot-separated identifiers
+    // then maps the resulting qualified name to a RegisteredTableColumnExpression. Shared between
+    // HandleStringToken (qualified column path) and GrabColumnExpression (entry-point path).
+    private RegisteredTableColumnExpression BuildQualifiedColumnExpression(System.Text.StringBuilder columnBuilder, IStatementReader reader)
+    {
         while (reader.TokenType == TokenType.Operator && reader.TokenValue == ".")
         {
             reader.Read(); // Skip the dot
@@ -202,8 +175,6 @@ public class StatementExpressionParser : SqlServerStatementExpressionParser
         }
 
         var columnToken = columnBuilder.ToString();
-
-        // Use base implementation to get the column expression
         var dataColumnId = GetColumnIdFromToken(columnToken);
         var tableSource = new RegisteredTableSource(1001, "FW", "DEPARTMENT", "DEPT");
         return dataColumnId switch