AddStatement now passes runtime context for custom handlers

YesNt.Interpreter/Runtime/IStatementContext.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+
+namespace YesNt.Interpreter.Runtime;
+
+/// <summary>
+/// Exposes the script runtime state accessible to custom statement handlers registered
+/// via <see cref="YesNtInterpreter.AddStatement"/>.
+/// </summary>
+public interface IStatementContext
+{
+    /// <summary>Gets the local variable table for the current scope.</summary>
+    Dictionary<string, string> Variables { get; }
+
+    /// <summary>Gets or sets the global variable table shared across all scopes.</summary>
+    Dictionary<string, string> GlobalVariables { get; set; }
+
+    /// <summary>Gets or sets the text of the line currently being processed.
+    /// Inline-substitution handlers (e.g. <c>%read_line</c>) write their result here.</summary>
+    string CurrentLine { get; set; }
+
+    /// <summary>Gets or sets the zero-based index of the next line to execute.
+    /// Set this to implement control-flow jumps inside a custom statement.</summary>
+    int LineNumber { get; set; }
+
+    /// <summary>Terminates execution with the given message.</summary>
+    /// <param name="message">The message written to debug output.</param>
+    /// <param name="isError">
+    /// <see langword="true"/> to signal an error termination;
+    /// <see langword="false"/> for a planned, non-error termination.
+    /// </param>
+    void Exit(string message, bool isError);
+}