feat: Introduce Hashline encoding/validation, implement core REPL and chat session logic, and establish initial project structure with a license and editor configuration.

Hashline/HashlineEncoder.cs

@@ -71,6 +71,8 @@ internal static class HashlineEncoder
     /// Computes a short file-level fingerprint: XOR of all per-line hashes (as bytes).
     /// Useful for cheap full-file staleness checks.
     /// </summary>
+    /// <param name="lines">All lines of the file (without trailing newlines).</param>
+    /// <returns>A 2-character hex fingerprint.</returns>
     public static string FileFingerprint(string[] lines)
     {
         int fp = 0;

Hashline/HashlineValidator.cs

@@ -83,6 +83,13 @@ internal static class HashlineValidator
     /// <summary>
     /// Validates both a start and end anchor, and ensures start &lt;= end.
     /// </summary>
+    /// <param name="startAnchor">The starting anchor string.</param>
+    /// <param name="endAnchor">The ending anchor string.</param>
+    /// <param name="lines">Current file lines (without newlines).</param>
+    /// <param name="startIndex">Resolved 0-based start index on success.</param>
+    /// <param name="endIndex">Resolved 0-based end index on success.</param>
+    /// <param name="error">Human-readable error message on failure.</param>
+    /// <returns>True if the range is valid; false otherwise.</returns>
     public static bool TryResolveRange(
         string startAnchor,
         string endAnchor,