Fix runtime crashes from missing bounds checks and swapped class files

[Copilot]

Several latent bugs across the codebase that would cause runtime exceptions under certain inputs, plus a class/filename mismatch that would silently break refactoring and tooling.

Bugs Fixed

• Signal.cs — IndexOutOfRangeException in array-subscript parsing loops: Inner while loops incremented the outer for loop variable i to consume dot-split parts without ever checking bounds. Cached the split result and added an early break on bounds overflow:

  // Before
  p1 = Unescape(Escape(LocalName).Split('.')[i]); // no bounds check
  
  // After
  var localNameParts = Escape(LocalName).Split('.');
  if (i >= localNameParts.Length) break;
  p1 = Unescape(localNameParts[i]);

• Signal.cs — IndexOutOfRangeException on empty strings: Three sites accessed p1[0] / pNe[0] without guarding against empty strings. Added p1.Length > 0 && guards.

• BaseOperationOrSignal.cs — IndexOutOfRangeException in GetFirstChildNotAnd(): Children[0] accessed without verifying Children is non-empty. Added && Children.Count > 0 to the is And check.

• Move.cs — Negative Cardinality: Children.Count() - 1 returns -1 on an empty collection. Changed to Children.Any() ? Children.Count() - 1 : 0.

• KopCodeHelper.cs — InvalidOperationException from .Last() on empty collections: Three call sites called .Last() on Children that could be empty. Fall back to the parent operation's OperationId when no children exist.

• AddCall.cs / MulCall.cs — Swapped class definitions: AddCall.cs contained MulCall and MulCall.cs contained AddCall. Swapped file contents to restore the correct class-to-file mapping.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>search codebase for issues</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes search codebase for issues #35

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.