[Feature]: CodeDom fallback — alias Object to UnityEngine.Object and hint to install Roslyn on compile failure #1439

What problem are you trying to solve?

With compiler: "auto" and Roslyn not installed, execute_code silently uses CodeDom (C# 6). Two things then cost agents retries:

1. Object is ambiguous in the generated wrapper (both System and UnityEngine are imported), so a very common Unity snippet fails:

   Line 6: `Object' is an ambiguous reference between `object' and `UnityEngine.Object'
   Line 6: `object' does not contain a definition for `FindObjectsByType'
   

   Every Object.FindObjectsByType<T>(...) / Object.Destroy(...) needs UnityEngine.Object. written out in full.
2. Failures from syntax newer than C# 6 (tuple deconstruction, is not, switch expressions, etc.) come back as raw compiler errors, with no hint that the backend is the cause.

What would you like to see?

• Add using Object = UnityEngine.Object; to the CodeDom wrapper (object keeps meaning System.Object). That matches what Unity scripts mean by Object in practice.
• When a CodeDom compile fails, append a one-line hint: "Compiled with CodeDom (C# 6). Install Roslyn for C# 12 (see docs), or use C# 6 syntax."

Prior art / how do you work around this today?

Fully qualify UnityEngine.Object and write C# 6 by hand. The agent relearns this after the first failure in each session.

Scope hint

Very small: one alias line plus an error-message suffix.

Environment

• Unity: 6000.3.8f1 (URP) · MCP for Unity: 10.2.1-beta.6 · Client: Claude Code · Transport: stdio · OS: Windows 11 Pro