fix: deduplicate CodeDom assembly references

[kpkhxlgy0]

Description

Fix CodeDom dynamic compilation failures when Unity has multiple loaded assemblies with the same simple name. The observed failure involved System.Security 2.0.0.0 and 4.0.0.0: excluding System.Security entirely avoided the duplicate-reference error but made types defined only in that assembly unavailable.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)
• Test update

Changes Made

• Preserve the existing netstandard facade exclusions used by the CodeDom backend.
• Deduplicate remaining CodeDom references by managed assembly simple name.
• Prefer the exact assembly identity referenced by the most loaded assemblies, then the higher version, then a stable path tie-break.
• Preserve System.Security instead of removing it from CodeDom references.
• Add portable EditMode regression coverage using temporary generated assemblies, without project-specific DLL paths.

Compatibility / Package Source

• Unity version(s) tested: Unity 2022.3.23f1 on Windows
• Package source used (#beta, #main, tag, branch, or file:): local file checkout based on CoplayDev/unity-mcp#beta at fc70dda7
• Resolved commit hash from Packages/packages-lock.json (if using a Git package URL): not applicable (file: checkout)

Testing/Screenshots/Recordings

• Python tests (cd Server && uv run pytest tests/ -v)
• Unity EditMode tests
• Unity PlayMode tests
• Package import/compile check
• Not applicable (explain why in Additional Notes)

Validation in the active Unity 2022.3 project:

• Package scripts compiled with no ExecuteCode or error CS Console entries.
• CodeDom selected System.Security, Version=4.0.0.0 from simultaneous 2.0.0.0 and 4.0.0.0 inputs.
• CodeDom compiled and resolved System.Security.Cryptography.ProtectedData from System.Security, Version=4.0.0.0.
• Equivalent temporary-assembly checks preserved a file named System.Security.dll with netstandard present and selected referenced version 1.0.0.0 over unreferenced version 2.0.0.0.

Documentation Updates

• I have added/removed/modified tools or resources
• If yes, I have updated all documentation files using:
  • The LLM prompt at tools/UPDATE_DOCS_PROMPT.md (recommended)
  • Manual review of the generated changes

No tool or resource surface changed.

Related Issues

None.

Additional Notes

The two Unity EditMode regression tests were added to ExecuteCodeTests.cs, but the standalone UnityMCPTests project was not opened or run locally. The active host project was used for package compilation and equivalent runtime checks.

Summary by CodeRabbit

• Bug Fixes

  • Improved CodeDom compilation reliability when projects include multiple versions of the same assembly.
  • Preserved required security assemblies during compilation with netstandard references.
  • Added smarter assembly selection to favor the version referenced by the running Unity environment.

• Tests

  • Added regression coverage for assembly filtering and duplicate assembly resolution.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e5f7b063-d6b3-4232-8d2f-26724a643d4d

📥 Commits

Reviewing files that changed from the base of the PR and between fc70dda and 6f4c812.

📒 Files selected for processing (2)

• MCPForUnity/Editor/Tools/ExecuteCode.cs
• TestProjects/UnityMCPTests/Assets/Tests/EditMode/Tools/ExecuteCodeTests.cs

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📝 Walkthrough

Walkthrough

Changes

CodeDom assembly filtering

Layer / File(s)	Summary
Assembly identity filtering MCPForUnity/Editor/Tools/ExecuteCode.cs	CodeDom filtering now deduplicates resolved assemblies by identity, preferring loaded-reference matches, then newer versions and deterministic paths, while preserving unresolved paths.
Filtering regression coverage TestProjects/UnityMCPTests/Assets/Tests/EditMode/Tools/ExecuteCodeTests.cs	Added compilation-based tests and helpers covering System.Security.dll preservation and duplicate assembly version selection.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• CoplayDev/unity-mcp#1001: Changes the same CodeDom netstandard assembly-path filtering logic.

Suggested reviewers: scriptwonder

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: deduplicating CodeDom assembly references.
Description check	✅ Passed	The description follows the template and includes the required sections, change summary, compatibility, testing, and notes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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