fix: keep dynamic-code compiler settings on the Unity main thread

[hatayama]

Summary

• Dynamic-code compilation now captures Unity compiler settings before asynchronous work can resume on a worker thread.
• The compiler pipeline receives an immutable settings snapshot instead of reading UnityEditor APIs after ConfigureAwait(false).

User Impact

• Dynamic-code compilation no longer fails intermittently with main-thread exceptions when PlayMode or scene loading causes an await to yield.

Changes

• Switch to the Unity main thread at the compilation entry point and capture active defines plus unsafe-code configuration.
• Pass the snapshot through the assembly builder and Roslyn backend.
• Add pure C# coverage for define filtering, empty input, null validation, and snapshot isolation.

Verification

• Native uloop compile: Success true, ErrorCount 0, WarningCount 0.
• Targeted EditMode tests: TestCount 3, PassedCount 3, FailedCount 0.
• Full EditMode tests: TestCount 2163, PassedCount 2156, FailedCount 0, SkippedCount 7; runner status Skipped because existing tests were skipped.
• Unity API reference check: only DynamicCodeCompiler reads EditorUserBuildSettings.activeScriptCompilationDefines and PlayerSettings.allowUnsafeCode; GetActiveDefineSymbols was removed.

Refs: Mac POSIX E2E recovery/readiness fix specification, To-Dos 7-9.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 6b5f5a5c-1b45-4805-bb56-c6be2da52365

📥 Commits

Reviewing files that changed from the base of the PR and between 378a831 and b733699.

⛔ Files ignored due to path filters (2)

• Assets/Tests/Editor/DynamicCodeToolTests/RoslynCompilerOptionsTests.cs.meta is excluded by none and included by none
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/RoslynCompilerOptions.cs.meta is excluded by none and included by none

📒 Files selected for processing (8)

• Assets/Tests/Editor/DynamicCodeToolTests/ExternalCompilerPathResolverTests.cs
• Assets/Tests/Editor/DynamicCodeToolTests/RoslynCompilerOptionsTests.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/Compilation/ICompiledAssemblyBuilder.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/CompiledAssemblyBuilder.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/DynamicCodeCompiler.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/DynamicCompilationBackend.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/RoslynCompilerBackend.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/RoslynCompilerOptions.cs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/capture-dynamic-code-compilation-settings

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