Unity Engine C# Editor & Runtime AI Skill Guide (Claude)

Overview & Engine Architecture

Unity 6000.x / 2022 LTS+ combines Scenes, Prefabs, ScriptableObjects, URP/HDRP/Built-in RP, and Editor-only automation via -batchmode -quit -executeMethod. Claude acts as a Principal Unity Engineer: CI builds, Addressables, deterministic player settings, and Editor/runtime assembly separation.

┌─────────────────────────────────────────────────────────────┐
│  Editor (UnityEditor)  →  -executeMethod / BuildPipeline    │
│  Player (runtime)      →  Mono / IL2CPP                     │
│  CI: one process per buildTarget; -activeBuildProfile       │
└─────────────────────────────────────────────────────────────┘

Version pin: Unity Editor version in ProjectSettings/ProjectVersion.txt — CI must use the same Hub editor (e.g. 6000.0.xf1). Command-line reference.

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When to use / when not to

Use when: automated builds, asset validation, playmode tests, Addressables content builds, batch import settings.

Do not use when: Unreal-specific Nanite workflows; server-side Unity without licensing review for headless batch (Unity licensing applies to build machines).

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Operational Capabilities & Agent Directives

1. Editor isolation: #if UNITY_EDITOR, Assets/**/Editor/, Editor asmdefs — never reference UnityEditor in runtime.
2. CI entry points: public static void X() only; EditorApplication.Exit(code) on failure; no modal dialogs in batchmode.
3. One target per invocation: pass -buildTarget StandaloneWindows64 or -activeBuildProfile "Assets/.../Windows.asset" — multi-target requires separate processes.
4. Deterministic builds: pin graphics tiers, disable random Application.targetFrameRate side effects in build scripts; use BuildOptions.StrictMode where available; log Application.unityVersion.
5. Color/URP: document active RP asset; linear color space + URP asset must match CI player settings or lighting differs from Editor.
6. Logs: always -logFile path; parse for Scripts have compiler errors before blaming runtime.

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Production C#: CI build + exit code

Assets/Editor/CiBuild.cs:

#if UNITY_EDITOR
using System.IO;
using UnityEditor;
using UnityEditor.Build.Reporting;
using UnityEngine;

public static class CiBuild
{
    public static void BuildWindowsCI()
    {
        var ok = BuildInternal(BuildTarget.StandaloneWindows64, "Builds/Win/Game.exe");
        EditorApplication.Exit(ok ? 0 : 1);
    }

    static bool BuildInternal(BuildTarget target, string location)
    {
        Directory.CreateDirectory(Path.GetDirectoryName(location)!);
        var report = BuildPipeline.BuildPlayer(new BuildPlayerOptions
        {
            scenes = EditorBuildSettingsScene.GetActiveSceneList(EditorBuildSettings.scenes),
            locationPathName = location,
            target = target,
            options = BuildOptions.CompressWithLz4HC
        });
        Debug.Log($"Build {report.summary.result} size={report.summary.totalSize}");
        return report.summary.result == BuildResult.Succeeded;
    }
}
#endif

& "C:\Program Files\Unity\Hub\Editor\6000.0.42f1\Editor\Unity.exe" `
  -batchmode -nographics -quit `
  -projectPath "$PWD" `
  -buildTarget StandaloneWindows64 `
  -executeMethod CiBuild.BuildWindowsCI `
  -logFile "$PWD\Logs\ci-build.log"

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Addressables / content pipeline (batch)

Use AddressableAssetSettings.BuildPlayerContent() from an Editor static method after -executeMethod imports complete. Fail CI if catalog hash changes without intentional bump (store catalog.json hash artifact).

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Failure taxonomy

Symptom	Cause	Fix
Hang after open	Modal dialog / missing -quit	-batchmode -quit; guard DisplayDialog
Wrong platform shaders	Missing -buildTarget / profile	Set -activeBuildProfile
UnityEditor in player	Editor script in runtime asmdef	Editor folder + asmdef platforms
Non-deterministic lighting	Different RP or color space	Serialize Quality/Graphics settings
License / activation	Batch on fresh VM	Unity license activation docs for CI

Reddit/forum pattern: parallel Unity instances on same project path fail — one lock per -projectPath.

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Agent Operational Directive

MANDATORY: Static -executeMethod in Editor assembly; explicit exit codes; -logFile; pin Editor version; separate CI job per build target.