Unity Yooasset Design Agent Skill

YooAsset - Design Rules

Advisory module. Every rule is distilled from YooAsset v2.3.18 (2025-12-04) source at Assets/YooAsset/. Each rule cites a concrete file/line so the reasoning is auditable and the AI does not improvise against stale memory.

> Mode: Documentation only — no REST skills to gate; load freely under any operating mode (Approval / Auto / Bypass).

When to Load This Module

Load before writing or reviewing any of:

• YooAssets.Initialize() / CreatePackage() / Destroy() bootstrap code
• default package shortcuts: YooAssets.SetDefaultPackage(...), YooAssets.LoadAssetAsync(...), YooAssets.CreateResourceDownloader(...)
• ResourcePackage.InitializeAsync(...) with any of the 5 EPlayMode variants
• LoadAssetSync/Async, LoadSubAssetsAsync, LoadAllAssetsAsync, LoadRawFileAsync, LoadSceneAsync and their matching Handle usage / release
• Patch flow: RequestPackageVersionAsync → UpdatePackageManifestAsync → CreateResourceDownloader → BeginDownload
• FileSystemParameters construction (Buildin / Cache / Editor / WebServer / WebRemote / custom)
• IDecryptionServices / IRemoteServices / IWebDecryptionServices implementations
• Editor-side AssetBundleBuilder.Run(...) and AssetBundleCollector configuration
• Any code branching on EOperationStatus / EFileClearMode / PackageDetails

Critical Rule Summary (memorize even if you skip the sub-docs)

| # | Rule | Source anchor |

|---|------|---------------|

| 1 | Call YooAssets.Initialize() before any CreatePackage() and keep it as a process-level singleton. A second call only logs a warning and returns, but normal architecture should gate it with YooAssets.Initialized. The call creates a [{nameof(YooAssets)}] driver GameObject via DontDestroyOnLoad to pump OperationSystem.Update(). Do not Destroy this driver yourself. | Runtime/YooAssets.cs:38-64 |

| 2 | ResourcePackage.InitializeAsync(...) has no separate EPlayMode argument: it infers play mode from the concrete InitializeParameters subclass. The five built-in subclasses map 1:1 to the five modes; an unknown subclass throws NotImplementedException, while a recognized but semantically wrong subclass wires the wrong file-system topology and fails later. | Runtime/ResourcePackage/ResourcePackage.cs:107-135, 170-181, Runtime/InitializeParameters.cs:8-110 |

| 3 | EditorSimulateMode works only when UNITY_EDITOR is defined; WebPlayMode works only when UNITY_WEBGL is defined (and every other mode is rejected on WebGL). | Runtime/ResourcePackage/ResourcePackage.cs:160-197 |

| 4 | Every AssetHandle / SubAssetsHandle / AllAssetsHandle / RawFileHandle / SceneHandle must be released via Release() or Dispose(). Without release, bundles never unload even with AutoUnloadBundleWhenUnused = true. | Runtime/ResourceManager/Handle/HandleBase.cs:21-40, Runtime/InitializeParameters.cs:48-49 |

| 5 | LoadAssetSync/Async performs a DEBUG-only type guard that rejects any Type derived from UnityEngine.Behaviour and any type not derived from UnityEngine.Object. Treat the restriction as architectural even though the guard is compiled out of non-DEBUG builds. | Runtime/ResourcePackage/ResourcePackage.cs:1172-1187 |

| 6 | YooAsset 2.3.18 includes default-package static shortcuts on YooAssets (SetDefaultPackage, Load*, CreateResourceDownloader, etc.). They are valid API, but architecture should prefer explicit ResourcePackage references in multi-package or library code. | Runtime/YooAssetsExtension.cs:16, 217-295, 479-506 |

| 7 | RequestPackageVersionAsync() returns RequestPackageVersionOperation (exposes .PackageVersion). There is no UpdatePackageVersionOperation class in 2.3.18 — if you think you remember one, you are confusing it with the older name. | Runtime/ResourcePackage/ResourcePackage.cs:225-231 |

| 8 | Before UpdatePackageManifestAsync, call UnloadAllAssetsAsync(); YooAsset logs a warning when loaders are still alive. | Runtime/ResourcePackage/ResourcePackage.cs:242-247 |

| 9 | Downloader callbacks (DownloadFinishCallback / DownloadUpdateCallback / DownloadErrorCallback / DownloadFileBeginCallback) must be assigned before BeginDownload(). They are delegate fields, not events — only one subscriber per slot. | Runtime/DownloadSystem + Runtime/ResourcePackage/Operation/DownloaderOperation.cs:86-101, 330-336 |

| 10 | ResourcePackage.DestroyAsync() must run before YooAssets.RemovePackage(). RemovePackage refuses when InitializeStatus != EOperationStatus.None. | Runtime/YooAssets.cs:177-190, Runtime/ResourcePackage/ResourcePackage.cs:210-218 |

| 11 | The patch flow is strictly ordered: InitializeAsync → RequestPackageVersionAsync → UpdatePackageManifestAsync(version) → CreateResourceDownloader → BeginDownload. Jumping ahead (e.g. loading assets between version and manifest) is unsupported. | Runtime/ResourcePackage/ResourcePackage.cs:225, 238, 972, Samples~/Space Shooter/.../PatchLogic/FsmNode/Fsm*.cs |

Sub-doc Routing

| Sub-doc | When to read |

|---------|--------------|

| INIT.md | Initialize / Destroy / CreatePackage / TryGetPackage / RemovePackage; single driver GameObject; OperationSystem loop |

| PLAYMODE.md | All 5 EPlayMode values, their matching InitializeParameters subclass, platform #if guards, and the runtime dispatch table |

| HANDLES.md | HandleBase API (Release / IsDone / Progress / Status / LastError / Completed / Task / IEnumerator), AssetHandle.Instantiate*, reference counting, AutoUnloadBundleWhenUnused |

| LOADING.md | LoadAsset, LoadSubAssets, LoadAllAssets, LoadRawFile, LoadScene — all overloads + Behaviour/Type rejection + LoadSceneParameters |

| UPDATE.md | Patch flow, RequestPackageVersionOperation, UpdatePackageManifestOperation, PreDownloadContentOperation, ResourceDownloaderOperation (4 callbacks, pause/resume/cancel, Combine) |

| FILESYSTEM.md | FileSystemParameters + 24 FileSystemParametersDefine constants + 5 factory helpers + IDecryptionServices / IRemoteServices / IWebDecryptionServices |

| BUILD.md | AssetBundleBuilder.Run(...), BuildParameters (Scriptable / Raw / Simulate), AssetBundleCollector, IFilterRule.FindAssetType, ScriptableBuildParameters.ReplaceAssetPathWithAddress |

| PITFALLS.md | 30 concrete hallucination pitfalls + legacy API migration section |

Routing to Other Modules

• Asmdef & assembly layout for YooAsset consumers → load asmdef
• Async orchestration across multiple YooAsset operations → load async
• Architecture-level decisions (Addressables vs YooAsset, single-package vs multi-package) → load architecture
• Performance review of load/release hot paths → load performance

Version Scope

This document targets YooAsset 2.3.18 (2025-12-04). Key recent history:

• 2.3.18 — added UNPACK_FILE_SYSTEM_ROOT file-system parameter, EFileClearMode.ClearBundleFilesByLocations, RawFileBuildParameters.IncludePathInHash.
• 2.3.17 — [CRITICAL] fixed a CRC-validation bug that let corrupted downloads pass verification on 2.3.15/2.3.16. Also fixed a Package-destroy race where an in-flight AssetBundle load could block unload.
• 2.3.16 — removed the downloader timeout parameter (use DOWNLOAD_WATCH_DOG_TIME on the cache file system instead). IFilterRule gained a required FindAssetType property.
• 2.3.15 — bumped the manifest binary format; installers built with 2.3.15+ are not readable by 2.3.14 or earlier clients and vice versa. Added FILE_VERIFY_MAX_CONCURRENCY, StripUnityVersion, preview UseWeakReferenceHandle (under YOOASSET_EXPERIMENTAL).

Source: Assets/YooAsset/CHANGELOG.md:5-275.

Migration Notes (hallucination shield)

| Legacy API (pre-2.3.18) | Status in 2.3.18 | Replacement | Source |

|-------------------------|------------------|-------------|--------|

| CreateResourceDownloader(count, retry, timeout) overload / ResourceDownloaderOperation.timeout property | Removed in 2.3.16 | Assign DOWNLOAD_WATCH_DOG_TIME on the CacheFileSystemParameters / BuildinFileSystemParameters | CHANGELOG.md:173-177, FileSystemParametersDefine.cs:18 |

| IFilterRule without a FindAssetType property | Breaking change in 2.3.16 — compilation breaks | Implement public string FindAssetType { get; } that returns a Unity asset-type filter string | CHANGELOG.md:179-192 |

| Old manifest binary (pre-2.3.15 client reading a 2.3.15+ manifest, or vice versa) | Wire-incompatible | Rebuild + re-ship installer; no runtime bridge exists | CHANGELOG.md:196-198 |

| YooAssets.LoadAsset(...) | Does not exist — method names include LoadAssetSync / LoadAssetAsync, not bare LoadAsset | package.LoadAssetAsync<T>(location) or YooAssets.LoadAssetAsync<T>(location) after SetDefaultPackage | Runtime/YooAssetsExtension.cs:217-295, Runtime/ResourcePackage/ResourcePackage.cs:641-732 |

| YooAssets.LoadAssetAsync(...) marked as hallucination | Outdated rule — 2.3.18 has this default-package shortcut | Prefer package.LoadAssetAsync<T>(location) for explicit ownership; static shortcut is acceptable only after YooAssets.SetDefaultPackage(package) | Runtime/YooAssetsExtension.cs:16, 260-295 |

| package.UnloadUnusedAssets() (synchronous) | Does not exist | package.UnloadUnusedAssetsAsync(int loopCount = 10) returns an UnloadUnusedAssetsOperation | Runtime/ResourcePackage/ResourcePackage.cs:355-361 |

| UpdatePackageVersionOperation class (often confused with the real type) | Does not exist | RequestPackageVersionOperation, with a .PackageVersion string property | Runtime/ResourcePackage/ResourcePackage.cs:225-231 |

| NetworkVariable<T> / OnValueChanged style sync for assets (leaked in from Netcode) | Does not exist in YooAsset | Subscribe AssetHandle.Completed event or await handle.Task / yield return handle | Runtime/ResourceManager/Handle/AssetHandle.cs:20-37, Runtime/ResourceManager/Handle/HandleBase.cs:152-173 |

| ResourceDownloaderOperation.OnDownloadFinishCallback (event-style) | Field is a plain delegate, not an event | Assign once: downloader.DownloadFinishCallback = OnFinish; — do not += (single-slot field) | Runtime/ResourcePackage/Operation/DownloaderOperation.cs:86-101 |

When in doubt, read the cited source — not your memory.