Upload and link extension and creative assets across ad types via the Google Ads API AssetService

Steps

1. Build an Asset message with the appropriate type-specific payload (e.g. ImageAsset with data, mime_type, and full_size) and wrap it in an AssetOperation.
2. Call AssetService.MutateAssets to create the asset and capture its returned resource_name — AssetService only supports create, never update or delete.
3. For assets that attach directly to an ad, such as Responsive Display images, link them inline during AdGroupAdService.MutateAdGroupAds rather than via a separate linking call.
4. For extension-style assets — sitelinks, callouts, structured snippets, calls, price, promotions, lead forms — link them at the appropriate level via CustomerAsset, CampaignAsset, or AdGroupAsset mutate calls.
5. For Performance Max, link assets via AssetGroupAsset, except Business Name and Logo, which use CampaignAsset when brand guidelines are enabled.
6. Check the ad-type-specific requirements pages (video upload, HTML5/media-bundle limits, Performance Max asset requirements) for exact size/format constraints before uploading, since these aren't documented on the general Assets overview page.