Dev:WorkflowKit.framework

WorkflowKit is the framework that acts as a backend to the Shortcuts app. It provides around 80% functionality of the Shortcuts app including (but not limited to) actions (though ActionKit also powers a lot of them), handles how shortcuts are imported, how they're stored, etc. It is noted that while it is technically added in 12.0, most of its functionality came in iOS 13.0.

For shortcuts signing, https://github.com/0xilis/RandomShortcutsRev/ covers a very rough reverse engineering, though be aware it's rather incomplete and may be inaccurate.

For examples on how to use this framework, see the Example Code section of this page.

WFWorkflowRecord
WFWorkflowRecord is how shortcuts are stored. The biggest thing is actions: Every action has an action identifier to identify an action (WFWorkflowActionIdentifier), and some have parameters of what is in said action (WFWorkflowActionParameters). However, it also handles other data about the shortcut, such as its name and minimum client version it can be imported on.

WFBundledActionProvider
WFBundledActionProvider is what provides WorkflowKit with what actions it loads.

WFAction
WFAction is basically the class that every shortcuts action uses. It should be noted that actions aren't all WFAction, but rather their own class that inherit from it (For example, WFExitShortcut in ActionKit).

WFShortcutExtractor
WFShortcutExtractor is a brand new class in iOS 15 dedicated to exporting shortcuts.

WFGallerySessionManager
WFGallerySessionManager handles various gallery things, such as uploading shortcuts to iCloud. Be aware that some methods in here do not have any code in release builds, such as deleteCollection/deleteBanner.

WFP2PSignedShortcutFileExporter
WFP2PSignedShortcutFileExporter is a brand new class in iOS 15 dedicated to signing contact signed shortcuts.

WFiCloudShortcutFileExporter
WFiCloudShortcutFileExporter is a brand new class in iOS 15 dedicated to signing iCloud signed shortcuts.