Moved all extension methods into extension blocks (#1155)

app/AGENTS.md

@@ -28,6 +28,7 @@ Key structure:
 ## Important Development Notes
 
 - **Naming conventions** - Constants, enum members, and `static readonly` fields use `UPPER_SNAKE_CASE` such as `MY_CONSTANT`.
+- **Extension members** - Declare extension methods in an `extension` block of their static class, one block per receiver, never with a `this` parameter: MWAIS0016 refuses the classic form. The `<param>` of the receiver, and of a generic block its `<typeparam>`, belongs on the block, not on its members. The one exception is a method with a `params` parameter, which stays classic until the SDK in `metadata.txt` carries the fix for dotnet/roslyn#80024: for a member of an extension block, the compiler warns about every argument passed one by one to a `params` parameter (CS8620), see `JsRuntimeExtensions`.
 - **Message Bus** - Singleton event bus for cross-component communication inside the .NET app
 - **Prompt injection reports** - The user hears once per action about what the filter removed, as soon as that action ends. Content which belongs to an action carries its scope from `PromptInjectionGuardService.BeginAction` down to where it is read or filtered; whatever is filtered without a scope is reported right away. Pass the scope as a parameter, never through a field or an `AsyncLocal`: the service serves the whole app, and the message bus delivers to other receivers in the execution context of whoever sends.
 - **Paths in stored data** - A stored path to a file which AI Studio keeps below the data directory, such as a transcript or a tokenizer copy, is relative to that directory, so that a backup or a copy of the data directory works on another computer, under another user name, or on another OS. Mark such a property with `[JsonConverter(typeof(DataDirectoryRelativePathConverter))]`, for a positional record parameter with `[property: ...]`; in memory, the path stays absolute. Better still, derive the path from IDs and store none, as `VisualBriefingStore` does. Paths to files of the user stay absolute. Chats stored before v26.10.1 are migrated by a compatibility shim, see `documentation/compatibility-shims/2026-10-relative-data-paths.md`.