Clarify MCP knowledge and messageBack

Author: Corina Gum

teams.md/src/pages/templates/in-depth-guides/html-widgets/README.mdx

@@ -10,6 +10,8 @@ HTML Widgets let your app render rich, interactive HTML inside a Teams message.
 A widget is an [MCP Apps (ext-apps)](https://github.com/modelcontextprotocol/ext-apps) surface that the Teams client renders in a sandboxed iframe.
 The widget can call tools on your app, send messages back, request display mode changes, open links, and contribute content to the model context for future turns.
 
+You do not need to know the MCP Apps protocol to build widgets. The SDK helpers handle the wire format and protocol handshake for you, and the links to the specification are here only if you want the underlying details.
+
 :::warning Preview
 HTML Widgets are in preview and the API surface may change.
 <LanguageInclude content={{"typescript": "Every widget type and helper is annotated `@experimental` in its JSDoc (diagnostic `ExperimentalTeamsHtmlWidget`) to mark it as preview.", "python": "Every widget type and helper is decorated with `@experimental` (`ExperimentalTeamsHtmlWidget`), which emits a runtime preview warning when it is used.", "csharp": "Every widget type and helper is guarded by the `ExperimentalTeamsHtmlWidget` compiler diagnostic, so you opt in explicitly to use them."}} />

teams.md/src/pages/templates/in-depth-guides/html-widgets/updating-model-context.mdx

@@ -7,8 +7,10 @@ title: 'Updating Model Context'
 # Updating Model Context
 
 A widget can contribute content to the model context so your app can use it on future turns.
-This is the widget-side equivalent of `Action.Submit` for adaptive cards: the widget reuses the existing messageBack mechanism, so the request arrives as a normal message activity.
-It is fire-and-forget, meaning your app does not send a response.
+
+Widgets send data back to your app over the same messageBack channel other Teams surfaces use, so the request arrives as an ordinary message activity. `ui/update-model-context` is the specific request for contributing to model context; other widget-to-app requests (such as [tool calls](./handling-tool-calls)) travel over the same channel with different methods. This particular request is fire-and-forget: your app does not send a response.
+
+(If you have used adaptive cards, this is the widget-side equivalent of `Action.Submit`.)
 
 :::warning Preview
 HTML Widgets are in preview and the API surface may change.