Don't show 406 error messages in AI.

AGENTS.md

@@ -212,6 +212,7 @@ api().request(MTPnamespace_MethodName(
   ```
 - For single constructors, use `.data()` shortcut
 - Include `.handleFloodErrors()` before `.send()` in rare cases where you want special case flood error handling
+- Silently ignore HTTP 406 errors in UI: the server uses 406 to mean "show nothing to the user". Guard toasts with `MTP::IgnoreError(error)` or use `MTP::ShowErrorFallback(show, error)` (both in `mtproto/mtproto_response.h`) which shows `error.type()` as a toast unless the error should be ignored.
 
 ## UI Styling
 

Telegram/SourceFiles/boxes/compose_ai_box.cpp

@@ -1203,6 +1203,10 @@ void ComposeAiContent::request() {
 				return;
 			}
 			weak->_requestId = 0;
+			if (MTP::IgnoreError(error)) {
+				weak->resetState(CardState::Waiting);
+				return;
+			}
 			weak->showError(error.type());
 		});
 }

Telegram/SourceFiles/mtproto/mtproto_response.h

@@ -57,6 +57,17 @@ inline bool IsDefaultHandledError(const Error &error) {
 	return IsTemporaryError(error);
 }
 
+inline bool IgnoreError(const Error &error) {
+	return error.code() == 406;
+}
+
+template <typename ShowPtr>
+void ShowErrorFallback(const ShowPtr &show, const Error &error) {
+	if (!IgnoreError(error)) {
+		show->showToast(error.type());
+	}
+}
+
 struct Response {
 	mtpBuffer reply;
 	mtpMsgId outerMsgId = 0;