[Refactor] (P13 W5 S4): a build without a transport answers the server-role question false.

MobileGL/MG_Backend/MGPipe/PipeInputs.h

@@ -1006,8 +1006,9 @@ namespace MobileGL::MG_Pipe {
     // inline that no caller in such a build ever has a reason to call twice - the disaggregated
     // arm above is the real one.
     inline PipeInputs& MGPipeClientInputs() { return gPipeInputs; }
-    // P13 W5: one block, no client-role stamp to withdraw.
+    // P13 W5: one block, no client-role stamp to withdraw - and no server role to be on.
     inline void MGPipeClientClearVerbBoundary() {}
+    inline constexpr Bool MGPipeServerArm() { return false; }
 #endif
 
     // Every field has storage or is forwarded, and nothing else.