fix: use IsPrimary() for touch pointer isPrimary instead of hardcoded id (#16099)

* Create react-native-windows-4ad3ddaf-1358-4ff0-9971-38a7db68266c.json

* fix: use IsPrimary() for touch pointer isPrimary instead of hardcoded ID check (#4)

activeTouch.isPrimary was set via `pointerId == 1`, which only works for
  mouse (MOUSE_POINTER_ID == 1). Windows touch pointer IDs are OS-allocated
  and essentially never 1, so isPrimary was always false for touch input.
  This meant touch pointers never triggered onClick (gated behind
  isPrimary && button == 0) and reported incorrect isPrimary in
  PointerEvents sent to JS.

  Replace with pointerPoint.Properties().IsPrimary(), which reads the OS
  POINTER_FLAG_PRIMARY flag directly. This API is already used elsewhere
  in the codebase (SwitchComponentView, WindowsTextInputComponentView,
  Composition.Input).

  (The diagnostics are pre-existing clang noise from missing PCH/Windows headers — not
  related to this change.)

Author: gmacmaster

change/react-native-windows-4ad3ddaf-1358-4ff0-9971-38a7db68266c.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "fix: use IsPrimary() for touch pointer isPrimary instead of hardcoded pointer ID check",
+  "packageName": "react-native-windows",
+  "email": "gordomacmaster@gmail.com",
+  "dependentChangeType": "patch"
+}

vnext/Microsoft.ReactNative/Fabric/Composition/CompositionEventHandler.cpp

@@ -1385,7 +1385,7 @@ void CompositionEventHandler::onPointerPressed(
 
     UpdateActiveTouch(activeTouch, ptScaled, ptLocal);
 
-    activeTouch.isPrimary = pointerId == 1;
+    activeTouch.isPrimary = pointerPoint.Properties().IsPrimary();
     // Map the Windows pointer ID to a small identifier (0–19) safe for use as a JS array index.
     // Windows touch IDs can be arbitrarily large (e.g. 2233), which causes React Native to warn
     // and corrupts touch state, leaving Pressables stuck after a scroll.