feat(keyboard): flag keyboard resizes as user interactions (#716)

Keyboard separator adjustments (arrow keys, Home/End, Enter
collapse/expand) originate from a real DOM event on the separator, so
they are user interactions just like pointer drags. Pass
isUserInteraction: true from adjustLayoutForSeparator (the sole keyboard
dispatch site, reached only from onDocumentKeyDown).

Imperative API calls (setLayout, etc.) remain false: the library cannot
attribute the caller's intent there. Update the onLayoutChanged JSDoc to
state the pointer+keyboard vs. library-driven boundary, and the keyboard
test to expect true.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Kenan Yıldız

lib/components/group/Group.test.tsx

@@ -101,9 +101,9 @@ describe("Group", () => {
         panelRef: RefObject<PanelImperativeHandle | null>;
       }) => Promise<void>,
       expectedLayout: Layout,
-      // `true` when the callback simulates a pointer drag (see #716);
-      // `false` for keyboard / imperative API / mount which fall under the
-      // "library-driven" bucket of the new flag.
+      // `true` when the callback simulates a direct separator manipulation —
+      // a pointer drag or a keyboard resize (see #716); `false` for imperative
+      // API / mount which fall under the "library-driven" bucket of the flag.
       expectedIsUserInteraction: boolean
     ) {
       setElementBoundsFunction((element) => {
@@ -197,7 +197,7 @@ describe("Group", () => {
           left: 55,
           right: 45
         },
-        false
+        true
       );
     });
 

lib/components/group/types.ts

@@ -161,9 +161,11 @@ export type GroupProps = HTMLAttributes<HTMLDivElement> & {
    * This method is recommended when saving layouts to some storage api.
    *
    * The second argument `isUserInteraction` is `true` when the change was
-   * caused by the user releasing a pointer drag, and `false` for every other
-   * source (programmatic `setLayout`, constraint recompute, default-size
-   * change, initial mount). See #716.
+   * caused by the user directly manipulating a separator — releasing a pointer
+   * drag or pressing a resize key (arrow keys, Home/End, Enter). It is `false`
+   * for every other source (programmatic `setLayout` and other imperative API
+   * calls, constraint recompute, default-size change, initial mount), because
+   * the library cannot attribute the caller's intent there. See #716.
    */
   onLayoutChanged?: (layout: Layout, isUserInteraction: boolean) => void;
 

lib/global/utils/adjustLayoutForSeparator.ts

@@ -43,12 +43,20 @@ export function adjustLayoutForSeparator(
   });
 
   if (!layoutsEqual(prevLayout, nextLayout)) {
-    updateMountedGroup(group, {
-      defaultLayoutDeferred: groupState.defaultLayoutDeferred,
-      derivedPanelConstraints: groupState.derivedPanelConstraints,
-      groupSize: groupState.groupSize,
-      layout: nextLayout,
-      separatorToPanels: groupState.separatorToPanels
-    });
+    updateMountedGroup(
+      group,
+      {
+        defaultLayoutDeferred: groupState.defaultLayoutDeferred,
+        derivedPanelConstraints: groupState.derivedPanelConstraints,
+        groupSize: groupState.groupSize,
+        layout: nextLayout,
+        separatorToPanels: groupState.separatorToPanels
+      },
+      // Keyboard resizes (arrow keys, Home/End, Enter collapse/expand) originate
+      // from a real DOM event on the separator, so they are user interactions
+      // just like pointer drags. This function is only reached from
+      // onDocumentKeyDown. See #716.
+      { isUserInteraction: true }
+    );
   }
 }