Notify Flutter inspector when navigating widget tree with keyboard (#9810)

* Notify Flutter inspector when navigating widget tree with keyboard

* Add inspector tree left/right keyboard navigation coverage

Updates inspector tree tests to cover left and right arrow navigation, including expand, next-row selection, and parent selection behavior. Also ensures left navigation to a parent notifies Flutter Inspector consistently with other keyboard selection changes.

* Fix inspector widget tree visibility issues during keyboard navigation

Resolves two regressions surfaced when navigating the inspector widget
tree with the arrow-left key.

1. Clicking a still-visible row used to call `expandPath` on the clicked
   node, which re-expanded the clicked node itself and undid any subtree
   collapses the user had just performed via the arrow-left key. Removed
   the call from `onSelectNode`; programmatic selection flows (search,
   on-device pick) continue to call `expandPath` via `syncTreeSelection`,
   so external selection still works correctly.

2. Collapsing all the way to the root via the arrow-left key shrank the
   visible rows down to a single row, which the inspector treated as a
   "still loading" state and replaced with a spinner — hiding the user's
   `[root]` row. Gated that branch on `!firstInspectorTreeLoadCompleted`
   so the spinner only shows during the initial load; afterwards a
   one-row tree renders as the legitimate single-row state.

Adds regression tests covering both behaviors.

* docs: add release notes for inspector keyboard navigation fixes (#9810)

* test: update inspector tree selection test for collapsed nodes

Author: muhammadkamel

packages/devtools_app/lib/src/screens/inspector/inspector_tree_controller.dart

@@ -357,7 +357,10 @@ class InspectorTreeController extends DisposableController
           return true;
         }
         if (selectionLocal.parent != null) {
-          return setSelectedNode(selectionLocal.parent);
+          return setSelectedNode(
+            selectionLocal.parent,
+            notifyFlutterInspector: true,
+          );
         }
         return false;
       },
@@ -399,8 +402,7 @@ class InspectorTreeController extends DisposableController
                   _numRows - 1,
                 ),
               )?.node;
-        setSelectedNode(nodeToSelect);
-        return true;
+        return setSelectedNode(nodeToSelect, notifyFlutterInspector: true);
       },
     );
   }
@@ -573,7 +575,12 @@ class InspectorTreeController extends DisposableController
     if (diagnostic != null && diagnostic.groupIsHidden) {
       diagnostic.hideableGroupLeader?.toggleHiddenGroup();
     }
-    expandPath(node);
+    // Intentionally do NOT call expandPath(node) here. User clicks happen on
+    // already-visible rows, so ancestors are already expanded; calling
+    // expandPath would also re-expand the clicked node itself, undoing any
+    // collapse the user just performed via the left arrow key. Programmatic
+    // selection paths (search, on-device pick) call expandPath themselves via
+    // [InspectorController.syncTreeSelection].
   }
 
   Rect getBoundingBox(InspectorTreeRow row) {
@@ -1142,8 +1149,12 @@ class _InspectorTreeState extends State<InspectorTree>
       valueListenable: treeControllerLocal.rowsInTree,
       builder: (context, rows, _) {
         // Note: The inspector rows contain only the fake root node when the
-        // inspector tree is shutdown.
-        if (rows.length <= 1) {
+        // inspector tree is shutdown. Only show the loading indicator on the
+        // initial tree load (before [firstInspectorTreeLoadCompleted] is set);
+        // after that, a one-row tree is the legitimate result of the user
+        // collapsing all the way to the root via the keyboard, and we should
+        // render the tree (with its single row) rather than a spinner.
+        if (rows.length <= 1 && !controller.firstInspectorTreeLoadCompleted) {
           // This works around a bug when Scrollbars are present on a short lived
           // widget.
           return const SizedBox(child: CenteredCircularProgressIndicator());

packages/devtools_app/release_notes/NEXT_RELEASE_NOTES.md

@@ -21,6 +21,9 @@ TODO: Remove this section if there are not any updates.
 
 - Deleted the option to use the legacy inspector.
   [#9782](https://github.com/flutter/devtools/pull/9782)
+- Fixed an issue where navigating the Inspector widget tree with the keyboard arrow keys did not update the selected widget in the connected Flutter app. [#9810](https://github.com/flutter/devtools/pull/9810)
+- Fixed an issue where clicking a widget row after collapsing a subtree with the left arrow key unexpectedly re-expanded the subtree. [#9810](https://github.com/flutter/devtools/pull/9810)
+- Fixed an issue where collapsing the Inspector widget tree to a single row with the left arrow key caused a loading spinner to appear instead of showing the root node. [#9810](https://github.com/flutter/devtools/pull/9810)
 
 ## Performance updates