fix(ios): report keyboard focus from the AX bridge's is-editing trait (#3163)

The simulator AX bridge published focused only from hasFocus, so a focused
TextField or TextEditor never read as focused. Derive it from traits bit 21,
the word XCTest maps hasKeyboardFocus to.

Author: okwasniewski

packages/platform-apple/src/snapshot-source/tree.test.ts

@@ -325,6 +325,31 @@ test('the bridge tree reads selected from the selected trait, matching the XCTes
   assert.equal(enabled(disabledSelected), false);
 });
 
+test('the bridge tree reads keyboard focus from the is-editing trait, matching the XCTest tree', () => {
+  const editor = (word?: unknown) => ({
+    [automationType]: 57,
+    [label]: 'Notes',
+    [frame]: { X: 16, Y: 184, Width: 370, Height: 150 },
+    ...(word === undefined ? {} : { [traits]: word }),
+    [children]: [],
+  });
+  const focused = (word?: unknown) =>
+    decodeSnapshotBridgeTree(
+      { [application]: 'Application', [children]: [editor(word)] },
+      { truncated: false },
+      limits,
+    ).nodes[1]?.focused;
+
+  // Real guest captures of a SwiftUI TextEditor on an iOS 27 simulator: the word gains exactly
+  // bit 21 when the editor takes keyboard focus and loses it when another field takes it.
+  const focusedEditorTraits = 140883519602688n;
+  const unfocusedEditorTraits = 140883517505536n;
+  assert.equal(focusedEditorTraits ^ unfocusedEditorTraits, 1n << 21n);
+  assert.equal(focused(focusedEditorTraits.toString()), true);
+  assert.equal(focused(unfocusedEditorTraits.toString()), undefined, 'unfocused omits focused');
+  assert.equal(focused(), undefined, 'no traits word leaves focused unknown');
+});
+
 test('the bridge tree rejects unknown fields, invalid frames, and bounded overflows', () => {
   assert.throws(
     () => decodeSnapshotBridgeTree({ [children]: [], unknown: true }, { truncated: false }, limits),

packages/platform-apple/src/snapshot-source/tree.ts

@@ -132,6 +132,13 @@ const NOT_ENABLED_TRAIT = 1n << 8n;
  */
 const SELECTED_TRAIT = 1n << 3n;
 
+/**
+ * The private is-editing trait UIKit sets on the text input that holds keyboard focus. XCTest
+ * derives `hasKeyboardFocus` from this word, and the runner path answers `focused: true` from that
+ * key, so the bridge derives the fact from this bit. Like `selected`, it is published only when set.
+ */
+const KEYBOARD_FOCUS_TRAIT = 1n << 21n;
+
 /**
  * A WebKit page — Safari's, or a `WKWebView`'s — lives in a WebContent process and reaches UIKit's
  * tree as an `AXRemoteElement` under the web view, with its children in that other process. The
@@ -247,6 +254,7 @@ function nodeFacts(
   // Publishes `selected: true` only when the selected bit is set and omits it otherwise — the same
   // shape the XCTest tree produces, so a `selected:` selector cannot tell the producers apart.
   const selected = traits === undefined || (traits & SELECTED_TRAIT) === 0n ? undefined : true;
+  const focused = traits === undefined || (traits & KEYBOARD_FOCUS_TRAIT) === 0n ? undefined : true;
   const userInteractionEnabled = optionalBoolean(value[ATTRIBUTE.userInteractionEnabled]);
   // Trimmed like the runner's `placeholderText`: a whitespace placeholder is no placeholder.
   const placeholder = optionalString(value[ATTRIBUTE.placeholder])?.trim();
@@ -271,6 +279,7 @@ function nodeFacts(
     ...(frame ? { rect: frame } : {}),
     ...(enabled === undefined ? {} : { enabled }),
     ...(selected === undefined ? {} : { selected }),
+    ...(focused === undefined ? {} : { focused }),
     ...(userInteractionEnabled === undefined ? {} : { userInteractionEnabled }),
     depth,
   };
@@ -391,7 +400,7 @@ function optionalScalar(value: unknown): string | undefined {
 
 /**
  * The guest sends the uint64 traits word as a decimal string so no bit is lost to a double. One
- * parse feeds every trait fact the tree publishes — `enabled` and `selected` — so a malformed word
+ * parse feeds every trait fact the tree publishes — `enabled`, `selected`, and `focused` — so a malformed word
  * fails the same way no matter which fact is read.
  */
 function traitsFromGuest(value: unknown): bigint | undefined {