fix: stabilize flaky AI snapshot tests

Fix race condition in expectFileDeleted test helper where fileExists()
was fired on every awaitsFor poll but the result was checked before the
promise resolved, causing one-poll-behind behavior and timeouts.

Make _createOrUpdateFile resilient to stale FileSystem cache: when
file.exists() returns true but getDocumentForPath fails (e.g. after a
delete+recreate cycle), fall back to creating the file on disk and retry.

Author: abose

src/core-ai/AISnapshotStore.js

@@ -254,18 +254,42 @@ define(function (require, exports, module) {
                 });
         }
 
+        function _createThenSet() {
+            const file = FileSystem.getFileForPath(vfsPath);
+            file.write("", function (writeErr) {
+                if (writeErr) {
+                    result.reject(new Error("Could not create file: " + writeErr));
+                    return;
+                }
+                _setContent();
+            });
+        }
+
         const file = FileSystem.getFileForPath(vfsPath);
         file.exists(function (existErr, exists) {
             if (exists) {
-                _setContent();
+                // File may appear to exist due to stale FS cache after a
+                // delete+recreate cycle. Try opening first; if it fails,
+                // recreate the file on disk and retry.
+                DocumentManager.getDocumentForPath(vfsPath)
+                    .done(function (doc) {
+                        try {
+                            doc.setText(content);
+                            saveDocToDisk(doc).always(function () {
+                                CommandManager.execute(Commands.CMD_OPEN, { fullPath: vfsPath })
+                                    .always(function () {
+                                        result.resolve();
+                                    });
+                            });
+                        } catch (err) {
+                            result.reject(err);
+                        }
+                    })
+                    .fail(function () {
+                        _createThenSet();
+                    });
             } else {
-                file.write("", function (writeErr) {
-                    if (writeErr) {
-                        result.reject(new Error("Could not create file: " + writeErr));
-                        return;
-                    }
-                    _setContent();
-                });
+                _createThenSet();
             }
         });
 

test/spec/ai-snapshot-test.js

@@ -143,8 +143,15 @@ define(function (require, exports, module) {
 
         async function expectFileDeleted(name) {
             let gone = false;
+            let checking = false;
             await awaitsFor(function () {
-                fileExists(name).then(function (e) { gone = !e; });
+                if (!checking && !gone) {
+                    checking = true;
+                    fileExists(name).then(function (e) {
+                        gone = !e;
+                        checking = false;
+                    });
+                }
                 return gone;
             }, name + " to be deleted", 5000);
         }