fix: make SheetViewState viewport test resilient to async IPC events

Replace waitForReload() with pendingReload() pattern that registers a
one-shot listener on onViewAttachmentsReloaded BEFORE the action, then
awaits the event AFTER the save/undo. This moves the areAllTilesLoaded
assertion to after the reload event resolves, where it is deterministic
(SheetViewState invalidates the viewport scene on the line before it
raises the event).

Previously, the test asserted areAllTilesLoaded === false immediately
after saveBriefcaseChanges, but under Electron IPC the push notification
can arrive after the IPC response, causing a race condition.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: hl662

full-stack-tests/core/src/frontend/hub/SheetViewState.test.ts

@@ -347,10 +347,14 @@ describe("SheetViewState", () => {
           await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
 
-          // Modify the placement of the attachment
-          async function waitForReload() {
-            await waitForViewAttachmentsToReload(view, async () => undefined);
-            await vp.waitForSceneCompletion();
+          // Register a one-shot listener for the reload event BEFORE the action
+          // that triggers it.  SheetViewState invalidates the viewport scene
+          // on the line before it raises onViewAttachmentsReloaded, so
+          // areAllTilesLoaded is guaranteed false right after this resolves.
+          function pendingReload(): Promise<void> {
+            return new Promise<void>((resolve) => {
+              view.onViewAttachmentsReloaded.addOnce(() => resolve());
+            });
           }
 
           // Modify the placement of the attachment
@@ -362,10 +366,11 @@ describe("SheetViewState", () => {
           await coreFullStackTestCommandIpc.updateElement(iModel.key, props);
 
           expect(vp.areAllTilesLoaded).to.be.true;
-          const reloadAfterUpdate = waitForReload();
+          const reloadAfterUpdate = pendingReload();
           await saveBriefcaseChanges(iModel);
-          expect(vp.areAllTilesLoaded).to.be.false;
           await reloadAfterUpdate;
+          expect(vp.areAllTilesLoaded).to.be.false;
+          await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
 
           // Verify the view reloaded the attachment with the updated placement.
@@ -377,10 +382,11 @@ describe("SheetViewState", () => {
           const newAttachmentId = await coreFullStackTestCommandIpc.insertElement(iModel.key, props);
 
           expect(vp.areAllTilesLoaded).to.be.true;
-          const reloadAfterInsert = waitForReload();
+          const reloadAfterInsert = pendingReload();
           await saveBriefcaseChanges(iModel);
-          expect(vp.areAllTilesLoaded).to.be.false;
           await reloadAfterInsert;
+          expect(vp.areAllTilesLoaded).to.be.false;
+          await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
 
           expect(view.viewAttachmentProps.length).to.equal(2);
@@ -390,10 +396,11 @@ describe("SheetViewState", () => {
           // Delete an attachment
           await deleteElements(iModel, [newAttachmentId]);
           expect(vp.areAllTilesLoaded).to.be.true;
-          const reloadAfterDelete = waitForReload();
+          const reloadAfterDelete = pendingReload();
           await saveBriefcaseChanges(iModel);
-          expect(vp.areAllTilesLoaded).to.be.false;
           await reloadAfterDelete;
+          expect(vp.areAllTilesLoaded).to.be.false;
+          await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
 
           expect(view.viewAttachmentProps.length).to.equal(1);
@@ -402,26 +409,29 @@ describe("SheetViewState", () => {
 
           // Undo everything so we don't affect subsequent tests (and to verify the Viewport reacts).
           // -- undo delete
-          const reloadAfterUndoDelete = waitForReload();
+          const reloadAfterUndoDelete = pendingReload();
           await iModel.txns.reverseSingleTxn();
-          expect(vp.areAllTilesLoaded).to.be.false;
           await reloadAfterUndoDelete;
+          expect(vp.areAllTilesLoaded).to.be.false;
+          await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
           expect(view.viewAttachmentProps.length).to.equal(2);
 
           // -- undo insert
-          const reloadAfterUndoInsert = waitForReload();
+          const reloadAfterUndoInsert = pendingReload();
           await iModel.txns.reverseSingleTxn();
-          expect(vp.areAllTilesLoaded).to.be.false;
           await reloadAfterUndoInsert;
+          expect(vp.areAllTilesLoaded).to.be.false;
+          await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
           expect(view.viewAttachmentProps.length).to.equal(1);
 
           // -- undo update
-          const reloadAfterUndoUpdate = waitForReload();
+          const reloadAfterUndoUpdate = pendingReload();
           await iModel.txns.reverseSingleTxn();
-          expect(vp.areAllTilesLoaded).to.be.false;
           await reloadAfterUndoUpdate;
+          expect(vp.areAllTilesLoaded).to.be.false;
+          await vp.waitForSceneCompletion();
           expect(vp.areAllTilesLoaded).to.be.true;
           expect(view.viewAttachmentProps.length).to.equal(1);
           expect(view.viewAttachmentProps[0].placement?.origin).to.deep.equal([100, 100]);