Bug: issue #924 failed verification — 5 expected tests missing and timing-dependent polling loops in 3 tests

[JoshuaRowePhantom]

Missing implementation

Original issue: #924 — Blocked: #805/#888 blocked by test timeouts in GitWorktreeReviewWorkspaceTabViewModelTests

Verification gap: tests missing / criteria violation

Detail:

Gap 1: Five expected tests from the issue's 'Expected Tests' table are absent from Phantom.Workspaces.Tests/GitWorktreeReviewWorkspaceTabViewModelTests.cs

1. RefreshAsync_ConcurrentInvocations_DoesNotMissIsRefreshingTrueEvent — Regression guard: attach \PropertyChanged\ while \IsRefreshing == true\ (constructor refresh in flight), trigger a second refresh, assert the observer eventually sees \alse\ and that \CurrentRefresh\ completes. This is the only test that would catch a recurrence of the missed-notification race.
2. RefreshAsync_CancelledMidFlight_LeavesIsRefreshingConsistent — Force cancellation of an in-flight refresh via a follow-up refresh, then assert \CurrentRefresh\ completes and \IsRefreshing == false\ at the end of the latest refresh.
3. RefreshAsync_SecondCallCancelsFirst_OldTaskCompletesWithoutMutatingVisibleState — Guards the atomic-swap invariant from GitWorktreeReviewWorkspaceTabViewModel tests fail when TargetBranch changed immediately after adding sentinel commits #888: cancelled refresh Bump actions/checkout from 4 to 7 #1 must not mutate \CommitList\ / \FileList\ / \FileDiffs.
4. CurrentRefresh_AfterConstructor_IsNonNullAndAwaitable — Dedicated contract test for the new public property (the behaviour exists inline in other tests but there is no standalone contract test).
5. CurrentRefresh_AfterTargetBranchChange_IsReplacedWithNewTask — Ensures the task reference is actually replaced after a branch change (not just that the new task completes).

Gap 2: Timing-dependent polling loops in 3 tests

The following three tests in GitWorktreeReviewWorkspaceTabViewModelTests.cs use while (vm.FileDiffs.Count == 0) { await Task.Delay(50); } as their primary synchronization mechanism for initial diff loading, which is a polling loop violating the timing-dependent test criterion:

• GitWorktreeReviewWorkspaceTabViewModel_ContextLines_TriggersRebuild
• GitWorktreeReviewWorkspaceTabViewModel_ContextLines_Zero_ShowsOnlyChangedLines
• GitWorktreeReviewWorkspaceTabViewModel_ContextLines_LargeValue_ShowsExtendedContext

These should be replaced with event-driven synchronization (e.g., subscribe to \FileDiffs.CollectionChanged\ with a \TaskCompletionSource\ before the VM is created, or expose a \CurrentRefresh\ await pattern that covers the initial diff build).