Flaky UI test: LargeInventoryTests fails clicking the last scrolled row #182

What

LargeInventoryTests.testLargeInventorySupportsNavigationAndLifecycleWorkflows intermittently fails at BerthlyUITests/LargeInventoryTests.swift:46, the tailContainer.click() on computeRow-container-099 after the compute list is scrolled to the bottom. All three known occurrences were on macOS 27, and it has not failed on the macOS 26 CI leg.

Not related to the line 31 Escape failure on macOS 27 that #175 fixed. That was a different bug in the same test.

Evidence

CI executions of each UI leg across PRs #175 to #181 on 2026-10-05:

All three failures have the same shape: the row resolves to a degenerate frame (zero size, at inf or y=768) at click time.

Where

Lines 36 to 46 of LargeInventoryTests.swift. The test scrolls the outline with scroll(byDeltaY: -10_000) three times, waits for hittable == true on computeRow-container-099 with a 5 s expectation, then clicks. The wait passes and the click then reports the element not hittable, so the frame goes bad between the check and the click.

This is a hypothesis, not confirmed: rows in the 100+ item list being recycled or re-laid out after programmatic scrolling. The test already carries a comment about a related "stale/degenerate frame" race on the very last row (machine-018), which it avoids by clicking container-099 instead. The same class of problem still happens one row higher.

Impact

The advisory macOS 27 UI leg goes red intermittently, about 1 execution in 8 so far, and each rerun costs about 30 minutes. ci.yml plans to promote the macOS 27 legs to required gates once they have a green track record, and this is the only flake that has stood in the way so far.

Ideas, none tried

• Re-resolve the row and retry the scroll and click as one unit, instead of check-then-click.
• Bring the row into view with the existing filter (setComputeFilter("container-099", ...), which the test already uses elsewhere) instead of scrolling to the end of a long list.
• Check whether the dataset size matters: the large fixture has 100 containers plus machines.

Repro

Intermittent, observed once in 6 local runs. Loop the single test:

for i in $(seq 1 12); do
  xcodebuild test -project Berthly.xcodeproj -scheme Berthly -destination 'platform=macOS' \
    -only-testing:BerthlyUITests/LargeInventoryTests/testLargeInventorySupportsNavigationAndLifecycleWorkflows
done