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An inspect screenshot can be stale for point clicks when its AX walk grows the layout #159

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Description

@iamnbutler

desktop_inspect captures the screenshot first, then walks the window's Accessibility tree. Some SwiftUI lists load rows as their children are read and get taller. So the walk can move content after the screenshot is taken, and a point read off that screenshot no longer lands on what it showed.

Repro (System Settings > Spotlight, macOS 27)

  1. Open x-apple.systempreferences:com.apple.Spotlight-Settings.extension and scroll the content to the bottom, so Search Privacy… is visible.
  2. desktop_inspect (accessibility mode). The screenshot shows Search Privacy… at about y=709 (global). Immediately afterwards a raw AX read gives its frame as y=757, and a mode: pixels capture shows the content has moved down by the same amount.
  3. A point click at the screenshot's position now targets whatever moved under it. Here that's the disabled Clear Clipboard History button, not Search Privacy….

Every full walk grows the "Results from Apps" list again: I saw 40–136 pt drifts across runs. The list shrinks back after a while, so the drift depends on timing.

Workaround

Take a mode: pixels snapshot just before the point click. It doesn't walk the tree, so its screenshot matches the layout the click sees. The #147 live check used this: AX inspect, element scroll, pixels snapshot, then a point click.

Related

#147 (fixed in #157) was the same mechanism inside the click: its own descendant walk moved the button off the point. The click now expands only elements whose frame contains the point. Inspect still walks the whole window, and the 200-element listing needs that walk.

Possible directions

  • Read frames back after the walk, and flag or refuse when they moved relative to the capture.
  • Capture the screenshot after the walk, or re-capture when the walk changed the frames of elements it had already read.
  • Have the point click compare its hit-test result against the snapshot's element at that point.
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