[teamleaderleo]

TooltipSurfaceTests.theFirstTooltipFadesInRisingAndAWarmNeighborsIsThereAtOnce (from #20528) failed on the macOS 27 report-only lane at the opacity read: "the first tooltip did not fade in" (run 38638271559). #20725 stopped that lane from exiting early, which is why the failure only showed up now.

Cause: the environment, not the product. The tooltip does fade in. The failure has two sources, both on the GitHub swift test lane, which runs every suite in one process on one main actor:

1. Timing. The test reads layer.animation(forKey: "opacity") after async waits. On a loaded host the 120 ms fade has finished, and Core Animation has removed it, before the test gets there. The same mini and code passed an hour later (run 38647037583).
2. Shared global state. Motion.reduceMotionOverride is process-global, so another suite can set or clear it while a tooltip test waits out the hover delay. Fixing (1) exposed this: in run 38662157909 the Reduce Motion test saw a rise that the tooltip legitimately added after another suite had turned Reduce Motion off.

Fix (test only):

• The test sets the tooltip surface layer's speed to 0, so its animations hold still, the same way the hover delay holds on the manual clock. The test reads the fade the tooltip actually starts, however late it gets there.
• Both fade tests work out from the fade's length which Reduce Motion setting the tooltip used when it showed: Reduce Motion caps a fade at one crossfade, so 0.1 s means on and 0.12 s means off. The test then checks that the rise matches that setting.
• A setting different from the test's own override is accepted only if another suite posted reduceMotionDidChange before the show.
• The first test also pins Motion.liveResizeOverride off, because a live resize drops the rise.

All the existing assertions are kept.

Testing

All runs use cmux-ci run --class light --label cmux --script scripts/ci/run-swift-testing-suites.sh --arg Packages/macOS/CmuxNext.

Red (abf6fec, rest waits 300 ms after the show):

• Steps: db6466f0e9935237d251203a, ac480c85c1511e9b9bdb7bc0, 30a79a4ca08c1420d80e335a, all on aws-m4pro-9 (has a display).
• Both fade tests fail at the opacity read with shown Back, visible true, same layer true, keys [], opacity 1.0.

Green:

• d3a2fc3: step bebc7978ca8e7eae02753523 on aws-m4pro-8.
• fa7fd95: step 3ac4cc4f6294660babfc59c1 on aws-m4pro-9.
• All three tooltip panel tests pass.

Not counted or not this PR:

• Steps that landed on headless hosts skip the fade tests, so they are not counted.
• SidebarInsertWhileDisplayAsleepTests is a base red in every one of those steps.

GitHub swift test lane: full-ci is added only to run cmux-next swift test on the GUI mini. Since #20543, PRs run swift test only under full-ci. The other full-ci lanes run too, but this PR is not checking them.

Not fixed here: theSurfaceIsFrostedGlassOrOpaqueUnderReduceTransparency sometimes reads shadowOpacity 0 on that lane. It already did on base (run 38638271559), and it passes on the fleet.

Changelog

none

🤖 Generated with Claude Code

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[github-actions]

Not verified: macOS jobs did not run: compile and app tests were skipped on 93bf8a9bfa; ci-status is green without them.

CI passes on 93bf8a9bfa (run 38687599009 attempt 1).
macOS jobs did not run: compile and app tests were skipped: Fast static checks skipped (the macos job needs both to succeed). Re-run CI once they pass, before merging.

Written by scripts/ci/classify_failures.py (ci-failure-attribution.yml); signatures are its SIGNATURES table. A machine verdict is the runner's fault, not this PR's; yours means the failing file is one this PR changes, also red on main that main's latest full suite fails the same way, seen on other PRs that it failed on another pull request's run lately.

[teamleaderleo]

Bead cx-bgshz created for this PR by the cmux coordinator.

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