How to reproduce:
1. Open the attached project "GridPlayerRepro"
2. In "GridRepro" scene, enter Play mode and observe the green "PASS" verdict and the 2x2 checkerboard
3. Build and Run the project
4. Observe the results
Expected results: The Player shows the same 2x2 checkerboard and green "PASS" verdict as the Editor, with cell0 at (0,0,100x60) and cell1 at (100,0,100x60)
Actual results: The Player shows a red "FAIL - grid layout is NOT applied" verdict and no checkerboard, because every grid cell collapses to (0,0,200x0) as if grid layout were disabled, and no warning or error is logged
Reproducible with: 6000.7.0a5
Can't test with: 6000.0.81f1, 6000.5.9f1, 6000.6.0b9, 6000.7.0a4 (No feature)
Reproducible on: macOS Tahoe 26.6 (M1 Max)
Not reproducible on: No other environment tested
Note: Not a regression - "display: grid" is new in 6000.7.0a5 and is absent from 6000.7.0a4. The project ships with "Enable Grid Layout" already on ("m_EnableGridLayout: 1" in ProjectSettings/UIToolkitProjectSettings.asset), and the on-screen verdict is computed from the measured layout so nothing has to be read off disk. Clicking the "Force LayoutNative.SetGridLayoutEnabled(true)" button in the Player makes the checkerboard appear and flips the verdict to PASS with no rebuild, which shows the layout solver is fine and only the project setting fails to reach the Player. "resolvedStyle.display" reports "Grid" in the Editor and in the Player both before and after the button, so the style resolves correctly and only the layout does not run.