[mbeczynski]

Change

• A race waits for 6 cars, not 9: the player's car plus as many as there are rivals (rivals pick their look from the loaded cars). Further cars don't start while the race screen is open: merging a model (up to 0.6 s) and the end of Entity(contentsOf:) (~90 ms) run on the main thread and caused hitches at the start of the race. The rest load after leaving the race screen. On the results screen loading froze the screen for 0.5–0.7 s, so it stays held there too.
• Load order: two at a time, the player's car first, then the smallest files. In catalogue order the heavy models were holding up the start.
• MainThreadSlices: mesh merge and applying baked AO run in ~6 ms slices with a 1 ms pause for a frame. In one go they blocked the main thread for 40–510 ms and 54–250 ms per car, and the turntable in the menu stopped.
• Frame-time log for the menu/garage. The race hitch log also covers the first 0.5 s after the scene is revealed.

Not changed: the ~0.5 s hitch when post-processing starts, under the loading screen. Our pipelines are ready at launch (0.01 s); the time is spent inside RealityKit before it calls our code.

Measurement (iPad M5 iOS 27 simulator, A/B alternating against main)

	main	this PR
cold start into a race	8.3–8.9 s	7.1–7.8 s
memory during the race	251–278 MB	204–231 MB
longest race frame	17–67 ms	17–50 ms
menu/garage, first 10 s: freezes > 100 ms	11	4–7
longest menu freeze	720–750 ms	440 ms (under the splash, before the menu shows)
total stall time in the menu	5.5–5.7 s	3.9–4.2 s

Tests

• Debug / Family / Release build
• XCUITest on a clean install: all 10 (Gameplay 7, GarageColors, AllTracks: every track and every car to the finish), passed; no new crash reports

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