Upper bound (ms) a foreground pass waits for an in-flight shadow store
before assembling the slice itself. A healthy shadow pass is budget-bounded
(≈ one frame budget + one level) and started a frame EARLIER than the
foreground, so it lands first; this only fires when the shadow has stalled
(a hung fetch has no timeout of its own). Well below the prefetcher's own
5 s stall guard, so a stuck shadow costs one visible hitch, not a freeze.
Upper bound (ms) a foreground pass waits for an in-flight shadow store before assembling the slice itself. A healthy shadow pass is budget-bounded (≈ one frame budget + one level) and started a frame EARLIER than the foreground, so it lands first; this only fires when the shadow has stalled (a hung fetch has no timeout of its own). Well below the prefetcher's own 5 s stall guard, so a stuck shadow costs one visible hitch, not a freeze.