fix: preserve available snapshot plan tiers

Author: thymikee

apple/runner/AgentDeviceRunner/AgentDeviceRunnerUITests/RunnerTests+SnapshotCapturePlan.swift

@@ -219,10 +219,9 @@ extension RunnerTests {
         treeCaptureSliceBudgetOverride: nil
       )
     }
-    // Preserve the ordinary plan exactly. Filtering unavailable tiers here
-    // would change physical-device fallback attribution on the normal path.
+    // Preserve the ordinary plan after removing tiers unavailable on the current platform.
     return EffectiveSnapshotCapturePlan(
-      plan: plan,
+      plan: availablePlan,
       xCTestChannelState: .normal,
       treeCaptureSliceBudgetOverride: nil
     )