By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Mutation: make the covering-test reorder gate pure and tested Address code-review follow-ups: - Extract reorderForMutationChild, a pure helper that reorders a mutation child's filtered forest cheapest-first only when execution-order randomisation is enabled and a baseline is present. The child now reads the baseline unconditionally and hands the flag + costs to this helper, so the gate (previously an inline IO conditional) is unit-testable. Behaviour is unchanged: reading the baseline when randomisation is off is a harmless extra read, and the helper yields the same forest. - Add gate tests: reorder when randomisation is on with a baseline, and leave the forest untouched when randomisation is off or no baseline is available. - Note in readAndUnionBaselineDirs that the slowest-wins baseline merge (chosen for safe timeouts) only affects ordering quality, never verdicts.