The placement PBT test validates that reshardCollection's zones/shardDistribution requests are honored regardless of which InitialSplitPolicy services them, across the cross-product of 4 shard-key shapes and 6 placement scenarios. Extend the model to also cover:

• Generalize shardDistributionShardListOnly targets to be built from shardNames dynamically (1..N shards) instead of a fixed pair.

• Add a shardDistributionPartitioned scenario: two shardDistribution entries splitting the key range across two shards at a fixed pivot, guarded via fc.pre() to skip keys with a hashed field (no meaningful numeric pivot there).

• Add a sameKeyResharding boolean axis to the model: when true, the collection starts already sharded on the target key, and the reshardCollection call sets forceRedistribution: true + a fresh reshardingUUID, combined with the placement request as usual.