Crate bench_pt_cache 

Page-table-cache bench guest (one image, two endpoints).

• Endpoint 0 (caller A): reads a count n from φ[7], derive_spawns a child Instance once (from its own image — the kernel’s derive_spawn falls back to the running frame’s image when the image slot is empty), then host_calls that resident child’s echo endpoint n times, summing the echoes. Because the child is an Owned sub-VM that HALT folds back into the same cnode slot, every iteration re-CALLs the same resident B.
• Endpoint 1 (echo B): returns its argument (φ[7]) unchanged. No data-region access ⇒ no CoW, no per-instance page-table delta.

Goal: a steady-state CALL into the resident B allocates nothing beyond a small KernelFrame — no per-CALL page-table rebuild. The companion tests/pt_cache_heap.rs measures that directly.