Crate spawn_parent_m 

Sub-VM parent guest. Set up by the test harness with:

• slot 3: Hash(image_s) — content-addressed Cap::Image for S.
• slot 5: Hash(input_data) — input Cap::Data for the call.

M mints a fresh prepared CNode, copies the input DataCap into its own slot[0] (the CALL scratchpad), derives a child Instance from Image S + the prepared CNode, and CALLs the child. When the child halts, the kernel reflects the child’s slot[0] (a fresh result DataCap) back into M’s slot[0]. M reads that DataCap and returns the resulting byte.