Function eval_loop_fabric_heap 

pub fn eval_loop_fabric_heap(lf: &LoopFabric, params: &[i64]) -> i64

Evaluate a FOREACH OVER A LOCAL HEAP LIST (seq_heap_ptr.is_some()). The prologue-heap island builds the list into a shared heap ONCE; then for each iv in 0..heap[list_ptr] the body runs with that heap THREADED — the element heap[list_ptr + 1 + iv] is destructured via HeapRead, and any collection op in the body reads/writes the same heap (so mutation across iterations persists). Bit-identical to the VM.