typedef struct {
  ...
    uint32_t    marker;
  ...
} km_core_context_item;

vs

typedef struct {
  ...
    uintptr_t             marker;          // MARKER type
  ...
} km_core_action_item;

Suggest converting both to uint32_t to be consistent about sizing. In practice uintptr_t is never going to be smaller than uint32_t, but I don't think we need a 64-bit value here. Note that we have an implicit assumption about markers being no larger than uint16_t within KMX processor (and perhaps elsewhere too).