Applies CCCL cub/agent/agent_radix_sort_downsweep.cuh design:
- union TempStorage reuses same shared memory across load/rank/scatter phases
- Translated: streaming parse state organized into 4 phases
(DETECT/HEADER/PARAMS/CLOSE) matching the tool call parse lifecycle
- Clear documentation of which state belongs to which parse phase
- Reset clears all phases at once like union initialization on new tile