- gate V4/B4 mismatch zones via PHASE_Z_B4_GATEKEEPER env (default OFF)
- record mismatch as adapter_needed_units with reason and mismatch_detail
- preserve render path byte-identical when flag unset
- run B1/B2/B4 placement planning in trace-only mode
- record placement_trace per rendered zone in debug output
- preserve existing render output and visual routing behavior