nx_doctor_build.nx

nx_doctor_build.nx -- the DOCTOR's build-heal (RACI: the FIX belongs to the Doctor, not the Conductor). When the Engineer detects a broken/miscompiled build, the Doctor's remedy is to REGENERATE it: the known-good compiler is non-deterministic, so a fresh compile usually emits a correct build -- regenerating the artifact IS the heal. doc_rebuild produces a fresh <src> -> <sout>(.s) -> <eout>(.elf); returns 0 on a clean build, <0 if it could not produce one. The Doctor only fixes (regenerates); the ENGINEER re-verifies (runs + canary), the CONDUCTOR orchestrates, the WARDEN/COUNCIL govern. Depends only on syscalls -- decoupled. license_tier: ORIGINAL