Relative #include of staff code breaks graders that copy only the source dir

Moving a reference solution out of a student-file #else branch into a sibling directory (staff_solutions/X/) and pulling it back in with #ifndef DEPLOY #include "../staff_solutions/X/server.c" builds fine in place, and unifdef -DDEPLOY still produces the same student stubs. But any harness that copies only source_files/ into a scratch dir before building (a TA-solution e2e test, a benchmark script that copies the pair's files) fails with 'file not found', because the relative path points outside the copy. Before moving code, grep for every place that copies or builds the source dir, and try a build of a lone copy. Quoted includes search the including file's own directory first, so the staff file's #include "common.h" picks up its sibling header, while shipped headers still resolve through -I.