Hojun-Cho
c3f994822d
After12436dd, lib/fmt and lib/log production code routed through os.write / os.exit. The test files (fmttest, logtest, memiotest) still carried the same @symbol("rt_syscall") syscall1ww / doexit stub block with the (now stale) os↔io collision rationale. Same mechanical drop as12436dd: add use os;, route fail() through os.exit, remove the stubs. Also reword the stale workaround comment in lib/memio/memio.ww covering rt_alloc/rt_free. The decls themselves stay until lib/os exports alloc/free as a follow-up. No combined.ww regen (these files aren't bootstrap-folded).