Real string core and process teardown; thin read/write/close/getpid/_exit syscall wrappers; the rest follows the stub convention (documented error return, errno = ENOSYS, TODO). syscall.c is the only kernel ABI surface; crt0.S is the static entry point, kept out of libc.a.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <[email protected]>
