Pseudo-terminals, and what tmux and htop needed around them

- /dev/ptmx and /dev/pts/N: Unix98 pairs with a full line discipline,
  window sizes, job control and hangup (kernel/dev/pty.c).
- The console speaks scroll regions, insert/delete line, SU/SD, RI/IND/NEL,
  DECSC/DECRC; swallows charset designations and private CSI sequences;
  and LF only returns the carriage under ONLCR.
- setsid() drops the controlling terminal, so a pane's pty becomes its ctty.
- pipe2() honours O_NONBLOCK and O_CLOEXEC (libevent's signal pipe).
- File modes are stored and enforced: chmod, fchmod(at), umask, creation
  modes; /tmp is 1777.
- /proc/stat has real user/system/idle; /proc/<pid>/task; kthread flag.
- SO_PEERCRED, IOV_MAX 1024.
- /proc/strace: name a program and its syscalls go to the kernel log.
- World gains htop, btop, tmux, mc, ncdu, fastfetch, games, X toys, NetSurf.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

include/core/defs.h

@@ -61,6 +61,10 @@ int             pciuser_mmio_ok(uint64 phys, uint64 len);
 void            pciuser_release_all(struct proc*);
 int             pciuser_owner_pid(int idx);
 int             proc_reincarnate(int status);
+void            proc_cputime(uint64 *user, uint64 *sys);
+// kernel/dev/procfs.c: /proc/strace
+int             strace_wanted(const char *name);
+int             proc_write_strace(int user_src, uint64 src, uint n);
 void            proc_kill_init(void);
 extern uint     init_generation;
 void            cprintf(char*, ...);
@@ -512,6 +516,7 @@ int             socksendto(struct socket*, char *buf, int n,
 int             sockbind_in(struct socket*, uint addr, ushort port);
 int             sockconnect_in(struct socket*, uint addr, ushort port);
 int             sock_domain(struct socket*);
+int             sock_peercred(struct socket*, int*, uint*, uint*);
 // Socket options. The syscall layer does the user-memory marshalling and these
 // do the work, because struct socket's fields live in kernel/net/unix.c and the
 // syscall layer deliberately cannot see them.