jobs: background execution (&), non-blocking reap, spin demo

- sys_reap: nohang reap of a finished zombie child (-> pid or 0).
- shell: 'cmd &' launches in the background (prints [pid], no wait); reaps
  finished jobs at the prompt ([pid done]). Foreground now waits for its own
  child specifically (loops wait(), reporting bg completions meanwhile) so kill
  reports the right pid.
- spin: a process that yields forever - a target for ps/kill.
- verified: spin &; ps shows it; kill <pid> removes just that one; immortal
  init; self-finishing bg worker reaped with [pid done].

1 files changed, 2 insertions, 0 deletions

diff --git a/c/gbos.h b/c/gbos.h
index 5f22a5a..f76d1e0 100644
--- a/c/gbos.h
+++ b/c/gbos.h
@@ -41,4 +41,6 @@ unsigned char lookup(const char *name);     /* command name -> program id    */
 unsigned char kill(unsigned char pid);      /* terminate a pid (1 is immortal)*/
 unsigned char psget(unsigned char slot, unsigned char *buf); /* {pid,state,prog}*/
 void          progname(unsigned char id, char *buf);         /* id -> name     */
+void          yield(void);
+unsigned char reap(void);                   /* reap a finished bg job, or 0   */
 #endif