docs(rt2): runtime-v2 track — the runtime beyond sockets
- five stories under docs/stories/runtime-v2/: 1 streaming subprocess
(42's follow-up; five forks incl. the mailbox-cap collision), 2 PTY,
3 signals-as-events (signalfd lean), 4 termios adoption, 5 SCM_RIGHTS
fd passing; 00-story states the arc — the plane learned sockets in
8/11/35, files in 6, this adds processes/terminals/signals
- build order 1 -> 2 -> 3; 4 and 5 startable alone; all readiness:
refine, brainstormed on demand
- board: Five tracks; "▸ runtime-v2" pending section; wmux section now
points at it; graph section 6 nodes carry runtime-v2 numbers + links
- wmux stories re-reference the track; prefix `rt2` claimed
- linkcheck: 0 broken
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit e0451cb4889bb3d03429c0276d03c090269a5ced)