post registry + 9ns --mntgen: the /srv translation

cloud9.post: servers post their socket under a name in
$XDG_RUNTIME_DIR/9p (post/unpost, posted, dial, Watch) and
serve.Runner.listenPosted posts a server by name, unposting on stop.
Names are budget-checked against the 108-byte socket path; a claim
binds+listens at a private temp path and takes the name with atomic
renames under flock (RENAME_NOREPLACE for free names, RENAME_EXCHANGE
grab-verify-commit for stale ones): the registry path is never unlinked
by a claim, live names refuse with AlreadyPosted, foreign files with
NotSocket, and unpost removes only the caller's inode-matched entry.
Watch surfaces inotify overflow and a replaced registry dir.

9ns --mntgen [--mount DIR] -- PROGRAM: one FUSE mount at /mnt/9p whose
synthetic root lists the posted registry (no connection made); a walk
into an unmounted name dials it and runs the existing bridge dispatch
in a per-server worker thread, routed by mount index in the node id's
top bits (ordinals never reused, cap 4096); a dead server answers EIO
on its subtree and is re-dialed on the next walk. The dial watches
stop_fd through Tversion (connectWatched). All existing 9ns forms are
unchanged.

9proc's unix listener no longer blind-unlinks its path: a foreign
non-socket is refused (Occupied), a live server is refused
(AlreadyListening), only a refused socket is cleared, and stop()
unlinks only the listener's own inode-matched socket.

Hardened by adversarial review (GLM 5.3 x2 + DeepSeek V4.1 Flash, all
high-thinking): double-bind races on one name (0 in 180k rounds),
foreign-file TOCTOU deletions (0 in 4M flips), a 255-byte-name listing
panic, inotify queue overflow silently dropped, listenPosted silently
overwriting, dial-time Tversion hangs wedging the dispatcher, --debug
silently ignored in mntgen, and xattr/statx probes answering EPERM on
the synthetic root (broke `ls -l /mnt/9p`).

Tests: root 80/80, 9ns 47/47, 9proc 60/60, integration 88/88 +
mntgen 37/37, adversarial 213/0, freestanding riscv32 gate green.

0 files changed, 0 insertions, 0 deletions