docs: the README and skill answer what dogfooding asked

A first-time user through a mount could not find how to get a terminal,
read path++text as a typo, did not know > on data replaces only the
addressed range, which regexps addr takes, that lock fails fast, what
errors is, where an unknown exec word goes (typed into a terminal, not an
error), that new panes are +New and a column's last pane leaves one, or
which 9ns mount other processes can see. The README (still 45 lines),
docs/fs.md and the skill now say.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 14 insertions, 4 deletions

diff --git a/.agents/skills/pardes-9p/SKILL.md b/.agents/skills/pardes-9p/SKILL.md
index 6fea5838..daf4c279 100644
--- a/.agents/skills/pardes-9p/SKILL.md
+++ b/.agents/skills/pardes-9p/SKILL.md
@@ -33,7 +33,9 @@ the `pid`, `version` and `panes` of a session new enough to serve it.
 `/mnt/9p/pardes` is the registry of posted sessions, mounted once for the
 machine. It is not the per-pane kernel mount the `Tty9p` builtin makes, which
 gives one pane's shell `$PARDES_MOUNT`; see [docs/v9fs.md](../../../docs/v9fs.md)
-for that. Either mountpoint serves the same tree.
+for that. Either mountpoint serves the same tree. A `9ns --unix SOCKET -- cmd`
+mount exists only inside `cmd`'s private namespace; to share one, use the
+registry (`9ns --mntgen`).
 
 A running session serves whatever binary started it. If a listing does not
 match this document, that session predates the change; restart it.
@@ -59,7 +61,9 @@ $m/ctl        the settings, one a line as a write takes them; write a setting or
               and the column words Delcol, Collapse, which act on that pane's column) go to
               $m/pane/<n>/ctl
 $m/commands   every builtin: `Word`, `Word arg`, then `root` or `pane` (which ctl takes it)
-$m/pane/new   open it to make a pane, read names it; rmdir $m/pane/<n> closes it
+$m/pane/new   open it to make a pane (a scratch named <dir>/+New), read names it;
+              rmdir $m/pane/<n> closes it; closing a column's last pane leaves a +New there
+$m/pane/<n>/errors  write-only: text appended to the +Errors pane of the pane's directory
 $m/os/        the host filesystem
 ```
 
@@ -74,7 +78,8 @@ n=$(cat "$m/pane/new")                          # make one, take its serial
 printf 'text\n' > "$m/pane/$n/body"             # append
 cat "$m/pane/$n/tag"                            # what its tagline offers
 echo notes.txt > "$m/pane/$n/name"              # rename the buffer
-echo Save > "$m/pane/$n/exec"                   # save it
+echo Save > "$m/pane/$n/exec"                   # save it (or to its ctl)
+echo Tty > "$m/pane/$n/ctl"                     # a terminal in its directory
 echo "/etc/hosts:3" > "$m/look"; cat "$m/look"  # open a file, see where it landed
 rmdir "$m/pane/$n"                              # close it, dirty or not
 ```
@@ -104,7 +109,12 @@ active pane from the root and at that pane from `$m/pane/<n>/look` and
 `$m/pane/<n>/exec`. Reading any of them answers the serials the last command
 made, or the pane it focused or acted on. A command that fails is reported in
 the editor, not as a write error, so inspect the resulting pane, index, message
-or screen; only a malformed line fails the write itself.
+or screen; only a malformed line fails the write itself. A word no builtin
+knows (a typo included) is typed into a terminal -- the pane itself if it is a
+terminal at its prompt, else one in the pane's directory, made if need be --
+and is not reported as an error. Every refused 9P write adds an `err <serial|->
+<file>: <why>` record to `$m/log`; through a mount the write itself only says
+`Invalid argument`.
 
 ## Edit through addresses, dot and the flag files