fix: attach_command from one builder; no kill/start_command; stop closes a row-less session (Issue #71)

- attach_command is `herdr --session <server> agent attach <herdr name>`
  (`default` written too), built by lib_py.agents.sanitize.attach_command;
  create, resume and reconcile all use it. kill_command and start_command
  are no longer written, and status --json drops start_command.
- The two raw kill-session hints (create exit 43, id_order's orphan) print a
  stop-skill command with --herdr-session instead.
- stop_session.sh closes a session that has no registry row, herdr only and
  without --agent, when herdr runs it inside this workspace; another
  workspace's session is refused (exit 5), a missing one is exit 1, one that
  survives kill-session is exit 6. The registry is not changed.
- Docs: only the SKILL.md lines these changes made wrong; the skill block
  pins follow. Tests that asserted the removed fields keep their intent
  (issue50: create's own row; issue21: no control-root path in
  attach_command; tier2: the new form and the absent fields). S11 pins the
  shim to 4243da5, which changed it on purpose.

Refs #71

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-monitor/scripts/reconcile.sh

@@ -566,7 +566,7 @@ def _pin_and_verify_resume(s, agent, cwd, uuid, degraded=False):
     actions.append(f"updated {id_name} id: {uuid}")
 
 
-from lib_py.agents.sanitize import sanitize_herdr_agent_name as _sanitize
+from lib_py.agents.sanitize import sanitize_herdr_agent_name as _sanitize, attach_command
 
 yaml_sessions = d.get('herdr_sessions', [])
 yaml_session_names = {s['name'] for s in yaml_sessions if s.get('name')}
@@ -656,7 +656,6 @@ if herdr_confirmed:
         _ambient = os.environ.get('HERDR_SESSION_NAME', '')
         if srv == 'default' and _ambient and _ambient != 'default':
             srv = _ambient
-        server_opt = f"-L {srv} " if srv != 'default' else ""
         # The shim resolves this from the pane's root process. Fall back to now
         # only if that failed: 'now' can merely over-estimate creation time,
         # which tightens the stale-transcript guard, whereas 0 disables it and
@@ -674,9 +673,7 @@ if herdr_confirmed:
             'herdr_server': srv,
             'herdr_workspace': _slug(pm['cwd']),
             'pane': {'index': 0, 'pid': pm['pid'], 'cmd': agent, 'cmd_full': cmd_full, 'cwd': pm['cwd']},
-            'start_command': f'HERDR_SESSION_NAME={srv} herdr new-session -d -s "{name}" -x 140 -y 40 -c "{pm["cwd"]}" "{cmd_full}"',
-            'attach_command': f'HERDR_SESSION_NAME={srv} herdr agent attach {name}',
-            'kill_command': f'herdr {server_opt}kill-session -t {name}',
+            'attach_command': attach_command(srv, name),
             'last_visible_status': 'running',
             'last_visible_note': 'auto-registered by monitor',
         }