feat(issue-21): persist and forward the control-plane binding in create/resume/stop; status and reconcile honor MAM_JOBS_DIR

A session row now records the control plane it belongs to, and the pane
gets it explicitly instead of relying on env inheritance.

- lib_py/control_plane.py (+ thin lib.sh wrappers mam_control_plane_json /
  mam_control_plane_prefix): the binding is WORKSPACE_ROOT,
  AGENT_SESSIONS_YAML, MAM_JOBS_DIR, DELEGATE_JOB_LOGS_DIR as absolute paths.
- create: the binding is always persisted on the row (`control_plane`) and
  forwarded to the pane only when it differs from what --workspace alone
  implies, as leading K=V tokens that lib.sh's new-session already turns into
  --env (fresh pane) or `env K=V` (reused idle pane). pane.cmd_full and
  start_command stay unprefixed. A binding with whitespace that would have to
  be forwarded is refused with exit 2 (lib.sh splits the flags unquoted); the
  ~/.local/bin wrapper path records the binding but warns it is not forwarded.
- resume: the row's binding wins over the caller's env (a difference is
  reported on stderr) and is forwarded again; a legacy row without one uses
  the caller's binding and update_yaml_resumed.sh records it.
- stop: registry order MAM_JOBS_DIR > the row's mam_jobs_dir >
  $WORKSPACE_ROOT/.mam/jobs > .mam/jobs, exported for delegate_publish_event.
- status: both get_job_status copies look in MAM_JOBS_DIR, the row's
  registry and the matching audit logs before the old candidates.
- reconcile: MAM_JOBS_DIR wins in the subscribe heredoc and is passed in.

Tests T3-0..T3-8 (mock herdr: forwarding is verified at the herdr-call level
only; real pane env propagation is left to item 7). T3-7 is a static guard.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017R3Eg7MEpSWnm1oB9ZPP6G

.agents/skills/multi-agent-mux-stop/scripts/stop_session.sh

@@ -132,7 +132,8 @@ for s in d.get('herdr_sessions', []):
     if s.get('name') == name:
         cwd = (s.get('pane') or {}).get('cwd', '')
         jid = s.get('delegate_job_id', '') or ''
-        print(json.dumps({'cwd': cwd, 'job_id': jid}))
+        cp = s.get('control_plane') or {}
+        print(json.dumps({'cwd': cwd, 'job_id': jid, 'mam_jobs_dir': cp.get('mam_jobs_dir', '') or ''}))
         sys.exit(0)
 sys.exit(7)
 ") || {
@@ -142,6 +143,13 @@ sys.exit(7)
 
 TARGET_CWD=$(printf '%s' "$MAPPED_DATA" | python3 -c 'import sys,json; print(json.load(sys.stdin).get("cwd",""))')
 DELEGATE_JOB_ID=$(printf '%s' "$MAPPED_DATA" | python3 -c 'import sys,json; print(json.load(sys.stdin).get("job_id",""))')
+# Issue #21: a row created against another control plane names its registry.
+# Order: MAM_JOBS_DIR > the row's control_plane.mam_jobs_dir > WORKSPACE_ROOT >
+# .mam/jobs; exported so delegate_publish_event (lib.sh) uses the same one.
+ROW_JOBS_DIR=$(printf '%s' "$MAPPED_DATA" | python3 -c 'import sys,json; print(json.load(sys.stdin).get("mam_jobs_dir",""))')
+if [ -z "${MAM_JOBS_DIR:-}" ] && [ -n "$ROW_JOBS_DIR" ]; then
+  export MAM_JOBS_DIR="$ROW_JOBS_DIR"
+fi
 DELEGATE_JOB_TOKEN=""
 DELEGATE_JOB_ATTEMPT=""
 if [ -n "$DELEGATE_JOB_ID" ]; then