feat(issue-50): create --onboard waits for the onboarding job to end (A)

The handshake only said the agent saw the prompt (#23). create_session.sh
now waits, after `started`, for the onboarding job to reach a terminal
status and makes that its own result, so the orchestrator learns it from
create's exit (MULTI_AGENT_RULES §6) instead of guessing from herdr's
agent_status:

- lib_py/delegation/wrapper.py: `wait-terminal` (completed|error|cancelled,
  `timeout` after --timeout, `missing` when the record is gone; stops with
  its caller via --watch-pid) and `onboard-exit` (completed 0, error or
  cancelled 44, timeout or missing 45). bash branches on the printed answer.
- lib.sh: delegate_wait_terminal / delegate_onboard_exit, thin calls.
- create_session.sh: `onboarding completed: job <id> (<n>s)` on stdout, or
  `last_visible_status: onboarding-<status>` on the row, the reason on stderr
  and `exit 44` / `exit 45` after `trap - EXIT` - the session is kept, as for
  a missing handshake. The "no started" path (error, exit 0 before) now ends
  with 44. MAM_ONBOARD_WAIT_S (default 600, floor 1) bounds the wait.
- worktree_prepare.sh: 44/45 pass through with "session and worktree kept".
- create SKILL.md exit table (44, 45) and the knob; the #42 inventory follows.
- tests/conftest.py: --onboard is the default, so ~60 sandbox create tests
  reach the new wait. The mock herdr now acts as the agent for create's
  onboarding prompt - it runs the publish commands the prompt names through
  the real publish_event.py - and MAM_ONBOARD_WAIT_S=3 caps a test that turns
  that off (MAM_MOCK_ONBOARD_HANDSHAKE=0 -> 44, `started` -> 45). The
  delegate-job wrapper's prompt has another shape and is never answered.
- tests/test_issue50_onboard.py: the decision tables, create in the sandbox
  (0 / 44 / 45, session kept, row note, trap window), the knob's integer
  rule, worktree_prepare's pass-through.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-create/scripts/create_session.sh

@@ -19,6 +19,8 @@
 #   4  = agent-sessions.yaml append failure
 #   42 = agent TUI never became ready and the process is gone
 #   43 = rollback could not kill the herdr session; it is still running (#23)
+#   44 = the onboarding job ended with error (or was cancelled); the session is kept (#50)
+#   45 = the onboarding job did not end within MAM_ONBOARD_WAIT_S; the session is kept (#50)
 set -euo pipefail
 
 _script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
@@ -316,6 +318,21 @@ for s in d.get('herdr_sessions', []):
 PYEOF
 }
 
+# _mark_row_note <note>
+# Issue #50: last_visible_status only. The row stays `running` with its
+# delegate_job_id: the session is alive and the job record is the evidence.
+_mark_row_note() {
+  local note="$1"
+  [ "${ROW_APPENDED:-0}" = "1" ] || return 0
+  atomic_dump_yaml "$AGENT_SESSIONS_YAML" SESSION_NAME="$SESSION_NAME" ROW_NOTE="$note" <<'PYEOF' || true
+name = os.environ['SESSION_NAME']
+for s in d.get('herdr_sessions', []):
+    if s.get('name') == name:
+        s['last_visible_status'] = os.environ['ROW_NOTE']
+        break
+PYEOF
+}
+
 # Trap for rolling back/cleaning up herdr session if script exits due to error
 cleanup_herdr_on_error() {
   local exit_code=$?
@@ -698,12 +715,38 @@ If you delegate any part of it with multi-agent-mux-delegate-job submit, add --p
     esac
     JOB_TERMINALIZED=1
   fi
+  # Issue #50: the handshake only said the agent saw the prompt. Wait for the
+  # onboarding itself to end; its result is this script's exit code, so the
+  # orchestrator learns it from create (MULTI_AGENT_RULES §6) instead of
+  # guessing from herdr's agent_status. A job marked `error` just above is
+  # terminal and returns at once.
+  ONBOARD_WAIT_S=$(mam_int_knob MAM_ONBOARD_WAIT_S 600 1)
+  ONBOARD_T0=$(date +%s)
+  ONBOARD_STATUS="$(delegate_wait_terminal "$DELEGATE_JOB_ID" "$ONBOARD_WAIT_S")"
+  ONBOARD_STATUS="${ONBOARD_STATUS:-missing}"
   # Trigger immediate priority reconcile cycle asynchronously
   # Issue #21 phase 2 (A8): the control root's reconcile/watchdog, never the
   # (unreviewed) copy in a worktree --workspace; identical paths by default.
   (bash "$SKILL_DIR/multi-agent-mux-monitor/scripts/reconcile.sh" --once >/dev/null 2>&1 &) || true
   WD_PID=$(start_watchdog "$DELEGATE_JOB_ID" "$WORKSPACE_ROOT")
   echo "watchdog PID: $WD_PID"
+  case "$ONBOARD_STATUS" in
+    completed)
+      echo "onboarding completed: job $DELEGATE_JOB_ID ($(( $(date +%s) - ONBOARD_T0 ))s)"
+      ;;
+    *)
+      # The session is kept, as for a missing handshake above: the row says
+      # what happened and the exit code tells the caller. The trap is cleared
+      # first - a non-zero exit must not roll a live session back.
+      _mark_row_note "onboarding-$ONBOARD_STATUS"
+      echo "ERROR: onboarding $ONBOARD_STATUS for '$SESSION_NAME': job $DELEGATE_JOB_ID; the session is kept" >&2
+      trap - EXIT
+      case "$(delegate_onboard_exit "$ONBOARD_STATUS")" in
+        44) exit 44 ;;
+        *) exit 45 ;;
+      esac
+      ;;
+  esac
 fi
 # Clear cleanup trap as registration was fully successful
 trap - EXIT