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/SKILL.md

@@ -91,7 +91,12 @@ The bootstrapped server receives a **sanitized copy of the caller's environment*
    this script applies to a TUI that never signalled ready). Re-send with
    `multi-agent-mux-delegate-job submit` once the agent is up; the prompt is
    never re-injected automatically. `MAM_ONBOARD_ACK_S` overrides how long that
-   wait is — distinct from the wrapper's `MAM_INJECT_ACK_GRACE_S`.
+   wait is — distinct from the wrapper's `MAM_INJECT_ACK_GRACE_S`. After the
+   handshake the script waits for the onboarding job to **end** (Issue #50,
+   `MAM_ONBOARD_WAIT_S`, default 600 s) and prints `onboarding completed: job <id>
+   (<n>s)`; an onboarding that ends with `error` exits 44 and one that does not
+   end in time exits 45, both keeping the session, with
+   `last_visible_status: onboarding-<status>` on the row.
 
    **Start-up dialogs** are answered for every agent, not only claude (#24). The
    blocking-modal signatures and their accept keys live in each agent adapter
@@ -171,6 +176,8 @@ bash .agents/skills/multi-agent-mux-create/scripts/create_session.sh --workspace
 | `--auto-trust` / `--no-auto-trust` | Answer a start-up directory-trust dialog or leave it to a human (`MAM_AUTO_TRUST`; default: answer) |
 | `--isolate` / `--no-isolate` | Legacy, no-op |
 
+`MAM_ONBOARD_WAIT_S` (default 600): how long `--onboard` waits for the onboarding job to end after the `started` handshake.
+
 | Exit | Meaning |
 |---|---|
 | 0 | Created; or `--dry-run` |
@@ -180,6 +187,8 @@ bash .agents/skills/multi-agent-mux-create/scripts/create_session.sh --workspace
 | 4 | The YAML already has a `running` row of that name. The YAML write raises it after spawn, and the herdr session is rolled back |
 | 42 | The TUI never became ready and the process is gone, or it is alive and `MAM_KILL_ON_READY_TIMEOUT=1` (rolled back) |
 | 43 | The rollback could not kill the herdr session; it is still running |
+| 44 | The onboarding job ended with `error` (or was cancelled); the session is kept (Issue #50) |
+| 45 | The onboarding job did not end within `MAM_ONBOARD_WAIT_S`, or its record is gone; the session is kept |
 | other | A later step failed and its code is passed through. The EXIT trap (`cleanup_herdr_on_error`) rolls back the herdr session and closes the onboarding job as `cancelled`; if that kill fails, the exit is 43 instead |
 
 ## Registering the session in agent-sessions.yaml
@@ -201,7 +210,7 @@ bash .agents/skills/multi-agent-mux-create/scripts/worktree_prepare.sh \
 - `--creator-agent` creates the creator through this skill with the control root's binding and `MAM_NO_SUBSCRIBER_DAEMON=1`; the row's `pane.cwd` is the worktree.
 - Prints `BASE=<sha>`: record it **before** delegating the implementation, then review with `run_loop.sh --worktree <WT> --base "$BASE" --review-only`.
 - A submodule path that is not initialised yet but already holds files refuses `--submodules` up front (exit 3, nothing changed): the clone would fail on it and a rollback could not tell those files from its own.
-- Exit codes: 0 ok, 1 git / submodule / create failure, 2 usage or path rule, 3 refused to protect existing content (nothing changed).
+- Exit codes: 0 ok, 1 git / submodule / create failure, 2 usage or path rule, 3 refused to protect existing content (nothing changed); 44/45 are create's (onboarding error / timeout with `--onboard`; session and worktree kept).
 - create itself: a control-plane binding that cannot be computed is refused (exit 2) for a `--workspace` other than the control root and warned about for the control root; the immediate reconcile and the watchdog run the control root's code.
 
 ## Pitfalls