Guard `brokerd_msg` set in order-mode dialog loop

Use `msg.setdefault('brokerd_msg', msg)` instead of blind assignment and
log a warning when the field was already populated.

Specifically, this avoids a self-reference field recursion which causes
crashes when using `tractor.devx.pformat.ppfmt()`..

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/ui/order_mode.py

@@ -1022,13 +1022,22 @@ async def open_order_mode(
             started.set()
 
             for oid, msg in ems_dialog_msgs.items():
-
                 # HACK ALERT: ensure a resp field is filled out since
                 # techincally the call below expects a ``Status``. TODO:
                 # parse into proper ``Status`` equivalents ems-side?
                 # msg.setdefault('resp', msg['broker_details']['resp'])
                 # msg.setdefault('oid', msg['broker_details']['oid'])
-                msg['brokerd_msg'] = msg
+                ya_msg: dict = msg.setdefault(
+                    'brokerd_msg',
+                    msg,
+                )
+                if msg is not ya_msg:
+                    log.warning(
+                        f'A `.brokerd_msg` was already set for ems-dialog msg?\n'
+                        f'oid: {oid!r}\n'
+                        f'ya_msg: {ya_msg!r}\n'
+                        f'msg: {ya_msg!r}\n'
+                    )
 
                 await process_trade_msg(
                     mode,