`_ems`: tolerate and warn on already popped execs

In the `translate_and_relay_brokerd_events()` loop task that is, such
that we never crash on a `status_msg = book._active.pop(oid)` in the
'closed' status handler whenever a double removal happens.

Turns out there were unforeseen races here when a benign backend error
would cause an order-mode dialog to be cancelled (incorrectly) and then
a UI side `.on_cancel()` would trigger too-early removal from the
`book._active` table despite the backend sending an actual 'closed'
event (much) later, this would crash on the now missing entry..

So instead we now,
- obviously use `book._active.pop(oid, None)`
- emit a `log.warning()` (not info lol) on a null-read and with a less
  "one-line-y" message explaining the double removal and maybe *why*.

piker/clearing/_ems.py

@@ -388,6 +388,7 @@ async def open_brokerd_dialog(
     for ep_name in [
         'open_trade_dialog',  # probably final name?
         'trades_dialogue',  # legacy
+        # ^!TODO, rm this since all backends ported no ?!?
     ]:
         trades_endpoint = getattr(
             brokermod,
@@ -1019,8 +1020,18 @@ async def translate_and_relay_brokerd_events(
                 )
 
                 if status == 'closed':
-                    log.info(f'Execution for {oid} is complete!')
-                    status_msg = book._active.pop(oid)
+                    log.info(
+                        f'Execution is complete!\n'
+                        f'oid: {oid!r}\n'
+                    )
+                    status_msg = book._active.pop(oid, None)
+                    if status_msg is None:
+                        log.warning(
+                            f'Order was already cleared from book ??\n'
+                            f'oid: {oid!r}\n'
+                            f'\n'
+                            f'Maybe the order cancelled before submitted ??\n'
+                        )
 
                 elif status == 'canceled':
                     log.cancel(f'Cancellation for {oid} is complete!')
@@ -1544,19 +1555,18 @@ async def maybe_open_trade_relays(
 
 @tractor.context
 async def _emsd_main(
-    ctx: tractor.Context,
+    ctx: tractor.Context,   # becomes `ems_ctx` below
     fqme: str,
     exec_mode: str,  # ('paper', 'live')
     loglevel: str|None = None,
 
-) -> tuple[
-    dict[
-        # brokername, acctid
-        tuple[str, str],
+) -> tuple[  # `ctx.started()` value!
+    dict[  # positions
+        tuple[str, str],  # brokername, acctid
         list[BrokerdPosition],
     ],
-    list[str],
-    dict[str, Status],
+    list[str],  # accounts
+    dict[str, Status],  # dialogs
 ]:
     '''
     EMS (sub)actor entrypoint providing the execution management