Nest nursery scope inside EMS ctx in order mode

Move the `trio.open_nursery()` + `collapse_eg()`
block to be nested inside `open_ems()` instead
of as a sibling — nursery tasks (order handling,
trade processing) depend on the EMS connection
staying alive.

Also,
- Default `'paper'` entry upfront in `accounts`
  dict and raise `ConfigurationError` with an
  actionable msg when a `brokerd_accounts` fqan
  isn't found in `accounts_def`.
- Use `msg.setdefault('brokerd_msg', msg)` for
  ems dialog msgs instead of blind assignment;
  warn if already set.
- Alias `asynccontextmanager as acm`.
- Use `fqan` var naming for fully-qualified
  account names, `broker_name` from `mkt.broker`.
- Tighten log msg formatting (`fqme!r`).

(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

@@ -19,7 +19,7 @@ Chart trading, the only way to scalp.
 
 """
 from __future__ import annotations
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager as acm
 from dataclasses import dataclass, field
 from decimal import Decimal
 from functools import partial
@@ -779,7 +779,7 @@ class OrderMode:
         return maybe_dialog
 
 
-@asynccontextmanager
+@acm
 async def open_order_mode(
     feed: Feed,
     godw: GodWidget,
@@ -814,6 +814,7 @@ async def open_order_mode(
 
     # spawn EMS actor-service
     async with (
+        # tractor.trionics.collapse_eg(),
         open_ems(
             fqme,
             loglevel=loglevel,
@@ -824,11 +825,10 @@ async def open_order_mode(
             brokerd_accounts,
             ems_dialog_msgs,
         ),
-        tractor.trionics.collapse_eg(),
-        trio.open_nursery() as tn,
-
     ):
-        log.info(f'Opening order mode for {fqme}')
+        log.info(
+            f'Opening order-mode for {fqme!r}'
+        )
 
         # annotations editors
         lines = LineEditor(godw=godw)
@@ -841,21 +841,34 @@ async def open_order_mode(
         trackers: dict[str, PositionTracker] = {}
 
         # load account names from ``brokers.toml``
+        broker_name: str = mkt.broker
         accounts_def: bidict[str, str | None] = config.load_accounts(
-            providers=[mkt.broker],
+            providers=[broker_name],
         )
 
         # XXX: ``brokerd`` delivers a set of account names that it
         # allows use of but the user also can define the accounts they'd
         # like to use, in order, in their `brokers.toml` file.
-        accounts: dict[str, str] = {}
-        for name in brokerd_accounts:
-            # ensure name is in ``brokers.toml``
-            accounts[name] = accounts_def[name]
+        accounts: dict[str, str] = {
+            'paper': 'paper',
+        }
+        fqan: str  # ex. 'kraken.spot'
+        for fqan in brokerd_accounts:
+            # ensure fully-qualified-account-name declared in `brokers.toml`
 
-        # always add a paper entry so that paper cleared
+            try:
+                accounts[fqan] = accounts_def[fqan]
+            except KeyError as ke:
+                raise config.ConfigurationError(
+                    f'The {broker_name!r} account {fqan!r} could not be found?\n'
+                    f'\n'
+                    f'Did you forget to define the correct account name in your `brokers.toml`?\n'
+                    f'{ppfmt(accounts_def)}\n'
+                ) from ke
+
+        # NOTE, always add a paper entry so that paper cleared
         # order dialogs can be tracked in the order mode UIs.
-        accounts['paper'] = 'paper'
+        # accounts['paper'] = 'paper'
 
         # first account listed is the one we select at startup
         # (aka order based selection).
@@ -940,6 +953,10 @@ async def open_order_mode(
         for name, tracker in trackers.items():
             order_pane.update_account_icons({name: tracker.live_pp})
 
+        async with (
+            tractor.trionics.collapse_eg(),
+            trio.open_nursery() as tn,
+        ):
             # top level abstraction which wraps all this crazyness into
             # a namespace..
             mode = OrderMode(
@@ -1028,7 +1045,17 @@ async def open_order_mode(
                     # 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,
@@ -1281,7 +1308,8 @@ async def process_trade_msg(
             # that should never happen tho?
             action: str = (
                 getattr(order, 'action', None)
-                or order['action']
+                or
+                order['action']
             )
             details: dict = msg.brokerd_msg