Always clear `Position._events` in `.from_msg()`..

Not sure why i ever thought it would work otherwise but, obviously if
you're replicating a `Position` from a **summary** (IPC) msg we
need to wipe any prior clearing events from the events history..
The main use for this loading mechanism is precisely if you don't have
local access to the txn ledger and need to represent a position from
a summary 🤦

Also, never bother with ledger file fqme "rewriting" if the backend has
no symcache support (yet) since obviously there's then no symbol set to
search for a better key xD

piker/accounting/_ledger.py

@@ -199,6 +199,7 @@ class TransactionLedger(UserDict):
                 tid,
                 txdict,
                 pairs=symcache.pairs,
+                symcache=symcache,
             )
             yield txn
 
@@ -231,6 +232,7 @@ class TransactionLedger(UserDict):
         '''
         is_paper: bool = self.account == 'paper'
 
+        symcache: SymbologyCache = self._symcache
         towrite: dict[str, Any] = {}
         for tid, txdict in self.tx_sort(self.data.copy()):
             # write blank-str expiry for non-expiring assets
@@ -241,12 +243,18 @@ class TransactionLedger(UserDict):
                 txdict['expiry'] = ''
 
             # (maybe) re-write old acro-key
-            if is_paper:
+            if (
+                is_paper
+                # if symcache is empty/not supported (yet), don't
+                # bother xD
+                and symcache.mktmaps
+            ):
                 fqme: str = txdict.pop('fqsn', None) or txdict['fqme']
                 bs_mktid: str | None = txdict.get('bs_mktid')
 
                 if (
-                    fqme not in self._symcache.mktmaps
+
+                    fqme not in symcache.mktmaps
                     or (
                         # also try to see if this is maybe a paper
                         # engine ledger in which case the bs_mktid
@@ -257,10 +265,10 @@ class TransactionLedger(UserDict):
                 ):
                     # always take any (paper) bs_mktid if defined and
                     # in the backend's cache key set.
-                    if bs_mktid in self._symcache.mktmaps:
+                    if bs_mktid in symcache.mktmaps:
                         fqme: str = bs_mktid
                     else:
-                        best_fqme: str = list(self._symcache.search(fqme))[0]
+                        best_fqme: str = list(symcache.search(fqme))[0]
                         log.warning(
                             f'Could not find FQME: {fqme} in qualified set?\n'
                             f'Qualifying and expanding {fqme} -> {best_fqme}'
@@ -371,7 +379,7 @@ def open_trade_ledger(
     if symcache is None:
 
         # XXX: be mega pendantic and ensure the caller knows what
-        # they're doing..
+        # they're doing!
         if not allow_from_sync_code:
             raise RuntimeError(
                 'You MUST set `allow_from_sync_code=True` when '

piker/accounting/_mktinfo.py

@@ -605,7 +605,7 @@ class MktPair(Struct, frozen=True):
         if isinstance(self.dst, Asset):
             return str(self.dst.atype)
 
-        return 'unknown'
+        return 'UNKNOWN'
 
     @property
     def price_tick_digits(self) -> int:

piker/accounting/_pos.py

@@ -292,11 +292,21 @@ class Position(Struct):
         msg: BrokerdPosition,
 
     ) -> None:
+        '''
+        Hard-set the current position from a remotely-received
+        (normally via IPC) msg by applying the msg as the one (and
+        only) txn in the `._events` table thus forcing the current
+        asset allocation blindly.
 
+        '''
         mkt: MktPair = self.mkt
         now_dt: pendulum.DateTime = now()
         now_str: str = str(now_dt)
 
+        # XXX: wipe all prior txn history since we wanted it we wouldn't
+        # be using this method to compute our state!
+        self._events.clear()
+
         # NOTE WARNING XXX: we summarize the pos with a single
         # summary transaction (for now) until we either pass THIS
         # type as msg directly from emsd or come up with a better
@@ -524,6 +534,9 @@ class Account(Struct):
             try:
                 mkt: MktPair = symcache.mktmaps[fqme]
             except KeyError:
+                if _mktmap_table is None:
+                    raise
+
                 # XXX: caller is allowed to provide a fallback
                 # mktmap table for the case where a new position is
                 # being added and the preloaded symcache didn't