Pass history shm "last index" in init msg, assign on feed

piker/data/feed.py

@@ -951,6 +951,7 @@ async def allocate_persistent_feed(
     # this task.
     msg = init_msg[symbol]
     msg['hist_shm_token'] = hist_shm.token
+    msg['startup_hist_index'] = hist_shm.index - 1
     msg['rt_shm_token'] = rt_shm.token
 
     # true fqsn
@@ -1040,6 +1041,7 @@ async def allocate_persistent_feed(
         await sample_and_broadcast(
             bus,
             rt_shm,
+            hist_shm,
             quote_stream,
             brokername,
             sum_tick_vlm
@@ -1222,6 +1224,8 @@ class Feed:
     stream: trio.abc.ReceiveChannel[dict[str, Any]]
     status: dict[str, Any]
 
+    startup_hist_index: int = 0
+
     throttle_rate: Optional[int] = None
 
     _trade_stream: Optional[AsyncIterator[dict[str, Any]]] = None
@@ -1361,13 +1365,14 @@ async def open_feed(
         ) as stream,
 
     ):
+        init = init_msg[bfqsn]
         # we can only read from shm
         hist_shm = attach_shm_array(
-            token=init_msg[bfqsn]['hist_shm_token'],
+            token=init['hist_shm_token'],
             readonly=True,
         )
         rt_shm = attach_shm_array(
-            token=init_msg[bfqsn]['rt_shm_token'],
+            token=init['rt_shm_token'],
             readonly=True,
         )
 
@@ -1382,6 +1387,7 @@ async def open_feed(
             stream=stream,
             _portal=portal,
             status={},
+            startup_hist_index=init['startup_hist_index'],
             throttle_rate=tick_throttle,
         )