Open feeds using `Portal.open_context()`

piker/data/feed.py

@@ -519,12 +519,13 @@ async def open_sample_step_stream(
     # created for all practical purposes
     async with maybe_open_context(
         acm_func=partial(
-            portal.open_stream_from,
+            portal.open_context,
             iter_ohlc_periods,
         ),
         kwargs={'delay_s': delay_s},
 
-    ) as (cache_hit, istream):
+    ) as (cache_hit, (ctx, first)):
+        async with ctx.open_stream() as istream:
             if cache_hit:
                 # add a new broadcast subscription for the quote stream
                 # if this feed is likely already in use