.ib.feed: only set `feed_is_live` after first quote

Move `feed_is_live.set()` to after receiving the first valid
quote instead of setting early on venue-closed path. Prevents
sampler registration when no live data expected.

Also,
- drop redundant `.set()` call in quote iteration loop
- add TODO note about sleeping until venue opens vs forever
- init `first_quote: dict` early for consistency

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/brokers/ib/feed.py

@@ -1115,6 +1115,7 @@ async def stream_quotes(
 
         con: Contract = details.contract
         first_ticker: Ticker|None = None
+        first_quote: dict[str, Any] = {}
 
         timeout: float = 1.6
         with trio.move_on_after(timeout) as quote_cs:
@@ -1167,15 +1168,14 @@ async def stream_quotes(
                 first_quote,
             ))
 
-            # it's not really live but this will unblock
-            # the brokerd feed task to tell the ui to update?
-            feed_is_live.set()
-
             # block and let data history backfill code run.
             # XXX obvi given the venue is closed, we never expect feed
             # to come up; a taskc should be the only way to
             # terminate this task.
             await trio.sleep_forever()
+            #
+            # ^^XXX^^TODO! INSTEAD impl a `trio.sleep()` for the
+            # duration until the venue opens!!
 
         # ?TODO, we could instead spawn a task that waits on a feed
         # to start and let it wait indefinitely..instead of this
@@ -1199,6 +1199,9 @@ async def stream_quotes(
             'Rxed init quote:\n'
             f'{pformat(first_quote)}'
         )
+        # signal `.data.feed` layer that mkt quotes are LIVE
+        feed_is_live.set()
+
         cs: trio.CancelScope|None = None
         startup: bool = True
         iter_quotes: trio.abc.Channel
@@ -1252,7 +1255,6 @@ async def stream_quotes(
                         # tick.
                         ticker = await iter_quotes.receive()
                         quote = normalize(ticker)
-                        feed_is_live.set()
                         fqme: str = quote['fqme']
                         await send_chan.send({fqme: quote})