feat(notify): Slack message for reconcile-booked closes (realized P&L)

Entries, deferrals and rejections posted to #trading-bot, but exits booked by the reconcile loop (bracket stop/take-profit legs that fill at Alpaca) were silent — the two Jun 9 stop-outs produced no message. Viktor asked for a Slack message on each position execution.

- move SlackNotifier to shared/ (now used by trade-executor AND api-gateway)

- add notify_close (ticker/qty/price/realized P&L/reason, win-loss emoji)

- reconcile loop notifies on each booked close, fail-soft; api-gateway config gains slack fields (channel defaults to trading-bot since the env carries only the bot token; chat:write.public covers posting)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/services/test_trade_reconcile.py

@@ -257,6 +257,60 @@ class TestReconcileBooksClose:
 
         assert session.added == []
 
+    async def test_booked_close_notifies_slack(self) -> None:
+        """A reconcile-booked close must post to Slack with realized P&L."""
+        entry = _entry_trade(broker_order_id="parent-1", price=100.0, qty=10.0)
+        tp = _leg(order_id="tp-1", status=OrderStatus.PENDING, filled_price=None)
+        sl = _leg(order_id="sl-1", status=OrderStatus.FILLED, filled_price=92.0)
+        broker = AsyncMock()
+        broker.get_order = AsyncMock(
+            return_value=_bracket(parent_id="parent-1", legs=[tp, sl])
+        )
+        session = _FakeSession([entry])
+        notifier = AsyncMock()
+
+        await reconcile_once(broker, _factory(session), notifier=notifier)
+
+        notifier.notify_close.assert_awaited_once()
+        kwargs = notifier.notify_close.await_args.kwargs
+        assert kwargs["ticker"] == "NVDA"
+        assert kwargs["qty"] == 10.0
+        assert kwargs["price"] == 92.0
+        assert kwargs["pnl"] == pytest.approx(-80.0)
+        assert kwargs["strategy_id"] == KEVIN_STRATEGY_UUID
+
+    async def test_no_notification_when_nothing_booked(self) -> None:
+        entry = _entry_trade(broker_order_id="parent-1")
+        tp = _leg(order_id="tp-1", status=OrderStatus.PENDING, filled_price=None)
+        sl = _leg(order_id="sl-1", status=OrderStatus.PENDING, filled_price=None)
+        broker = AsyncMock()
+        broker.get_order = AsyncMock(
+            return_value=_bracket(parent_id="parent-1", legs=[tp, sl])
+        )
+        session = _FakeSession([entry])
+        notifier = AsyncMock()
+
+        await reconcile_once(broker, _factory(session), notifier=notifier)
+
+        notifier.notify_close.assert_not_awaited()
+
+    async def test_notifier_failure_does_not_block_booking(self) -> None:
+        """Slack is an observer — its failure must not lose the Trade row."""
+        entry = _entry_trade(broker_order_id="parent-1", price=100.0, qty=10.0)
+        sl = _leg(order_id="sl-1", status=OrderStatus.FILLED, filled_price=92.0)
+        broker = AsyncMock()
+        broker.get_order = AsyncMock(
+            return_value=_bracket(parent_id="parent-1", legs=[sl])
+        )
+        session = _FakeSession([entry])
+        notifier = AsyncMock()
+        notifier.notify_close = AsyncMock(side_effect=RuntimeError("slack down"))
+
+        await reconcile_once(broker, _factory(session), notifier=notifier)
+
+        assert len(session.added) == 1
+        assert session.committed
+
 
 # ---------------------------------------------------------------------------
 # Idempotency
@@ -405,7 +459,7 @@ class TestReconcileLoop:
         cfg = _config()
         calls = 0
 
-        async def boom(broker, sf):  # noqa: ANN001
+        async def boom(broker, sf, notifier=None):  # noqa: ANN001
             nonlocal calls
             calls += 1
             if calls == 1: