feat(trade-executor): Slack notifications on trade + risk-rejection

SlackNotifier posts a short message to a Slack incoming webhook on:
  - trade-executor submits an order (filled or pending)
  - RiskManager rejects a signal (except outside_market_hours, which
    spams every poll when the bot tries to trade after-hours)

Key properties:
  - No-op when slack_webhook_url is empty (fail-soft default).
  - HTTP errors are swallowed — a Slack outage MUST NOT crash the
    consumer loop; the trade already happened on Alpaca.
  - Kevin-strategy signals tagged "Meet Kevin" in the message so I can
    tell which strategy fired.

Wiring:
  - TradeExecutorConfig.slack_webhook_url + TRADING_SLACK_WEBHOOK_URL
    env var, sourced from Vault secret/trading-bot/slack_webhook_url
    via existing ExternalSecret.
  - SlackNotifier passed to process_signal; both rejection + post-trade
    paths call it.

Tests: 7 new (no-op when disabled, post calls webhook with correct
text, Kevin strategy tag, swallows HTTP errors, suppresses noisy
rejections).

tests/services/trade_executor/test_slack_notifier.py

@@ -0,0 +1,142 @@
+"""Tests for the SlackNotifier used by trade-executor."""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from decimal import Decimal
+from unittest.mock import AsyncMock, patch
+from uuid import UUID, uuid4
+
+import pytest
+
+from services.trade_executor.slack_notifier import SlackNotifier
+from shared.constants.kevin import KEVIN_STRATEGY_UUID
+from shared.schemas.trading import (
+    OrderResult,
+    OrderSide,
+    OrderStatus,
+    SignalDirection,
+    TradeSignal,
+)
+
+
+def _signal(strategy_id=None, target_dollars=None) -> TradeSignal:
+    return TradeSignal(
+        ticker="NVDA",
+        direction=SignalDirection.LONG,
+        strength=0.85,
+        strategy_sources=["meet_kevin:buy:0.85"],
+        timestamp=datetime.now(timezone.utc),
+        strategy_id=strategy_id,
+        target_dollars=target_dollars,
+    )
+
+
+def _filled_order(ticker="NVDA", qty=10, price=217.50) -> OrderResult:
+    return OrderResult(
+        order_id=str(uuid4()),
+        ticker=ticker,
+        side=OrderSide.BUY,
+        qty=qty,
+        filled_price=price,
+        status=OrderStatus.FILLED,
+        timestamp=datetime.now(timezone.utc),
+    )
+
+
+class TestSlackNotifierNoWebhook:
+    """Empty webhook_url -> notifier is a no-op (returns without raising)."""
+
+    @pytest.mark.asyncio
+    async def test_notify_trade_noop(self):
+        notifier = SlackNotifier(webhook_url="")
+        # should not raise even with no mock
+        await notifier.notify_trade(_signal(), _filled_order())
+
+    @pytest.mark.asyncio
+    async def test_notify_rejection_noop(self):
+        notifier = SlackNotifier(webhook_url="")
+        await notifier.notify_rejection(_signal(), "outside_market_hours")
+
+
+class TestSlackNotifierTradePost:
+    @pytest.mark.asyncio
+    async def test_trade_post_calls_webhook(self):
+        notifier = SlackNotifier(webhook_url="https://hooks.slack.test/abc")
+        with patch("httpx.AsyncClient") as mock_client_cls:
+            mock_client = AsyncMock()
+            mock_post = AsyncMock(return_value=AsyncMock(status_code=200))
+            mock_client.post = mock_post
+            mock_client_cls.return_value.__aenter__.return_value = mock_client
+            await notifier.notify_trade(
+                _signal(strategy_id=KEVIN_STRATEGY_UUID),
+                _filled_order(qty=10, price=217.50),
+            )
+        mock_post.assert_called_once()
+        url, kwargs = mock_post.call_args.args[0], mock_post.call_args.kwargs
+        assert url == "https://hooks.slack.test/abc"
+        payload = kwargs["json"]
+        assert "NVDA" in payload["text"]
+        assert "10" in payload["text"]
+        assert "217.50" in payload["text"]
+
+    @pytest.mark.asyncio
+    async def test_trade_post_strategy_tag_when_kevin(self):
+        notifier = SlackNotifier(webhook_url="https://hooks.slack.test/abc")
+        with patch("httpx.AsyncClient") as mock_client_cls:
+            mock_client = AsyncMock()
+            mock_client.post = AsyncMock(return_value=AsyncMock(status_code=200))
+            mock_client_cls.return_value.__aenter__.return_value = mock_client
+            await notifier.notify_trade(
+                _signal(strategy_id=KEVIN_STRATEGY_UUID),
+                _filled_order(),
+            )
+        payload = mock_client.post.call_args.kwargs["json"]
+        assert "Meet Kevin" in payload["text"]
+
+    @pytest.mark.asyncio
+    async def test_trade_post_swallows_http_errors(self):
+        """A failed Slack post must NOT bubble up — the trade already
+        happened; we shouldn't crash the consumer loop because Slack is
+        having a bad day."""
+        notifier = SlackNotifier(webhook_url="https://hooks.slack.test/abc")
+        with patch("httpx.AsyncClient") as mock_client_cls:
+            mock_client = AsyncMock()
+            mock_client.post = AsyncMock(side_effect=Exception("network down"))
+            mock_client_cls.return_value.__aenter__.return_value = mock_client
+            # should NOT raise
+            await notifier.notify_trade(_signal(), _filled_order())
+
+
+class TestSlackNotifierRejectionPost:
+    @pytest.mark.asyncio
+    async def test_rejection_post_calls_webhook(self):
+        notifier = SlackNotifier(webhook_url="https://hooks.slack.test/abc")
+        with patch("httpx.AsyncClient") as mock_client_cls:
+            mock_client = AsyncMock()
+            mock_client.post = AsyncMock(return_value=AsyncMock(status_code=200))
+            mock_client_cls.return_value.__aenter__.return_value = mock_client
+            await notifier.notify_rejection(
+                _signal(strategy_id=KEVIN_STRATEGY_UUID),
+                reason="kevin_daily_trade_cap",
+            )
+        payload = mock_client.post.call_args.kwargs["json"]
+        assert "REJECTED" in payload["text"]
+        assert "kevin_daily_trade_cap" in payload["text"]
+        assert "NVDA" in payload["text"]
+
+    @pytest.mark.asyncio
+    async def test_rejection_post_skips_noise(self):
+        """outside_market_hours fires every minute when the bot tries to
+        trade after-hours — we don't want a Slack barrage. The notifier
+        skips it."""
+        notifier = SlackNotifier(
+            webhook_url="https://hooks.slack.test/abc",
+            quiet_rejections={"outside_market_hours"},
+        )
+        with patch("httpx.AsyncClient") as mock_client_cls:
+            mock_client = AsyncMock()
+            mock_client.post = AsyncMock()
+            mock_client_cls.return_value.__aenter__.return_value = mock_client
+            await notifier.notify_rejection(_signal(), "outside_market_hours")
+        mock_client.post.assert_not_called()