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).

services/trade_executor/config.py

@@ -22,4 +22,7 @@ class TradeExecutorConfig(BaseConfig):
     kevin_equity_drawdown_halt_pct: float = 0.20  # 20% drawdown → permanent pause
     kevin_daily_loss_circuit_pct: float = 0.05  # 5% daily loss → 24h pause
 
+    # Slack webhook for per-trade notifications (empty → notifier no-ops).
+    slack_webhook_url: str = ""
+
     model_config = {"env_prefix": "TRADING_"}

services/trade_executor/main.py

@@ -19,6 +19,7 @@ from sqlalchemy.ext.asyncio import async_sessionmaker
 
 from services.trade_executor.config import TradeExecutorConfig
 from services.trade_executor.risk_manager import RiskManager
+from services.trade_executor.slack_notifier import SlackNotifier
 from shared.broker.alpaca_broker import AlpacaBroker
 from shared.db import create_db
 from shared.models.trading import Trade as TradeModel
@@ -45,6 +46,7 @@ async def process_signal(
     publisher: StreamPublisher,
     counters: dict,
     db_session_factory: async_sessionmaker | None = None,
+    slack_notifier: SlackNotifier | None = None,
 ) -> None:
     """Process a single trade signal: risk check, order, record, publish.
 
@@ -68,6 +70,8 @@ async def process_signal(
     if not approved:
         logger.info("Signal REJECTED for %s: %s", signal.ticker, reason)
         counters["rejections"].add(1, {"reason": reason.split(" ")[0]})
+        if slack_notifier is not None:
+            await slack_notifier.notify_rejection(signal, reason)
         return
 
     # --- Step 2: calculate position size ---
@@ -149,6 +153,10 @@ async def process_signal(
         result.status.value,
     )
 
+    # --- Step 8: notify slack (best-effort, fail-soft) ---
+    if slack_notifier is not None:
+        await slack_notifier.notify_trade(signal, result)
+
 
 async def run(config: TradeExecutorConfig | None = None) -> None:
     """Main service loop.
@@ -196,6 +204,11 @@ async def run(config: TradeExecutorConfig | None = None) -> None:
     # --- Risk manager ---
     risk_manager = RiskManager(config, broker, redis=redis)
 
+    # --- Slack notifier (no-op when slack_webhook_url is empty) ---
+    slack_notifier = SlackNotifier(webhook_url=config.slack_webhook_url)
+    if slack_notifier.enabled:
+        logger.info("Slack notifications enabled")
+
     # --- Database (for persisting trades) ---
     db_session_factory = None
     try:
@@ -219,7 +232,15 @@ async def run(config: TradeExecutorConfig | None = None) -> None:
                 break
             try:
                 signal_msg = TradeSignal.model_validate(data)
-                await process_signal(signal_msg, risk_manager, broker, publisher, counters, db_session_factory)
+                await process_signal(
+                    signal_msg,
+                    risk_manager,
+                    broker,
+                    publisher,
+                    counters,
+                    db_session_factory,
+                    slack_notifier,
+                )
             except Exception:
                 logger.exception("Error processing signal: %s", data)
     finally:

services/trade_executor/slack_notifier.py

@@ -0,0 +1,94 @@
+"""Slack webhook notifier for trade-executor.
+
+Posts a short message on each successful order submit and on
+notable risk rejections. No-op when the webhook URL is empty.
+
+Designed to fail-soft: a Slack outage MUST NOT bubble up and crash
+the consumer loop. The trade has already happened on Alpaca — Slack
+is a downstream observer, not a transactional dependency.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Iterable
+
+import httpx
+
+from shared.constants.kevin import KEVIN_STRATEGY_UUID
+from shared.schemas.trading import OrderResult, TradeSignal
+
+logger = logging.getLogger(__name__)
+
+
+# Reasons we DON'T want to spam Slack about. outside_market_hours fires
+# every poll when a fresh signal lands after-hours — silencing it keeps
+# Slack signal-to-noise high.
+_DEFAULT_QUIET = frozenset({"outside_market_hours"})
+
+
+class SlackNotifier:
+    def __init__(
+        self,
+        webhook_url: str,
+        quiet_rejections: Iterable[str] | None = None,
+    ) -> None:
+        self.webhook_url = webhook_url or ""
+        self.quiet_rejections = frozenset(
+            quiet_rejections if quiet_rejections is not None else _DEFAULT_QUIET
+        )
+
+    @property
+    def enabled(self) -> bool:
+        return bool(self.webhook_url)
+
+    async def notify_trade(self, signal: TradeSignal, result: OrderResult) -> None:
+        if not self.enabled:
+            return
+        text = self._format_trade(signal, result)
+        await self._post(text)
+
+    async def notify_rejection(self, signal: TradeSignal, reason: str) -> None:
+        if not self.enabled:
+            return
+        if reason in self.quiet_rejections:
+            return
+        text = self._format_rejection(signal, reason)
+        await self._post(text)
+
+    # ------------------------------------------------------------------
+    # Internal
+    # ------------------------------------------------------------------
+
+    def _strategy_tag(self, signal: TradeSignal) -> str:
+        if signal.strategy_id == KEVIN_STRATEGY_UUID:
+            return "Meet Kevin"
+        return "trading-bot"
+
+    def _format_trade(self, signal: TradeSignal, result: OrderResult) -> str:
+        tag = self._strategy_tag(signal)
+        price = (
+            f"${result.filled_price:.2f}"
+            if result.filled_price is not None
+            else "—"
+        )
+        return (
+            f":chart_with_upwards_trend: *{tag}*: "
+            f"{result.side.value} {result.qty:g} {result.ticker} @ {price}  "
+            f"(conviction {signal.strength:.2f}, status {result.status.value})"
+        )
+
+    def _format_rejection(self, signal: TradeSignal, reason: str) -> str:
+        tag = self._strategy_tag(signal)
+        return (
+            f":no_entry: *{tag}*: REJECTED {signal.ticker} — {reason} "
+            f"(conviction {signal.strength:.2f})"
+        )
+
+    async def _post(self, text: str) -> None:
+        payload = {"text": text}
+        try:
+            async with httpx.AsyncClient(timeout=5.0) as client:
+                await client.post(self.webhook_url, json=payload)
+        except Exception as exc:
+            logger.warning("Slack post failed (swallowed): %s", exc)