From 5a41402644748c866ea0743352539a095e55142b Mon Sep 17 00:00:00 2001
From: Peter Woolery <peter@research.bike>
Date: Fri, 8 May 2026 12:12:05 -0700
Subject: [PATCH] feat: wire SendGridEmailBackend with from_email/reply_to
 settings

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
---
 backend/app/config.py               |  2 ++
 backend/app/services/email.py       | 29 +++++++++++++++------
 backend/tests/test_email_backend.py | 40 +++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 8 deletions(-)
 create mode 100644 backend/tests/test_email_backend.py

diff --git a/backend/app/config.py b/backend/app/config.py
index 6543457..0fe3fbd 100644
--- a/backend/app/config.py
+++ b/backend/app/config.py
@@ -8,6 +8,8 @@ class Settings(BaseSettings):
     DATABASE_URL: str = ""
 
     SENDGRID_API_KEY: Optional[str] = None
+    SENDGRID_FROM_EMAIL: str = "peter@research.bike"
+    SENDGRID_REPLY_TO: str = "peter@research.bike"
     EMAIL_BACKEND: str = "console"
     LUCKY_CA_URL: str = "https://www.luckyncal.com"
     # Swiftly product API (replaces Playwright path). The bearer JWT is
diff --git a/backend/app/services/email.py b/backend/app/services/email.py
index af61b49..d9ed734 100644
--- a/backend/app/services/email.py
+++ b/backend/app/services/email.py
@@ -8,12 +8,14 @@ intentionally left to be wired in R3-C.
 from __future__ import annotations
 
 import json
-import os
 import sys
 from datetime import datetime, timezone
 from pathlib import Path
 from typing import Optional, Protocol
 
+from sendgrid import SendGridAPIClient
+from sendgrid.helpers.mail import Mail, ReplyTo
+
 from app.config import settings
 
 
@@ -66,11 +68,10 @@ class ConsoleEmailBackend:
 
 
 class SendGridEmailBackend:
-    """Stub. Wire in R3-C (real SendGrid client + sandbox mode + retries).
-
-    Deliberately raises so a misconfigured prod env fails loudly instead of
-    silently dropping mail.
-    """
+    def __init__(self) -> None:
+        self._client = SendGridAPIClient(settings.SENDGRID_API_KEY)
+        self._from_email = settings.SENDGRID_FROM_EMAIL
+        self._reply_to = settings.SENDGRID_REPLY_TO
 
     def send(
         self,
@@ -78,8 +79,20 @@ class SendGridEmailBackend:
         subject: str,
         html: str,
         text: Optional[str] = None,
-    ) -> None:  # pragma: no cover - stub
-        raise NotImplementedError("Wire SendGrid in R3-C")
+    ) -> None:
+        message = Mail(
+            from_email=self._from_email,
+            to_emails=to,
+            subject=subject,
+            html_content=html,
+            plain_text_content=text,
+        )
+        message.reply_to = ReplyTo(self._reply_to)
+        response = self._client.send(message)
+        if response.status_code >= 400:
+            raise RuntimeError(
+                f"SendGrid error {response.status_code}: {response.body}"
+            )
 
 
 def get_email_backend() -> EmailBackend:
diff --git a/backend/tests/test_email_backend.py b/backend/tests/test_email_backend.py
new file mode 100644
index 0000000..5a020d7
--- /dev/null
+++ b/backend/tests/test_email_backend.py
@@ -0,0 +1,40 @@
+"""Unit tests for SendGridEmailBackend — no Postgres needed."""
+import pytest
+
+
+def test_sendgrid_send_calls_api(monkeypatch):
+    calls = []
+
+    class FakeResponse:
+        status_code = 202
+        body = b""
+
+    class FakeClient:
+        def send(self, msg):
+            calls.append(msg)
+            return FakeResponse()
+
+    monkeypatch.setattr("app.services.email.SendGridAPIClient", lambda _key: FakeClient())
+
+    from app.services.email import SendGridEmailBackend
+    backend = SendGridEmailBackend()
+    backend.send(to="to@example.com", subject="Hello", html="<p>Hi</p>")
+
+    assert len(calls) == 1
+
+
+def test_sendgrid_raises_on_4xx(monkeypatch):
+    class FakeResponse:
+        status_code = 400
+        body = b"bad request"
+
+    class FakeClient:
+        def send(self, msg):
+            return FakeResponse()
+
+    monkeypatch.setattr("app.services.email.SendGridAPIClient", lambda _key: FakeClient())
+
+    from app.services.email import SendGridEmailBackend
+    backend = SendGridEmailBackend()
+    with pytest.raises(RuntimeError, match="400"):
+        backend.send(to="to@example.com", subject="Hello", html="<p>Hi</p>")