Add email sent/failed structured logging

Implement email logging per observability spec:
- Add structured logging for email sent (info level) and failed (error level)
- Include userId, type, and recipient fields in log events
- Add userId parameter to email functions (sendDailyEmail, sendPeriodConfirmationEmail, sendTokenExpirationWarning)
- Update cron routes (notifications, garmin-sync) to pass userId

6 new tests added to email.test.ts (now 30 tests total)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/email.test.ts

@@ -2,8 +2,10 @@
 // ABOUTME: Tests email composition, subject lines, and Resend integration.
 import { afterEach, describe, expect, it, vi } from "vitest";
 
-const { mockSend } = vi.hoisted(() => ({
+const { mockSend, mockLoggerInfo, mockLoggerError } = vi.hoisted(() => ({
   mockSend: vi.fn().mockResolvedValue({ id: "mock-email-id" }),
+  mockLoggerInfo: vi.fn(),
+  mockLoggerError: vi.fn(),
 }));
 
 // Mock the resend module before importing email utilities
@@ -13,6 +15,14 @@ vi.mock("resend", () => ({
   },
 }));
 
+// Mock the logger
+vi.mock("@/lib/logger", () => ({
+  logger: {
+    info: mockLoggerInfo,
+    error: mockLoggerError,
+  },
+}));
+
 import type { DailyEmailData } from "./email";
 import {
   sendDailyEmail,
@@ -277,3 +287,135 @@ describe("sendTokenExpirationWarning", () => {
     });
   });
 });
+
+describe("email structured logging", () => {
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  const sampleDailyEmailData: DailyEmailData = {
+    to: "user@example.com",
+    cycleDay: 15,
+    phase: "OVULATION",
+    decision: {
+      status: "TRAIN",
+      reason: "Body battery high",
+      icon: "💪",
+    },
+    bodyBatteryCurrent: 85,
+    bodyBatteryYesterdayLow: 45,
+    hrvStatus: "Balanced",
+    weekIntensity: 60,
+    phaseLimit: 80,
+    remainingMinutes: 20,
+    seeds: "Sesame",
+    carbRange: "100-150g",
+    ketoGuidance: "No",
+  };
+
+  describe("sendDailyEmail logging", () => {
+    it("logs email sent with info level on success", async () => {
+      await sendDailyEmail(sampleDailyEmailData, "user-123");
+      expect(mockLoggerInfo).toHaveBeenCalledWith(
+        expect.objectContaining({
+          userId: "user-123",
+          type: "daily",
+          recipient: "user@example.com",
+        }),
+        "Email sent",
+      );
+    });
+
+    it("logs email failed with error level on failure", async () => {
+      const error = new Error("Resend API failed");
+      mockSend.mockRejectedValueOnce(error);
+
+      await expect(
+        sendDailyEmail(sampleDailyEmailData, "user-123"),
+      ).rejects.toThrow("Resend API failed");
+
+      expect(mockLoggerError).toHaveBeenCalledWith(
+        expect.objectContaining({
+          userId: "user-123",
+          type: "daily",
+          err: error,
+        }),
+        "Email failed",
+      );
+    });
+  });
+
+  describe("sendPeriodConfirmationEmail logging", () => {
+    it("logs email sent with info level on success", async () => {
+      await sendPeriodConfirmationEmail(
+        "user@example.com",
+        new Date("2025-01-15"),
+        31,
+        "user-456",
+      );
+      expect(mockLoggerInfo).toHaveBeenCalledWith(
+        expect.objectContaining({
+          userId: "user-456",
+          type: "period_confirmation",
+          recipient: "user@example.com",
+        }),
+        "Email sent",
+      );
+    });
+
+    it("logs email failed with error level on failure", async () => {
+      const error = new Error("Resend API failed");
+      mockSend.mockRejectedValueOnce(error);
+
+      await expect(
+        sendPeriodConfirmationEmail(
+          "user@example.com",
+          new Date("2025-01-15"),
+          31,
+          "user-456",
+        ),
+      ).rejects.toThrow("Resend API failed");
+
+      expect(mockLoggerError).toHaveBeenCalledWith(
+        expect.objectContaining({
+          userId: "user-456",
+          type: "period_confirmation",
+          err: error,
+        }),
+        "Email failed",
+      );
+    });
+  });
+
+  describe("sendTokenExpirationWarning logging", () => {
+    it("logs email sent with info level on success", async () => {
+      await sendTokenExpirationWarning("user@example.com", 14, "user-789");
+      expect(mockLoggerInfo).toHaveBeenCalledWith(
+        expect.objectContaining({
+          userId: "user-789",
+          type: "warning",
+          recipient: "user@example.com",
+        }),
+        "Email sent",
+      );
+    });
+
+    it("logs email failed with error level on failure", async () => {
+      const error = new Error("Resend API failed");
+      mockSend.mockRejectedValueOnce(error);
+
+      await expect(
+        sendTokenExpirationWarning("user@example.com", 14, "user-789"),
+      ).rejects.toThrow("Resend API failed");
+
+      expect(mockLoggerError).toHaveBeenCalledWith(
+        expect.objectContaining({
+          userId: "user-789",
+          type: "warning",
+          err: error,
+        }),
+        "Email failed",
+      );
+    });
+  });
+});

src/lib/email.ts

@@ -2,6 +2,7 @@
 // ABOUTME: Sends daily training notifications and period confirmation emails.
 import { Resend } from "resend";
 
+import { logger } from "@/lib/logger";
 import { emailSentTotal } from "@/lib/metrics";
 
 const resend = new Resend(process.env.RESEND_API_KEY);
@@ -28,7 +29,10 @@ export interface DailyEmailData {
   ketoGuidance: string;
 }
 
-export async function sendDailyEmail(data: DailyEmailData): Promise<void> {
+export async function sendDailyEmail(
+  data: DailyEmailData,
+  userId?: string,
+): Promise<void> {
   const subject = `Today's Training: ${data.decision.icon} ${data.decision.status}`;
 
   const body = `Good morning!
@@ -53,20 +57,27 @@ ${data.decision.icon} ${data.decision.reason}
 ---
 Auto-generated by PhaseFlow`;
 
-  await resend.emails.send({
-    from: EMAIL_FROM,
-    to: data.to,
-    subject,
-    text: body,
-  });
+  try {
+    await resend.emails.send({
+      from: EMAIL_FROM,
+      to: data.to,
+      subject,
+      text: body,
+    });
 
-  emailSentTotal.inc({ type: "daily" });
+    logger.info({ userId, type: "daily", recipient: data.to }, "Email sent");
+    emailSentTotal.inc({ type: "daily" });
+  } catch (err) {
+    logger.error({ userId, type: "daily", err }, "Email failed");
+    throw err;
+  }
 }
 
 export async function sendPeriodConfirmationEmail(
   to: string,
   lastPeriodDate: Date,
   cycleLength: number,
+  userId?: string,
 ): Promise<void> {
   const subject = "🔵 Period Tracking Updated";
 
@@ -78,17 +89,28 @@ Your calendar will update automatically within 24 hours.
 ---
 Auto-generated by PhaseFlow`;
 
-  await resend.emails.send({
-    from: EMAIL_FROM,
-    to,
-    subject,
-    text: body,
-  });
+  try {
+    await resend.emails.send({
+      from: EMAIL_FROM,
+      to,
+      subject,
+      text: body,
+    });
+
+    logger.info(
+      { userId, type: "period_confirmation", recipient: to },
+      "Email sent",
+    );
+  } catch (err) {
+    logger.error({ userId, type: "period_confirmation", err }, "Email failed");
+    throw err;
+  }
 }
 
 export async function sendTokenExpirationWarning(
   to: string,
   daysUntilExpiry: number,
+  userId?: string,
 ): Promise<void> {
   const isUrgent = daysUntilExpiry <= 7;
 
@@ -112,12 +134,18 @@ This will ensure your training recommendations continue to use fresh Garmin data
 ---
 Auto-generated by PhaseFlow`;
 
-  await resend.emails.send({
-    from: EMAIL_FROM,
-    to,
-    subject,
-    text: body,
-  });
+  try {
+    await resend.emails.send({
+      from: EMAIL_FROM,
+      to,
+      subject,
+      text: body,
+    });
 
-  emailSentTotal.inc({ type: "warning" });
+    logger.info({ userId, type: "warning", recipient: to }, "Email sent");
+    emailSentTotal.inc({ type: "warning" });
+  } catch (err) {
+    logger.error({ userId, type: "warning", err }, "Email failed");
+    throw err;
+  }
 }