feat(slice-4): honest delivery failure — send-before-commit + 502 delivery_failed (INV-9; closes #7)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/domains/accounts/service.py

@@ -18,9 +18,16 @@ from datetime import datetime, timedelta, timezone
 import psycopg
 
 from app.platform import config
-from app.platform.mailer import Mailer
+from app.platform.mailer import Mailer, MailerError
 
-from .errors import CodeExhausted, CodeExpired, CodeMismatch, InvalidEmail, ResendCooldown
+from .errors import (
+    CodeExhausted,
+    CodeExpired,
+    CodeMismatch,
+    DeliveryFailed,
+    InvalidEmail,
+    ResendCooldown,
+)
 from .models import Account
 
 # INV-3 constants — the one-time-code policy.
@@ -82,17 +89,23 @@ def request_code(conn: psycopg.Connection, mailer: Mailer, email: str) -> None:
         "INSERT INTO auth_code (email, code_hash, expires_at) VALUES (%s, %s, %s)",
         (email, _hash_code(code), now + CODE_TTL),
     )
-    conn.commit()
 
-    mailer.send(
-        to=email,
-        subject=f"Your ecomm code: {code}",
-        body=(
-            f"Your ecomm one-time code is {code}.\n"
-            f"It is valid for {int(CODE_TTL.total_seconds() // 60)} minutes.\n"
-            "If you didn't request this, ignore this message."
-        ),
-    )
+    # Send BEFORE commit (ecomm#7): a refused delivery rolls the row back, so no orphan
+    # code blocks the 60s cooldown and the caller can honestly retry at once (INV-9).
+    try:
+        mailer.send(
+            to=email,
+            subject=f"Your ecomm code: {code}",
+            body=(
+                f"Your ecomm one-time code is {code}.\n"
+                f"It is valid for {int(CODE_TTL.total_seconds() // 60)} minutes.\n"
+                "If you didn't request this, ignore this message."
+            ),
+        )
+    except MailerError as exc:
+        conn.rollback()
+        raise DeliveryFailed(str(exc)) from exc
+    conn.commit()
 
 
 def verify(conn: psycopg.Connection, email: str, code: str) -> tuple[Account, bool]: