🩹(backend) fix case-insensitive email deduplication in merge command

The management command that merges users with duplicate emails was
comparing emails in a case-insensitive manner, which left some
duplicates in the database when their emails only differed by case.

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to
 
 - 🚀(front) fix frontend build failure
 - 🐛(makefile) fix args in make test
+- 🩹(backend) fix case-insensitive email deduplication in merge command
 
 ## [1.22.0] - 2026-07-03
 

src/backend/core/management/commands/merge_duplicate_users.py

@@ -6,6 +6,7 @@ from django.contrib.auth import get_user_model
 from django.core.management.base import BaseCommand, CommandError
 from django.db import transaction
 from django.db.models import Count
+from django.db.models.functions import Lower
 
 from core.models import File, RecordingAccess, ResourceAccess, RoleChoices
 
@@ -20,11 +21,14 @@ ROLE_PRIORITY = {
 
 class Command(BaseCommand):
     """
-    Merge duplicate users sharing the same email into the most recently created one.
+    Merge duplicate users sharing the same email (case-insensitive) into the
+    most recently created one.
 
-    The KEPT user is the most recently created. All room memberships, recording
-    accesses and files are transferred to it. When a conflict exists, the
-    higher-privilege role wins. Stale users are then deleted.
+    Emails are compared case-insensitively, so 'John@Example.com' and
+    'john@example.com' are treated as duplicates. The KEPT user is the most
+    recently created. All room memberships, recording accesses and files are
+    transferred to it. When a conflict exists, the higher-privilege role wins.
+    Stale users are then deleted.
     Each email group is processed inside a single database transaction.
     """
 
@@ -56,13 +60,16 @@ class Command(BaseCommand):
             users_qs = users_qs.filter(email__icontains=email_filter)
             self.stdout.write(f"[INFO] Filtering emails containing '{email_filter}'.\n")
 
+        # Group emails case-insensitively so 'John@X.com' and 'john@x.com'
+        # are detected as duplicates of each other.
         duplicate_emails = (
             users_qs.exclude(email__isnull=True)
             .exclude(email="")
-            .values("email")
+            .annotate(email_lower=Lower("email"))
+            .values("email_lower")
             .annotate(cnt=Count("id"))
             .filter(cnt__gt=1)
-            .values_list("email", flat=True)
+            .values_list("email_lower", flat=True)
         )
 
         if not duplicate_emails:
@@ -78,9 +85,12 @@ class Command(BaseCommand):
         failed_emails = []
 
         for email in duplicate_emails:
+            # Case-insensitive lookup to fetch every casing variant of the email.
             # Secondary sort by id ensures a stable, deterministic order when
             # created_at timestamps are equal (common in tests and bulk imports).
-            users = list(User.objects.filter(email=email).order_by("created_at", "id"))
+            users = list(
+                User.objects.filter(email__iexact=email).order_by("created_at", "id")
+            )
             kept_user = users[-1]
             stale_users = users[:-1]
 
@@ -120,6 +130,10 @@ class Command(BaseCommand):
                 failed_emails.append(email)
                 self.stderr.write(f"[ERROR] Failed to merge '{email}': {exc}")
 
+            if not kept_user.email.islower():
+                kept_user.email = kept_user.email.lower()
+                kept_user.save(update_fields=["email"])
+
         if failed_emails:
             raise CommandError(
                 f"Failed to merge {len(failed_emails)} email group(s): {', '.join(failed_emails)}"

src/backend/core/tests/management/test_management_merge_duplicate_users.py

@@ -36,6 +36,26 @@ def test_merge_keeps_most_recently_created_user():
     assert User.objects.filter(id=user2.id).exists()
 
 
+def test_merge_user_case_insensitive():
+    """Emails differing only by case should be treated as duplicates and merged,
+    keeping the most recently created user."""
+    user1 = UserFactory(email="Dup@example.com")
+    user2 = UserFactory(email="dup@example.com")
+    call_command("merge_duplicate_users")
+
+    assert not User.objects.filter(id=user1.id).exists()
+    assert User.objects.filter(id=user2.id).exists()
+
+    user3 = UserFactory(email="joe@example.com")
+    user4 = UserFactory(email="Joe@example.com")
+    call_command("merge_duplicate_users")
+    assert not User.objects.filter(id=user3.id).exists()
+    assert User.objects.filter(id=user4.id).exists()
+
+    user4.refresh_from_db()
+    assert user4.email.islower()
+
+
 def test_merge_deletes_all_stale_users():
     """Command should delete all stale users and keep only the most recently created one."""
     email = "many@example.com"
@@ -457,4 +477,4 @@ def test_merge_email_filter_is_case_insensitive():
     UserFactory(email="user1@Example.com")
     UserFactory(email="user1@Example.com")
     call_command("merge_duplicate_users", email_filter="@example.com")
-    assert User.objects.filter(email="user1@Example.com").count() == 1
+    assert User.objects.filter(email="user1@example.com").count() == 1