fix(teams): Deduplicate project features list (#112326)

When a project belongs to multiple teams, the team serializer was
building the projects list from the ProjectTeam join table without
deduplicating. This meant `get_features_for_projects()` iterated the
same project N times (once per team it belongs to), appending features
to the same list each time. The features array in the response ended up
with N copies of every feature.

Deduplicates the project list before passing it to `serialize()`.

You can see duplicates in the production endpoint
https://us.sentry.io/api/0/organizations/sentry/teams/

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: scttcper

src/sentry/api/serializers/models/team.py

@@ -249,7 +249,9 @@ def get_attrs(
 
         if self._expand("projects"):
             project_teams = ProjectTeam.objects.get_for_teams_with_org_cache(item_list)
-            projects = [pt.project for pt in project_teams]
+
+            # A project can be on multiple teams, dedupe before serializing
+            projects = list({pt.project_id: pt.project for pt in project_teams}.values())
 
             projects_by_id = {
                 project.id: data

tests/sentry/api/serializers/test_team.py

@@ -277,6 +277,20 @@ def test_simple(self) -> None:
             "externalTeams": [],
         }
 
+    def test_project_on_multiple_teams_no_duplicate_features(self) -> None:
+        """A project belonging to multiple teams should not have its features list duplicated."""
+        user = self.create_user(username="foo")
+        organization = self.create_organization()
+        team1 = self.create_team(organization=organization)
+        team2 = self.create_team(organization=organization)
+        self.create_project(teams=[team1, team2], organization=organization)
+
+        result = serialize([team1, team2], user, TeamWithProjectsSerializer())
+        features = result[0]["projects"][0]["features"]
+
+        assert len(features) > 0
+        assert features == list(dict.fromkeys(features))
+
 
 class TeamSCIMSerializerTest(TestCase):
     def test_simple_with_members(self) -> None: