From bb05d6579a7a7d7a3a41aa3bbd120084a46e76d0 Mon Sep 17 00:00:00 2001
From: Paul Chobert <paul@chobert.fr>
Date: Wed, 28 Oct 2026 16:01:28 +0100
Subject: [PATCH] Leave the user's own membership out of server announcement
 timelines

A timeline reaching back to the user's leave or kick ended with that
membership after the synthetic join in `required_state`, so clients saw
the user as having left. The user's own membership events are now dropped
from the timeline of a server announcement room, as they already are from
its `required_state`.
---
 synapse/handlers/sliding_sync/__init__.py     |  7 +++
 .../sliding_sync/test_server_announcements.py | 47 +++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/synapse/handlers/sliding_sync/__init__.py b/synapse/handlers/sliding_sync/__init__.py
index 33ae0f9bde..20e646fac0 100644
--- a/synapse/handlers/sliding_sync/__init__.py
+++ b/synapse/handlers/sliding_sync/__init__.py
@@ -803,6 +803,13 @@ class SlidingSyncHandler:
                 != Membership.JOIN,
                 filter_send_to_client=True,
             )
+            if is_server_announcement:
+                timeline_events = [
+                    timeline_event
+                    for timeline_event in timeline_events
+                    if timeline_event.event.type != EventTypes.Member
+                    or timeline_event.event.state_key != user.to_string()
+                ]
 
             # TODO: Handle timeline gaps (`get_timeline_gaps()`)
 
diff --git a/tests/rest/client/sliding_sync/test_server_announcements.py b/tests/rest/client/sliding_sync/test_server_announcements.py
index 6b02a993c2..53cb067ac3 100644
--- a/tests/rest/client/sliding_sync/test_server_announcements.py
+++ b/tests/rest/client/sliding_sync/test_server_announcements.py
@@ -138,6 +138,21 @@ class SlidingSyncServerAnnouncementsTestCase(SlidingSyncBase):
         )
         self.assertEqual(membership["content"], {"membership": Membership.JOIN})
 
+    def _assert_no_own_membership_in_timeline(
+        self, room: JsonDict, user_id: str
+    ) -> None:
+        """Assert that the timeline of `room` holds no membership event of
+        `user_id`.
+        """
+        self.assertEqual(
+            [
+                event
+                for event in room["timeline"]
+                if event["type"] == EventTypes.Member and event["state_key"] == user_id
+            ],
+            [],
+        )
+
     def test_new_connection_delivers_announcements(self) -> None:
         """A new connection gets an announcement room with its most recent
         announcements and the state asked for.
@@ -224,6 +239,21 @@ class SlidingSyncServerAnnouncementsTestCase(SlidingSyncBase):
         room = self._assert_delivered(response, self.former)
         self.assertEqual(self._timeline_ids(room), [event_id])
 
+    def test_self_left_member_full_timeline(self) -> None:
+        """A self-left member whose timeline reaches back to their leave gets the
+        synthetic join, and not their leave in the timeline.
+        """
+        self.helper.leave(self.room_id, self.former, tok=self.former_tok)
+        event_id = self._announce("hello")
+
+        response, _ = self.do_sync(
+            self._sync_body(timeline_limit=10), tok=self.former_tok
+        )
+
+        room = self._assert_delivered(response, self.former)
+        self._assert_no_own_membership_in_timeline(room, self.former)
+        self.assertEqual(self._timeline_ids(room)[-1], event_id)
+
     def test_self_left_member_on_existing_connection(self) -> None:
         """A member who leaves the room themselves while their connection is open
         gets later announcements as a non-member, with the synthetic join.
@@ -277,6 +307,23 @@ class SlidingSyncServerAnnouncementsTestCase(SlidingSyncBase):
         room = self._assert_delivered(response, self.former)
         self.assertEqual(self._timeline_ids(room), [event_id])
 
+    def test_removed_member_existing_connection_full_timeline(self) -> None:
+        """A member removed from the configured senders while their connection is
+        open gets later announcements with the synthetic join, and not their kick
+        in the timeline.
+        """
+        sync_body = self._sync_body(timeline_limit=10)
+        _, pos = self.do_sync(sync_body, tok=self.former_tok)
+        self._remove_former()
+        _, pos = self.do_sync(sync_body, since=pos, tok=self.former_tok)
+        event_id = self._announce("hello")
+
+        response, _ = self.do_sync(sync_body, since=pos, tok=self.former_tok)
+
+        room = self._assert_delivered(response, self.former)
+        self._assert_no_own_membership_in_timeline(room, self.former)
+        self.assertEqual(self._timeline_ids(room)[-1], event_id)
+
     def test_stays_in_list(self) -> None:
         """An announcement room already sent on a connection stays in the list
         when nothing new was announced.