From 3f3c6494922dff0c426c787cfc21bd43c0902a77 Mon Sep 17 00:00:00 2001
From: Jason Robinson <jasonr@element.io>
Date: Fri, 24 Jul 2026 15:08:23 +0300
Subject: [PATCH] Fix field tracking never re-sending fields

---
 synapse/handlers/sliding_sync/extensions.py   |  9 ++++---
 .../sliding_sync/test_extension_profiles.py   | 25 ++++++++++++++++++-
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/synapse/handlers/sliding_sync/extensions.py b/synapse/handlers/sliding_sync/extensions.py
index 26852eef26..516a54a19c 100644
--- a/synapse/handlers/sliding_sync/extensions.py
+++ b/synapse/handlers/sliding_sync/extensions.py
@@ -1264,19 +1264,20 @@ class SlidingSyncExtensionHandler:
                 # We don't use a cache here as for non-lazy sync we always
                 # send changes and/or fields the client asked for, if relevant
                 # as above joined condition.
+                updated_fields: set[str] = updated_user_fields.get(
+                    profile_user_id, set()
+                )
                 user_fields = (
                     user_fields
                     if profile_user_id in joined_room_user_ids
-                    else set(updated_user_fields.get(profile_user_id, [])).intersection(
-                        profile_data.keys()
-                    )
+                    else updated_fields.intersection(profile_data.keys())
                 )
                 for field_name in user_fields:
                     # Ensure we don't send the field unnecessarely to the client, if
                     # we've sent it down in this connection before, and it hasn't been
                     # updated.
                     if (
-                        field_name in updated_user_fields.keys()
+                        field_name in updated_fields
                         or previous_connection_state.profile_updates.have_sent_field(
                             profile_user_id, field_name
                         ).status
diff --git a/tests/rest/client/sliding_sync/test_extension_profiles.py b/tests/rest/client/sliding_sync/test_extension_profiles.py
index 63b08d7896..58871dfb3b 100644
--- a/tests/rest/client/sliding_sync/test_extension_profiles.py
+++ b/tests/rest/client/sliding_sync/test_extension_profiles.py
@@ -644,12 +644,35 @@ class SlidingSyncProfilesTestCase(SlidingSyncBase):
         }
 
         # Make an incremental Sliding Sync request
-        response_body, _ = self.do_sync(sync_body, since=from_token, tok=self.tok)
+        response_body, from_token = self.do_sync(
+            sync_body, since=from_token, tok=self.tok
+        )
         # We should not get other user re-sent
         self.assertIsNone(
             response_body["extensions"].get("org.matrix.msc4262.profiles"),
         )
 
+        # Set a new field value and ensure our tracking doesn't swallow updates
+        self.get_success(
+            self.profile_handler.set_field(
+                target_user=UserID.from_string(self.other_user),
+                requester=create_requester(self.other_user),
+                field_name="displayname",
+                new_value="new displayname",
+            )
+        )
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=self.tok)
+        self.assertEqual(
+            response_body["extensions"]["org.matrix.msc4262.profiles"]["users"][
+                "@other_user:test"
+            ],
+            {
+                "updated": {
+                    "displayname": "new displayname",
+                },
+            },
+        )
+
     @override_config({"include_profile_updates_in_sync": True})
     def test_removed_fields_get_sent_down_as_removed(self) -> None:
         """