When redacting, keep event fields around that maintain the historical event structure intact (MSC2716) (#10538)

* Keep event fields that maintain the historical event structure intact

Fix https://github.com/matrix-org/synapse/issues/10521

* Add changelog

* Bump room version

* Better changelog text

* Fix up room version after develop merge

1 files changed, 7 insertions, 1 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index a0c07f62f4..b6da2f60af 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -17,7 +17,7 @@ from typing import Any, Mapping, Union
 
 from frozendict import frozendict
 
-from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.constants import EventContentFields, EventTypes, RelationTypes
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.util.async_helpers import yieldable_gather_results
@@ -135,6 +135,12 @@ def prune_event_dict(room_version: RoomVersion, event_dict: dict) -> dict:
         add_fields("history_visibility")
     elif event_type == EventTypes.Redaction and room_version.msc2176_redaction_rules:
         add_fields("redacts")
+    elif room_version.msc2716_redactions and event_type == EventTypes.MSC2716_INSERTION:
+        add_fields(EventContentFields.MSC2716_NEXT_CHUNK_ID)
+    elif room_version.msc2716_redactions and event_type == EventTypes.MSC2716_CHUNK:
+        add_fields(EventContentFields.MSC2716_CHUNK_ID)
+    elif room_version.msc2716_redactions and event_type == EventTypes.MSC2716_MARKER:
+        add_fields(EventContentFields.MSC2716_MARKER_INSERTION)
 
     allowed_fields = {k: v for k, v in event_dict.items() if k in allowed_keys}