From 606ce6b57ec3d7104d8c5690e4a92bc59a3f116a Mon Sep 17 00:00:00 2001
From: Kegan Dougal <7190048+kegsay@users.noreply.github.com>
Date: Mon, 9 Mar 2026 15:50:10 +0000
Subject: [PATCH] Additional review comments: non-test files

---
 synapse/event_auth.py                                 | 11 +++++------
 synapse/storage/databases/main/events.py              |  4 +++-
 synapse/storage/databases/main/purge_events.py        |  4 ++++
 .../schema/main/delta/93/04_state_dag_fwd_extrems.sql |  2 +-
 4 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 20fe55f9b5..9af3f6740a 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -215,7 +215,7 @@ async def check_state_independent_auth_rules(
             # we should have all the prev state events by now, so if we do not, that suggests
             # a synapse programming error
             known_prev_state_event_ids = set(prev_state_events)
-            raise RuntimeError(
+            raise AssertionError(
                 f"Event {event.event_id} has unknown prev_state_events "
                 + f"{len(prev_state_events)} != {len(prev_state_events_ids)} "
                 + f"{prev_state_events_ids - known_prev_state_event_ids} missing "
@@ -538,11 +538,10 @@ def _check_create(event: "EventBase") -> None:
         raise AuthError(403, "Create event has prev events")
 
     # State DAGs 1.2 If it has any prev_state_events, reject.
-    if (
-        event.room_version.msc4242_state_dags
-        and cast(FrozenEventVMSC4242, event).prev_state_events
-    ):
-        raise AuthError(403, "Create event has prev state events")
+    if event.room_version.msc4242_state_dags:
+        assert isinstance(event, FrozenEventVMSC4242)
+        if len(event.prev_state_events) > 0:
+            raise AuthError(403, "Create event has prev state events")
 
     if event.room_version.msc4291_room_ids_as_hashes:
         # 1.2 If the create event has a room_id, reject
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index 87a674f5a8..2df1b0a6d4 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -2996,12 +2996,14 @@ class PersistEventsStore:
                 },
             )
             return
+        assert len(event.prev_state_events) > 0
         self.db_pool.simple_upsert_many_txn(
             txn,
             table="msc4242_state_dag_edges",
             key_names=["room_id", "event_id", "prev_state_event_id"],
             key_values=[
-                (event.room_id, event.event_id, prev_state_event) for prev_state_event in event.prev_state_events
+                (event.room_id, event.event_id, prev_state_event)
+                for prev_state_event in event.prev_state_events
             ],
             value_names=(),
             value_values=(),
diff --git a/synapse/storage/databases/main/purge_events.py b/synapse/storage/databases/main/purge_events.py
index d55ea5cf7d..fe8079c201 100644
--- a/synapse/storage/databases/main/purge_events.py
+++ b/synapse/storage/databases/main/purge_events.py
@@ -71,6 +71,10 @@ purge_room_tables_with_room_id_column = (
     # so must be deleted first.
     "sliding_sync_joined_rooms",
     "sliding_sync_membership_snapshots",
+    # Note: msc4242_state_dag_forward_extremities/edges have a foreign key to the `events` table
+    # so must be deleted first.
+    "msc4242_state_dag_forward_extremities",
+    "msc4242_state_dag_edges",
     "events",
     "federation_inbound_events_staging",
     "receipts_graph",
diff --git a/synapse/storage/schema/main/delta/93/04_state_dag_fwd_extrems.sql b/synapse/storage/schema/main/delta/93/04_state_dag_fwd_extrems.sql
index a91b49d5ad..2fdb96b25c 100644
--- a/synapse/storage/schema/main/delta/93/04_state_dag_fwd_extrems.sql
+++ b/synapse/storage/schema/main/delta/93/04_state_dag_fwd_extrems.sql
@@ -17,7 +17,7 @@ CREATE TABLE IF NOT EXISTS msc4242_state_dag_forward_extremities(
     event_id TEXT NOT NULL REFERENCES events(event_id) ON DELETE CASCADE,
     -- it doesn't make sense to reference the same event multiple times, and this uniqueness
     -- index is also used to delete events once they are no longer forward extremities.
-    UNIQUE (event_id, room_id)
+    UNIQUE (event_id)
 );
 -- When creating events, we want to select all forward extremities for a room which this index helps with.
 CREATE INDEX msc4242_state_dag_room ON msc4242_state_dag_forward_extremities(room_id);