fix: Don't accidentally continue with fallback room version

Fixes a potential issue where continuwuity correctly defaults to room v1
when encountering an unknown room version, but then fails to *stop*
processing when it encounters the room version it doesn't actually
understand.

src/core/matrix/event/id.rs

@@ -1,4 +1,7 @@
-use ruma::{CanonicalJsonObject, OwnedEventId, room_version_rules::RoomVersionRules};
+use ruma::{
+	CanonicalJsonObject, EventId, OwnedEventId,
+	room_version_rules::{EventIdFormatVersion, RoomVersionRules},
+};
 use serde_json::value::RawValue as RawJsonValue;
 
 use crate::{Result, err};
@@ -24,8 +27,11 @@ pub fn gen_event_id(
 	value: &CanonicalJsonObject,
 	room_version_rules: &RoomVersionRules,
 ) -> Result<OwnedEventId> {
+	assert_ne!(
+		room_version_rules.event_id_format,
+		EventIdFormatVersion::V1,
+		"Continuwuity does not support PDU v1"
+	);
 	let reference_hash = ruma::signatures::reference_hash(value, room_version_rules)?;
-	let event_id: OwnedEventId = format!("${reference_hash}").try_into()?;
-
-	Ok(event_id)
+	Ok(EventId::new_v2_or_v3(&reference_hash)?)
 }

src/service/rooms/event_handler/parse_incoming_pdu.rs

@@ -1,13 +1,15 @@
 use std::str::FromStr;
 
 use conduwuit::{
-	Err, Result, err,
+	Err, Error, Result, err,
 	matrix::event::{gen_event_id, gen_event_id_canonical_json},
 };
 use itertools::Itertools;
 use ruma::{
 	CanonicalJsonObject, CanonicalJsonValue, EventId, OwnedEventId, OwnedRoomId, RoomId,
-	RoomVersionId, room_version_rules::RoomVersionRules,
+	RoomVersionId,
+	api::error::{ErrorKind, IncompatibleRoomVersionErrorData},
+	room_version_rules::RoomVersionRules,
 };
 use serde_json::value::RawValue as RawJsonValue;
 
@@ -102,14 +104,25 @@ impl super::Service {
 
 		let room_version_rules = match room_version_rules {
 			| Some(r) => r,
-			| None => &self
-				.services
-				.state
-				.get_room_version(&room_id)
-				.await
-				.unwrap_or(RoomVersionId::V1)
-				.rules()
-				.expect("room version must be supported"),
+			| None => {
+				let room_version = self
+					.services
+					.state
+					.get_room_version(&room_id)
+					.await
+					.map_err(|_| err!(Request(NotFound("no version associated with room ID"))))?;
+				if matches!(room_version, RoomVersionId::V1 | RoomVersionId::V2) {
+					return Err(Error::BadRequest(
+						ErrorKind::IncompatibleRoomVersion(
+							IncompatibleRoomVersionErrorData::new(room_version),
+						),
+						"Room version is too old.",
+					));
+				}
+				&room_version
+					.rules()
+					.expect("room version must be supported")
+			},
 		};
 
 		let (event_id, value) =