Add protection for autoredacting events flagged as spam from policy servers

src/commands/CommandHandler.ts

@@ -228,6 +228,7 @@ export async function handleCommand(roomId: string, event: { content: { body: st
                 "!mjolnir msc4284_set <room alias/ID> unset                          - Unset/disable the policy server in a specific room. Same constraints as the room ID/alias set command.\n" +
                 "!mjolnir msc4284_set * <policy server name>                         - Set the policy server for all Mjolnir-protected rooms.\n" +
                 "!mjolnir msc4284_set * unset                                        - Unset/disable the policy server for all Mjolnir-protected rooms\n" +
+                "!mjolnir synapse_ext policy_server_spammy <true|false>              - Enable/disable receiving events flagged as spammy by policy servers. Requires compatible server.\n" +
                 ""; // empty segment to reduce diff noise
 
             const botMenu =

src/commands/SynapseExtensionsCommand.ts

@@ -0,0 +1,45 @@
+/*
+Copyright 2025 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { Mjolnir } from "../Mjolnir";
+
+type SynapseAdminConfig = {
+    return_soft_failed_events?: boolean;
+    return_policy_server_spammy_events?: boolean;
+};
+
+const SYNAPSE_ADMIN_ACCOUNT_DATA_TYPE = "io.element.synapse.admin_client_config";
+
+// !mjolnir synapse_ext <'policy_server_spammy'> <true|false>
+export async function execSynapseExtensionsCommand(roomId: string, event: any, mjolnir: Mjolnir, parts: string[]) {
+    const extension = parts[2];
+
+    if (extension === "policy_server_spammy") {
+        let currentConfig: SynapseAdminConfig = {};
+        try {
+            currentConfig = await mjolnir.client.getAccountData(SYNAPSE_ADMIN_ACCOUNT_DATA_TYPE);
+        } catch (e) {
+            // assume unset
+        }
+        await mjolnir.client.setAccountData(SYNAPSE_ADMIN_ACCOUNT_DATA_TYPE, {
+            return_soft_failed_events: currentConfig.return_soft_failed_events ?? false,
+            return_policy_server_spammy_events: parts[3] === "true",
+        });
+        await mjolnir.client.unstableApis.addReactionToEvent(roomId, event["event_id"], "✅");
+    } else {
+        await mjolnir.client.replyNotice(roomId, event, "Unknown extension, please check the help for more information.");
+    }
+}

src/protections/ProtectionManager.ts

@@ -35,6 +35,7 @@ import { NsfwProtection } from "./NsfwProtection";
 import { MentionSpam } from "./MentionSpam";
 import { MessageIsVideo } from "./MessageIsVideo";
 import { FirstMessageIsLink } from "./FirstMessageIsLink";
+import {RedactPolicyServerFlaggedEvents} from "./RedactPolicyServerFlaggedEvents";
 
 const PROTECTIONS: Protection[] = [
     new FirstMessageIsImage(),
@@ -50,6 +51,7 @@ const PROTECTIONS: Protection[] = [
     new MentionSpam(),
     new MessageIsVideo(),
     new FirstMessageIsLink(),
+    new RedactPolicyServerFlaggedEvents(),
 ];
 
 const ENABLED_PROTECTIONS_EVENT_TYPE = "org.matrix.mjolnir.enabled_protections";

src/protections/RedactPolicyServerFlaggedEvents.ts

@@ -0,0 +1,37 @@
+/*
+Copyright 2025 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { Protection } from "./IProtection";
+import { Mjolnir } from "../Mjolnir";
+
+export class RedactPolicyServerFlaggedEvents extends Protection {
+    settings = {};
+
+    public get name(): string {
+        return "RedactPolicyServerFlaggedEvents";
+    }
+
+    public get description(): string {
+        return "Redacts events that are flagged by the policy server as probable spam. Requires enabling the policy_server_spammy Synapse extension (see help command for info).";
+    }
+
+    public async handleEvent(mjolnir: Mjolnir, roomId: string, event: any): Promise<any> {
+        if (event["unsigned"]?.["io.element.synapse.policy_server_spammy"] === true) {
+            console.log(`Redacting ${event["event_id"]} in ${roomId} due to policy server flagging it as spam.`);
+            await mjolnir.client.redactEvent(roomId, event["event_id"], "Probable spam");
+        }
+    }
+}