From be3eb5284e6fa4ec61aa6716792f7b2fefd495d9 Mon Sep 17 00:00:00 2001
From: Jannis Braun <151788261+TheZwiss@users.noreply.github.com>
Date: Sat, 25 Apr 2026 21:42:57 +0200
Subject: [PATCH] feat(federation): permanent-failure callback registry

---
 .../src/utils/federationRollback.test.ts      | 41 +++++++++++++++++++
 .../server/src/utils/federationRollback.ts    | 39 ++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 packages/server/src/utils/federationRollback.test.ts
 create mode 100644 packages/server/src/utils/federationRollback.ts

diff --git a/packages/server/src/utils/federationRollback.test.ts b/packages/server/src/utils/federationRollback.test.ts
new file mode 100644
index 00000000..0e5bcb10
--- /dev/null
+++ b/packages/server/src/utils/federationRollback.test.ts
@@ -0,0 +1,41 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import {
+  registerPermanentFailureCallback,
+  invokePermanentFailureCallback,
+  _resetCallbacks,
+} from './federationRollback.js';
+
+describe('permanent-failure callback registry', () => {
+  beforeEach(() => _resetCallbacks());
+
+  it('invokes the registered callback when called by eventType', () => {
+    const cb = vi.fn();
+    registerPermanentFailureCallback('friend_request_create', cb);
+    invokePermanentFailureCallback('friend_request_create', 'msg-123', 'recipient_not_found');
+    expect(cb).toHaveBeenCalledWith('msg-123', 'recipient_not_found');
+  });
+
+  it('is a no-op for unregistered event types', () => {
+    expect(() =>
+      invokePermanentFailureCallback('unknown_event_type', 'msg-1', 'whatever')
+    ).not.toThrow();
+  });
+
+  it('replaces a previously-registered callback for the same eventType', () => {
+    const old = vi.fn();
+    const fresh = vi.fn();
+    registerPermanentFailureCallback('e1', old);
+    registerPermanentFailureCallback('e1', fresh);
+    invokePermanentFailureCallback('e1', 'msg-9', 'reason');
+    expect(old).not.toHaveBeenCalled();
+    expect(fresh).toHaveBeenCalledWith('msg-9', 'reason');
+  });
+
+  it('swallows errors thrown by the callback (logs but does not throw)', () => {
+    registerPermanentFailureCallback('boom', () => { throw new Error('test'); });
+    const errSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+    expect(() => invokePermanentFailureCallback('boom', 'msg-x', 'r')).not.toThrow();
+    expect(errSpy).toHaveBeenCalled();
+    errSpy.mockRestore();
+  });
+});
diff --git a/packages/server/src/utils/federationRollback.ts b/packages/server/src/utils/federationRollback.ts
new file mode 100644
index 00000000..8512e3d0
--- /dev/null
+++ b/packages/server/src/utils/federationRollback.ts
@@ -0,0 +1,39 @@
+/**
+ * Permanent-failure callback registry for outbox events.
+ *
+ * When the federation worker observes a receiver-acknowledged terminal
+ * rejection (4xx with a recognized reason like 'recipient_not_found'),
+ * it invokes the registered callback for the eventType so the originating
+ * instance can roll back any local state created at queue time.
+ *
+ * Callbacks are NEVER invoked on transient failures (5xx, network errors,
+ * retry exhaustion). Only on receiver-acknowledged terminal rejections.
+ *
+ * Errors thrown by callbacks are logged but not re-thrown — rollback failure
+ * must not prevent the outbox entry from being deleted.
+ */
+type PermanentFailureCallback = (messageId: string, reason: string) => void;
+
+const callbacks = new Map<string, PermanentFailureCallback>();
+
+export function registerPermanentFailureCallback(eventType: string, cb: PermanentFailureCallback): void {
+  callbacks.set(eventType, cb);
+}
+
+export function invokePermanentFailureCallback(eventType: string, messageId: string, reason: string): void {
+  const cb = callbacks.get(eventType);
+  if (!cb) return;
+  try {
+    cb(messageId, reason);
+  } catch (err) {
+    console.error(
+      `[federation-rollback] callback for ${eventType} (msg=${messageId}, reason=${reason}) threw:`,
+      err,
+    );
+  }
+}
+
+/** Test-only: clear the registry between tests. */
+export function _resetCallbacks(): void {
+  callbacks.clear();
+}