refactor(federation): extract getOurOrigin() into shared federationAuth export

Consolidates 4 inline constructions of the instance origin URL into a
single shared function. Removes the private copy in federationWorker
and two ad-hoc domainOrigin variables in federationOutbox.

packages/server/src/utils/federationAuth.ts

@@ -1,4 +1,5 @@
 import { createHmac, randomBytes, timingSafeEqual } from 'node:crypto';
+import { config } from '../config.js';
 
 const DEFAULT_MAX_AGE_MS = 15 * 60 * 1000; // 15 minutes
 
@@ -122,3 +123,14 @@ export function parseFederationHeaders(
 
   return { origin, timestamp: timestampMs, signature };
 }
+
+/**
+ * Return the canonical origin URL for this instance.
+ * Uses DOMAIN env var for production, falls back to localhost for dev.
+ */
+export function getOurOrigin(): string {
+  if (config.domain) {
+    return `https://${config.domain}`;
+  }
+  return `http://localhost:${config.port}`;
+}

packages/server/src/utils/federationOutbox.ts

@@ -4,7 +4,7 @@ import { eq, and } from 'drizzle-orm';
 import { generateSnowflake } from './snowflake.js';
 import crypto from 'node:crypto';
 import type { FederationRelayEvent, FederationRelayParticipant, FederationRelayAttachment, DmMessageWithUser } from '@backspace/shared';
-import { config } from '../config.js';
+import { getOurOrigin } from './federationAuth.js';
 
 // ─── Settings Cache ──────────────────────────────────────────────────────────
 
@@ -229,7 +229,7 @@ export function getDmParticipants(dmChannelId: string): FederationRelayParticipa
     .where(eq(schema.dmMembers.dmChannelId, dmChannelId))
     .all();
 
-  const domainOrigin = config.domain ? `https://${config.domain}` : '';
+  const domainOrigin = getOurOrigin();
 
   return members.map(m => ({
     homeUserId: m.homeUserId || m.id,
@@ -252,7 +252,7 @@ export function queueDmRelay(
   dmChannelId: string,
   eventType: 'create' | 'update',
 ): void {
-  const domainOrigin = config.domain ? `https://${config.domain}` : `http://localhost:${config.port}`;
+  const domainOrigin = getOurOrigin();
 
   const attachments: FederationRelayAttachment[] = (message.attachments ?? []).map(a => ({
     id: a.id,
@@ -300,7 +300,7 @@ export function buildRelayPayload(
   return {
     userId: user.id,
     homeUserId: user.homeUserId || user.id,
-    homeInstance: user.homeInstance || config.domain || '',
+    homeInstance: user.homeInstance || getOurOrigin(),
     content: message.content,
     replyToId: message.replyToId ?? null,
     editedAt: message.editedAt ?? null,

packages/server/src/utils/federationWorker.ts

@@ -3,7 +3,7 @@ import * as schema from '../db/schema.js';
 import { eq, and, lte, asc, inArray } from 'drizzle-orm';
 import { config } from '../config.js';
 import { isFederationRelayEnabled } from './federationOutbox.js';
-import { buildFederationHeaders } from './federationAuth.js';
+import { buildFederationHeaders, getOurOrigin } from './federationAuth.js';
 import { generateSnowflake } from './snowflake.js';
 import { getDmMessageWithUser } from '../routes/dm.js';
 import { connectionManager } from '../ws/handler.js';
@@ -63,17 +63,6 @@ function getBackoffMs(attempt: number): number {
   return BACKOFF_SCHEDULE_MS[Math.max(0, index)] ?? 86_400_000;
 }
 
-/**
- * Build the origin URL for this instance.
- * Uses DOMAIN env var for production, falls back to localhost for dev.
- */
-function getOurOrigin(): string {
-  if (config.domain) {
-    return `https://${config.domain}`;
-  }
-  return `http://localhost:${config.port}`;
-}
-
 /**
  * Get the effective max upload size from instance settings or config fallback.
  */
@@ -627,7 +616,7 @@ async function runInitialSyncForNewPeers(): Promise<void> {
 
   if (unsyncedPeers.length === 0) return;
 
-  const ourOrigin = config.domain ? `https://${config.domain}` : `http://localhost:${config.port}`;
+  const ourOrigin = getOurOrigin();
 
   for (const peer of unsyncedPeers) {
     try {