diff --git a/scripts/init-first-agent.ts b/scripts/init-first-agent.ts
index fc61b9c..61a17d6 100644
--- a/scripts/init-first-agent.ts
+++ b/scripts/init-first-agent.ts
@@ -48,6 +48,7 @@ import { addMember } from '../src/modules/permissions/db/agent-group-members.js'
 import { getUserRoles, grantRole } from '../src/modules/permissions/db/user-roles.js';
 import { upsertUser } from '../src/modules/permissions/db/users.js';
 import { initGroupFilesystem } from '../src/group-init.js';
+import { namespacedPlatformId } from '../src/platform-id.js';
 import type { AgentGroup, MessagingGroup } from '../src/types.js';
 
 type Role = 'owner' | 'admin' | 'member';
@@ -137,32 +138,6 @@ function namespacedUserId(channel: string, raw: string): string {
   return raw.includes(':') ? raw : `${channel}:${raw}`;
 }
 
-/**
- * Determine whether a platform ID needs a channel-type prefix.
- *
- * Chat SDK adapters (Telegram, Discord, Slack, Teams, etc.) namespace their
- * platform IDs with a channel prefix: "telegram:123456", "discord:guild:chan".
- * The router stores `channel_type` and `platform_id` in separate columns, but
- * Chat SDK adapters send the prefixed form as the platform_id, so this script
- * must match that format.
- *
- * Native adapters (Signal, WhatsApp) use their own ID formats and send them
- * as-is — no channel prefix. Signal sends raw phone numbers (+15551234567)
- * for DMs and "group:<id>" for group chats. WhatsApp sends JIDs containing
- * '@' (<phone>@s.whatsapp.net, <groupId>@g.us). Prefixing these would cause
- * a mismatch between what the adapter sends and what the DB stores, breaking
- * message routing.
- */
-function namespacedPlatformId(channel: string, raw: string): string {
-  if (raw.startsWith(`${channel}:`)) return raw;
-  // Native WhatsApp JIDs contain '@' — no prefix needed.
-  if (raw.includes('@')) return raw;
-  // Native Signal IDs: phone numbers (+...) and group IDs (group:...).
-  if (raw.startsWith('+') || raw.startsWith('group:')) return raw;
-  // Chat SDK adapters — add the channel prefix.
-  return `${channel}:${raw}`;
-}
-
 function generateId(prefix: string): string {
   return `${prefix}-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
 }
diff --git a/setup/register.ts b/setup/register.ts
index ff194fc..7bd5ae3 100644
--- a/setup/register.ts
+++ b/setup/register.ts
@@ -20,6 +20,7 @@ import {
 import { isValidGroupFolder } from '../src/group-folder.js';
 import { initGroupFilesystem } from '../src/group-init.js';
 import { log } from '../src/log.js';
+import { namespacedPlatformId } from '../src/platform-id.js';
 import { resolveSession, writeSessionMessage } from '../src/session-manager.js';
 import { emitStatus } from './status.js';
 
@@ -112,12 +113,10 @@ export async function run(args: string[]): Promise<void> {
     process.exit(4);
   }
 
-  // Chat SDK adapters prefix platform IDs with the channel type
-  // (e.g. "telegram:123", "discord:guild:channel"). Normalize here so
-  // the stored ID always matches what the adapter sends at runtime.
-  if (!parsed.platformId.startsWith(`${parsed.channel}:`)) {
-    parsed.platformId = `${parsed.channel}:${parsed.platformId}`;
-  }
+  // Normalize platform_id to the same shape the adapter will emit at runtime,
+  // so the router's (channel_type, platform_id) lookup matches what we store.
+  // Chat SDK adapters prefix, native adapters (WhatsApp/iMessage/Signal) don't.
+  parsed.platformId = namespacedPlatformId(parsed.channel, parsed.platformId);
 
   log.info('Registering channel', parsed);
 
@@ -167,8 +166,13 @@ export async function run(args: string[]): Promise<void> {
   if (!existing) {
     newlyWired = true;
     const mgaId = generateId('mga');
-    const engageMode = parsed.trigger || !parsed.requiresTrigger ? 'pattern' : 'mention';
-    const engagePattern = parsed.trigger ? parsed.trigger : (!parsed.requiresTrigger ? '.' : null);
+    // Mirrors scripts/init-first-agent.ts:wireIfMissing so both setup paths
+    // create rows with the same shape. Groups default to 'mention' (bot only
+    // responds when addressed); DMs default to 'pattern'/'.' (respond to
+    // every message). An explicit --trigger overrides the pattern regex.
+    const isGroup = messagingGroup.is_group === 1;
+    const engageMode: 'pattern' | 'mention' = isGroup && !parsed.trigger ? 'mention' : 'pattern';
+    const engagePattern: string | null = engageMode === 'pattern' ? parsed.trigger || '.' : null;
     createMessagingGroupAgent({
       id: mgaId,
       messaging_group_id: messagingGroup.id,
@@ -177,7 +181,7 @@ export async function run(args: string[]): Promise<void> {
       engage_pattern: engagePattern,
       sender_scope: 'all',
       ignored_message_policy: 'drop',
-      session_mode: parsed.sessionMode,
+      session_mode: parsed.sessionMode as 'shared' | 'per-thread' | 'agent-shared',
       priority: 0,
       created_at: new Date().toISOString(),
     });
diff --git a/src/platform-id.ts b/src/platform-id.ts
new file mode 100644
index 0000000..1c49325
--- /dev/null
+++ b/src/platform-id.ts
@@ -0,0 +1,23 @@
+/**
+ * Determine whether a platform ID needs a channel-type prefix.
+ *
+ * Chat SDK adapters (Telegram, Discord, Slack, Teams, etc.) namespace their
+ * platform IDs with a channel prefix: "telegram:123456", "discord:guild:chan".
+ * The router stores channel_type and platform_id in separate columns, but
+ * Chat SDK adapters send the prefixed form as the platform_id — so any code
+ * that writes messaging_groups rows must produce the same shape the adapter
+ * will later emit as event.platformId, or router lookups miss and messages
+ * get silently dropped.
+ *
+ * Native adapters (Signal, WhatsApp, iMessage) use their own ID formats and
+ * send them as-is — no channel prefix. WhatsApp/iMessage emit JIDs/emails
+ * containing '@'. Signal emits raw phone numbers ('+15551234567') for DMs
+ * and 'group:<id>' for group chats. Prefixing any of these would cause a
+ * mismatch with what the adapter later emits.
+ */
+export function namespacedPlatformId(channel: string, raw: string): string {
+  if (raw.startsWith(`${channel}:`)) return raw;
+  if (raw.includes('@')) return raw;
+  if (raw.startsWith('+') || raw.startsWith('group:')) return raw;
+  return `${channel}:${raw}`;
+}