diff --git a/backend/__tests__/service/agentsRuntime.crossAgent.test.js b/backend/__tests__/service/agentsRuntime.crossAgent.test.js
index 8cd0a156c5..716bb0ceae 100644
--- a/backend/__tests__/service/agentsRuntime.crossAgent.test.js
+++ b/backend/__tests__/service/agentsRuntime.crossAgent.test.js
@@ -17,6 +17,7 @@
 const express = require('express');
 const request = require('supertest');
 const jwt = require('jsonwebtoken');
+const mongoose = require('mongoose');
 
 const { setupMongoDb, closeMongoDb } = require('../utils/testUtils');
 
@@ -25,6 +26,7 @@ const Pod = require('../../models/Pod');
 const { AgentRegistry, AgentInstallation } = require('../../models/AgentRegistry');
 const AgentMemory = require('../../models/AgentMemory');
 const AgentAsk = require('../../models/AgentAsk');
+const AgentMessageService = require('../../services/agentMessageService');
 
 // Stub the event service before requiring routes.
 jest.mock('../../services/agentEventService', () => ({
@@ -219,6 +221,102 @@ describe('Cross-agent HTTP routes (ADR-003 Phase 4)', () => {
     });
   });
 
+  describe('POST /agent-dm authorization', () => {
+    const openDm = (target, originPodId) => request(app)
+      .post('/api/agents/runtime/agent-dm')
+      .set('Authorization', `Bearer ${aliceToken}`)
+      .send({ target, ...(originPodId ? { originPodId: String(originPodId) } : {}) });
+
+    const outsider = async () => {
+      const agentName = `outsider-${new mongoose.Types.ObjectId().toString().slice(-8)}`;
+      const user = await User.create({
+        username: agentName,
+        email: `${agentName}@agents.commonly.local`,
+        password: 'password123',
+        isBot: true,
+        botMetadata: { agentName, instanceId: 'default' },
+      });
+      return { agentName, user };
+    };
+
+    it('keeps the co-pod agent-name path and posts a notice in its authorized origin', async () => {
+      const notice = jest.spyOn(AgentMessageService, 'postMessage').mockResolvedValue({});
+      try {
+        const res = await openDm({ agentName: 'bob' }, pod._id);
+        expect(res.status).toBe(200);
+        expect(res.body.room.type).toBe('agent-dm');
+        expect(notice).toHaveBeenCalledWith(expect.objectContaining({
+          agentName: 'commonly-bot', podId: String(pod._id),
+        }));
+      } finally {
+        notice.mockRestore();
+      }
+    });
+
+    it('keeps an authorized alias as a target name when the agents share a pod', async () => {
+      pod.contacts.set('peer', { agentName: 'bob', instanceId: 'default' });
+      await pod.save();
+      const res = await openDm({ alias: 'peer' }, pod._id);
+      expect(res.status).toBe(200);
+      expect(res.body.room.type).toBe('agent-dm');
+    });
+
+    it('refuses an alias pinned in another pod before reading its contacts or posting a notice', async () => {
+      const { agentName, user } = await outsider();
+      const foreign = await Pod.create({
+        name: 'Foreign pin', type: 'team', createdBy: adminUser._id,
+        members: [adminUser._id, user._id],
+        contacts: { reach: { agentName, instanceId: 'default' } },
+      });
+      const notice = jest.spyOn(AgentMessageService, 'postMessage').mockResolvedValue({});
+      const originRead = jest.spyOn(Pod, 'findById');
+      try {
+        const res = await openDm({ alias: 'reach' }, foreign._id);
+        expect(res.status).toBe(403);
+        expect(originRead).not.toHaveBeenCalledWith(String(foreign._id));
+        expect(await Pod.countDocuments({ type: 'agent-dm', members: { $all: [user._id] } })).toBe(0);
+        expect(notice).not.toHaveBeenCalled();
+      } finally {
+        originRead.mockRestore();
+        notice.mockRestore();
+      }
+    });
+
+    it('refuses a caller-owned pod pin when the target shares no pod', async () => {
+      const { agentName, user } = await outsider();
+      const alice = await User.findOne({ 'botMetadata.agentName': 'alice', isBot: true });
+      const ownPod = await Pod.create({
+        name: 'Caller pin', type: 'team', createdBy: alice._id,
+        members: [alice._id], contacts: { reach: { agentName, instanceId: 'default' } },
+      });
+      await AgentInstallation.create({
+        agentName: 'alice', instanceId: 'default', podId: ownPod._id,
+        installedBy: adminUser._id, status: 'active', version: '1.0.0',
+      });
+      const res = await openDm({ alias: 'reach' }, ownPod._id);
+      expect(res.status).toBe(403);
+      expect(res.body.rule).toBe('sharePod');
+      expect(await Pod.countDocuments({ type: 'agent-dm', members: { $all: [user._id] } })).toBe(0);
+    });
+
+    it('does not send a notice to a foreign origin even when the target shares a pod', async () => {
+      const foreign = await Pod.create({
+        name: 'Foreign notice', type: 'team', createdBy: adminUser._id,
+        members: [adminUser._id],
+      });
+      const roomsBefore = await Pod.countDocuments({ type: 'agent-dm' });
+      const notice = jest.spyOn(AgentMessageService, 'postMessage').mockResolvedValue({});
+      try {
+        const res = await openDm({ agentName: 'bob' }, foreign._id);
+        expect(res.status).toBe(403);
+        expect(await Pod.countDocuments({ type: 'agent-dm' })).toBe(roomsBefore);
+        expect(notice).not.toHaveBeenCalled();
+      } finally {
+        notice.mockRestore();
+      }
+    });
+  });
+
   // ----------------------------------------------------------------------- //
   // GET /memory/shared                                                      //
   // ----------------------------------------------------------------------- //
diff --git a/backend/routes/agentsRuntime.ts b/backend/routes/agentsRuntime.ts
index 6e4d8887e7..df7fbd5e18 100644
--- a/backend/routes/agentsRuntime.ts
+++ b/backend/routes/agentsRuntime.ts
@@ -1070,6 +1070,18 @@ router.post('/agent-dm', phase4RateLimit, agentRuntimeAuth, async (req: any, res
     if (!target || typeof target !== 'object') {
       return res.status(400).json({ message: 'target is required' });
     }
+    const originPodIdSafe = typeof originPodId === 'string' ? originPodId.trim() : '';
+    if (originPodId !== undefined && !originPodIdSafe) {
+      return res.status(400).json({ message: 'originPodId must be a pod id' });
+    }
+    // The runtime-auth middleware has already resolved this token's active
+    // installations. An origin is a place this agent works, not a pod named
+    // by the request body; checking it here also protects alias lookup below.
+    if (originPodIdSafe && !(req.agentInstallations || []).some(
+      (entry: any) => String(entry.podId).toLowerCase() === originPodIdSafe.toLowerCase(),
+    )) {
+      return res.status(403).json({ message: 'Agent is not installed in origin pod' });
+    }
 
     // Resolve the target User row. Accept three shapes:
     //   { agentName, instanceId? } → look up the bot User row directly.
@@ -1142,12 +1154,8 @@ router.post('/agent-dm', phase4RateLimit, agentRuntimeAuth, async (req: any, res
       // priority but only when an originPodId is given.
       const alias = String(target.alias).trim().toLowerCase();
       let bound: { agentName: string; instanceId: string } | null = null;
-      // Coerce to string before findById so a malicious request body of
-      // `{ originPodId: { $gt: '' } }` can't slip through Mongoose's
-      // implicit object-as-query interpretation. CodeQL flagged this.
-      const originPodIdStr = originPodId ? String(originPodId) : '';
-      if (originPodIdStr) {
-        const originPod = await Pod.findById(originPodIdStr).select('contacts members').lean();
+      if (originPodIdSafe) {
+        const originPod = await Pod.findById(originPodIdSafe).select('contacts').lean();
         const fromPod = originPod?.contacts?.[alias];
         if (fromPod && fromPod.agentName) bound = { agentName: fromPod.agentName, instanceId: fromPod.instanceId || 'default' };
       }
@@ -1180,22 +1188,15 @@ router.post('/agent-dm', phase4RateLimit, agentRuntimeAuth, async (req: any, res
       return res.status(400).json({ message: 'Cannot DM yourself' });
     }
 
-    // §3.7 co-pod-member rule. Bypass when an admin has pinned the
-    // target via originPodId's pod.contacts (admin-binding carve-out).
-    let authorizedByPodBinding = false;
-    const originPodIdSafe = originPodId ? String(originPodId) : '';
-    if (originPodIdSafe && target.alias) {
-      const originPod = await Pod.findById(originPodIdSafe).select('contacts').lean();
-      authorizedByPodBinding = !!originPod?.contacts?.[String(target.alias).toLowerCase()];
-    }
-    if (!authorizedByPodBinding) {
-      const shared = await DMService.sharePod(callerAgentUser._id, targetUser._id);
-      if (!shared) {
-        return res.status(403).json({
-          message: 'No shared pod with target — refused per co-pod-member rule',
-          rule: 'sharePod',
-        });
-      }
+    // Contacts choose a target; they do not grant that target access to the
+    // caller. Every path, including aliases pinned by a pod creator, needs a
+    // shared pod before it can create a DM or install the peer into it.
+    const shared = await DMService.sharePod(callerAgentUser._id, targetUser._id);
+    if (!shared) {
+      return res.status(403).json({
+        message: 'No shared pod with target — refused per co-pod-member rule',
+        rule: 'sharePod',
+      });
     }
 
     // Build member metadata for both sides so AgentInstallation upserts
diff --git a/docs/plans/agent-collaboration-surfaces.md b/docs/plans/agent-collaboration-surfaces.md
index bf7b6c637e..52ba8a9583 100644
--- a/docs/plans/agent-collaboration-surfaces.md
+++ b/docs/plans/agent-collaboration-surfaces.md
@@ -344,8 +344,10 @@ tests at the service boundary.
    autoJoin gate. Single source of truth for the rule.
 6. **Endpoint**: `POST /api/agents/runtime/agent-dm`
    - body: `{ target: { agentName, instanceId } | { userId } | { alias }, originPodId? }`
-   - Resolves target via §3.2, runs §3.7 check, creates DM,
-     drops event in `originPodId` if provided.
+   - Resolves target via §3.2, runs §3.7 for every target shape
+     (a contact pin is resolution, not DM authority), and creates the DM.
+     `originPodId` must be an active installation of the caller before
+     its contacts are read or a DM-started event is posted there.
    - 403 with structured reason if §3.7 fails.
 7. **Sidebar (V2)**: list `agent-dm` rows under their own group;
    visibility per §3.7 (any user sharing a pod with either