diff --git a/backend/__tests__/unit/services/neverConnectedMentionService.test.js b/backend/__tests__/unit/services/neverConnectedMentionService.test.js
new file mode 100644
index 0000000000..cc148c5971
--- /dev/null
+++ b/backend/__tests__/unit/services/neverConnectedMentionService.test.js
@@ -0,0 +1,98 @@
+// TASK-655 item 3: a person's @mention of a Bring your own agent that has never
+// polled gets one system line in the room, at most one per agent per UTC day.
+
+const mockFindUser = jest.fn();
+const mockFindInstall = jest.fn();
+const mockFindBot = jest.fn();
+const mockEmitNotConnected = jest.fn();
+const mockHasLineToday = jest.fn();
+
+jest.mock('../../../models/User', () => ({
+  findById: (...args) => mockFindUser(...args),
+  findOne: (...args) => mockFindBot(...args),
+}));
+jest.mock('../../../models/AgentRegistry', () => ({
+  AgentInstallation: { findOne: (...args) => mockFindInstall(...args) },
+}));
+jest.mock('../../../services/systemActionLineService', () => ({
+  emitNotConnectedLine: (...args) => mockEmitNotConnected(...args),
+  hasNotConnectedLineToday: (...args) => mockHasLineToday(...args),
+}));
+
+const chain = (value) => ({ select: () => ({ lean: async () => value }) });
+const leanOnly = (value) => ({ lean: async () => value });
+
+const { noteNeverConnectedMention } = require('../../../services/neverConnectedMentionService');
+
+const NOW = new Date('2026-10-31T20:00:00.000Z');
+const byoInstall = {
+  agentName: 'nova',
+  instanceId: 'default',
+  installedBy: 'owner-1',
+  status: 'active',
+  config: { runtime: { host: 'byo', runtimeType: 'openclaw' } },
+  runtimeTokens: [],
+};
+const botRow = (tokens = []) => ({
+  _id: 'bot-1',
+  username: 'nova',
+  profilePicture: null,
+  botMetadata: { displayName: 'Nova', instanceId: 'default' },
+  agentRuntimeTokens: tokens,
+});
+const args = {
+  podId: 'pod-1',
+  agentName: 'nova',
+  instanceId: 'default',
+  senderId: 'human-1',
+  messageId: '555',
+  threadRootId: null,
+  now: NOW,
+};
+
+beforeEach(() => {
+  jest.clearAllMocks();
+  mockFindUser.mockReturnValue(chain({ isBot: false }));
+  mockFindInstall.mockReturnValue(leanOnly(byoInstall));
+  mockFindBot.mockReturnValue(chain(botRow([])));
+  mockHasLineToday.mockResolvedValue(false);
+  mockEmitNotConnected.mockResolvedValue(undefined);
+});
+
+it('posts one not-connected line when a person mentions a BYO agent that never polled', async () => {
+  const posted = await noteNeverConnectedMention(args);
+
+  expect(posted).toBe(true);
+  expect(mockHasLineToday).toHaveBeenCalledWith('pod-1', 'nova:default', NOW);
+  expect(mockEmitNotConnected).toHaveBeenCalledTimes(1);
+  expect(mockEmitNotConnected.mock.calls[0][0]).toMatchObject({
+    podId: 'pod-1',
+    actorUserId: 'bot-1',
+    agentKey: 'nova:default',
+    messageId: '555',
+  });
+});
+
+it('stays silent for a bot sender', async () => {
+  mockFindUser.mockReturnValue(chain({ isBot: true }));
+  expect(await noteNeverConnectedMention(args)).toBe(false);
+  expect(mockEmitNotConnected).not.toHaveBeenCalled();
+});
+
+it('stays silent once the agent has a live credential use', async () => {
+  mockFindBot.mockReturnValue(chain(botRow([{ lastUsedAt: new Date(NOW.getTime() - 60 * 1000) }])));
+  expect(await noteNeverConnectedMention(args)).toBe(false);
+  expect(mockEmitNotConnected).not.toHaveBeenCalled();
+});
+
+it('stays silent when a line for this agent already sits in the pod today', async () => {
+  mockHasLineToday.mockResolvedValue(true);
+  expect(await noteNeverConnectedMention(args)).toBe(false);
+  expect(mockEmitNotConnected).not.toHaveBeenCalled();
+});
+
+it('stays silent when there is no active install', async () => {
+  mockFindInstall.mockReturnValue(leanOnly(null));
+  expect(await noteNeverConnectedMention(args)).toBe(false);
+  expect(mockEmitNotConnected).not.toHaveBeenCalled();
+});
diff --git a/backend/services/agentMentionService.ts b/backend/services/agentMentionService.ts
index 4f111f51cf..76bc7c04d2 100644
--- a/backend/services/agentMentionService.ts
+++ b/backend/services/agentMentionService.ts
@@ -19,6 +19,13 @@ const { assertAgentRuntimeMayJoinPod } = require('./outsiderGrantAgentJoinPolicy
 // eslint-disable-next-line global-require
 const chatSummarizerService = require('./chatSummarizerService');
 // eslint-disable-next-line global-require, @typescript-eslint/no-require-imports
+const { noteNeverConnectedMention } = require('./neverConnectedMentionService') as {
+  noteNeverConnectedMention: (args: {
+    podId: string; agentName: string; instanceId: string; senderId: string;
+    messageId: string | null; threadRootId?: string | number | null;
+  }) => Promise<boolean>;
+};
+// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports
 const { maybeFireWelcomeWake } = require('./welcomeWakeService') as {
   maybeFireWelcomeWake: (opts: Record<string, unknown>) => Promise<unknown>;
 };
@@ -1951,6 +1958,24 @@ const enqueueMentions = async ({
           skipped.push(`${directMatch.agentName}:loop-dampened`);
           return;
         }
+        // TASK-655: a person mentioning a never-connected BYO agent is told
+        // once a day, in the room. The mention still queues below.
+        if (sender?.isBot === false) {
+          try {
+            await noteNeverConnectedMention({
+              podId,
+              agentName: directMatch.agentName,
+              instanceId: directMatch.instanceId,
+              senderId: String(userId),
+              messageId: message?._id || message?.id ? String(message?._id || message?.id) : null,
+              threadRootId,
+            });
+          } catch (error) {
+            // The mention is already persisted and still queues; a failed
+            // notice must never drop or block the delivery.
+            console.warn('[not-connected] notice failed:', (error as Error).message);
+          }
+        }
         try {
           if (directMatch.agentName === 'commonly-bot') {
             pod = pod || await Pod.findById(podId).lean();
diff --git a/backend/services/neverConnectedMentionService.ts b/backend/services/neverConnectedMentionService.ts
new file mode 100644
index 0000000000..323c86e910
--- /dev/null
+++ b/backend/services/neverConnectedMentionService.ts
@@ -0,0 +1,84 @@
+import { emitNotConnectedLine, hasNotConnectedLineToday } from './systemActionLineService';
+import { deriveAgentState } from './agentStateService';
+
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const User = require('../models/User');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const { AgentInstallation } = require('../models/AgentRegistry');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const AgentIdentityService = require('./agentIdentityService');
+
+/**
+ * TASK-655 item 3. A person @mentions a Bring your own agent that has never
+ * polled. The mention still queues (it is delivered the moment the agent
+ * connects), but the room now says so once, as a reply to the mention, so the
+ * person is not left waiting on silence.
+ *
+ * ONE DERIVATION. "Never connected" is `deriveAgentState` returning
+ * `never-connected`, the same verdict the Your Team row and the stalled-connect
+ * nudge use. There is no second rule here.
+ *
+ * Silent when: the sender is a bot (agents do not get told they are unseen),
+ * the install is not active, the agent is not in the never-connected state, or
+ * a line for this agent already sits in the pod today.
+ */
+export async function noteNeverConnectedMention({
+  podId,
+  agentName,
+  instanceId,
+  senderId,
+  messageId,
+  threadRootId,
+  now = new Date(),
+}: {
+  podId: string;
+  agentName: string;
+  instanceId: string;
+  senderId: string;
+  messageId: string | number | null;
+  threadRootId?: string | number | null;
+  now?: Date;
+}): Promise<boolean> {
+  const sender = await User.findById(senderId).select('isBot').lean() as { isBot?: boolean } | null;
+  if (!sender || sender.isBot) return false;
+
+  const install = await AgentInstallation.findOne({
+    podId, agentName, instanceId, status: 'active',
+  }).lean() as Record<string, unknown> | null;
+  if (!install) return false;
+
+  const agent = await User.findOne({
+    isBot: true,
+    'botMetadata.agentName': agentName,
+    'botMetadata.instanceId': instanceId,
+  }).select('username profilePicture botMetadata agentRuntimeTokens').lean() as {
+    _id: unknown; username?: string; profilePicture?: string | null;
+    botMetadata?: { displayName?: string; instanceId?: string };
+    agentRuntimeTokens?: Array<{ lastUsedAt?: Date | string | null }>;
+  } | null;
+  if (!agent) return false;
+
+  const derived = deriveAgentState(
+    install as Parameters<typeof deriveAgentState>[0],
+    agent.agentRuntimeTokens || [],
+    '',
+    now.getTime(),
+  );
+  if (derived.state !== 'never-connected') return false;
+
+  const agentKey = `${agentName}:${instanceId}`;
+  if (await hasNotConnectedLineToday(podId, agentKey, now)) return false;
+
+  await emitNotConnectedLine({
+    podId,
+    actorUserId: String(agent._id),
+    actorUsername: agent.username || agentName,
+    actorAvatarUrl: agent.profilePicture || null,
+    actorIsBot: true,
+    agentLabel: AgentIdentityService.resolveAgentDisplayLabel(agent, agentName),
+    agentKey,
+    messageId,
+    threadRootId: threadRootId ?? null,
+  });
+  return true;
+}
diff --git a/backend/services/systemActionLineService.ts b/backend/services/systemActionLineService.ts
index 748ee1c334..6534b54c7f 100644
--- a/backend/services/systemActionLineService.ts
+++ b/backend/services/systemActionLineService.ts
@@ -130,3 +130,53 @@ export async function emitUnansweredMentionLine(line: UnansweredMentionLine): Pr
     attempts: line.attempts,
   }, { threadRootId: line.threadRootId ?? null, replyToMessageId: line.messageId });
 }
+
+/**
+ * TASK-655. A person mentioned a Bring your own agent that has never polled.
+ * Without this line the mention waits in a queue nobody reads and the person
+ * sees silence. Placed as a reply to their mention, like the line above.
+ * Callers dedupe with `hasNotConnectedLineToday`: one per agent per UTC day.
+ */
+export interface NotConnectedLine extends SystemLineActor {
+  agentLabel: string;
+  agentKey: string;
+  messageId: string | number | null;
+  threadRootId?: string | number | null;
+}
+
+export async function emitNotConnectedLine(line: NotConnectedLine): Promise<void> {
+  const content = `${line.agentLabel} isn't connected yet, so it won't see this until it runs. `
+    + 'Run the connect command shown on its page.';
+  await insertSystemLine(line, content, {
+    kind: 'system-action',
+    action: 'agent-not-connected',
+    actorName: line.agentLabel,
+    agentKey: line.agentKey,
+  }, { threadRootId: line.threadRootId ?? null, replyToMessageId: line.messageId });
+}
+
+/**
+ * Whether a not-connected line for this agent already sits in the pod since
+ * UTC midnight. A missing pool reads as "already posted": no line is better
+ * than a second line the person did not need.
+ */
+export async function hasNotConnectedLineToday(
+  podId: string,
+  agentKey: string,
+  now: Date = new Date(),
+): Promise<boolean> {
+  // eslint-disable-next-line global-require, @typescript-eslint/no-require-imports
+  const { pool } = require('../config/db-pg') as {
+    pool: { query: (sql: string, params: unknown[]) => Promise<{ rows: unknown[] }> } | null;
+  };
+  if (!pool) return true;
+  const startOfDay = new Date(Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate()));
+  const { rows } = await pool.query(
+    `SELECT 1 FROM messages
+     WHERE pod_id = $1 AND message_type = 'system' AND created_at >= $2
+       AND payload->>'action' = 'agent-not-connected' AND payload->>'agentKey' = $3
+     LIMIT 1`,
+    [podId, startOfDay, agentKey],
+  );
+  return rows.length > 0;
+}