feat(gateway): per-platform gateway_restart_notification flag

Adds an opt-out toggle on PlatformConfig that gates both restart
lifecycle pings: the "♻ Gateway restarted" message sent to the chat
that issued /restart, and the "♻️ Gateway online" home-channel
startup notification. Defaults to True so existing deployments are
unaffected.

The motivating split is operator vs. end-user surfaces: a back-channel
like Telegram should keep these pings, while a Slack workspace shared
with end users should not surface gateway lifecycle noise.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/gateway/test_config.py

@@ -57,6 +57,19 @@ class TestPlatformConfigRoundtrip:
         restored = PlatformConfig.from_dict({"enabled": "false"})
         assert restored.enabled is False
 
+    def test_gateway_restart_notification_defaults_true(self):
+        assert PlatformConfig().gateway_restart_notification is True
+        assert PlatformConfig.from_dict({}).gateway_restart_notification is True
+
+    def test_gateway_restart_notification_roundtrip_false(self):
+        pc = PlatformConfig(enabled=True, gateway_restart_notification=False)
+        restored = PlatformConfig.from_dict(pc.to_dict())
+        assert restored.gateway_restart_notification is False
+
+    def test_gateway_restart_notification_coerces_quoted_false(self):
+        restored = PlatformConfig.from_dict({"gateway_restart_notification": "false"})
+        assert restored.gateway_restart_notification is False
+
 
 class TestGetConnectedPlatforms:
     def test_returns_enabled_with_token(self):

tests/gateway/test_restart_notification.py

@@ -496,6 +496,82 @@ async def test_send_restart_notification_logs_warning_on_sendresult_failure(
     assert not notify_path.exists()
 
 
+@pytest.mark.asyncio
+async def test_send_home_channel_startup_notification_skipped_when_flag_disabled(
+    tmp_path, monkeypatch
+):
+    """Per-platform opt-out: gateway_restart_notification=False mutes the home-channel ping."""
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+
+    runner, adapter = make_restart_runner()
+    runner.config.platforms[Platform.TELEGRAM].home_channel = HomeChannel(
+        platform=Platform.TELEGRAM,
+        chat_id="home-42",
+        name="Ops Home",
+    )
+    runner.config.platforms[Platform.TELEGRAM].gateway_restart_notification = False
+    adapter.send = AsyncMock()
+
+    delivered = await runner._send_home_channel_startup_notifications()
+
+    assert delivered == set()
+    adapter.send.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_send_home_channel_startup_notification_default_flag_true(
+    tmp_path, monkeypatch
+):
+    """Default behavior is unchanged: missing flag means notifications still fire."""
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+
+    runner, adapter = make_restart_runner()
+    # Sanity-check the dataclass default — guards against future refactors
+    # silently flipping the default to False.
+    assert runner.config.platforms[Platform.TELEGRAM].gateway_restart_notification is True
+
+    runner.config.platforms[Platform.TELEGRAM].home_channel = HomeChannel(
+        platform=Platform.TELEGRAM,
+        chat_id="home-42",
+        name="Ops Home",
+    )
+    adapter.send = AsyncMock(return_value=SendResult(success=True, message_id="home"))
+
+    delivered = await runner._send_home_channel_startup_notifications()
+
+    assert delivered == {("telegram", "home-42", None)}
+    adapter.send.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_send_restart_notification_skipped_when_flag_disabled(
+    tmp_path, monkeypatch
+):
+    """The /restart originator's notification also honors the per-platform flag.
+
+    Slack used by end users → flag off → no "Gateway restarted" message even
+    when an end user accidentally triggers /restart. The marker file is still
+    cleaned up so the notification doesn't leak into the next boot.
+    """
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+
+    notify_path = tmp_path / ".restart_notify.json"
+    notify_path.write_text(json.dumps({
+        "platform": "telegram",
+        "chat_id": "42",
+    }))
+
+    runner, adapter = make_restart_runner()
+    runner.config.platforms[Platform.TELEGRAM].gateway_restart_notification = False
+    adapter.send = AsyncMock()
+
+    delivered_target = await runner._send_restart_notification()
+
+    assert delivered_target is None
+    adapter.send.assert_not_called()
+    assert not notify_path.exists()
+
+
 @pytest.mark.asyncio
 async def test_send_restart_notification_logs_info_on_sendresult_success(
     tmp_path, monkeypatch, caplog