feat(gateway): also gate pre-restart "Gateway restarting" notification

Extend the gateway_restart_notification flag to cover
_notify_active_sessions_of_shutdown — the message that fires just
before drain ("⚠️ Gateway restarting — Your current task will be
interrupted. Send any message after restart and I'll try to resume
where you left off.") sent to active sessions and home channels.

Same operator/end-user reasoning: on a Slack workspace shared with
end users, "Gateway restarting" reads as "the bot is broken" — the
operator should be able to suppress it consistently with the other
two lifecycle pings rather than having a partial opt-out.

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

gateway/run.py

@@ -2458,6 +2458,14 @@ class GatewayRunner:
                 if not adapter:
                     continue
 
+                platform_cfg = self.config.platforms.get(platform)
+                if platform_cfg is not None and not platform_cfg.gateway_restart_notification:
+                    logger.info(
+                        "Shutdown notification suppressed for active session: %s has gateway_restart_notification=false",
+                        platform_str,
+                    )
+                    continue
+
                 # Include thread_id if present so the message lands in the
                 # correct forum topic / thread.
                 metadata = {"thread_id": thread_id} if thread_id else None
@@ -2488,6 +2496,14 @@ class GatewayRunner:
             if not home or not home.chat_id:
                 continue
 
+            platform_cfg = self.config.platforms.get(platform)
+            if platform_cfg is not None and not platform_cfg.gateway_restart_notification:
+                logger.info(
+                    "Shutdown notification suppressed for home channel: %s has gateway_restart_notification=false",
+                    platform.value,
+                )
+                continue
+
             dedup_key = (platform.value, str(home.chat_id), str(home.thread_id) if home.thread_id else None)
             if dedup_key in notified:
                 continue

tests/gateway/test_restart_drain.py

@@ -257,6 +257,40 @@ async def test_shutdown_notification_send_failure_does_not_block():
     await runner._notify_active_sessions_of_shutdown()
 
 
+@pytest.mark.asyncio
+async def test_shutdown_notification_suppressed_when_flag_disabled():
+    """Active-session ping is muted when gateway_restart_notification=False on the platform."""
+    from gateway.config import Platform
+
+    runner, adapter = make_restart_runner()
+    runner._restart_requested = True
+    runner.config.platforms[Platform.TELEGRAM].gateway_restart_notification = False
+    session_key = "agent:main:telegram:dm:999"
+    runner._running_agents[session_key] = MagicMock()
+
+    await runner._notify_active_sessions_of_shutdown()
+
+    assert adapter.sent == []
+
+
+@pytest.mark.asyncio
+async def test_shutdown_notification_home_channel_suppressed_when_flag_disabled():
+    """Home-channel ping during shutdown is muted when the flag is False."""
+    from gateway.config import HomeChannel, Platform
+
+    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
+
+    await runner._notify_active_sessions_of_shutdown()
+
+    assert adapter.sent == []
+
+
 @pytest.mark.asyncio
 async def test_shutdown_notification_uses_persisted_origin_for_colon_ids():
     """Shutdown notifications should route from persisted origin, not reparsed keys."""