ignore active-only tailscale peers in ip discovery

agent/nix_builder_autoscaler/runtime/ec2.py

@@ -260,7 +260,7 @@ class EC2Runtime(RuntimeAdapter):
 
     @staticmethod
     def _peer_is_online(peer: dict[str, Any]) -> bool:
-        return bool(peer.get("Online") or peer.get("Active"))
+        return bool(peer.get("Online"))
 
     @staticmethod
     def _peer_hostname(peer: dict[str, Any]) -> str | None:

agent/nix_builder_autoscaler/tests/test_runtime_ec2.py

@@ -249,6 +249,55 @@ class TestDescribeInstance:
         info = runtime.describe_instance("i-running1")
         assert info["tailscale_ip"] is None
 
+    @patch.object(
+        EC2Runtime,
+        "_read_tailscale_status",
+        return_value={
+            "Peer": {
+                "stale": {
+                    "HostName": "nix-builder-slot001",
+                    "Online": False,
+                    "Active": True,
+                    "TailscaleIPs": ["100.64.0.10"],
+                },
+                "current": {
+                    "HostName": "nix-builder-slot001",
+                    "Online": True,
+                    "Active": False,
+                    "TailscaleIPs": ["100.64.0.11"],
+                },
+            }
+        },
+    )
+    def test_ignores_active_but_offline_stale_peer(self, _mock_status):
+        ec2_client = boto3.client("ec2", region_name="us-east-1")
+        stubber = Stubber(ec2_client)
+
+        launch_time = datetime(2026, 1, 15, 12, 30, 0, tzinfo=UTC)
+        response = {
+            "Reservations": [
+                {
+                    "Instances": [
+                        {
+                            "InstanceId": "i-running1",
+                            "State": {"Code": 16, "Name": "running"},
+                            "LaunchTime": launch_time,
+                            "Tags": [{"Key": "AutoscalerSlot", "Value": "slot001"}],
+                        }
+                    ],
+                }
+            ],
+        }
+        stubber.add_response(
+            "describe_instances",
+            response,
+            {"InstanceIds": ["i-running1"]},
+        )
+        runtime = _make_runtime(stubber, ec2_client)
+
+        info = runtime.describe_instance("i-running1")
+        assert info["tailscale_ip"] == "100.64.0.11"
+
     def test_localapi_permission_error_returns_none(self):
         ec2_client = boto3.client("ec2", region_name="us-east-1")
         runtime = EC2Runtime(_make_config(), _client=ec2_client)