SIENTIAPDE-1975: align the gateway write path with the Laborious

- GW1: write commands (C2) carry only the server_id; ServerConfigResolver
  resolves the connection (command override, live pooled connection,
  connectors, opc-servers) with a 60 s cache and a 10 s negative cache.
- GW2: write_status keeps the worst outcome (ok < error < session_bad,
  pending/NULL replaced), same rule as the Laborious, built with SQLAlchemy
  Core (no SQL formatting).
- GW3: update_write_status never raises; outcome (updated, kept,
  row_not_found, invalid, error) logged and counted
  (opc_write_status_update_total); runs off the event loop.
- GW4: the reason of a failed write is logged; opc_write_status_by_model
  shows the last outcome; a bad timestamp is a failed write, not an
  exception.
- GW5: the NATS first connect gives up after 5 s (nats-py's defaults block
  the main loop for about 4 minutes while NATS is down); reconnection after
  it is unbounded; idle_sweep restarts a connection closed for good; stop()
  is safe on a closed connection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/test_gateway_runtime.py

@@ -39,6 +39,7 @@ def mocks(monkeypatch):
     patched['pool'].release_idle = AsyncMock()
     patched['NatsWriteConsumer'].return_value.start = AsyncMock()
     patched['NatsWriteConsumer'].return_value.stop = AsyncMock()
+    patched['NatsWriteConsumer'].return_value.closed = False
     patched['GrpcServer'].return_value.start = AsyncMock()
     patched['GrpcServer'].return_value.stop = AsyncMock()
     return patched
@@ -173,3 +174,47 @@ async def test_idle_sweep_releases_idle_connections(mocks):
     await runtime.idle_sweep()
 
     mocks['pool'].release_idle.assert_awaited_once_with(42.0)
+
+
+def test_write_engine_resolves_servers_from_the_pool_and_mongo(mocks):
+    """SIENTIAPDE-1975 GW1: write commands carry only the server_id."""
+    data_manager = MagicMock()
+    runtime = gr.GatewayRuntime(
+        config=GatewayConfig(),
+        data_manager=data_manager,
+        pool=mocks['pool'],
+        logger=MagicMock(),
+        notification_handler=MagicMock(),
+        metrics_controller=MagicMock(),
+    )
+
+    _, kwargs = mocks['WriteEngine'].call_args
+    assert kwargs['servers'] is runtime.servers
+    assert runtime.servers.pool is mocks['pool']
+    assert runtime.servers.mongo is data_manager.mongo_repository
+
+
+@pytest.mark.asyncio
+async def test_idle_sweep_restarts_a_closed_nats_connection(mocks):
+    runtime = make_runtime(pool=mocks['pool'])
+    nats_mock = mocks['NatsWriteConsumer'].return_value
+    await runtime.start()
+    assert nats_mock.start.await_count == 1
+
+    nats_mock.closed = True  # closed for good (e.g. by the server)
+    await runtime.idle_sweep()
+
+    assert nats_mock.start.await_count == 2
+    assert runtime._nats_started is True
+    runtime.logger.warning.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_idle_sweep_leaves_a_live_nats_connection_alone(mocks):
+    runtime = make_runtime(pool=mocks['pool'])
+    nats_mock = mocks['NatsWriteConsumer'].return_value
+    await runtime.start()
+
+    await runtime.idle_sweep()
+
+    assert nats_mock.start.await_count == 1