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/connection/test_pool.py

@@ -342,3 +342,23 @@ async def test_connect_server_uri_still_wins_for_application_uri():
     # must match the certificate SAN URI (BadCertificateUriInvalid otherwise)
     assert fake_client.application_uri == 'urn:sientia:opc-ingestor'
     assert fake_client.name == pool.pod_id
+
+
+@pytest.mark.asyncio
+async def test_config_for_returns_a_copy_of_the_live_connection_settings():
+    pool = make_pool()
+    cfg = {'url': 'opc.tcp://h:4840', 'server_uri': 'urn:h', 'use_security': False}
+    with patch('ingestor.connection.pool.Client', return_value=AsyncMock()):
+        await pool.get(1, cfg)
+
+    found = pool.config_for('1')
+    assert found == cfg
+    found['url'] = 'mutated'
+    assert pool.config_for(1)['url'] == 'opc.tcp://h:4840'
+
+    await pool.evict('1')
+    assert pool.config_for('1') is None
+
+
+def test_config_for_unknown_server_is_none():
+    assert make_pool().config_for('missing') is None