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>

ingestor/engines/write.py

@@ -18,6 +18,7 @@ from sientia_do.observability.sientia_monitoring import SientiaMonitoring
 import ingestor.metrics as metrics
 from ingestor.connection.clock import MonotonicClock
 from ingestor.connection.pool import OpcConnectionPool
+from ingestor.connection.servers import ServerConfigResolver
 from ingestor.converters import ConversionError, to_typed_value
 from ingestor.io.data_sink import DataSink
 
@@ -77,9 +78,13 @@ class WriteEngine(SientiaMonitoring):
         write_timestamp: bool = True,
         write_quality: bool = True,
         min_pause_s: float = 0.0,
+        servers: ServerConfigResolver | None = None,
     ):
         self.pool = pool
         self.sink = sink
+        # Resolves the server connection by server_id (SIENTIAPDE-1975 GW1). Without it,
+        # only the connection carried by the command itself is used.
+        self.servers = servers
         self.write_timestamp = write_timestamp
         self.write_quality = write_quality
         self.min_pause_s = min_pause_s
@@ -105,11 +110,24 @@ class WriteEngine(SientiaMonitoring):
         except ConversionError as e:
             return await self._emit_error(cmd, 'conversion', str(e), 'error')
 
-        dv = self._build_datavalue(cmd, typed)
+        try:
+            dv = self._build_datavalue(cmd, typed)
+        except (KeyError, TypeError, ValueError) as e:
+            # write_timestamp on with a missing or non-ISO timestamp.
+            return await self._emit_error(cmd, 'bad_timestamp', repr(e), 'error')
+
+        try:
+            server_cfg = await self._server_cfg(cmd)
+        except Exception as e:
+            return await self._emit_error(cmd, 'server_lookup', str(e), 'error')
+        if server_cfg is None:
+            return await self._emit_error(
+                cmd, 'server_not_found', f'OPC server {cmd["server_id"]} is not configured', 'error'
+            )
 
         start = self.clock.elapsed()
         try:
-            client = await self.pool.get(cmd['server_id'], self._server_cfg(cmd))
+            client = await self.pool.get(cmd['server_id'], server_cfg)
             node = client.get_node(cmd['addr'])
             await node.write_value(dv)
         except Exception as e:
@@ -127,10 +145,14 @@ class WriteEngine(SientiaMonitoring):
                 now = self.clock.elapsed()
         self._last_write_at = now
 
-    def _server_cfg(self, cmd: dict) -> dict:
-        # ponytail: minimal cfg built straight from the C2 message. Resolving
-        # the full connector config (url/security) from the connectors DB by
-        # server_id is F4 wiring, not this task — pool is mocked in tests.
+    async def _server_cfg(self, cmd: dict) -> dict | None:
+        """Connection settings of the target server: resolved by server_id (connection
+        carried by the command, live pooled connection, connectors, opc-servers), or only
+        the ones carried by the command when no resolver is wired."""
+        if self.servers is not None:
+            return await self.servers.resolve(str(cmd['server_id']), cmd)
+        if not cmd.get('url'):
+            return None
         return {
             'url': cmd.get('url'),
             'use_security': cmd.get('use_security', False),
@@ -156,6 +178,12 @@ class WriteEngine(SientiaMonitoring):
         return isinstance(exc, UaStatusCodeError) and type(exc).__name__ in _SESSION_BAD_NAMES
 
     async def _emit_error(self, cmd: dict, error_type: str, message: str, status: str):
+        # The reason only lives here: the row gets write_status alone (SIENTIAPDE-1975).
+        self.logger.error(
+            f'OPC write failed ({status}, {error_type}): server={cmd.get("server_id")} '
+            f'addr={cmd.get("addr")} model_id={cmd.get("model_id")} '
+            f'timestamp={cmd.get("timestamp")}: {message}'
+        )
         tags = {'pod_id': self.pod_id, 'server_name': cmd.get('server_id', 'unknown')}
         await self.emit_metric(
             metric_object=metrics.OPC_ERROR_BY_TYPE, tags={**tags, 'error_type': error_type}
@@ -164,6 +192,17 @@ class WriteEngine(SientiaMonitoring):
             metric_object=metrics.OPC_WRITE_TOTAL,
             tags={**tags, 'model_id': cmd.get('model_id', 'unknown'), 'result': 'error'},
         )
+        # Same series as a success (status='ok'), so it always shows the last outcome.
+        await self.emit_metric(
+            metric_object=metrics.OPC_WRITE_STATUS_BY_MODEL,
+            method='set',
+            value=0,
+            tags={
+                'pod_id': self.pod_id,
+                'model_id': cmd.get('model_id', 'unknown'),
+                'status': 'ok',
+            },
+        )
         result = WriteResult(ok=False, status=status, opc_status_code=error_type, message=message)
         await self.sink.update_write_status(cmd, result)
         return result