Merge pull request #40 from Aignosi/fix/SIENTIAPDE-1811-fix

SIENTIAPDE-1811: Update dependencies, gitignore, and strengthen OPC UA error handling

.gitignore

@@ -51,4 +51,8 @@ catboost_info/
 
 .ruff_cache/
 .mypy_cache/
-mlruns/
+mlruns/
+
+relatorio*
+openspec/
+.cursor/

README.md

@@ -48,6 +48,7 @@ A comprehensive, Temporal-based ML orchestration system for industrial data proc
   - [Prediction Operation Metrics](#prediction-operation-metrics)
   - [OPC Export Metrics](#opc-export-metrics)
   - [Data Quality Metrics](#data-quality-metrics)
+- [OPC UA Communication](#opc-ua-communication)
 - [Configuration](#configuration-1)
   - [Environment Variables](#environment-variables)
   - [OPC Configuration](#opc-configuration)
@@ -164,7 +165,7 @@ Laborious uses a Temporal-based architecture with strong separation of concerns
 - `connectors_config.py`: Env-driven configuration builders
 - `models/minio_dataframe_payload.py`: MinIO-offloaded DataFrame payload model
 - `repository/model_repository.py`: MLFlow operations and retraining
-- `repository/opc_repository.py`: OPC communication and writes
+- `repository/opc_repository.py`: OPC UA client, writes, session recovery (see [OPC UA Communication](#opc-ua-communication))
 - `repository/minio_manager.py`: MinIO object storage operations
 - `filters/conditional_filters.py` and `filters/mlflow_filters.py`
 
@@ -779,6 +780,15 @@ The Laborious system exposes comprehensive Prometheus metrics for operational vi
   - Labels: `pod_id`, `model_name`, `workflow_name`, `opc_server_id`
   - Buckets: [0.01, 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0]
 
+OPC UA session and write diagnostics (Prometheus, `laborious/metrics.py`):
+
+- `opc_connections_initiated_total`, `opc_connections_failed_total`, `opc_connection_status`
+- `opc_session_created_total`, `opc_session_closed_total`, `opc_session_revised_timeout_milliseconds`
+- `opc_write_attempts_total` (label `result`: `OK` or exception name, e.g. `BadSessionIdInvalid`)
+- `opc_write_inter_arrival_over_session_timeout_total`
+
+See [OPC UA Communication](#opc-ua-communication) for semantics, concurrency, and confidence codes **12** / **14**.
+
 ### Data Quality Metrics
 - Filter pass/fail rates through notification system
 - MLFlow API response validation metrics
@@ -810,7 +820,7 @@ The Laborious system exposes comprehensive Prometheus metrics for operational vi
 | `OPC_CERT_PATH` | OPC client certificate path | `None` | No |
 | `OPC_PRIVATE_KEY_PATH` | OPC private key path | `None` | No |
 | `OPC_SERVER_CERT_PATH` | OPC server certificate path | `None` | No |
-| `OPC_RECONNECTION_INTERVAL` | OPC reconnection interval (ms) | `120` | No |
+| `OPC_RECONNECTION_INTERVAL` | Minimum seconds between OPC reconnects | `120` | No |
 | `PI_WEB_API_BASE_URL` | PI Web API server base URL | `None` | No |
 | `PI_WEB_API_AUTH_TYPE` | PI Web API authentication type (basic/bearer) | `None` | No |
 | `PI_WEB_API_AUTH_TOKEN` | PI Web API authentication token | `None` | No |
@@ -903,6 +913,12 @@ Legacy MinIO object layout (relative key):
 `training_datasets/{model_name}/{object_prefix}_{timestamp}.parquet` where `object_prefix` is sanitized
 (slashes replaced by underscores) to keep a stable model-level directory.
 
+## OPC UA Communication
+
+Full reference: **[docs/opc-communication.md](docs/opc-communication.md)** (connection lifecycle, Tier-1 `Bad*` reconnect, connection lock / session readiness, metrics, PostgreSQL confidence **12** vs **14**, tests).
+
+Implementation plan: [`.cursor/plans/opc_bad_reconnect_ac4c6045.plan.md`](.cursor/plans/opc_bad_reconnect_ac4c6045.plan.md).
+
 ### OPC Configuration
 
 For multiple OPC servers, use the `OPC_CONFIG` environment variable:
@@ -1126,8 +1142,10 @@ laborious/
    - Ensure proper connection pool configuration
 
 4. **OPC Connection Failures**
-   - Verify OPC server is accessible
+   - See [docs/opc-communication.md](docs/opc-communication.md)
+   - Verify OPC server is accessible and `OPC_RECONNECTION_INTERVAL` is appropriate
    - Check certificate and key file paths
+   - Correlate `opc_write_attempts_total` with `opc_session_*` metrics; count session errors via `prediction_confidence = 14`
    - Review OPC server logs for connection issues
 
 5. **PI Web API Connection Failures**

docs/opc-communication.md

@@ -0,0 +1,170 @@
+# OPC UA communication (Laborious)
+
+Laborious exports predictions to OPC UA servers through `OpcRepository` ([`laborious/utils/repository/opc_repository.py`](../laborious/utils/repository/opc_repository.py)) and the Temporal activity layer in [`laborious/activities/opc.py`](../laborious/activities/opc.py).
+
+Implementation plan for session/channel recovery on Tier-1 `Bad*` errors: [`.cursor/plans/opc_bad_reconnect_ac4c6045.plan.md`](../.cursor/plans/opc_bad_reconnect_ac4c6045.plan.md).
+
+## Architecture
+
+```text
+Worker (long-lived)
+  └── OpcRepository per OPC server id (from OPC_CONFIG / env)
+        ├── connect / disconnect / validate_connection (read-only)
+        ├── _connect_locked / _reconnect_locked (under _connection_lock)
+        ├── write_data (single attempt per call)
+        └── background reconnect on Tier-1 Bad*, protocol closed, or stale session
+
+Temporal activity write_opc_data
+  └── OPC.manage_output_tags → write_data per tag (sequential per activity)
+```
+
+One worker process holds one `OpcRepository` instance per configured server. Multiple Temporal activities can call `write_data` concurrently on the same repository.
+
+## Connection lifecycle
+
+| Phase | Behavior |
+|-------|----------|
+| Startup | `init_opc()` creates repositories and calls `connect()` → `_connect_locked()` |
+| Steady state | `validate_connection()` is read-only (`protocol.state` only); `_session_ready` is checked in `write_data` |
+| Tier-1 Bad* / protocol closed | `_start_reconnect` → `_run_reconnect` → `_reconnect_locked()` (respects `reconnection_interval`) |
+| Write | `write_data()` checks reconnect task, `_session_ready`, validates protocol, then one `get_node` + `write_value` |
+| Shutdown | `close()` disconnects all repositories |
+
+### Session and channel timeouts
+
+Requested session and secure-channel lifetime: **10 minutes** (`OPC_UA_SESSION_AND_CHANNEL_TIMEOUT_MS` in `opc_repository.py`). The server may revise these values; negotiated values are logged after connect and exposed as `opc_session_revised_timeout_milliseconds`.
+
+### Reconnection interval
+
+`OPC_RECONNECTION_INTERVAL` is in **seconds** (default `120`). It gates **background** reconnect after Tier-1 `Bad*`, closed protocol, or stale session (`last_reconnection_time` is updated only in `_reconnect_locked()`). It limits load on the OPC server when many workflows fail at once.
+
+## Concurrency: connection lock and session readiness
+
+To allow **multiple concurrent writes** when the session is healthy, but **block all writes** while the connection is being torn down or re-established:
+
+| Primitive | Role |
+|-----------|------|
+| `_connection_lock` (`asyncio.Lock`) | Held for the entire `disconnect` → `connect` path. Only one connection-maintenance task at a time. |
+| `_session_ready` (`asyncio.Event`) | Set when a session is ready for writes; cleared before reconnect starts and set again after a successful connect. |
+
+**Connection methods (caller holds `_connection_lock` for `_*_locked` helpers):**
+
+| Method | Role |
+|--------|------|
+| `_create_client()` | Create asyncua `Client` + optional `set_security`; raises if `client` already exists |
+| `_open_session()` | `client.connect()` + metrics; raises if session already open or client missing |
+| `_connect_locked()` | `_create_client()` (when needed) + `_open_session()`; raises if already connected |
+| `_disconnect_locked()` | Teardown session and clear `client` |
+| `_reconnect_locked()` | `_disconnect_locked()` + `_connect_locked()`; sets `last_reconnection_time` |
+
+Public `connect()` / `disconnect()` acquire the lock and call `_connect_locked()` / `_disconnect_locked()`.
+
+**Write path (`write_data`):**
+
+1. If a reconnect task is **in flight** → **fail immediately** (`opc_error_kind=reconnect_in_progress`).
+2. If `_session_ready` is cleared and no task is running → schedule reconnect (`SessionNotReady`); fail with `connection_lost` or `reconnect_in_progress` if a task started.
+3. `validate_connection()` checks `protocol.state` only (read-only). If closed → schedule reconnect (`ProtocolClosed`) and fail with `opc_error_kind=connection_lost`.
+4. Single `get_node` + `write_value` (no retry). Tier-1 `Bad*` on write also schedules reconnect.
+
+**Reconnect path (`_run_reconnect`):**
+
+1. `_start_reconnect` clears `_session_ready` and schedules the task when the interval allows and `_allow_reconnect` is true.
+2. `async with _connection_lock:` → `_reconnect_locked()`.
+3. `_session_ready` is set on successful `_open_session()`.
+4. `disconnect()` sets `_allow_reconnect=False` so shutdown does not respawn sessions.
+
+A second `_connect_locked()` while a session is already open raises `OpcSessionAlreadyConnectedError` (disconnect first).
+
+**asyncua note:** Concurrent `write_value` on the same session is only safe if the stack tolerates it. If production shows issues, serialize writes with an optional `asyncio.Semaphore(1)` while keeping the connection lock semantics above.
+
+**Future threads:** replace `asyncio.Lock` / `Event` with `threading` primitives or route all OPC I/O through one dedicated loop.
+
+## Reconnect triggers
+
+Background reconnect is scheduled when:
+
+- `validate_connection()` sees a closed or missing protocol (`ProtocolClosed`).
+- `_session_ready` is clear after a failed reconnect (`SessionNotReady`).
+- A write raises a Tier-1 `UaStatusCodeError` in `RECONNECTABLE_OPC_BAD_NAMES`.
+
+For Tier-1 `Bad*` when the server invalidates the session (e.g. `BadSessionIdInvalid`) but the client still sees transport as open, `write_data` fails once, records the OPC status in metrics, and **schedules** reconnect if:
+
+- The exception is a `UaStatusCodeError` whose name is in `RECONNECTABLE_OPC_BAD_NAMES` (see plan), and
+- `reconnection_interval` has elapsed since `last_reconnection_time`, and
+- No reconnect task is already running.
+
+There is **no write retry**: the failed export is not sent again in the same activity.
+
+## Prediction confidence and PostgreSQL comments
+
+| `prediction_confidence` | Meaning |
+|-------------------------|---------|
+| (unchanged) | Successful OPC export |
+| **12** | Generic OPC write failure (`OPC_WRITTING_ERROR_CONFIDENCE`) |
+| **14** | Tier-1 session/channel `Bad*` on export (`OPC_SESSION_BAD_CONFIDENCE`) |
+| **14** | Write while reconnect in progress (`OPC_SESSION_BAD_CONFIDENCE`, comment `OPC UA reconnect in progress`) |
+| **13** | PI Web API write failure (separate path) |
+
+Session/channel errors use a stable comment for counting:
+
+```text
+OPC UA session/channel error: BadSessionIdInvalid
+```
+
+Reconnect-in-progress exports use:
+
+```text
+OPC UA reconnect in progress
+```
+
+Example SQL:
+
+```sql
+SELECT count(*) FROM predictions WHERE prediction_confidence = 14;
+SELECT count(*) FROM predictions WHERE comments LIKE 'OPC UA session/channel error:%';
+```
+
+## Prometheus metrics (`opc_*`)
+
+Defined in [`laborious/metrics.py`](../laborious/metrics.py). Do not rename in production without a dashboard migration.
+
+| Metric | Purpose |
+|--------|---------|
+| `opc_connections_initiated_total` | Connection attempts |
+| `opc_connections_failed_total` | Failed connects |
+| `opc_connection_status` | Gauge 1=connected, 0=disconnected |
+| `opc_session_created_total` | Session established after connect |
+| `opc_session_closed_total` | Disconnect initiated |
+| `opc_session_revised_timeout_milliseconds` | Negotiated session timeout (ms) |
+| `opc_write_attempts_total` | Per write; label `result` = `OK` or exception name |
+| `opc_write_inter_arrival_over_session_timeout_total` | Successful writes spaced longer than revised session timeout |
+
+Legacy activity metrics: `laborious_prediction_opc_writing_count`, `laborious_prediction_opc_writing_response_time_monitor`.
+
+## Environment variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `OPC_CONFIG` | — | JSON map of server configs (overrides single-server env) |
+| `OPC_ID` | `1` | Server id |
+| `OPC_URL` | `opc.tcp://localhost:4840` | Endpoint |
+| `OPC_SERVER_NAME` | `default_server` | Label for metrics/logs |
+| `OPC_SERVER_URI` | same as URL | Application URI / cert SAN |
+| `OPC_CERT_PATH` | — | Client certificate (secure mode) |
+| `OPC_PRIVATE_KEY_PATH` | — | Client private key |
+| `OPC_SERVER_CERT_PATH` | — | Server certificate |
+| `OPC_RECONNECTION_INTERVAL` | `120` | Minimum seconds between reconnects |
+
+## Operations checklist
+
+- Correlate `BadSessionIdInvalid` in `opc_write_attempts_total` with `opc_session_closed_total` / `opc_session_created_total` (reconnect may finish after the row is stored with confidence 14).
+- Use confidence **14** and comment prefix for session invalidation rates; use **12** for other OPC failures.
+- Respect `OPC_RECONNECTION_INTERVAL` under parallel load; bursts of confidence 14 are expected until the next successful cycle.
+
+## Related tests
+
+- Unit: [`tests/laborious/utils/repository/test_opc_repository.py`](../tests/laborious/utils/repository/test_opc_repository.py)
+- Unit: [`tests/laborious/activities/test_opc.py`](../tests/laborious/activities/test_opc.py)
+- E2E (mock OPC): [`e2e/test_predictions_batch_format_export.py`](../e2e/test_predictions_batch_format_export.py)
+- E2E (in-process asyncua server + real `OpcRepository`): [`e2e/test_opc_real_server.py`](../e2e/test_opc_real_server.py) — scenarios 3.1.2, 3.2.2, 3.2.4, 3.2.5
+- Scenarios: [`e2e/scenarios.md`](../e2e/scenarios.md)

e2e/conftest.py

@@ -2,7 +2,14 @@
 Pytest configuration and fixtures for E2E tests.
 """
 
+import sys
 from unittest.mock import AsyncMock, MagicMock, patch
+
+# E2E workflows under test do not run ModelAnalysis; stub before Activities import.
+_model_analysis_module = MagicMock()
+_model_analysis_module.ModelAnalysis = MagicMock
+sys.modules.setdefault('sientia', MagicMock())
+sys.modules.setdefault('sientia.ModelAnalysis', _model_analysis_module)
 from io import BytesIO
 
 import pandas as pd
@@ -14,6 +21,7 @@ from testcontainers.postgres import PostgresContainer
 from temporalio.testing import WorkflowEnvironment
 from temporalio.worker import Worker
 
+from e2e.opc_test_server import OpcE2ETestServer
 from laborious.activities.activities import Activities
 from laborious.workflows.predictions_batch import PredictionsBatch
 from laborious.workflows.sub_workflows.prediction_process import PredictionProcess
@@ -297,6 +305,19 @@ def mock_opc_repository():
     mock_repo.disconnect = AsyncMock()
     return mock_repo
 
+
+@pytest_asyncio.fixture
+async def opc_e2e_server():
+    """
+    In-process asyncua OPC UA server for E2E tests against OpcRepository.
+    """
+    server = OpcE2ETestServer()
+    await server.start()
+    try:
+        yield server
+    finally:
+        await server.stop()
+
 @pytest_asyncio.fixture
 def patch_create_engine(postgres_engine):
     """Patch create_engine to return test postgres_engine."""
@@ -577,3 +598,84 @@ async def temporal_worker_real_minio(temporal_test_env, test_activities_real_min
         activities=_worker_activity_list(test_activities_real_minio),
     ) as worker:
         yield worker
+
+
+@pytest_asyncio.fixture(scope='function')
+async def test_activities_real_opc(
+    postgres_engine,
+    postgres_container,
+    opc_e2e_server: OpcE2ETestServer,
+    mock_logger,
+    notification_handler,
+    metrics_controller,
+    patch_create_engine,
+    patch_minio_repository,
+    patch_mlflow,
+    patch_pi_web_api_repository,
+):
+    """
+    Activities with a real OpcRepository connected to the in-process OPC UA server.
+    """
+    activities = Activities(
+        postgres_config={
+            'host': 'localhost',
+            'port': postgres_container.get_exposed_port(5432),
+            'user': 'test',
+            'password': 'test',
+            'dbname': 'test',
+            'min_connections': 1,
+            'max_connections': 5,
+        },
+        mlflow_config={
+            'host': 'http://localhost',
+            'port': '5000',
+            'username': 'test',
+            'password': 'test',
+        },
+        minio_config={
+            'endpoint_url': 'localhost:9000',
+            'access_key': 'test',
+            'secret_key': 'test',
+            'default_bucket': 'test-bucket',
+            'retention_hours': 24,
+            'secure': False,
+        },
+        opc_config={
+            '1': {
+                'id': '1',
+                'server_name': 'e2e-opc',
+                'url': opc_e2e_server.url,
+                'server_uri': opc_e2e_server.url,
+                'cert_path': None,
+                'private_key_path': None,
+                'server_cert_path': None,
+                'reconnection_interval': 0,
+            }
+        },
+        pi_web_api_config={
+            'base_url': 'http://localhost:8080',
+            'auth_type': 'bearer',
+            'auth_token': 'test_token',
+        },
+        logger=mock_logger,
+        notification_handler=notification_handler,
+    )
+    await activities.init_opc()
+    repo = activities.opc_repository['1']
+    assert repo._session_ready.is_set(), 'OPC E2E server connection failed during init_opc'
+    try:
+        yield activities
+    finally:
+        await activities.shutdown()
+
+
+@pytest_asyncio.fixture(scope='function')
+async def temporal_worker_real_opc(temporal_test_env, test_activities_real_opc):
+    """Temporal worker backed by Activities using the in-process OPC UA server."""
+    async with Worker(
+        temporal_test_env.client,
+        task_queue='test-queue',
+        workflows=[PredictionsBatch, PredictionProcess, FormatAndExportPrediction],
+        activities=_worker_activity_list(test_activities_real_opc),
+    ) as worker:
+        yield worker

e2e/helpers.py

@@ -64,7 +64,8 @@ def assert_prediction(
     prediction: float = 0.5,
     prediction_confidence: int | Decimal = 0,
     prediction_status: str = 'Good',
-    comments: str = '',
+    comments: str | None = None,
+    comments_contains: str | None = None,
 ) -> None:
     """
     Assert exactly one prediction row exists for model_id with expected columns.
@@ -75,7 +76,8 @@ def assert_prediction(
         prediction: Expected prediction value.
         prediction_confidence: Expected confidence (int or Decimal for numeric column).
         prediction_status: Expected status string.
-        comments: Expected comments string.
+        comments: Expected exact comments string (optional).
+        comments_contains: Substring expected in comments when queued (optional).
     """
     import pytest
 
@@ -98,7 +100,12 @@ def assert_prediction(
             str(prediction_confidence)
         ), f'Expected prediction_confidence={prediction_confidence}, got {row[2]}'
         assert row[3] == prediction_status, f"Expected prediction_status='{prediction_status}', got {row[3]}"
-        assert row[4] == comments, f"Expected comments='{comments}', got {row[4]}"
+        if comments is not None:
+            assert row[4] == comments, f"Expected comments='{comments}', got {row[4]}"
+        if comments_contains is not None:
+            assert comments_contains in row[4], (
+                f"Expected comments to contain '{comments_contains}', got {row[4]}"
+            )
 
 
 def assert_continue(

e2e/opc_test_server.py

@@ -0,0 +1,189 @@
+"""
+In-process OPC UA server for E2E tests (asyncua).
+
+Provides writable prediction/confidence nodes and optional write faults
+(Tier-1 BadSessionIdInvalid via PreWrite callback).
+"""
+
+from __future__ import annotations
+
+import socket
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+from asyncua import Server, ua
+from asyncua.common.callback import CallbackType
+from asyncua.common.utils import ServiceError
+
+if TYPE_CHECKING:
+    from asyncua.common.node import Node
+
+
+UNKNOWN_NODE_ID = 'ns=99;i=9999'
+
+
+@dataclass(frozen=True)
+class OpcE2ENodeIds:
+    """NodeId strings used in opc_output_config for E2E workflows."""
+
+    prediction: str
+    confidence: str
+    unknown: str = UNKNOWN_NODE_ID
+
+
+class OpcE2ETestServer:
+    """
+    Ephemeral asyncua server with Laborious E2E variables and controllable faults.
+
+    Args:
+        host: Bind address (default 127.0.0.1).
+    """
+
+    def __init__(self, host: str = '127.0.0.1') -> None:
+        self._host = host
+        self._server: Server | None = None
+        self._prediction_node: Node | None = None
+        self._confidence_node: Node | None = None
+        self._session_bad_on_write = False
+        self._url: str | None = None
+        self._node_ids: OpcE2ENodeIds | None = None
+
+    @property
+    def url(self) -> str:
+        if self._url is None:
+            raise RuntimeError('OPC E2E server is not started')
+        return self._url
+
+    @property
+    def node_ids(self) -> OpcE2ENodeIds:
+        if self._node_ids is None:
+            raise RuntimeError('OPC E2E server is not started')
+        return self._node_ids
+
+    def set_session_bad_on_write(self, enabled: bool) -> None:
+        """
+        When enabled, every client Write is rejected with BadSessionIdInvalid.
+
+        Args:
+            enabled (bool): Turn Tier-1 session fault injection on or off.
+        """
+        self._session_bad_on_write = enabled
+
+    async def start(self) -> OpcE2ENodeIds:
+        """
+        Start the OPC UA server on a free TCP port.
+
+        Return:
+            OpcE2ENodeIds: NodeId strings for prediction and confidence tags.
+        """
+        port = _free_port(self._host)
+        self._url = f'opc.tcp://{self._host}:{port}/freeopcua/server/'
+
+        server = Server()
+        server.set_endpoint(self._url)
+        await server.init()
+        server.iserver.callback_service.addListener(
+            CallbackType.PreWrite,
+            self._pre_write_callback,
+        )
+
+        idx = await server.register_namespace('http://sientia.test/laborious-e2e')
+        e2e_object = await server.nodes.objects.add_object(idx, 'LaboriousE2E')
+        prediction = await e2e_object.add_variable(
+            idx,
+            'Prediction',
+            ua.Variant(0.0, ua.VariantType.Float),
+        )
+        confidence = await e2e_object.add_variable(
+            idx,
+            'Confidence',
+            ua.Variant(0.0, ua.VariantType.Float),
+        )
+        await prediction.set_writable()
+        await confidence.set_writable()
+
+        await server.start()
+        self._server = server
+        self._prediction_node = prediction
+        self._confidence_node = confidence
+        self._node_ids = OpcE2ENodeIds(
+            prediction=prediction.nodeid.to_string(),
+            confidence=confidence.nodeid.to_string(),
+        )
+        return self._node_ids
+
+    async def stop(self) -> None:
+        """Stop the OPC UA server and release the listening port."""
+        if self._server is not None:
+            await self._server.stop()
+            self._server = None
+        self._prediction_node = None
+        self._confidence_node = None
+        self._url = None
+        self._node_ids = None
+        self._session_bad_on_write = False
+
+    async def read_prediction(self) -> float:
+        """
+        Read the current prediction variable value from the address space.
+
+        Return:
+            float: Stored prediction value.
+        """
+        if self._prediction_node is None:
+            raise RuntimeError('OPC E2E server is not started')
+        value = await self._prediction_node.read_value()
+        return float(value)
+
+    async def read_confidence(self) -> float:
+        """
+        Read the current confidence variable value from the address space.
+
+        Return:
+            float: Stored confidence value.
+        """
+        if self._confidence_node is None:
+            raise RuntimeError('OPC E2E server is not started')
+        value = await self._confidence_node.read_value()
+        return float(value)
+
+    async def _pre_write_callback(self, _event, _service) -> None:
+        if self._session_bad_on_write:
+            raise ServiceError(ua.StatusCodes.BadSessionIdInvalid)
+
+
+def _free_port(host: str) -> int:
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+        sock.bind((host, 0))
+        return int(sock.getsockname()[1])
+
+
+def build_opc_output_config(
+    node_ids: OpcE2ENodeIds,
+    *,
+    prediction_tag: str | None = None,
+    confidence_tag: str | None = None,
+    prediction_only: bool = False,
+    server_key: str = '1',
+) -> dict[str, dict]:
+    """
+    Build opc_output_config for PredictionsBatch using real server NodeIds.
+
+    Args:
+        node_ids (OpcE2ENodeIds): Node ids from OpcE2ETestServer.
+        prediction_tag (str | None): Override prediction NodeId (default: node_ids.prediction).
+        confidence_tag (str | None): Override confidence NodeId (default: node_ids.confidence).
+        prediction_only (bool): When True, omit confidence_tags (single write per activity).
+        server_key (str): OPC server id key in opc_output_config.
+
+    Return:
+        dict: opc_output_config payload for workflow input.
+    """
+    pred = prediction_tag if prediction_tag is not None else node_ids.prediction
+    conf = confidence_tag if confidence_tag is not None else node_ids.confidence
+    server_config: dict = {
+        'prediction_tags': {pred: {'data_type': 'float'}},
+    }
+    if not prediction_only:
+        server_config['confidence_tags'] = {conf: {'data_type': 'float'}}
+    return {server_key: server_config}

e2e/scenarios.md

@@ -8,6 +8,8 @@ This document describes all possible test scenarios for the `predictions_batch`
 - **Dependencies**: install dev requirements (includes `testcontainers[postgres,minio]`).
 - **Invocation**: run only integration-marked tests, for example: `pytest e2e/ -m integration`.
 - **MinIO tests**: `e2e/test_minio_offload.py` exercises real S3 uploads; other E2E modules continue to mock MinIO on the worker used by most scenarios.
+- **OPC tests (real server)**: `e2e/test_opc_real_server.py` uses an in-process **asyncua** server and real `OpcRepository` (`test_activities_real_opc`). Scenarios 3.1.2, 3.2.2, 3.2.4, and 3.2.5 are covered there. Other E2E modules keep the OPC mock.
+- Run only OPC real-server tests: `pytest e2e/test_opc_real_server.py -m "integration and opc"`.
 
 ## Workflow Overview
 
@@ -495,6 +497,48 @@ These paths do **not** rely on Temporal activity retries for export failures: th
 
 ---
 
+#### Scenario 3.2.4: OPC Session / Channel Bad* (Tier-1)
+**Description**: OPC write fails with a Tier-1 session or channel status (e.g. `BadSessionIdInvalid`) while transport may still appear open on the client
+
+**Input**:
+- Valid prediction and OPC output config
+- Mock or server returning Tier-1 `UaStatusCodeError` on write (no write retry in the same activity)
+
+**Expected Behavior**:
+- `write_opc_data` fails forward for affected tags; background reconnect may be scheduled if `OPC_RECONNECTION_INTERVAL` allows
+- Workflow **completes**
+- PostgreSQL row uses **`prediction_confidence` 14** and comment prefix `OPC UA session/channel error:` (including OPC status name)
+- `opc_write_attempts_total` records `result=BadSessionIdInvalid` (or matching status); no second write attempt in the same activity
+
+**Assertions**:
+- Workflow completes
+- `prediction_confidence = 14`
+- `comments` matches `OPC UA session/channel error:%`
+- Generic OPC error confidence **12** is not used for this case
+
+**Reference**: [docs/opc-communication.md](../docs/opc-communication.md), plan `.cursor/plans/opc_bad_reconnect_ac4c6045.plan.md`
+
+---
+
+#### Scenario 3.2.5: OPC Write Blocked During Reconnect
+**Description**: A write is attempted while the repository is reconnecting (session not ready)
+
+**Input**:
+- Valid prediction
+- Simulated slow reconnect (e.g. delayed `connect`) or concurrent writes where the first triggers reconnect
+
+**Expected Behavior**:
+- Second write (or parallel write) is rejected **immediately** when reconnect is in progress or `_session_ready` is cleared — **without** calling `write_value`
+- No wait/sleep on the write path; no duplicate `connect` from parallel writers (connection lock)
+- `prediction_confidence = 14`, `comments = OPC UA reconnect in progress` (distinguish from Tier-1 `Bad*` via comment prefix in SQL)
+
+**Assertions**:
+- At most one reconnect sequence (`disconnect` + `connect`) for the overlapping window
+- No write retry after failure
+- Tests in `test_opc_repository` (unit) and optional e2e in `test_predictions_batch_format_export.py`
+
+---
+
 #### Scenario 3.2.3: PI Web API Partial Write Error
 **Description**: Two prediction tags attempt to be written to PI Web API, but only one succeeds
 

e2e/test_opc_real_server.py

@@ -0,0 +1,194 @@
+"""
+E2E tests for OPC export using an in-process asyncua server and real OpcRepository.
+
+Covers scenarios 3.1.2, 3.2.2, 3.2.4, and 3.2.5 from e2e/scenarios.md.
+Mock-based OPC tests remain in test_predictions_batch_format_export.py.
+"""
+
+import asyncio
+
+import pytest
+from temporalio.testing import WorkflowEnvironment
+from temporalio.worker import Worker
+
+from e2e.helpers import assert_prediction, insert_sample_data, make_workflow_id, start_and_await_workflow
+from e2e.opc_test_server import UNKNOWN_NODE_ID, OpcE2ETestServer, build_opc_output_config
+from e2e.test_predictions_batch_format_export import get_base_input_data
+from laborious.activities.activities import Activities
+from laborious.activities.opc import OPC_RECONNECT_IN_PROGRESS_COMMENT
+from laborious.utils.repository.opc_repository import OpcRepository
+from laborious.workflows.predictions_batch import PredictionsBatch
+
+
+async def _slow_reconnect_under_lock(repo: OpcRepository, hold_seconds: float = 0.75) -> None:
+    """
+    Hold the connection lock briefly so concurrent writes see reconnect_in_progress.
+
+    Args:
+        repo (OpcRepository): Connected repository.
+        hold_seconds (float): Time to keep the lock before reconnecting.
+    """
+    async with repo._connection_lock:
+        await asyncio.sleep(hold_seconds)
+        await repo._reconnect_locked()
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+@pytest.mark.opc
+async def test_scenario_3_1_2_export_with_opc_only_real_server(
+    temporal_test_env: WorkflowEnvironment,
+    temporal_worker_real_opc: Worker,
+    test_activities_real_opc: Activities,
+    opc_e2e_server: OpcE2ETestServer,
+    postgres_engine,
+):
+    """
+    Scenario 3.1.2 (real OPC): connect, write prediction and confidence, verify server values.
+    """
+    client = temporal_test_env.client
+    model_id = 412
+    insert_sample_data(postgres_engine, model_id, [23.5, 78.2])
+
+    input_data = get_base_input_data(model_id)
+    input_data['opc_output_config'] = build_opc_output_config(opc_e2e_server.node_ids)
+    input_data['pi_web_api_output_config'] = None
+
+    await start_and_await_workflow(
+        client,
+        PredictionsBatch.run,
+        input_data,
+        make_workflow_id('test-opc-real-happy'),
+    )
+
+    test_activities_real_opc.pi_web_api_client.write_value.assert_not_called()
+    assert await opc_e2e_server.read_prediction() == pytest.approx(0.5)
+    assert await opc_e2e_server.read_confidence() == pytest.approx(0.0)
+    assert_prediction(postgres_engine, model_id)
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+@pytest.mark.opc
+async def test_scenario_3_2_2_opc_write_error_real_server(
+    temporal_test_env: WorkflowEnvironment,
+    temporal_worker_real_opc: Worker,
+    test_activities_real_opc: Activities,
+    opc_e2e_server: OpcE2ETestServer,
+    postgres_engine,
+):
+    """
+    Scenario 3.2.2 (real OPC): unknown NodeId yields generic write failure (confidence 12).
+    """
+    client = temporal_test_env.client
+    model_id = 422
+    insert_sample_data(postgres_engine, model_id, [23.5, 78.2])
+
+    node_ids = opc_e2e_server.node_ids
+    input_data = get_base_input_data(model_id)
+    input_data['opc_output_config'] = build_opc_output_config(
+        node_ids,
+        prediction_tag=UNKNOWN_NODE_ID,
+        confidence_tag=UNKNOWN_NODE_ID,
+    )
+    input_data['pi_web_api_output_config'] = None
+
+    await start_and_await_workflow(
+        client,
+        PredictionsBatch.run,
+        input_data,
+        make_workflow_id('test-opc-real-bad-node'),
+    )
+
+    assert_prediction(
+        postgres_engine,
+        model_id,
+        prediction_confidence=12,
+        comments='Some data could not be written to OPC servers',
+    )
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+@pytest.mark.opc
+async def test_scenario_3_2_4_opc_session_bad_real_server(
+    temporal_test_env: WorkflowEnvironment,
+    temporal_worker_real_opc: Worker,
+    test_activities_real_opc: Activities,
+    opc_e2e_server: OpcE2ETestServer,
+    postgres_engine,
+):
+    """
+    Scenario 3.2.4 (real OPC): server PreWrite fault injects BadSessionIdInvalid (confidence 14).
+    """
+    client = temporal_test_env.client
+    model_id = 424
+    insert_sample_data(postgres_engine, model_id, [23.5, 78.2])
+
+    opc_e2e_server.set_session_bad_on_write(True)
+    try:
+        input_data = get_base_input_data(model_id)
+        input_data['opc_output_config'] = build_opc_output_config(
+            opc_e2e_server.node_ids,
+            prediction_only=True,
+        )
+        input_data['pi_web_api_output_config'] = None
+
+        await start_and_await_workflow(
+            client,
+            PredictionsBatch.run,
+            input_data,
+            make_workflow_id('test-opc-real-session-bad'),
+        )
+    finally:
+        opc_e2e_server.set_session_bad_on_write(False)
+
+    assert_prediction(
+        postgres_engine,
+        model_id,
+        prediction_confidence=14,
+        comments_contains='OPC UA session/channel error: BadSessionIdInvalid',
+    )
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+@pytest.mark.opc
+async def test_scenario_3_2_5_opc_write_blocked_during_reconnect_real_server(
+    temporal_test_env: WorkflowEnvironment,
+    temporal_worker_real_opc: Worker,
+    test_activities_real_opc: Activities,
+    opc_e2e_server: OpcE2ETestServer,
+    postgres_engine,
+):
+    """
+    Scenario 3.2.5 (real OPC): writes rejected while reconnect holds the connection lock.
+    """
+    client = temporal_test_env.client
+    model_id = 425
+    insert_sample_data(postgres_engine, model_id, [23.5, 78.2])
+
+    repo = test_activities_real_opc.opc_repository['1']
+    repo._session_ready.clear()
+    reconnect_task = asyncio.create_task(_slow_reconnect_under_lock(repo))
+
+    input_data = get_base_input_data(model_id)
+    input_data['opc_output_config'] = build_opc_output_config(opc_e2e_server.node_ids)
+    input_data['pi_web_api_output_config'] = None
+
+    try:
+        await start_and_await_workflow(
+            client,
+            PredictionsBatch.run,
+            input_data,
+            make_workflow_id('test-opc-real-reconnect-block'),
+        )
+    finally:
+        await reconnect_task
+
+    assert_prediction(
+        postgres_engine,
+        model_id,
+        prediction_confidence=14,
+        comments_contains=OPC_RECONNECT_IN_PROGRESS_COMMENT,
+    )

e2e/test_predictions_batch_format_export.py

@@ -153,7 +153,6 @@ async def test_scenario_3_1_1_default_prediction_export(
                 'addr_1',
                 0,
                 'float',
-                ANY,
                 {
                     'model_id': 311,
                     'model_name': 'test_model',
@@ -165,7 +164,6 @@ async def test_scenario_3_1_1_default_prediction_export(
                 'addr_2',
                 2,
                 'float',
-                ANY,
                 {
                     'model_id': 311,
                     'model_name': 'test_model',
@@ -252,20 +250,28 @@ async def test_scenario_3_1_2_export_with_opc_only(
     opc_write_data = cast(Any, test_activities.opc_repository['1'].write_data)
     opc_write_data.assert_has_calls(
         [
-            call('addr_1', 0.5, 'float', ANY,
-            {
-                'model_id': 312,
-                'model_name': 'test_model',
-                'schedule_name': 'test-schedule',
-                'workflow_name': 'predictions_batch',
-            }),
-            call('addr_2', 0, 'float', ANY,
-            {
-                'model_id': 312,
-                'model_name': 'test_model',
-                'schedule_name': 'test-schedule',
-                'workflow_name': 'predictions_batch',
-            }),
+            call(
+                'addr_1',
+                0.5,
+                'float',
+                {
+                    'model_id': 312,
+                    'model_name': 'test_model',
+                    'schedule_name': 'test-schedule',
+                    'workflow_name': 'predictions_batch',
+                },
+            ),
+            call(
+                'addr_2',
+                0,
+                'float',
+                {
+                    'model_id': 312,
+                    'model_name': 'test_model',
+                    'schedule_name': 'test-schedule',
+                    'workflow_name': 'predictions_batch',
+                },
+            ),
         ]
     )
 
@@ -500,20 +506,28 @@ async def test_scenario_3_1_5_export_without_transformed_data(
     opc_write_data = cast(Any, test_activities.opc_repository['1'].write_data)
     opc_write_data.assert_has_calls(
         [
-            call('addr_1', 0.5, 'float', ANY,
-            {
-                'model_id': 315,
-                'model_name': 'test_model',
-                'schedule_name': 'test-schedule',
-                'workflow_name': 'predictions_batch',
-            }),
-            call('addr_2', 0, 'float', ANY,
-            {
-                'model_id': 315,
-                'model_name': 'test_model',
-                'schedule_name': 'test-schedule',
-                'workflow_name': 'predictions_batch',
-            }),
+            call(
+                'addr_1',
+                0.5,
+                'float',
+                {
+                    'model_id': 315,
+                    'model_name': 'test_model',
+                    'schedule_name': 'test-schedule',
+                    'workflow_name': 'predictions_batch',
+                },
+            ),
+            call(
+                'addr_2',
+                0,
+                'float',
+                {
+                    'model_id': 315,
+                    'model_name': 'test_model',
+                    'schedule_name': 'test-schedule',
+                    'workflow_name': 'predictions_batch',
+                },
+            ),
         ]
     )
 
@@ -646,7 +660,68 @@ async def test_scenario_3_2_2_opc_write_error(
         prediction_confidence=12,
         comments='Some data could not be written to OPC servers',
     )
-    
+
+
+@pytest.mark.asyncio
+@pytest.mark.integration
+async def test_scenario_3_2_4_opc_session_bad_error(
+    temporal_test_env: WorkflowEnvironment,
+    temporal_worker: Worker,
+    test_activities: Activities,
+    postgres_engine,
+):
+    """
+    Scenario 3.2.4: OPC session/channel Tier-1 Bad* (e.g. BadSessionIdInvalid).
+
+    PostgreSQL stores prediction_confidence 14 and a stable session error comment.
+    """
+    client = temporal_test_env.client
+
+    model_id = 324
+
+    insert_sample_data(postgres_engine, model_id, [23.5, 78.2])
+
+    opc_write_data = cast(Any, test_activities.opc_repository['1'].write_data)
+    opc_write_data.return_value = (
+        False,
+        {
+            'notification_id': 'OPC_WRITE_DATA_ERROR_1',
+            'message': 'BadSessionIdInvalid',
+            'block': 'opc_repository',
+            'level': NotificationLevel.ERROR,
+            'attachment_content': 'BadSessionIdInvalid',
+            'opc_error_kind': 'session_bad',
+            'opc_status': 'BadSessionIdInvalid',
+        },
+    )
+
+    input_data = get_base_input_data(model_id)
+    input_data['opc_output_config'] = {
+        '1': {
+            'prediction_tags': {
+                'addr_1': {
+                    'data_type': 'float',
+                }
+            },
+            'confidence_tags': {
+                'addr_2': {
+                    'data_type': 'float',
+                }
+            },
+        }
+    }
+    input_data['pi_web_api_output_config'] = None
+
+    await start_and_await_workflow(
+        client, PredictionsBatch.run, input_data, make_workflow_id('test-opc-session-bad')
+    )
+
+    assert_prediction(
+        postgres_engine,
+        model_id,
+        prediction_confidence=14,
+        comments='OPC UA session/channel error: BadSessionIdInvalid',
+    )
 
 
 @pytest.mark.asyncio

inter_arrival.py

@@ -0,0 +1,25 @@
+# %%
+
+# Load logs.txt
+with open('logs.txt', 'r') as file:
+    lines = file.readlines()
+
+# %%
+import re
+# Grep "inter-arrival_s=number" with regex
+intervals = []
+for line in lines:
+    match = re.search(r'inter-arrival_s=([0-9.]+)', line)
+    if match:
+        intervals.append(float(match.group(1)))
+# %%
+
+print(intervals)
+# %%
+import matplotlib.pyplot as plt
+plt.plot(intervals)
+plt.ylabel('Inter-arrival time (s)')
+plt.xlabel('Sample')
+plt.title('Inter-arrival time distribution')
+plt.show()
+# %%

laborious/activities/opc.py

@@ -15,6 +15,45 @@ with workflow.unsafe.imports_passed_through():
     from laborious.utils.repository.opc_repository import OpcRepository
 
 OPC_WRITTING_ERROR_CONFIDENCE = 12
+OPC_SESSION_BAD_CONFIDENCE = 14
+OPC_SESSION_BAD_COMMENT_PREFIX = 'OPC UA session/channel error:'
+OPC_WRITTING_ERROR_MESSAGE = 'Some data could not be written to OPC servers'
+OPC_RECONNECT_IN_PROGRESS_COMMENT = 'OPC UA reconnect in progress'
+OPC_COMMENT_SEPARATOR = ' | '
+
+
+def _opc_session_bad_comment(opc_status: str | None) -> str:
+    status = opc_status or 'Unknown'
+    return f'{OPC_SESSION_BAD_COMMENT_PREFIX} {status}'
+
+
+def _apply_opc_write_error(
+    error_info: dict[str, Any] | None,
+    session_bad_seen: bool,
+    session_bad_status: str | None,
+    reconnect_in_progress_seen: bool,
+) -> tuple[bool, str | None, bool]:
+    """
+    Update session/reconnect flags from an OPC write error payload.
+
+    Args:
+        error_info: Repository error details, or None when the write succeeded.
+        session_bad_seen: Whether a session_bad error was seen so far.
+        session_bad_status: Last known OPC status for session errors.
+        reconnect_in_progress_seen: Whether reconnect_in_progress was seen so far.
+
+    Return:
+        Updated (session_bad_seen, session_bad_status, reconnect_in_progress_seen).
+    """
+    if not error_info:
+        return session_bad_seen, session_bad_status, reconnect_in_progress_seen
+
+    kind = error_info.get('opc_error_kind')
+    if kind == 'session_bad':
+        return True, error_info.get('opc_status', session_bad_status), reconnect_in_progress_seen
+    if kind == 'reconnect_in_progress':
+        return session_bad_seen, session_bad_status, True
+    return session_bad_seen, session_bad_status, reconnect_in_progress_seen
 
 
 class OPC(SientiaMonitoring):
@@ -118,29 +157,18 @@ class OPC(SientiaMonitoring):
         data_type: str,
         tag_type: str,
         metadata: dict[str, Any],
-    ) -> float | None:
+    ) -> tuple[float | None, dict[str, Any] | None]:
         """
         Write data to a specific OPC server tag with comprehensive error handling.
 
-        This method provides a secure and reliable way to write data to OPC servers
-        with automatic error handling, notification integration, and detailed logging.
-        It validates server availability before attempting write operations and
-        provides comprehensive error reporting for operational monitoring.
-
-        Args:
-            - server_id (str): The id of the OPC server.
-            - tag (str): The tag to write to.
-            - data (Any): The data to write.
-            - data_type (str): The data type.
-            - tag_type (str): The tag type.
-
-        Returns:
-            - bool: True if the data was written successfully, False otherwise.
+        Return:
+            tuple[float | None, dict[str, Any] | None]: Response time on success, or
+                (None, error info_data) on repository failure.
         """
 
         try:
             is_success, info_data = await self.opc_repository[server_id].write_data(
-                tag, data, data_type, self.logger, metadata
+                tag, data, data_type, metadata
             )
             if not is_success:
                 await self.send_notification_async(
@@ -151,8 +179,8 @@ class OPC(SientiaMonitoring):
                     level=info_data.get('level', NotificationLevel.ERROR),
                     attachment_content=info_data.get('attachment_content', None),
                 )
-                return None
-            return info_data['response_time']
+                return None, info_data
+            return info_data['response_time'], None
         except Exception as e:
             trace = traceback.format_exc()
             await self.send_notification_async(
@@ -199,13 +227,69 @@ class OPC(SientiaMonitoring):
             return False
         return True
 
+    async def _write_tags_from_config(
+        self,
+        server_id: str,
+        tags_config: dict[str, dict[str, Any]],
+        data: DataFrame,
+        data_column: str,
+        tag_type: str,
+        log_label: str,
+        metadata: dict[str, Any],
+    ) -> tuple[dict[str, float | None], bool, str | None, bool]:
+        """
+        Write a group of OPC tags and collect response times and error flags.
+
+        Args:
+            server_id: Target OPC server identifier.
+            tags_config: Tag name to configuration mapping.
+            data: DataFrame with prediction/confidence columns.
+            data_column: Column name whose first row value is written.
+            tag_type: Tag category passed to write_data ('prediction' or 'confidence').
+            log_label: Human-readable label for success logs.
+            metadata: Context metadata for logging and notifications.
+
+        Return:
+            (response_times, session_bad_seen, session_bad_status, reconnect_in_progress_seen)
+        """
+        response_times: dict[str, float | None] = {}
+        session_bad_seen = False
+        session_bad_status: str | None = None
+        reconnect_in_progress_seen = False
+
+        for tag, tag_config in tags_config.items():
+            response_time, error_info = await self.write_data(
+                server_id=server_id,
+                tag=tag,
+                data=data.head(1)[data_column].values[0],
+                data_type=tag_config['data_type'],
+                tag_type=tag_type,
+                metadata=metadata,
+            )
+            session_bad_seen, session_bad_status, reconnect_in_progress_seen = (
+                _apply_opc_write_error(
+                    error_info,
+                    session_bad_seen,
+                    session_bad_status,
+                    reconnect_in_progress_seen,
+                )
+            )
+            if response_time is not None:
+                self.info(
+                    f'{log_label} written to OPC server {server_id} for tag {tag}.',
+                    metadata,
+                )
+            response_times[tag] = response_time
+
+        return response_times, session_bad_seen, session_bad_status, reconnect_in_progress_seen
+
     async def manage_output_tags(
         self,
         server_id: str,
         config: dict[str, Any],
         data: DataFrame,
         metadata: dict[str, Any],
-    ) -> tuple[bool, dict[str, float | None]]:
+    ) -> tuple[bool, dict[str, float | None], bool, str | None, bool]:
         """
         Manage the writing of prediction and confidence data to OPC server tags.
 
@@ -232,46 +316,47 @@ class OPC(SientiaMonitoring):
                 - overall_success: True if all configured tags were written successfully
                 - total_tags_written: Count of successfully written tags
         """
-
         response_times: dict[str, float | None] = {}
+        session_bad_seen = False
+        session_bad_status: str | None = None
+        reconnect_in_progress_seen = False
 
-        if 'prediction_tags' in config:
-            for tag, tag_config in config['prediction_tags'].items():
-                response_time = await self.write_data(
-                    server_id=server_id,
-                    tag=tag,
-                    data=data.head(1)['prediction'].values[0],
-                    data_type=tag_config['data_type'],
-                    tag_type='prediction',
-                    metadata=metadata,
-                )
-                if response_time is not None:
-                    self.info(
-                        f'Prediction data written to OPC server {server_id} for tag {tag}.',
-                        metadata,
-                    )
-                response_times[tag] = response_time
-
-        if 'confidence_tags' in config:
-            for tag, tag_config in config['confidence_tags'].items():
-                response_time = await self.write_data(
-                    server_id=server_id,
-                    tag=tag,
-                    data=data.head(1)['prediction_confidence'].values[0],
-                    data_type=tag_config['data_type'],
-                    tag_type='confidence',
-                    metadata=metadata,
-                )
-                if response_time is not None:
-                    self.info(
-                        f'Confidence data written to OPC server {server_id} for tag {tag}.',
-                        metadata,
-                    )
-                response_times[tag] = response_time
+        tag_groups = (
+            ('prediction_tags', 'prediction', 'prediction', 'Prediction data'),
+            ('confidence_tags', 'prediction_confidence', 'confidence', 'Confidence data'),
+        )
+        for config_key, data_column, tag_type, log_label in tag_groups:
+            if config_key not in config:
+                continue
+            (
+                group_times,
+                group_session_bad,
+                group_status,
+                group_reconnect,
+            ) = await self._write_tags_from_config(
+                server_id=server_id,
+                tags_config=config[config_key],
+                data=data,
+                data_column=data_column,
+                tag_type=tag_type,
+                log_label=log_label,
+                metadata=metadata,
+            )
+            response_times.update(group_times)
+            if group_session_bad:
+                session_bad_seen = True
+                session_bad_status = group_status or session_bad_status
+            if group_reconnect:
+                reconnect_in_progress_seen = True
 
         success = None not in response_times.values()
-
-        return success, response_times
+        return (
+            success,
+            response_times,
+            session_bad_seen,
+            session_bad_status,
+            reconnect_in_progress_seen,
+        )
 
     @activity.defn(name='write_opc_data')
     async def write_opc_data(
@@ -301,6 +386,9 @@ class OPC(SientiaMonitoring):
         self.info(f'Data to write: {data.size} rows', metadata)
 
         success = True
+        session_bad_seen = False
+        session_bad_status: str | None = None
+        reconnect_in_progress_seen = False
 
         metrics: dict[str, dict[str, float | None]] = {}
 
@@ -309,22 +397,48 @@ class OPC(SientiaMonitoring):
                 success = False
                 continue
 
-            local_success, local_response_times = await self.manage_output_tags(
-                server_id, config, data, metadata
-            )
+            (
+                local_success,
+                local_response_times,
+                local_session_bad,
+                local_status,
+                local_reconnect_in_progress,
+            ) = await self.manage_output_tags(server_id, config, data, metadata)
             metrics[server_id] = local_response_times
             local_count = len(local_response_times)
             success = success and local_success
+            if local_session_bad:
+                session_bad_seen = True
+                session_bad_status = local_status or session_bad_status
+            if local_reconnect_in_progress:
+                reconnect_in_progress_seen = True
 
             self.info(
                 f'Process completed for OPC server {server_id}: {local_count} of {len(config.get("prediction_tags", []))} prediction tags and {len(config.get("confidence_tags", []))} confidence tags',
                 metadata,
             )
 
-        return self.process_confidence(data, success, metadata), metrics
+        return (
+            self.process_confidence(
+                data,
+                success,
+                metadata,
+                session_bad=session_bad_seen,
+                opc_status=session_bad_status,
+                reconnect_in_progress=reconnect_in_progress_seen,
+            ),
+            metrics,
+        )
 
     def process_confidence(
-        self, data: DataFrame, success: bool, metadata: dict[str, Any]
+        self,
+        data: DataFrame,
+        success: bool,
+        metadata: dict[str, Any],
+        *,
+        session_bad: bool = False,
+        opc_status: str | None = None,
+        reconnect_in_progress: bool = False,
     ) -> dict[Hashable, Any]:
         """
         Process prediction confidence based on OPC write operation success.
@@ -352,16 +466,26 @@ class OPC(SientiaMonitoring):
             This allows downstream systems to handle data quality appropriately.
         """
 
-        message = 'Some data could not be written to OPC servers'
-
         if not success:
-            data['prediction_confidence'] = OPC_WRITTING_ERROR_CONFIDENCE
-            data['comments'] = message
+            comment_parts: list[str] = []
+            confidence = OPC_WRITTING_ERROR_CONFIDENCE
+
+            if session_bad:
+                comment_parts.append(_opc_session_bad_comment(opc_status))
+                confidence = OPC_SESSION_BAD_CONFIDENCE
+            if reconnect_in_progress:
+                comment_parts.append(OPC_RECONNECT_IN_PROGRESS_COMMENT)
+                confidence = OPC_SESSION_BAD_CONFIDENCE
+            if not comment_parts:
+                comment_parts.append(OPC_WRITTING_ERROR_MESSAGE)
+
+            comments = OPC_COMMENT_SEPARATOR.join(comment_parts)
+            data['prediction_confidence'] = confidence
+            data['comments'] = comments
             self.debug(
-                f'{message}, setting confidence to  {OPC_WRITTING_ERROR_CONFIDENCE}.',
+                f'OPC write issues, confidence={confidence}, comments={comments}',
                 metadata,
             )
-
         else:
             self.debug('Data written to OPC servers successfully.', metadata)
 

laborious/metrics.py

@@ -89,6 +89,40 @@ OPC_CONNECTION_STATUS = Gauge(
     ['pod_id', 'server_name', 'server_url'],
 )
 
+_OPC_SESSION_DEBUG_LABELS = ['pod_id', 'server_name', 'runtime', 'opc_server_id', 'session_id']
+
+OPC_SESSION_CREATED_TOTAL = Counter(
+    'opc_session_created_total',
+    'OPC UA sessions established (after successful connect)',
+    _OPC_SESSION_DEBUG_LABELS,
+)
+
+OPC_SESSION_CLOSED_TOTAL = Counter(
+    'opc_session_closed_total',
+    'OPC UA client disconnects completed (session tear-down initiated)',
+    _OPC_SESSION_DEBUG_LABELS,
+)
+
+OPC_SESSION_REVISED_TIMEOUT_MS = Gauge(
+    'opc_session_revised_timeout_milliseconds',
+    'Server-revised OPC UA session timeout (RevisedSessionTimeout) in ms after connect',
+    _OPC_SESSION_DEBUG_LABELS,
+)
+
+OPC_WRITE_ATTEMPT_LABELS = [*_OPC_SESSION_DEBUG_LABELS, 'model_id', 'model_name', 'result']
+
+OPC_WRITE_ATTEMPTS_TOTAL = Counter(
+    'opc_write_attempts_total',
+    'OPC UA write attempts with session and outcome (result=OK or exception class name)',
+    OPC_WRITE_ATTEMPT_LABELS,
+)
+
+OPC_WRITE_INTER_ARRIVAL_OVER_SESSION_TIMEOUT_TOTAL = Counter(
+    'opc_write_inter_arrival_over_session_timeout_total',
+    'Successful writes where seconds since the previous successful write exceeded RevisedSessionTimeout (ms)',
+    _OPC_SESSION_DEBUG_LABELS,
+)
+
 # ================== Model metrics ==================
 
 MODEL_READ_LAG = Histogram(

laborious/utils/repository/opc_repository.py

@@ -9,6 +9,7 @@ from typing import Any
 from asyncua import Client
 from asyncua.crypto.security_policies import SecurityPolicyBasic256
 from asyncua.ua import DataValue, Variant, VariantType
+from asyncua.ua.uaerrors import UaStatusCodeError
 from sientia_do.notifications.handlers import CoreNotificationHandler as NotificationHandler
 from sientia_do.notifications.models import NotificationLevel
 from sientia_do.observability.logger import Logger
@@ -17,6 +18,119 @@ from sientia_do.observability.sientia_monitoring import SientiaMonitoring
 
 from laborious import metrics
 
+# Requested session and secure channel lifetime (ms) before server revision; 10 minutes.
+OPC_UA_SESSION_AND_CHANNEL_TIMEOUT_MS = 10 * 60 * 1000
+
+
+class OpcClientAlreadyExistsError(RuntimeError):
+    """Raised when _create_client is called while self.client is already set."""
+
+
+class OpcSessionAlreadyConnectedError(RuntimeError):
+    """Raised when _open_session is called while a UA session is already open."""
+
+
+class OpcClientNotInitializedError(RuntimeError):
+    """Raised when _open_session is called before _create_client."""
+
+
+RECONNECTABLE_OPC_BAD_NAMES: frozenset[str] = frozenset(
+    {
+        'BadSessionIdInvalid',
+        'BadSessionClosed',
+        'BadSessionNotActivated',
+        'BadSecureChannelIdInvalid',
+        'BadSecureChannelClosed',
+        'BadSecureChannelTokenUnknown',
+        'BadTcpSecureChannelUnknown',
+        'BadServerNotConnected',
+        'BadConnectionClosed',
+        'BadDisconnect',
+        'BadConnectionRejected',
+        'BadCommunicationError',
+        'BadRequestInterrupted',
+        'BadUnknownResponse',
+        'BadTimeout',
+        'BadRequestTimeout',
+        'BadSequenceNumberInvalid',
+        'BadSequenceNumberUnknown',
+        'BadSecurityModeInsufficient',
+        'BadRequestHeaderInvalid',
+        'BadInvalidState',
+    }
+)
+
+
+def _opc_authentication_token_str(client: Client | None) -> str:
+    """
+    Serialize the current OPC UA authentication token (session handle) for logging and metrics.
+
+    Return:
+        str: Token string, or "unknown" if unavailable.
+    """
+    if client is None:
+        return 'unknown'
+    try:
+        proto = client.uaclient.protocol
+        if proto is None:
+            return 'unknown'
+        tok = getattr(proto, 'authentication_token', None)
+        if tok is None:
+            return 'unknown'
+        return str(tok)
+    except Exception:
+        return 'unknown'
+
+
+def _opc_status_from_exception(exc: BaseException) -> str:
+    """
+    Resolve OPC UA status name from an exception, including chained UaStatusCodeError causes.
+
+    Args:
+        exc (BaseException): Raised error from asyncua.
+
+    Return:
+        str: Status class name or generic Python exception name.
+    """
+    current: BaseException | None = exc
+    while current is not None:
+        if isinstance(current, UaStatusCodeError):
+            return type(current).__name__
+        current = current.__cause__
+    return type(exc).__name__
+
+
+def is_reconnectable_opcua_bad(exc: BaseException) -> bool:
+    """
+    Return whether the exception is a Tier-1 OPC UA Bad* that should trigger reconnect.
+
+    Args:
+        exc (BaseException): Raised error from get_node or write_value.
+
+    Return:
+        bool: True if reconnect should be scheduled.
+    """
+    return _opc_status_from_exception(exc) in RECONNECTABLE_OPC_BAD_NAMES
+
+
+def _model_labels_from_write_metadata(metadata: dict[str, Any] | None) -> dict[str, str]:
+    """
+    Extract model_id and model_name from write metadata for Prometheus labels.
+
+    Args:
+        metadata (dict[str, Any] | None): Context passed into write_data; may omit keys.
+
+    Return:
+        dict[str, str]: Labels model_id and model_name, defaulting to "unknown".
+    """
+    if not metadata:
+        return {'model_id': 'unknown', 'model_name': 'unknown'}
+    return {
+        'model_id': str(metadata.get('model_id', 'unknown')),
+        'model_name': str(metadata.get('model_name', 'unknown')),
+    }
+
+
 data_type_map = {
     'float': {
         'converter': float,
@@ -63,8 +177,6 @@ class OpcRepository(SientiaMonitoring):
         self.cert_path = cert_path
         self.private_key_path = private_key_path
         self.server_cert_path = server_cert_path
-        self.logger = logger
-        self.error_count = 0
         self.reconnection_interval = reconnection_interval
         self.last_reconnection_time: None | datetime = None
         self.disconnection_interval = 10.0
@@ -79,27 +191,79 @@ class OpcRepository(SientiaMonitoring):
             'workflow_name': 'opc_repository',
             'schedule_name': '-',
         }
+        self._last_write_mono: float | None = None
+        self._connection_lock = asyncio.Lock()
+        self._session_ready = asyncio.Event()
+        self._reconnect_task: asyncio.Task[None] | None = None
+        self._allow_reconnect = True
 
-    async def set_security(self):
+    def _opc_debug_tags(self, session_id: str) -> dict[str, str]:
         """
-        Configures the security settings for the OPC UA client.
-        This method sets up the security policy, certificates, and timeouts
-        required for establishing a secure connection with the OPC UA server.
+        Build Prometheus/log label tags for OPC session-scoped metrics.
+
+        Args:
+            session_id (str): OPC UA session token string.
+
+        Return:
+            dict[str, str]: Labels pod_id, server_name, runtime, opc_server_id, session_id.
+        """
+        return {
+            'pod_id': str(getattr(self, 'pod_id', 'unknown')),
+            'server_name': self.server_name,
+            'runtime': str(getattr(self, 'runtime', 'unknown')),
+            'opc_server_id': self.id,
+            'session_id': session_id,
+        }
+
+    def _is_session_open(self) -> bool:
+        """
+        Return whether the asyncua client has an open transport session.
+
+        Return:
+            bool: True when protocol exists and is not closed.
+        """
+        if self.client is None:
+            return False
+        try:
+            proto = self.client.uaclient.protocol
+            return proto is not None and proto.state != 'closed'
+        except Exception:
+            return False
+
+    def _reconnection_window_elapsed(self) -> bool:
+        """
+        Return whether enough time has passed since the last reconnect attempt.
+
+        Return:
+            bool: True if a new reconnect is allowed.
+        """
+        if self.last_reconnection_time is None:
+            return True
+        return (
+            datetime.now() - self.last_reconnection_time
+        ).total_seconds() > self.reconnection_interval
+
+    def _not_connected_error(self) -> dict[str, Any]:
+        """
+        Build the standard error payload when validate_connection finds no open protocol.
+
+        Return:
+            dict[str, Any]: Notification fields for OPC_CONNECTION_NOT_READY.
+        """
+        return {
+            'notification_id': f'OPC_CONNECTION_NOT_READY_{self.id}',
+            'message': f'OPC server {self.id} is not connected',
+            'block': 'opc_repository',
+            'level': NotificationLevel.WARNING,
+        }
+
+    async def set_security(self) -> None:
+        """
+        Configure certificates and timeouts on the asyncua client.
+
         Raises:
-            ValueError: If either the certificate path or private key path is not provided.
-        Attributes:
-            - cert_path (str): Path to the client's certificate file.
-            - private_key_path (str): Path to the client's private key file.
-            - server_cert_path (str, optional): Path to the server's certificate file.
-            - server_uri (str): The URI of the server to be used as the application URI.
-            - client (opcua.Client): The OPC UA client instance.
-            - logger (logging.Logger): Logger instance for logging information.
-        Security Settings:
-            - Security Policy: Basic256
-            - Secure Channel Timeout: 10,000,000 ms
-            - Session Timeout: 10,000,000 ms
+            ValueError: If cert paths or client are missing.
         """
-
         if self.cert_path is None or self.private_key_path is None:
             raise ValueError(
                 'Certificate and private key paths must be provided for secure connection.'
@@ -113,91 +277,107 @@ class OpcRepository(SientiaMonitoring):
             raise ValueError('Client must be initialized before setting security')
 
         self.client.application_uri = self.server_uri
-        self.logger.custom_info('Setting security...', self.metadata)
+        self.info('Setting security...', self.metadata)
         await self.client.set_security(
             SecurityPolicyBasic256,
             certificate=str(cert),
             private_key=str(private_key),
             server_certificate=str(server_cert) if server_cert else None,
         )
-        self.client.secure_channel_timeout = 10000000
-        self.client.session_timeout = 10000000
+        self.client.secure_channel_timeout = OPC_UA_SESSION_AND_CHANNEL_TIMEOUT_MS
+        self.client.session_timeout = OPC_UA_SESSION_AND_CHANNEL_TIMEOUT_MS
 
-    async def connect(self) -> tuple[bool, dict[str, Any]]:
+    async def _create_client(self) -> None:
         """
-        Establishes a connection to the OPC server.
-        This method initializes the OPC client using the provided URL and
-        sets up security if a certificate path is specified. It then
-        attempts to connect to the server and logs the connection status.
+        Instantiate the asyncua Client and apply security when configured.
+
+        Caller must hold _connection_lock. Does not open a UA session.
+
         Raises:
-            Exception: If the connection to the OPC server fails.
+            OpcClientAlreadyExistsError: If self.client is already set.
         """
+        if self.client is not None:
+            raise OpcClientAlreadyExistsError(
+                f'OPC client already exists for server {self.id}; '
+                'call disconnect() before creating a new client'
+            )
 
-        self.client = Client(self.url, timeout=10, watchdog_intervall=3600000)  # type: ignore[attr-defined]
-
+        self.client = Client(self.url, timeout=10, watchdog_intervall=50)  # type: ignore[attr-defined]
         self.client.name = self.pod_id
         self.client.application_name = self.pod_id
         pod_uri = self.pod_id.replace('-', ':')
         self.client.application_uri = pod_uri
         self.client.product_uri = pod_uri
-
         if self.cert_path:
             await self.set_security()
-        self.logger.custom_info(
-            f'Starting connection to OPC server {self.id}:{self.server_name}...', self.metadata
-        )
-        return await self.try_connect()
 
-    async def try_connect(self) -> tuple[bool, dict[str, Any]]:
+    async def _open_session(self) -> tuple[bool, dict[str, Any]]:
         """
-        Attempt to establish connection to the OPC server.
+        Open the OPC UA session on the existing client.
 
-        This method performs the actual connection attempt to the OPC server
-        and handles connection failures with comprehensive error reporting.
-        It updates reconnection timing and provides detailed error information
-        for operational monitoring and debugging.
+        Caller must hold _connection_lock.
 
-        Returns:
-            tuple[bool, dict[str, Any]]: Connection result
-                - bool: True if connection successful, False otherwise
-                - dict: Error information if connection failed
+        Raises:
+            OpcClientNotInitializedError: If self.client is None.
+            OpcSessionAlreadyConnectedError: If a session is already open.
+
+        Return:
+            tuple[bool, dict[str, Any]]: Success flag and error payload on connect failure.
         """
+        if self.client is None:
+            raise OpcClientNotInitializedError(
+                f'OPC client is not initialized for server {self.id}; '
+                'call _create_client() before opening a session'
+            )
+        if self._is_session_open():
+            raise OpcSessionAlreadyConnectedError(
+                f'OPC session already connected for server {self.id}; '
+                'call disconnect() before connecting again'
+            )
 
         tags = {
             'pod_id': self.pod_id,
             'server_name': self.server_name,
         }
         await self.emit_metric(metrics.OPC_CONNECTIONS_TOTAL, tags)
+
         try:
-            self.last_reconnection_time = datetime.now()
-            if self.client is None:
-                return False, {
-                    'notification_id': f'OPC_CONNECTION_ERROR_{self.id}',
-                    'message': 'Client is not initialized',
-                    'block': 'opc_repository',
-                    'level': NotificationLevel.ERROR,
-                }
             await self.client.connect()
 
+            session_id = _opc_authentication_token_str(self.client)
+            revised_session_timeout_ms = int(self.client.session_timeout)
+            revised_secure_channel_timeout_ms = int(self.client.secure_channel_timeout)
+            self.info(
+                f'OPC new session connected opc_server_id={self.id} session_id={session_id} '
+                f'revised_session_timeout_ms={revised_session_timeout_ms} '
+                f'revised_secure_channel_timeout_ms={revised_secure_channel_timeout_ms}',
+                self.metadata,
+            )
+            await self.emit_metric(
+                metrics.OPC_SESSION_CREATED_TOTAL, self._opc_debug_tags(session_id)
+            )
+            await self.emit_metric(
+                metric_object=metrics.OPC_SESSION_REVISED_TIMEOUT_MS,
+                method='set',
+                tags=self._opc_debug_tags(session_id),
+                value=revised_session_timeout_ms,
+            )
             await self.emit_metric(
                 metric_object=metrics.OPC_CONNECTION_STATUS,
                 method='set',
-                tags={
-                    **tags,
-                    'server_url': self.url,
-                },
+                tags={**tags, 'server_url': self.url},
                 value=1,
             )
 
+            self._last_write_mono = None
+            self._session_ready.set()
             return True, {}
+
         except Exception as e:
-            await self.disconnect()
-
+            await self._disconnect_locked()
             trace = traceback.format_exc()
-            self.logger.custom_error(trace, self.metadata)
-
+            self.error(trace, self.metadata)
             await self.emit_metric(metrics.OPC_CONNECTIONS_FAILED, tags)
-
             return False, {
                 'notification_id': f'OPC_CONNECTION_ERROR_{self.id}',
                 'message': f'Failed to connect to OPC server: {e}',
@@ -206,21 +386,45 @@ class OpcRepository(SientiaMonitoring):
                 'attachment_content': trace,
             }
 
-    async def disconnection_fallback(self) -> list:
-        """
-        Tries 5 times to disconnect from the OPC UA server, with a delay of 100ms x try.
+    async def _connect_locked(self) -> tuple[bool, dict[str, Any]]:
         """
+        Create the client when absent, then open a UA session.
 
+        Caller must hold _connection_lock.
+
+        Raises:
+            OpcSessionAlreadyConnectedError: If a session is already open.
+
+        Return:
+            tuple[bool, dict[str, Any]]: Result from _open_session on connect failure.
+        """
+        if self._is_session_open():
+            raise OpcSessionAlreadyConnectedError(
+                f'OPC session already connected for server {self.id}; '
+                'call disconnect() before connecting again'
+            )
+        if self.client is None:
+            await self._create_client()
+        return await self._open_session()
+
+    async def _disconnection_fallback(self) -> list[dict[str, Any]]:
+        """
+        Try up to five times to disconnect from the OPC UA server.
+        """
         assert self.client is not None
-        error_stack = []
+        error_stack: list[dict[str, Any]] = []
         for i in range(5):
             try:
-                self.logger.info(f'Disconnecting from OPC UA server, attempt {i + 1} of 5')
+                self.info(
+                    f'Disconnecting from OPC UA server, attempt {i + 1} of 5',
+                    self.metadata,
+                )
                 await self.client.disconnect()
                 return []
             except Exception as e:
-                self.logger.error(
-                    f'Failed to disconnect from OPC UA server in attempt {i + 1} of 5: {e}'
+                self.error(
+                    f'Failed to disconnect from OPC UA server in attempt {i + 1} of 5: {e}',
+                    self.metadata,
                 )
                 error_stack.append(
                     {
@@ -232,18 +436,26 @@ class OpcRepository(SientiaMonitoring):
                 await asyncio.sleep(self.disconnection_interval * i)
         return error_stack
 
-    async def disconnect(self):
+    async def _disconnect_locked(self) -> None:
         """
-        Gracefully disconnect from the OPC server.
+        Tear down the current session and client.
 
-        This method safely terminates the connection to the OPC server
-        and cleans up client resources. It handles disconnection errors
-        gracefully and ensures proper resource cleanup.
+        Caller must hold _connection_lock.
         """
+        self._last_write_mono = None
+        self._session_ready.clear()
+
         if self.client is None:
             return
 
-        errors = await self.disconnection_fallback()
+        session_id = _opc_authentication_token_str(self.client)
+        self.info(
+            f'OPC disconnecting opc_server_id={self.id} session_id={session_id}',
+            self.metadata,
+        )
+        await self.emit_metric(metrics.OPC_SESSION_CLOSED_TOTAL, self._opc_debug_tags(session_id))
+
+        errors = await self._disconnection_fallback()
         if errors:
             await self.send_notification_async(
                 metadata=self.metadata,
@@ -254,7 +466,8 @@ class OpcRepository(SientiaMonitoring):
                 attachment_content=json.dumps(errors, indent=4),
             )
         else:
-            self.logger.warning(f'Disconnected from OPC server {self.id} successfully')
+            self.warning(f'Disconnected from OPC server {self.id} successfully', self.metadata)
+
         await self.emit_metric(
             metric_object=metrics.OPC_CONNECTION_STATUS,
             method='set',
@@ -265,186 +478,388 @@ class OpcRepository(SientiaMonitoring):
             },
             value=0,
         )
-
         self.client = None
 
+    async def _reconnect_locked(self) -> tuple[bool, dict[str, Any]]:
+        """
+        Close the current session and open a new one.
+
+        Caller must hold _connection_lock. Records last_reconnection_time for interval gating.
+
+        Return:
+            tuple[bool, dict[str, Any]]: Result from _connect_locked after teardown.
+        """
+        self.last_reconnection_time = datetime.now()
+        await self._disconnect_locked()
+        return await self._connect_locked()
+
+    async def connect(self) -> tuple[bool, dict[str, Any]]:
+        """
+        Open an OPC UA session under the connection lock (worker initialization).
+        """
+        async with self._connection_lock:
+            self.info(
+                f'Starting connection to OPC server {self.id}:{self.server_name}...',
+                self.metadata,
+            )
+            return await self._connect_locked()
+
+    async def disconnect(self) -> None:
+        """
+        Gracefully disconnect from the OPC server under the connection lock.
+
+        Disables background reconnect so late writes during worker shutdown do not
+        respawn sessions.
+        """
+        async with self._connection_lock:
+            self._allow_reconnect = False
+            await self._disconnect_locked()
+
     async def validate_connection(self) -> tuple[bool, dict[str, Any]]:
         """
-        Validate and maintain OPC server connection health.
+        Read-only check that the asyncua protocol is open.
 
-        This method performs comprehensive connection validation and
-        implements automatic reconnection logic for production reliability.
-        It handles various connection states and implements intelligent
-        reconnection strategies with error counting and timing controls.
+        Caller must ensure _session_ready before writing. Does not connect or reconnect.
 
-        Connection Validation:
-            1. Checks client existence and connection state
-            2. Implements error counting with automatic disconnection
-            3. Enforces reconnection timing windows
-            4. Provides detailed error reporting and notifications
+        Return:
+            tuple[bool, dict[str, Any]]: (True, {}) when open, otherwise (False, error).
+        """
+        if self._is_session_open():
+            return True, {}
+        self.error(f'OPC server {self.id} is not connected', self.metadata)
+        return False, self._not_connected_error()
 
-        Reconnection Strategy:
-            - Error Count Threshold: Disconnects after 5 consecutive errors
-            - Reconnection Window: Enforces minimum intervals between attempts
-            - Automatic Recovery: Attempts reconnection when conditions allow
-            - State Monitoring: Continuously monitors connection health
+    def _reconnect_task_in_progress(self) -> bool:
+        """
+        Return whether a background reconnect task is currently running.
+
+        Return:
+            bool: True when a reconnect task exists and has not finished.
+        """
+        return self._reconnect_task is not None and not self._reconnect_task.done()
+
+    async def _start_reconnect(self, reason: str, session_id: str) -> None:
+        """
+        Schedule a background reconnect when allowed by interval and task state.
+
+        Clears _session_ready before starting the task. No-op when _allow_reconnect is
+        False, the reconnection window has not elapsed, or a reconnect is already running.
 
         Args:
-            None
-
-        Returns:
-            tuple[bool, dict[str, Any]]: Connection validation result
-                - bool: True if connection is healthy, False otherwise
-                - dict: Error information if validation fails
+            reason (str): Trigger for reconnect (OPC status name or synthetic reason).
+            session_id (str): Session token before failure.
         """
-        if self.client is None:
-            return await self.connect()
+        if not self._allow_reconnect:
+            return
+        if not self._reconnection_window_elapsed():
+            self.warning(
+                f'OPC reconnect skipped reason=reconnection_window opc_server_id={self.id} '
+                f'reconnect_reason={reason}',
+                self.metadata,
+            )
+            return
+        if self._reconnect_task_in_progress():
+            self.warning(
+                f'OPC reconnect skipped reason=in_progress opc_server_id={self.id} '
+                f'reconnect_reason={reason}',
+                self.metadata,
+            )
+            return
 
-        # if self.error_count > 5: # NOSONAR
-        #     self.logger.custom_warning(
-        #         f'OPC server {self.id} will be disconnected due to multiple errors', self.metadata
-        #     )
-        #     try:
-        #         await self.disconnect()
-        #     except Exception as e:
-        #         trace = traceback.format_exc()
-        #         self.logger.custom_error(
-        #             f'Failed to disconnect from OPC server: {e}', self.metadata
-        #         )
-        #         self.logger.custom_error(trace, self.metadata)
-        #     self.logger.custom_info(
-        #         f'Attempting to reconnect to OPC server {self.id}...', self.metadata
-        #     )
-        #     return await self.connect()
+        self._session_ready.clear()
+        self.info(
+            f'OPC reconnect scheduled reconnect_reason={reason} opc_server_id={self.id} '
+            f'old_session_id={session_id}',
+            self.metadata,
+        )
+        self._reconnect_task = asyncio.create_task(self._run_reconnect(reason, session_id))
 
-        # Check if client is connected using asyncua's connection state
+    async def _run_reconnect(self, reason: str, session_id: str) -> None:
+        """
+        Background task that tears down and re-establishes the OPC UA session.
+
+        Args:
+            reason (str): Trigger for reconnect (OPC status or ProtocolClosed).
+            session_id (str): Previous session token string for logging.
+        """
         try:
-            if (
-                self.client.uaclient.protocol is None
-                or self.client.uaclient.protocol.state == 'closed'
-            ):
-                # OPC server is not connected
-                self.logger.custom_error(f'OPC server {self.id} is not connected', self.metadata)
-                if (
-                    self.last_reconnection_time is None
-                    or (datetime.now() - self.last_reconnection_time).total_seconds()
-                    > self.reconnection_interval
-                ):
-                    await self.disconnect()
-                    self.logger.custom_info(
-                        f'Trying to reconnect to OPC server {self.id}...', self.metadata
+            async with self._connection_lock:
+                self.info(
+                    f'OPC reconnect started reconnect_reason={reason} opc_server_id={self.id} '
+                    f'old_session_id={session_id}',
+                    self.metadata,
+                )
+                success, error = await self._reconnect_locked()
+            if not success:
+                self.error(
+                    f'OPC reconnect failed reconnect_reason={reason} opc_server_id={self.id}',
+                    self.metadata,
+                )
+                if error:
+                    self.error(error.get('message', ''), self.metadata)
+        except Exception:
+            self.error(
+                f'OPC reconnect task failed opc_server_id={self.id} reconnect_reason={reason}',
+                self.metadata,
+            )
+            self.error(traceback.format_exc(), self.metadata)
+
+    async def _log_write_inter_arrival(self, session_id: str, node: str) -> None:
+        """
+        Log elapsed wall time since the previous successful OPC write on this repository.
+
+        Args:
+            session_id (str): Current OPC UA session token string.
+            node (str): Node id written in this operation.
+        """
+        now = time.monotonic()
+        if self._last_write_mono is not None:
+            delta_s = now - self._last_write_mono
+            self.info(
+                f'OPC write inter-arrival_s={delta_s:.6f} opc_server_id={self.id} '
+                f'session_id={session_id} node={node}',
+                self.metadata,
+            )
+            if self.client is not None:
+                session_timeout_ms = float(self.client.session_timeout)
+                if session_timeout_ms > 0 and delta_s > (session_timeout_ms / 1000.0):
+                    await self.emit_metric(
+                        metrics.OPC_WRITE_INTER_ARRIVAL_OVER_SESSION_TIMEOUT_TOTAL,
+                        self._opc_debug_tags(session_id),
                     )
-                    return await self.connect()
+        self._last_write_mono = now
 
-                return False, {
-                    'notification_id': f'OPC_CONNECTION_AWAITING_RECONNECTION_WINDOW_{self.id}',
-                    'message': f'OPC server {self.id} is not connected, waiting for next reconnection window...',
-                    'block': 'opc_repository',
-                    'level': NotificationLevel.WARNING,
-                }
-            return True, {}
-        except Exception as e:
-            trace = traceback.format_exc()
-            message = f'Failed to validate connection to OPC server: {e}'
-            self.logger.custom_error(message, self.metadata)
-            return False, {
-                'notification_id': f'OPC_CONNECTION_CHECK_ERROR_{self.id}',
-                'message': message,
-                'block': 'opc_repository',
-                'level': NotificationLevel.ERROR,
-                'attachment_content': trace,
-            }
+    async def _emit_opc_write_metric(
+        self, session_id: str, result: str, metadata: dict[str, Any] | None
+    ) -> None:
+        """
+        Emit opc_write_attempts_total for a single write attempt outcome.
 
-    async def write_data(
-        self, node: str, value: Any, data_type: str, logger: Logger, metadata: dict[str, Any]
+        Args:
+            session_id (str): OPC UA session token string, or "unknown".
+            result (str): Outcome label (OK, OPC status name, ProtocolClosed, etc.).
+            metadata (dict[str, Any] | None): Write context for model_id/model_name labels.
+        """
+        await self.emit_metric(
+            metrics.OPC_WRITE_ATTEMPTS_TOTAL,
+            {
+                **self._opc_debug_tags(session_id),
+                **_model_labels_from_write_metadata(metadata),
+                'result': result,
+            },
+        )
+
+    def _write_failure_payload(
+        self,
+        notification_id: str,
+        message: str,
+        level: NotificationLevel = NotificationLevel.ERROR,
+        attachment_content: str | None = None,
+        opc_error_kind: str | None = None,
+        opc_status: str | None = None,
+    ) -> dict[str, Any]:
+        """
+        Build a structured error dict returned from failed write_data paths.
+
+        Args:
+            notification_id (str): Stable notification identifier.
+            message (str): Human-readable failure message.
+            level (NotificationLevel): Severity for downstream notifications.
+            attachment_content (str | None): Optional traceback or diagnostic text.
+            opc_error_kind (str | None): Classifier (session_bad, connection_lost, etc.).
+            opc_status (str | None): OPC UA status name or synthetic reason.
+
+        Return:
+            dict[str, Any]: Error payload consumed by the OPC activity layer.
+        """
+        payload: dict[str, Any] = {
+            'notification_id': notification_id,
+            'message': message,
+            'block': 'opc_repository',
+            'level': level,
+        }
+        if attachment_content is not None:
+            payload['attachment_content'] = attachment_content
+        if opc_error_kind is not None:
+            payload['opc_error_kind'] = opc_error_kind
+        if opc_status is not None:
+            payload['opc_status'] = opc_status
+        return payload
+
+    async def _handle_tier1_bad(
+        self,
+        exc: BaseException,
+        session_id: str,
+        node: str,
+        metadata: dict[str, Any],
+        phase: str,
     ) -> tuple[bool, dict[str, Any]]:
         """
-        Write data to OPC server with comprehensive validation and monitoring.
-
-        This method provides secure and reliable data writing to OPC servers
-        with automatic connection validation, data type conversion, and
-        comprehensive error handling. It implements performance monitoring
-        and metrics collection for operational visibility.
-
-        Data Writing Process:
-            1. Connection validation and automatic reconnection
-            2. Node validation and error handling
-            3. Data type conversion and validation
-            4. OPC data writing with timestamp
-            5. Performance metrics collection
-            6. Error handling and notification
+        Record metrics/logs and schedule reconnect after a Tier-1 Bad* error.
 
         Args:
-            node (str): OPC node identifier to write data to
-            value (Any): Data value to write to the OPC node
-            data_type (str): Data type for OPC conversion
-            logger (Logger): Logger instance for operation logging
-            metadata (dict[str, Any]): Context metadata for logging and metrics
+            exc (BaseException): Tier-1 OPC UA error.
+            session_id (str): Session token at failure time.
+            node (str): Node id being written.
+            metadata (dict[str, Any]): Write context.
+            phase (str): get_node or write_value.
 
-        Returns:
-            tuple[bool, dict[str, Any]]: Write operation result
-                - bool: True if write successful, False otherwise
-                - dict: Error information if write failed
+        Return:
+            tuple[bool, dict[str, Any]]: Always (False, error payload).
         """
+        opc_status = _opc_status_from_exception(exc)
+        trace = traceback.format_exc()
+        self.error(trace, metadata)
+        await self._emit_opc_write_metric(session_id, opc_status, metadata)
+        self.error(
+            f'OPC write failed opc_status={opc_status} opc_server_id={self.id} '
+            f'session_id={session_id} model_id={metadata.get("model_id", "unknown")} '
+            f'model_name={metadata.get("model_name", "unknown")} node={node} phase={phase}',
+            metadata,
+        )
+        await self._start_reconnect(opc_status, session_id)
+        return False, self._write_failure_payload(
+            notification_id=f'OPC_WRITE_DATA_ERROR_{self.id}',
+            message=f'Failed to {phase} on OPC server: {exc} | metadata: {metadata}',
+            attachment_content=trace,
+            opc_error_kind='session_bad',
+            opc_status=opc_status,
+        )
 
-        is_connected, error = await self.validate_connection()
+    async def _write_reconnect_in_progress(
+        self, metadata: dict[str, Any]
+    ) -> tuple[bool, dict[str, Any]]:
+        """
+        Fail a write because a background reconnect task is already running.
 
+        Args:
+            metadata (dict[str, Any]): Write context passed through to the activity.
+
+        Return:
+            tuple[bool, dict[str, Any]]: (False, error info with opc_error_kind reconnect_in_progress).
+        """
+        await self._emit_opc_write_metric('unknown', 'ReconnectInProgress', metadata)
+        self.warning(
+            f'OPC write rejected reconnect_in_progress opc_server_id={self.id} '
+            f'model_id={metadata.get("model_id", "unknown")} '
+            f'model_name={metadata.get("model_name", "unknown")}',
+            metadata,
+        )
+        return False, {
+            'notification_id': f'OPC_WRITE_RECONNECT_IN_PROGRESS_{self.id}',
+            'message': f'OPC write skipped: reconnect in progress | metadata: {metadata}',
+            'block': 'opc_repository',
+            'level': NotificationLevel.WARNING,
+            'opc_error_kind': 'reconnect_in_progress',
+        }
+
+    async def _write_connection_lost(
+        self, metadata: dict[str, Any], opc_status: str
+    ) -> tuple[bool, dict[str, Any]]:
+        """
+        Fail a write after scheduling reconnect for a closed or stale session.
+
+        Args:
+            metadata (dict[str, Any]): Write context passed through to the activity.
+            opc_status (str): Synthetic reason (ProtocolClosed, SessionNotReady).
+
+        Return:
+            tuple[bool, dict[str, Any]]: (False, error info with opc_error_kind connection_lost).
+        """
+        await self._emit_opc_write_metric('unknown', opc_status, metadata)
+        return False, self._write_failure_payload(
+            notification_id=f'OPC_WRITE_CONNECTION_LOST_{self.id}',
+            message=f'OPC write skipped: connection lost ({opc_status}) | metadata: {metadata}',
+            level=NotificationLevel.WARNING,
+            opc_error_kind='connection_lost',
+            opc_status=opc_status,
+        )
+
+    async def write_data(
+        self, node: str, value: Any, data_type: str, metadata: dict[str, Any]
+    ) -> tuple[bool, dict[str, Any]]:
+        """
+        Write data to OPC server with a single attempt and background reconnect scheduling.
+
+        Reconnect is scheduled on Tier-1 Bad*, closed protocol, or stale session readiness.
+        There is no retry within the same call.
+
+        Args:
+            node (str): OPC UA node id to write.
+            value (Any): Value to convert and send.
+            data_type (str): Logical type key (float, int, bool, str, double).
+            metadata (dict[str, Any]): Activity context (model_id, model_name, etc.).
+
+        Return:
+            tuple[bool, dict[str, Any]]: (True, {response_time}) on success, or
+                (False, structured error info) on failure.
+        """
+        if self._reconnect_task_in_progress():
+            return await self._write_reconnect_in_progress(metadata)
+
+        if not self._session_ready.is_set():
+            session_id = _opc_authentication_token_str(self.client)
+            await self._start_reconnect('SessionNotReady', session_id)
+            if self._reconnect_task_in_progress():
+                return await self._write_reconnect_in_progress(metadata)
+            return await self._write_connection_lost(metadata, 'SessionNotReady')
+
+        is_connected, _error = await self.validate_connection()
         if not is_connected:
-            return False, error
+            session_id = _opc_authentication_token_str(self.client)
+            await self._start_reconnect('ProtocolClosed', session_id)
+            return await self._write_connection_lost(metadata, 'ProtocolClosed')
 
         start_time = time.time()
+        session_id = _opc_authentication_token_str(self.client)
 
         try:
-            # ignored because self.validate_connection is called before, so we know self.client is not None
             node_obj = self.client.get_node(node)  # type: ignore[union-attr]
         except Exception as e:
+            if is_reconnectable_opcua_bad(e):
+                return await self._handle_tier1_bad(e, session_id, node, metadata, 'get_node')
             trace = traceback.format_exc()
-            logger.custom_error(trace, metadata.get('schedule_name', 'N/A'))
-            self.error_count += 1
-            return False, {
-                'notification_id': f'OPC_WRITE_GET_NODE_ERROR_{self.id}',
-                'message': f'Failed to get node from OPC server: {e} | metadata: {metadata}',
-                'block': 'opc_repository',
-                'level': NotificationLevel.ERROR,
-                'attachment_content': trace,
-            }
+            self.error(trace, metadata)
+            await self._emit_opc_write_metric(
+                session_id, f'GetNodeError:{type(e).__name__}', metadata
+            )
+            return False, self._write_failure_payload(
+                notification_id=f'OPC_WRITE_GET_NODE_ERROR_{self.id}',
+                message=f'Failed to get node from OPC server: {e} | metadata: {metadata}',
+                attachment_content=trace,
+            )
 
         if data_type not in data_type_map:
-            return False, {
-                'notification_id': f'OPC_WRITE_DATA_TYPE_ERROR_{self.id}',
-                'message': f'Unsupported data type: {data_type} | metadata: {metadata}',
-                'block': 'opc_repository',
-                'level': NotificationLevel.ERROR,
-            }
+            await self._emit_opc_write_metric(session_id, 'UnsupportedDataType', metadata)
+            return False, self._write_failure_payload(
+                notification_id=f'OPC_WRITE_DATA_TYPE_ERROR_{self.id}',
+                message=f'Unsupported data type: {data_type} | metadata: {metadata}',
+            )
 
         data = data_type_map[data_type]['converter'](value)
-        logger.custom_info(f'Writing {data} - {type(data)} to {node}', metadata)
-        # now = datetime.now() # NOSONAR
+        self.info(f'Writing {data} - {type(data)} to {node}', metadata)
         ua_data = DataValue(
             Variant(data, data_type_map[data_type]['opc_type']),
-            # SourceTimestamp=DateTime( # NOSONAR
-            #     now.year, now.month, now.day, now.hour, now.minute, now.second, now.microsecond # NOSONAR
-            # ), # NOSONAR
         )
 
         try:
             await node_obj.write_value(ua_data)
-
             end_time = time.time()
             response_time = end_time - start_time
-
         except Exception as e:
+            if is_reconnectable_opcua_bad(e):
+                return await self._handle_tier1_bad(e, session_id, node, metadata, 'write_value')
             trace = traceback.format_exc()
-            logger.custom_error(trace, metadata)
-            self.error_count += 1
-            return False, {
-                'notification_id': f'OPC_WRITE_DATA_ERROR_{self.id}',
-                'message': f'Failed to write data to OPC server: {e} | metadata: {metadata}',
-                'block': 'opc_repository',
-                'level': NotificationLevel.ERROR,
-                'attachment_content': trace,
-            }
-        self.error_count = 0
+            self.error(trace, metadata)
+            await self._emit_opc_write_metric(session_id, type(e).__name__, metadata)
+            return False, self._write_failure_payload(
+                notification_id=f'OPC_WRITE_DATA_ERROR_{self.id}',
+                message=f'Failed to write data to OPC server: {e} | metadata: {metadata}',
+                attachment_content=trace,
+            )
+
+        await self._emit_opc_write_metric(session_id, 'OK', metadata)
+        await self._log_write_inter_arrival(session_id, node)
 
         return True, {
             'response_time': response_time,

laborious/worker/worker.py

@@ -63,7 +63,7 @@ with workflow.unsafe.imports_passed_through():
     )
     from laborious.workflows.sub_workflows.prediction_process import PredictionProcess
 
-POD_ID = os.getenv('POD_ID')
+POD_ID = os.getenv('HOSTNAME')
 SDK_METRICS_PORT = int(os.getenv('HTTP_SDK_METRICS_PORT', '9091'))
 
 
@@ -205,6 +205,7 @@ async def main():
                 activities.cleanup_minio_objects_expired,
                 activities.repeat_last_prediction,
                 activities.export_data_to_postgres,
+                activities.export_payload_to_postgres,
                 activities.write_metrics,
                 # Pi Web API
                 activities.write_pi_web_api_data,

pyproject.toml

@@ -121,6 +121,7 @@ markers = [
     "asyncio: marks tests as async",
     "integration: marks tests as integration tests",
     "unit: marks tests as unit tests",
+    "opc: marks tests that use the in-process OPC UA server (OpcRepository E2E)",
 ]
 
 [tool.coverage.run]

requirements-dev.txt

@@ -18,3 +18,4 @@ testcontainers[postgres,minio] # PostgreSQL and MinIO containers for E2E tests
 # Development Tools
 ipython>=8.12.0          # Enhanced Python shell
 ipdb>=0.13.13            # IPython debugger
+ipykernel==6.30.1        # IPython kernel for Jupyter notebooks

requirements-light.txt

@@ -3,7 +3,7 @@ psycopg2-binary
 sqlalchemy
 asyncua
 redis
-git+ssh://git@github.com/Aignosi/sientia-dataops-library.git@1.10.4
+git+ssh://git@github.com/Aignosi/sientia-dataops-library.git@1.12.0
 prometheus-client
 botocore
 boto3

tests/laborious/activities/test_opc.py

@@ -5,7 +5,16 @@ from pandas import DataFrame
 from pytest import mark
 from sientia_do.notifications.models import NotificationLevel
 
-from laborious.activities.opc import OPC
+from laborious.activities.opc import (
+    OPC,
+    OPC_COMMENT_SEPARATOR,
+    OPC_RECONNECT_IN_PROGRESS_COMMENT,
+    OPC_SESSION_BAD_COMMENT_PREFIX,
+    OPC_SESSION_BAD_CONFIDENCE,
+    OPC_WRITTING_ERROR_CONFIDENCE,
+    OPC_WRITTING_ERROR_MESSAGE,
+    _apply_opc_write_error,
+)
 
 metadata = {
     'metadata': {
@@ -206,7 +215,7 @@ WRITE_DATA_CASES = [
 async def test_write_data_success(opc, tag, data_type, data):
     opc.opc_repository['server1'].write_data.return_value = (True, {'response_time': 0.1})
 
-    result = await opc.write_data(
+    response_time, error_info = await opc.write_data(
         server_id='server1',
         tag=tag,
         data=data,
@@ -214,10 +223,9 @@ async def test_write_data_success(opc, tag, data_type, data):
         tag_type='prediction',
         metadata=metadata,
     )
-    assert result == 0.1
-    opc.opc_repository['server1'].write_data.assert_called_once_with(
-        tag, data, data_type, opc.logger, metadata
-    )
+    assert response_time == 0.1
+    assert error_info is None
+    opc.opc_repository['server1'].write_data.assert_called_once_with(tag, data, data_type, metadata)
 
 
 @mark.asyncio
@@ -233,7 +241,7 @@ async def test_write_data_failed(opc):
         },
     )
 
-    result = await opc.write_data(
+    response_time, error_info = await opc.write_data(
         server_id='server1',
         tag='tag1',
         data=50,
@@ -241,7 +249,8 @@ async def test_write_data_failed(opc):
         tag_type='prediction',
         metadata=metadata,
     )
-    assert result is None
+    assert response_time is None
+    assert error_info is not None
 
     opc.send_notification_async.assert_called_once_with(
         metadata=metadata,
@@ -281,17 +290,211 @@ async def test_write_data_exception(opc):
         raise AssertionError('Expected an exception to be raised')
 
 
+@mark.parametrize(
+    'error_info,initial_seen,initial_status,initial_reconnect,expected',
+    [
+        (None, False, None, False, (False, None, False)),
+        ({}, False, None, False, (False, None, False)),
+        (
+            {'opc_error_kind': 'session_bad', 'opc_status': 'BadSessionIdInvalid'},
+            False,
+            None,
+            False,
+            (True, 'BadSessionIdInvalid', False),
+        ),
+        (
+            {'opc_error_kind': 'session_bad', 'opc_status': 'NewStatus'},
+            True,
+            'OldStatus',
+            False,
+            (True, 'NewStatus', False),
+        ),
+        (
+            {'opc_error_kind': 'session_bad'},
+            True,
+            'KeptStatus',
+            False,
+            (True, 'KeptStatus', False),
+        ),
+        (
+            {'opc_error_kind': 'reconnect_in_progress'},
+            False,
+            None,
+            False,
+            (False, None, True),
+        ),
+        (
+            {'opc_error_kind': 'other'},
+            True,
+            'Status',
+            True,
+            (True, 'Status', True),
+        ),
+    ],
+)
+def test_apply_opc_write_error(
+    error_info, initial_seen, initial_status, initial_reconnect, expected
+):
+    result = _apply_opc_write_error(
+        error_info,
+        initial_seen,
+        initial_status,
+        initial_reconnect,
+    )
+    assert result == expected
+
+
+@mark.asyncio
+async def test_write_tags_from_config_prediction_success(opc):
+    opc.write_data = AsyncMock(return_value=(0.1, None))
+    data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
+    tags_config = {'tag1': {'data_type': 'float'}}
+
+    response_times, session_bad, opc_status, reconnect = await opc._write_tags_from_config(
+        server_id='server1',
+        tags_config=tags_config,
+        data=data,
+        data_column='prediction',
+        tag_type='prediction',
+        log_label='Prediction data',
+        metadata=metadata['metadata'],
+    )
+
+    assert response_times == {'tag1': 0.1}
+    assert session_bad is False
+    assert opc_status is None
+    assert reconnect is False
+    opc.write_data.assert_called_once_with(
+        server_id='server1',
+        tag='tag1',
+        data=0.75,
+        data_type='float',
+        tag_type='prediction',
+        metadata=metadata['metadata'],
+    )
+
+
+@mark.asyncio
+async def test_write_tags_from_config_confidence_success(opc):
+    opc.write_data = AsyncMock(return_value=(0.2, None))
+    data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
+    tags_config = {'tag2': {'data_type': 'float'}}
+
+    response_times, session_bad, opc_status, reconnect = await opc._write_tags_from_config(
+        server_id='server1',
+        tags_config=tags_config,
+        data=data,
+        data_column='prediction_confidence',
+        tag_type='confidence',
+        log_label='Confidence data',
+        metadata=metadata['metadata'],
+    )
+
+    assert response_times == {'tag2': 0.2}
+    assert session_bad is False
+    assert opc_status is None
+    assert reconnect is False
+    opc.write_data.assert_called_once_with(
+        server_id='server1',
+        tag='tag2',
+        data=0.95,
+        data_type='float',
+        tag_type='confidence',
+        metadata=metadata['metadata'],
+    )
+
+
+@mark.asyncio
+async def test_write_tags_from_config_write_failure(opc):
+    opc.write_data = AsyncMock(return_value=(None, {}))
+    data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
+
+    response_times, session_bad, opc_status, reconnect = await opc._write_tags_from_config(
+        server_id='server1',
+        tags_config={'tag1': {'data_type': 'float'}},
+        data=data,
+        data_column='prediction',
+        tag_type='prediction',
+        log_label='Prediction data',
+        metadata=metadata['metadata'],
+    )
+
+    assert response_times == {'tag1': None}
+    assert session_bad is False
+    assert opc_status is None
+    assert reconnect is False
+
+
+@mark.asyncio
+async def test_write_tags_from_config_session_bad(opc):
+    opc.write_data = AsyncMock(
+        return_value=(
+            None,
+            {
+                'opc_error_kind': 'session_bad',
+                'opc_status': 'BadSessionIdInvalid',
+            },
+        )
+    )
+    data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
+
+    response_times, session_bad, opc_status, reconnect = await opc._write_tags_from_config(
+        server_id='server1',
+        tags_config={'tag1': {'data_type': 'float'}},
+        data=data,
+        data_column='prediction',
+        tag_type='prediction',
+        log_label='Prediction data',
+        metadata=metadata['metadata'],
+    )
+
+    assert response_times == {'tag1': None}
+    assert session_bad is True
+    assert opc_status == 'BadSessionIdInvalid'
+    assert reconnect is False
+
+
+@mark.asyncio
+async def test_write_tags_from_config_reconnect_in_progress(opc):
+    opc.write_data = AsyncMock(
+        return_value=(
+            None,
+            {'opc_error_kind': 'reconnect_in_progress'},
+        )
+    )
+    data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
+
+    response_times, session_bad, opc_status, reconnect = await opc._write_tags_from_config(
+        server_id='server1',
+        tags_config={'tag1': {'data_type': 'float'}},
+        data=data,
+        data_column='prediction',
+        tag_type='prediction',
+        log_label='Prediction data',
+        metadata=metadata['metadata'],
+    )
+
+    assert response_times == {'tag1': None}
+    assert session_bad is False
+    assert opc_status is None
+    assert reconnect is True
+
+
 @mark.asyncio
 async def test_manage_output_tags_success(opc):
-    opc.write_data = AsyncMock(return_value=0.1)
-
+    opc._write_tags_from_config = AsyncMock(
+        side_effect=[
+            ({'tag1': 0.1}, False, None, False),
+            ({'tag2': 0.1}, False, None, False),
+        ]
+    )
     data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
     config = {
         'prediction_tags': {'tag1': {'data_type': 'float'}},
         'confidence_tags': {'tag2': {'data_type': 'float'}},
     }
 
-    output_data, opc_metrics = await opc.manage_output_tags(
+    output_data, opc_metrics, session_bad, opc_status, reconnect = await opc.manage_output_tags(
         server_id='server1',
         config=config,
         data=data,
@@ -300,83 +503,53 @@ async def test_manage_output_tags_success(opc):
 
     assert output_data is True
     assert opc_metrics == {'tag1': 0.1, 'tag2': 0.1}
-    opc.write_data.assert_has_calls(
-        [
-            call(
-                server_id='server1',
-                tag='tag1',
-                data=0.75,
-                data_type='float',
-                tag_type='prediction',
-                metadata=metadata['metadata'],
-            ),
-            call(
-                server_id='server1',
-                tag='tag2',
-                data=0.95,
-                data_type='float',
-                tag_type='confidence',
-                metadata=metadata['metadata'],
-            ),
-        ]
-    )
+    assert session_bad is False
+    assert opc_status is None
+    assert reconnect is False
+    assert opc._write_tags_from_config.await_count == 2
 
 
 @mark.asyncio
-@mark.parametrize('side_effect', [[0.1, None], [None, 0.2]])
-async def test_manage_output_tags_failed(opc, side_effect):
-    opc.write_data = AsyncMock(side_effect=side_effect)
+async def test_manage_output_tags_failed(opc):
+    opc._write_tags_from_config = AsyncMock(
+        side_effect=[
+            ({'tag1': 0.1}, False, None, False),
+            ({'tag2': None}, False, None, False),
+        ]
+    )
     data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
     config = {
         'prediction_tags': {'tag1': {'data_type': 'float'}},
         'confidence_tags': {'tag2': {'data_type': 'float'}},
     }
-    output_data, opc_metrics = await opc.manage_output_tags(
+
+    output_data, opc_metrics, _, _, _ = await opc.manage_output_tags(
         server_id='server1',
         config=config,
         data=data,
         metadata=metadata['metadata'],
     )
+
     assert output_data is False
-    assert opc_metrics == {'tag1': side_effect[0], 'tag2': side_effect[1]}
-    opc.write_data.assert_has_calls(
-        [
-            call(
-                server_id='server1',
-                tag='tag1',
-                data=0.75,
-                data_type='float',
-                tag_type='prediction',
-                metadata=metadata['metadata'],
-            ),
-            call(
-                server_id='server1',
-                tag='tag2',
-                data=0.95,
-                data_type='float',
-                tag_type='confidence',
-                metadata=metadata['metadata'],
-            ),
-        ]
-    )
+    assert opc_metrics == {'tag1': 0.1, 'tag2': None}
 
 
 @mark.asyncio
 async def test_manage_output_tags_do_nothing(opc):
-    opc.write_data = AsyncMock(return_value=0.1)
+    opc._write_tags_from_config = AsyncMock()
     data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
-    config = {
-        '_invalid_key': {'tag1': {'data_type': 'float'}},
-    }
-    output_data, opc_metrics = await opc.manage_output_tags(
+    config = {'_invalid_key': {'tag1': {'data_type': 'float'}}}
+
+    output_data, opc_metrics, _, _, _ = await opc.manage_output_tags(
         server_id='server1',
         config=config,
         data=data,
         metadata=metadata['metadata'],
     )
+
     assert output_data is True
     assert opc_metrics == {}
-    opc.write_data.assert_not_called()
+    opc._write_tags_from_config.assert_not_called()
 
 
 @mark.asyncio
@@ -395,7 +568,9 @@ async def test_write_opc_data_success(mock_dataframe, opc):
     }
 
     # Act
-    opc.manage_output_tags = AsyncMock(return_value=(True, {'tag1': 0.1, 'tag2': 0.2}))
+    opc.manage_output_tags = AsyncMock(
+        return_value=(True, {'tag1': 0.1, 'tag2': 0.2}, False, None, False)
+    )
 
     opc.process_confidence = MagicMock(return_value={'data': 'data'})
     output_data, opc_metrics = await opc.write_opc_data(input_data)
@@ -413,6 +588,9 @@ async def test_write_opc_data_success(mock_dataframe, opc):
         mock_dataframe.return_value,
         True,
         metadata['metadata'],
+        session_bad=False,
+        opc_status=None,
+        reconnect_in_progress=False,
     )
 
 
@@ -462,13 +640,91 @@ async def test_write_opc_data_no_validate_server(opc):
     ],
 )
 def test_process_confidence(opc, data, success, expected):
-    # Act
-    result = opc.process_confidence(data, success, metadata)
-
-    # Assert
+    result = opc.process_confidence(data, success, metadata['metadata'])
     assert result['prediction_confidence'][0] == expected
 
 
+def test_process_confidence_session_bad(opc):
+    data = DataFrame({'prediction_confidence': [0.9]})
+    result = opc.process_confidence(
+        data,
+        False,
+        metadata['metadata'],
+        session_bad=True,
+        opc_status='BadSessionIdInvalid',
+    )
+    assert result['prediction_confidence'][0] == OPC_SESSION_BAD_CONFIDENCE
+    assert result['comments'][0].startswith(OPC_SESSION_BAD_COMMENT_PREFIX)
+    assert 'BadSessionIdInvalid' in result['comments'][0]
+
+
+def test_process_confidence_generic_failure(opc):
+    data = DataFrame({'prediction_confidence': [0.9]})
+    result = opc.process_confidence(data, False, metadata['metadata'])
+    assert result['prediction_confidence'][0] == OPC_WRITTING_ERROR_CONFIDENCE
+    assert result['comments'][0] == OPC_WRITTING_ERROR_MESSAGE
+
+
+@mark.asyncio
+async def test_manage_output_tags_merges_error_flags(opc):
+    opc._write_tags_from_config = AsyncMock(
+        side_effect=[
+            ({'tag1': None}, True, 'BadSessionIdInvalid', False),
+            ({'tag2': 0.2}, False, None, True),
+        ]
+    )
+    data = DataFrame({'prediction': [0.75], 'prediction_confidence': [0.95]})
+    config = {
+        'prediction_tags': {'tag1': {'data_type': 'float'}},
+        'confidence_tags': {'tag2': {'data_type': 'float'}},
+    }
+
+    (
+        success,
+        metrics,
+        session_bad_seen,
+        opc_status,
+        reconnect_in_progress,
+    ) = await opc.manage_output_tags('server1', config, data, metadata['metadata'])
+
+    assert success is False
+    assert session_bad_seen is True
+    assert reconnect_in_progress is True
+    assert opc_status == 'BadSessionIdInvalid'
+    assert metrics == {'tag1': None, 'tag2': 0.2}
+
+
+def test_process_confidence_reconnect_in_progress(opc):
+    data = DataFrame({'prediction_confidence': [0.9]})
+    result = opc.process_confidence(
+        data,
+        False,
+        metadata['metadata'],
+        reconnect_in_progress=True,
+    )
+    assert result['prediction_confidence'][0] == OPC_SESSION_BAD_CONFIDENCE
+    assert result['comments'][0] == OPC_RECONNECT_IN_PROGRESS_COMMENT
+
+
+def test_process_confidence_concatenates_multiple_comments(opc):
+    data = DataFrame({'prediction_confidence': [0.9]})
+    session_comment = f'{OPC_SESSION_BAD_COMMENT_PREFIX} BadSessionIdInvalid'
+
+    result = opc.process_confidence(
+        data,
+        False,
+        metadata['metadata'],
+        session_bad=True,
+        opc_status='BadSessionIdInvalid',
+        reconnect_in_progress=True,
+    )
+
+    assert result['prediction_confidence'][0] == OPC_SESSION_BAD_CONFIDENCE
+    assert result['comments'][0] == OPC_COMMENT_SEPARATOR.join(
+        [session_comment, OPC_RECONNECT_IN_PROGRESS_COMMENT]
+    )
+
+
 @mark.asyncio
 async def test_validate_server(opc):
     assert await opc.validate_server('server1', metadata) is True

tests/laborious/utils/repository/test_opc_repository.py

@@ -1,12 +1,20 @@
+import asyncio
 import json
 from datetime import datetime
 from unittest.mock import ANY, AsyncMock, MagicMock, Mock, patch
 
 import pytest
 from asyncua.crypto.security_policies import SecurityPolicyBasic256
+from asyncua.ua.uaerrors import BadNodeIdUnknown, BadSessionIdInvalid
 from sientia_do.notifications.models import NotificationLevel
 
-from laborious.utils.repository.opc_repository import OpcRepository
+from laborious.utils.repository.opc_repository import (
+    OpcClientAlreadyExistsError,
+    OpcClientNotInitializedError,
+    OpcRepository,
+    OpcSessionAlreadyConnectedError,
+    is_reconnectable_opcua_bad,
+)
 
 
 @pytest.fixture
@@ -33,6 +41,11 @@ def opc_repository(mock_logger):
     repository.send_notification = MagicMock()
     repository.send_notification_async = AsyncMock()
     repository.emit_metric = AsyncMock()
+    repository.info = MagicMock()
+    repository.error = MagicMock()
+    repository.warning = MagicMock()
+    repository.debug = MagicMock()
+    repository._session_ready.set()
     return repository
 
 
@@ -65,7 +78,6 @@ def test_init(opc_repository):
     assert opc_repository.reconnection_interval == 60
     assert opc_repository.client is None
     assert opc_repository.last_reconnection_time is None
-    assert opc_repository.error_count == 0
 
 
 @pytest.mark.asyncio
@@ -80,8 +92,8 @@ async def test_set_security(opc_repository, mock_client):
         private_key='/path/to/key.pem',
         server_certificate='/path/to/server_cert.pem',
     )
-    assert mock_client.secure_channel_timeout == 10000000
-    assert mock_client.session_timeout == 10000000
+    assert mock_client.secure_channel_timeout == 600_000
+    assert mock_client.session_timeout == 600_000
 
 
 @pytest.mark.asyncio
@@ -106,48 +118,95 @@ async def test_set_security_missing_client(opc_repository):
 
 @pytest.mark.asyncio
 async def test_connect_with_security(opc_repository, mock_client):
-    opc_repository.try_connect = AsyncMock(return_value=(True, {}))
+    opc_repository._create_client = AsyncMock()
+    opc_repository._open_session = AsyncMock(return_value=(True, {}))
     result = await opc_repository.connect()
 
-    opc_repository.try_connect.assert_called_once()
-    assert opc_repository.client == mock_client
+    opc_repository._create_client.assert_called_once()
+    opc_repository._open_session.assert_called_once()
     assert result == (True, {})
 
 
 @pytest.mark.asyncio
 async def test_connect_without_security(opc_repository, mock_client):
     opc_repository.cert_path = None
-    opc_repository.try_connect = AsyncMock(return_value=(True, {}))
+    opc_repository._create_client = AsyncMock()
+    opc_repository._open_session = AsyncMock(return_value=(True, {}))
     opc_repository.set_security = AsyncMock()
     result = await opc_repository.connect()
 
-    opc_repository.try_connect.assert_called_once()
+    opc_repository._create_client.assert_called_once()
+    opc_repository._open_session.assert_called_once()
     opc_repository.set_security.assert_not_called()
-    assert opc_repository.client == mock_client
     assert result == (True, {})
 
 
 @pytest.mark.asyncio
-async def test_try_connect_success(opc_repository):
-    opc_repository.last_reconnection_time = None
+async def test_connect_raises_when_session_already_open(opc_repository, mock_client):
+    opc_repository.client = mock_client
+    proto = MagicMock()
+    proto.state = 'open'
+    mock_client.uaclient = MagicMock(protocol=proto)
+
+    with pytest.raises(OpcSessionAlreadyConnectedError, match='disconnect'):
+        await opc_repository.connect()
+
+
+@pytest.mark.asyncio
+async def test_create_client_raises_when_client_exists(opc_repository, mock_client):
+    opc_repository.client = mock_client
+
+    with pytest.raises(OpcClientAlreadyExistsError, match='already exists'):
+        await opc_repository._create_client()
+
+
+@pytest.mark.asyncio
+async def test_open_session_success(opc_repository):
+    closed_proto = MagicMock()
+    closed_proto.state = 'closed'
     opc_repository.client = AsyncMock()
-    result = await opc_repository.try_connect()
+    opc_repository.client.uaclient = MagicMock(protocol=closed_proto)
+    opc_repository.client.session_timeout = 600_000
+    opc_repository.client.secure_channel_timeout = 600_000
+
+    open_proto = MagicMock()
+    open_proto.state = 'open'
+    open_proto.authentication_token = 'tok'
+
+    async def connect_side_effect():
+        opc_repository.client.uaclient.protocol = open_proto
+
+    opc_repository.client.connect = AsyncMock(side_effect=connect_side_effect)
+
+    result = await opc_repository._open_session()
 
     opc_repository.client.connect.assert_called_once()
-    assert opc_repository.last_reconnection_time is not None
+    assert opc_repository.last_reconnection_time is None
     assert result == (True, {})
+    assert opc_repository._session_ready.is_set()
 
 
 @pytest.mark.asyncio
-async def test_try_connect_fail(opc_repository):
-    opc_repository.last_reconnection_time = None
-    opc_repository.disconnect = AsyncMock()
+async def test_open_session_raises_when_already_connected(opc_repository, mock_client):
+    opc_repository.client = mock_client
+    proto = MagicMock()
+    proto.state = 'open'
+    mock_client.uaclient = MagicMock(protocol=proto)
+
+    with pytest.raises(OpcSessionAlreadyConnectedError, match='disconnect'):
+        await opc_repository._open_session()
+
+
+@pytest.mark.asyncio
+async def test_open_session_fail(opc_repository):
+    opc_repository._disconnect_locked = AsyncMock()
     opc_repository.client = MagicMock()
-    opc_repository.client.connect.side_effect = Exception('Test error')
+    opc_repository.client.uaclient = MagicMock(protocol=MagicMock(state='closed'))
+    opc_repository.client.connect = AsyncMock(side_effect=Exception('Test error'))
 
-    is_connected, error_data = await opc_repository.try_connect()
+    is_connected, error_data = await opc_repository._open_session()
 
-    opc_repository.disconnect.assert_called_once()
+    opc_repository._disconnect_locked.assert_called_once()
     opc_repository.client.connect.assert_called_once()
     assert is_connected is False
     assert error_data['notification_id'] == f'OPC_CONNECTION_ERROR_{opc_repository.id}'
@@ -158,25 +217,18 @@ async def test_try_connect_fail(opc_repository):
 
 
 @pytest.mark.asyncio
-async def test_try_connect_no_client(opc_repository):
+async def test_open_session_raises_when_no_client(opc_repository):
     opc_repository.client = None
-    result = await opc_repository.try_connect()
-    assert result == (
-        False,
-        {
-            'notification_id': f'OPC_CONNECTION_ERROR_{opc_repository.id}',
-            'message': 'Client is not initialized',
-            'block': 'opc_repository',
-            'level': NotificationLevel.ERROR,
-        },
-    )
+
+    with pytest.raises(OpcClientNotInitializedError, match='not initialized'):
+        await opc_repository._open_session()
 
 
 @pytest.mark.asyncio
 async def test_disconnection_fallback_success(opc_repository, mock_client):
     opc_repository.client = mock_client
     mock_client.disconnect.return_value = True
-    result = await opc_repository.disconnection_fallback()
+    result = await opc_repository._disconnection_fallback()
 
     mock_client.disconnect.assert_called_once()
     assert result == []
@@ -186,7 +238,7 @@ async def test_disconnection_fallback_success(opc_repository, mock_client):
 async def test_disconnection_fallback_fail(opc_repository, mock_client):
     opc_repository.client = mock_client
     mock_client.disconnect.side_effect = Exception('Test error')
-    result = await opc_repository.disconnection_fallback()
+    result = await opc_repository._disconnection_fallback()
     assert result == [
         {'attempt': 1, 'error': 'Test error', 'traceback': ANY},
         {'attempt': 2, 'error': 'Test error', 'traceback': ANY},
@@ -200,11 +252,12 @@ async def test_disconnection_fallback_fail(opc_repository, mock_client):
 @pytest.mark.asyncio
 async def test_disconnect(opc_repository, mock_client):
     opc_repository.client = mock_client
-    opc_repository.disconnection_fallback = AsyncMock(return_value=[])
+    opc_repository._disconnection_fallback = AsyncMock(return_value=[])
     await opc_repository.disconnect()
 
-    opc_repository.disconnection_fallback.assert_called_once()
+    opc_repository._disconnection_fallback.assert_called_once()
     assert opc_repository.client is None
+    assert opc_repository._allow_reconnect is False
 
 
 @pytest.mark.asyncio
@@ -216,12 +269,12 @@ async def test_disconnect_no_client(opc_repository):
 @pytest.mark.asyncio
 async def test_disconnect_error(opc_repository, mock_client):
     opc_repository.client = mock_client
-    opc_repository.disconnection_fallback = AsyncMock(
+    opc_repository._disconnection_fallback = AsyncMock(
         return_value=[{'attempt': 1, 'error': 'Test error', 'traceback': 'text'}]
     )
     await opc_repository.disconnect()
 
-    opc_repository.disconnection_fallback.assert_called_once()
+    opc_repository._disconnection_fallback.assert_called_once()
     opc_repository.send_notification_async.assert_called_once_with(
         metadata=opc_repository.metadata,
         notification_id=f'OPC_DISCONNECTION_ERROR_{opc_repository.id}',
@@ -238,91 +291,24 @@ async def test_disconnect_error(opc_repository, mock_client):
 @pytest.mark.asyncio
 async def test_validate_connection_none_client(opc_repository):
     opc_repository.client = None
-    opc_repository.connect = AsyncMock(return_value=(True, {}))
     response = await opc_repository.validate_connection()
-    assert response == (True, {})
-    opc_repository.connect.assert_called_once()
-
-
-# @pytest.mark.asyncio
-# async def test_validate_connection_error_count_disconnect_error(opc_repository):
-#     opc_repository.error_count = 6
-#     opc_repository.client = AsyncMock()
-#     opc_repository.disconnect = AsyncMock(side_effect=Exception('Test error'))
-#     opc_repository.connect = AsyncMock(return_value=(True, {}))
-
-#     response = await opc_repository.validate_connection()
-#     assert response == opc_repository.connect.return_value
-#     opc_repository.disconnect.assert_called_once()
-#     opc_repository.connect.assert_called_once()
-#     opc_repository.logger.custom_error.assert_has_calls(
-#         [
-#             call('Failed to disconnect from OPC server: Test error', ANY),
-#         ]
-#     )
+    assert response == (False, opc_repository._not_connected_error())
 
 
 @pytest.mark.asyncio
-async def test_validate_connection_error_validate_connection_error(opc_repository):
-    opc_repository.client = MagicMock(uaclient=Exception('Test error'))
-    opc_repository.error_count = 0
-
-    response = await opc_repository.validate_connection()
-
-    assert response == (
-        False,
-        {
-            'notification_id': f'OPC_CONNECTION_CHECK_ERROR_{opc_repository.id}',
-            'message': "Failed to validate connection to OPC server: 'Exception' object has no attribute 'protocol'",
-            'block': 'opc_repository',
-            'level': NotificationLevel.ERROR,
-            'attachment_content': ANY,
-        },
-    )
-
-
-@pytest.mark.asyncio
-@patch('laborious.utils.repository.opc_repository.datetime')
-async def test_validate_connection_lost_not_time_to_reconnect(_mock_datetime, opc_repository):
-    _mock_datetime.now = MagicMock(return_value=datetime(2025, 1, 1, 0, 0, 0))
-    opc_repository.error_count = 0
+async def test_validate_connection_session_not_open(opc_repository):
     opc_repository.client = MagicMock()
     opc_repository.client.uaclient.protocol = None
-    opc_repository.last_reconnection_time = datetime(2025, 1, 1, 0, 0, 0)
-    opc_repository.connect = MagicMock(return_value=(True, {}))
 
     response = await opc_repository.validate_connection()
-    opc_repository.connect.assert_not_called()
-    assert response == (
-        False,
-        {
-            'notification_id': f'OPC_CONNECTION_AWAITING_RECONNECTION_WINDOW_{opc_repository.id}',
-            'message': f'OPC server {opc_repository.id} is not connected, waiting for next reconnection window...',
-            'block': 'opc_repository',
-            'level': NotificationLevel.WARNING,
-        },
-    )
 
-
-@pytest.mark.asyncio
-@patch('laborious.utils.repository.opc_repository.datetime')
-async def test_validate_connection_lost_time_to_reconnect(mock_datetime, opc_repository):
-    mock_datetime.now = MagicMock(return_value=datetime(2025, 1, 1, 1, 0, 0))
-    opc_repository.error_count = 0
-    opc_repository.client = AsyncMock()
-    opc_repository.client.uaclient.protocol = None
-    opc_repository.last_reconnection_time = datetime(2025, 1, 1, 0, 0, 0)
-    opc_repository.connect = AsyncMock(return_value=(True, {}))
-
-    response = await opc_repository.validate_connection()
-    opc_repository.connect.assert_called_once()
-    assert response == opc_repository.connect.return_value
+    assert response == (False, opc_repository._not_connected_error())
+    opc_repository.error.assert_called_once()
 
 
 @pytest.mark.asyncio
 async def test_validate_connection_success(opc_repository):
     opc_repository.client = MagicMock()
-    opc_repository.error_count = 0
     opc_repository.client.uaclient.protocol = MagicMock()
     opc_repository.client.uaclient.protocol.state = 'open'
 
@@ -337,9 +323,7 @@ async def test_write_data_validate_connection_do_nothing(opc_repository):
     mock_node = AsyncMock()
     opc_repository.client.get_node.return_value = mock_node
 
-    result = await opc_repository.write_data(
-        'ns=2;s=TestNode', 42.0, 'float', opc_repository.logger, metadata['metadata']
-    )
+    result = await opc_repository.write_data('ns=2;s=TestNode', 42.0, 'float', metadata['metadata'])
 
     opc_repository.validate_connection.assert_called_once()
     opc_repository.client.get_node.assert_called_once_with('ns=2;s=TestNode')
@@ -348,28 +332,29 @@ async def test_write_data_validate_connection_do_nothing(opc_repository):
 
 @pytest.mark.asyncio
 async def test_write_data_validate_connection_failed(opc_repository):
-    opc_repository.validate_connection = AsyncMock(return_value=(False, {}))
-    opc_repository.client = AsyncMock()
-    opc_repository.error_count = 0
+    opc_repository.client = MagicMock()
+    opc_repository.client.uaclient.protocol = MagicMock(state='closed')
+    opc_repository._start_reconnect = AsyncMock()
 
-    result = await opc_repository.write_data(
-        'ns=2;s=TestNode', 42.0, 'float', opc_repository.logger, metadata['metadata']
+    is_success, error_data = await opc_repository.write_data(
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
     )
 
-    opc_repository.validate_connection.assert_called_once()
-    opc_repository.client.get_node.assert_not_called()
-    assert result == (False, {})
+    opc_repository._start_reconnect.assert_called_once()
+    assert opc_repository._start_reconnect.call_args.args[0] == 'ProtocolClosed'
+    assert is_success is False
+    assert error_data['opc_error_kind'] == 'connection_lost'
+    assert error_data['opc_status'] == 'ProtocolClosed'
 
 
 @pytest.mark.asyncio
 async def test_write_data_get_node_failed(opc_repository):
     opc_repository.validate_connection = AsyncMock(return_value=(True, {}))
     opc_repository.client = AsyncMock()
-    opc_repository.error_count = 0
     opc_repository.client.get_node = MagicMock(side_effect=Exception('Test error'))
 
     is_success, error_data = await opc_repository.write_data(
-        'ns=2;s=TestNode', 42.0, 'float', opc_repository.logger, metadata['metadata']
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
     )
 
     opc_repository.validate_connection.assert_called_once()
@@ -393,7 +378,7 @@ async def test_write_data_invalid_data_type(opc_repository, mock_client):
     mock_client.get_node = MagicMock(return_value=mock_node)
 
     is_success, error_data = await opc_repository.write_data(
-        'ns=2;s=TestNode', 42.0, 'invalid_type', opc_repository.logger, metadata['metadata']
+        'ns=2;s=TestNode', 42.0, 'invalid_type', metadata['metadata']
     )
 
     opc_repository.validate_connection.assert_called_once()
@@ -417,9 +402,7 @@ async def test_write_data(opc_repository, mock_client):
     mock_node = AsyncMock()
     mock_client.get_node = MagicMock(return_value=mock_node)
 
-    result = await opc_repository.write_data(
-        'ns=2;s=TestNode', 42.0, 'float', opc_repository.logger, metadata['metadata']
-    )
+    result = await opc_repository.write_data('ns=2;s=TestNode', 42.0, 'float', metadata['metadata'])
 
     mock_client.get_node.assert_called_once_with('ns=2;s=TestNode')
     mock_node.write_value.assert_called_once()
@@ -431,12 +414,11 @@ async def test_write_data_write_value_failed(opc_repository, mock_client):
     opc_repository.validate_connection = AsyncMock(return_value=(True, {}))
     opc_repository.client = mock_client
     mock_node = AsyncMock()
-    opc_repository.error_count = 0
     mock_client.get_node = MagicMock(return_value=mock_node)
     mock_node.write_value.side_effect = Exception('Test error')
 
     is_success, error_data = await opc_repository.write_data(
-        'ns=2;s=TestNode', 42.0, 'float', opc_repository.logger, metadata['metadata']
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
     )
 
     opc_repository.validate_connection.assert_called_once()
@@ -451,3 +433,178 @@ async def test_write_data_write_value_failed(opc_repository, mock_client):
     assert error_data['block'] == 'opc_repository'
     assert error_data['level'] == NotificationLevel.ERROR
     assert error_data['attachment_content'] is not None
+
+
+def test_is_reconnectable_opcua_bad():
+    assert is_reconnectable_opcua_bad(BadSessionIdInvalid()) is True
+    assert is_reconnectable_opcua_bad(BadNodeIdUnknown()) is False
+    assert is_reconnectable_opcua_bad(Exception('other')) is False
+
+
+@pytest.mark.asyncio
+async def test_write_data_bad_session_id_invalid_schedules_reconnect(opc_repository, mock_client):
+    opc_repository.validate_connection = AsyncMock(return_value=(True, {}))
+    opc_repository.client = mock_client
+    opc_repository._start_reconnect = AsyncMock()
+    mock_node = AsyncMock()
+    mock_client.get_node = MagicMock(return_value=mock_node)
+    mock_node.write_value.side_effect = BadSessionIdInvalid()
+
+    is_success, error_data = await opc_repository.write_data(
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
+    )
+
+    mock_node.write_value.assert_called_once()
+    opc_repository._start_reconnect.assert_called_once()
+    assert is_success is False
+    assert error_data['opc_error_kind'] == 'session_bad'
+    assert error_data['opc_status'] == 'BadSessionIdInvalid'
+
+
+@pytest.mark.asyncio
+async def test_write_data_reconnect_in_progress_immediate(opc_repository):
+    opc_repository._session_ready.clear()
+    opc_repository._reconnect_task = asyncio.create_task(asyncio.sleep(60))
+    opc_repository.validate_connection = AsyncMock()
+
+    is_success, error_data = await opc_repository.write_data(
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
+    )
+
+    opc_repository._reconnect_task.cancel()
+    with pytest.raises(asyncio.CancelledError):
+        await opc_repository._reconnect_task
+    opc_repository._reconnect_task = None
+
+    opc_repository.validate_connection.assert_not_called()
+    assert is_success is False
+    assert error_data['opc_error_kind'] == 'reconnect_in_progress'
+
+
+@pytest.mark.asyncio
+async def test_start_reconnect_skips_within_interval(opc_repository):
+    opc_repository.last_reconnection_time = datetime.now()
+    opc_repository.reconnection_interval = 3600
+
+    await opc_repository._start_reconnect('BadSessionIdInvalid', 'tok')
+
+    assert opc_repository._reconnect_task is None
+
+
+@pytest.mark.asyncio
+async def test_write_data_protocol_closed_schedules_reconnect(opc_repository):
+    opc_repository.client = MagicMock()
+    opc_repository.client.uaclient.protocol = MagicMock(state='closed')
+    opc_repository._start_reconnect = AsyncMock()
+
+    is_success, error_data = await opc_repository.write_data(
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
+    )
+
+    opc_repository._start_reconnect.assert_called_once()
+    assert opc_repository._start_reconnect.call_args.args[0] == 'ProtocolClosed'
+    assert is_success is False
+    assert error_data['opc_error_kind'] == 'connection_lost'
+    assert error_data['opc_status'] == 'ProtocolClosed'
+
+
+@pytest.mark.asyncio
+async def test_write_data_protocol_closed_skips_reconnect_within_interval(opc_repository):
+    opc_repository.client = MagicMock()
+    opc_repository.client.uaclient.protocol = MagicMock(state='closed')
+    opc_repository.last_reconnection_time = datetime.now()
+    opc_repository.reconnection_interval = 3600
+
+    is_success, error_data = await opc_repository.write_data(
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
+    )
+
+    assert opc_repository._reconnect_task is None
+    assert is_success is False
+    assert error_data['opc_error_kind'] == 'connection_lost'
+
+
+@pytest.mark.asyncio
+async def test_write_data_after_failed_reconnect_schedules_again(opc_repository):
+    opc_repository._session_ready.clear()
+    opc_repository.reconnection_interval = 0
+    opc_repository.last_reconnection_time = None
+    opc_repository._reconnect_locked = AsyncMock(
+        return_value=(False, {'message': 'connect failed'})
+    )
+
+    await opc_repository.write_data('ns=2;s=TestNode', 42.0, 'float', metadata['metadata'])
+    await asyncio.sleep(0.1)
+    assert opc_repository._reconnect_locked.call_count == 1
+    assert not opc_repository._reconnect_task_in_progress()
+
+    await opc_repository.write_data('ns=2;s=TestNode', 42.0, 'float', metadata['metadata'])
+    await asyncio.sleep(0.1)
+    assert opc_repository._reconnect_locked.call_count == 2
+
+
+@pytest.mark.asyncio
+async def test_write_data_after_disconnect_does_not_schedule_reconnect(opc_repository, mock_client):
+    opc_repository.client = mock_client
+    proto = MagicMock()
+    proto.state = 'closed'
+    mock_client.uaclient = MagicMock(protocol=proto)
+    opc_repository._disconnection_fallback = AsyncMock(return_value=[])
+    await opc_repository.disconnect()
+
+    is_success, error_data = await opc_repository.write_data(
+        'ns=2;s=TestNode', 42.0, 'float', metadata['metadata']
+    )
+
+    assert opc_repository._reconnect_task is None
+    assert is_success is False
+    assert error_data['opc_error_kind'] == 'connection_lost'
+
+
+@pytest.mark.asyncio
+async def test_parallel_bad_writes_single_reconnect_task(opc_repository, mock_client):
+    opc_repository.validate_connection = AsyncMock(return_value=(True, {}))
+    opc_repository.client = mock_client
+    opc_repository.reconnection_interval = 0
+    opc_repository.last_reconnection_time = None
+    mock_node = AsyncMock()
+    mock_client.get_node = MagicMock(return_value=mock_node)
+    mock_node.write_value.side_effect = BadSessionIdInvalid()
+
+    connect_count = 0
+
+    async def slow_reconnect():
+        nonlocal connect_count
+        connect_count += 1
+        await asyncio.sleep(0.05)
+        opc_repository._session_ready.set()
+        return True, {}
+
+    opc_repository._reconnect_locked = slow_reconnect
+
+    results = await asyncio.gather(
+        opc_repository.write_data('ns=2;s=TestNode', 1.0, 'float', metadata['metadata']),
+        opc_repository.write_data('ns=2;s=TestNode2', 2.0, 'float', metadata['metadata']),
+    )
+    await asyncio.sleep(0.15)
+
+    assert connect_count <= 1
+    assert 1 <= mock_node.write_value.call_count <= 2
+    error_kinds = [r[1].get('opc_error_kind') for r in results]
+    assert error_kinds.count('session_bad') >= 1
+    assert all(k in ('session_bad', 'reconnect_in_progress') for k in error_kinds)
+
+
+@pytest.mark.asyncio
+@patch('laborious.utils.repository.opc_repository.datetime')
+async def test_reconnect_locked_sets_last_reconnection_time(mock_datetime, opc_repository):
+    mock_datetime.now = MagicMock(return_value=datetime(2025, 1, 1, 12, 0, 0))
+    opc_repository._disconnect_locked = AsyncMock()
+    opc_repository._connect_locked = AsyncMock(return_value=(True, {}))
+
+    result = await opc_repository._reconnect_locked()
+
+    opc_repository._disconnect_locked.assert_called_once()
+    opc_repository._connect_locked.assert_called_once()
+    assert result == (True, {})
+    assert opc_repository.last_reconnection_time == datetime(2025, 1, 1, 12, 0, 0)

values.yaml

@@ -17,8 +17,8 @@ image:
 imagePullSecrets:
 - name: docker-hub-secret
 # This is to override the chart name.
-nameOverride: "sientia-laborious-worker"
-fullnameOverride: "sientia-laborious-worker"
+nameOverride: "sientia-laborious-legacy-worker"
+fullnameOverride: "sientia-laborious-legacy-worker"
 namespace: sientia
 
 # This section builds out the service account more information can be found here: https://kubernetes.io/docs/concepts/security/service-accounts/
@@ -31,7 +31,7 @@ serviceAccount:
   annotations: {}
   # The name of the service account to use.
   # If not set and create is true, a name is generated using the fullname template
-  name: "sientia-laborious-worker"
+  name: "sientia-laborious-legacy-worker"
 
 # This is for setting Kubernetes Annotations to a Pod.
 # For more information checkout: https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/
@@ -157,7 +157,7 @@ env:
   - name: GITHUB_REPO_URL
     value: "git@github.com:Aignosi/sientia-dataops-laborious_temporal.git"
   - name: GITHUB_BRANCH
-    value: "feature/SIENTIAPDE-1712"
+    value: "fix/SIENTIAPDE-1811"
   - name: PYTHON_APP
     value: "laborious.worker.worker"
 
@@ -307,7 +307,7 @@ ssh:
 
 # kubectl create secret docker-registry docker-hub-secret --namespace sientia --docker-server=http://aignosi.azurecr.io --docker-username=aignosi --docker-password=5I5zpQ6sRaHqX1hD3dr+2mo647yO3FRc359/wu6gsP+ACRDRz5mp
 
-# helm upgrade --install sientia-laborious-worker sientia/sientia-module -n sientia --create-namespace -f ./values.yaml --version 0.6.0
+# helm upgrade --install sientia-laborious-legacy-worker sientia/sientia-module -n sientia --create-namespace -f ./values.yaml --version 0.6.0
 
 # kubectl create secret generic git-ssh-key-sientia-laborious-worker \
 #   --namespace sientia \