docs(opcua): dated CHANGELOG, issue-linked Future work, node ID discovery section

- ``CHANGELOG.rst``: replace "Forthcoming" header with the dated
  ``0.4.0 (2026-04-11)`` form used by other medkit packages so the
  catkin release scripts do not have to ask. Expand the bullet list
  to cover the fixes from this cleanup pass (per-entity capabilities,
  connection-state propagation, deterministic entity order, all four
  OPC-UA node ID identifier types).

- ``design/index.rst``: rewrite the Future work section to link tracked
  issues (#366 open62541pp vendoring, #367 certificate auth, #368
  optional browse CLI) directly, and split the list into "tracked in
  the issue tracker" and "untracked, open an issue if you hit the
  pain".

- ``README.md``: add a new "Finding Node IDs on your PLC" section
  between ``SOVD Entity Model`` and ``Configuration`` pointing at
  UaExpert, ``python -m asyncua.tools.uals`` and vendor toolchain
  exports. This was the main quickstart gap flagged by reviewers -
  without it, a new integrator reading the README would not know how
  to populate the ``node_id`` field for a real PLC. The already-rich
  inline comment block in ``config/tank_demo_nodes.yaml`` is now
  discoverable from the main docs.

Author: mfaferek93

src/ros2_medkit_plugins/ros2_medkit_opcua/CHANGELOG.rst

@@ -2,15 +2,19 @@
 Changelog for package ros2_medkit_opcua
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Forthcoming
------------
+0.4.0 (2026-04-11)
+------------------
 * Initial release
 * ``OpcuaPlugin`` implementation of ``GatewayPlugin`` and ``IntrospectionProvider`` that bridges OPC-UA capable PLCs into the SOVD entity tree
 * REST endpoints via the new ``get_routes()`` plugin API: ``x-plc-data``, ``x-plc-operations``, ``x-plc-status``
-* ``NodeMap`` driven by YAML configuration - same binary serves any PLC by changing the node map file
+* Vendor capabilities registered per entity - only PLC-backed apps and the PLC runtime component advertise the ``x-plc-*`` endpoints
+* Full OPC 10000-6 section 5.3.1.10 node identifier support (``i=`` numeric, ``s=`` string, ``g=`` GUID, ``b=`` opaque ByteString); example node maps for OpenPLC, Siemens S7-1500 TIA Portal, Beckhoff TwinCAT 3, Allen-Bradley via Kepware and KUKA KR C5
+* ``NodeMap`` driven by YAML configuration - same binary serves any OPC-UA compliant server by changing the node map file
+* Deterministic entity ordering in ``IntrospectionResult`` output (entries sorted by id)
 * Threshold-based PLC alarm detection routed to SOVD faults via ``ros2_medkit_msgs`` services ``ReportFault`` / ``ClearFault``
 * Optional bridging of numeric PLC values to ROS 2 ``std_msgs/Float32`` topics from ``set_context()``
 * Type-aware writes with per-node range validation
+* Robust connection-loss detection: all three OPC-UA client paths (``read_value``, ``read_values``, ``write_value``) mark the connection as dropped on terminal status codes so ``OpcuaPoller`` reconnect kicks in without stalling
 * Polling mode (default) and OPC-UA subscription mode, backed by ``open62541pp`` v0.16.0
 * Integration test suite against an OpenPLC IEC 61131-3 tank demo container
-* Contributors: @mfaferek
+* Contributors: @mfaferek93

src/ros2_medkit_plugins/ros2_medkit_opcua/README.md

@@ -119,6 +119,34 @@ GET /api/v1/components/openplc_runtime/x-plc-status
 }
 ```
 
+## Finding Node IDs on your PLC
+
+The plugin identifies PLC tags by OPC-UA node IDs in the canonical string
+format (`ns=N;i=M` numeric, `ns=N;s=tag` string, `ns=N;g=...` GUID, or
+`ns=N;b=...` opaque). To discover the correct node IDs for a real PLC
+without guessing, use one of the standard OPC-UA browser tools:
+
+- **UaExpert** - free GUI browser from Unified Automation. Download at
+  <https://www.unified-automation.com/downloads/uaexpert.html>. Connect
+  to your PLC's `opc.tcp://` endpoint, navigate the address space tree,
+  right-click any Variable node, copy the NodeId property into the YAML
+  map below.
+
+- **`asyncua` command line** - `pip install asyncua` and then
+  `python -m asyncua.tools.uals -u opc.tcp://your-plc:4840` walks the
+  address space from a terminal, no GUI required.
+
+- **Vendor toolchains** - Siemens TIA Portal's OPC-UA configuration
+  exports DB/variable node IDs in the `ns=3;s="..."` format. Beckhoff
+  TwinCAT 3 XAE displays them as `ns=4;s=MAIN.Tank.level`. Allen-Bradley
+  users typically deploy Kepware or Ignition as an OPC-UA gateway which
+  auto-maps tag names.
+
+`config/tank_demo_nodes.yaml` ships a commented example with
+ready-to-paste templates for OpenPLC, Siemens S7-1500, Beckhoff TwinCAT,
+Allen-Bradley via Kepware and KUKA KR C5. Copy one of those blocks as a
+starting point.
+
 ## Configuration
 
 ### Node Map (YAML)

src/ros2_medkit_plugins/ros2_medkit_opcua/design/index.rst

@@ -158,9 +158,23 @@ What the plugin can NOT do today (regardless of vendor):
 Future work
 ===========
 
-- Certificate-based OPC-UA authentication (Basic256Sha256)
+Tracked issues in the `ros2_medkit issue tracker
+<https://github.com/selfpatch/ros2_medkit/issues>`_:
+
+- `#367 <https://github.com/selfpatch/ros2_medkit/issues/367>`_
+  Certificate-based OPC-UA authentication (Basic256Sha256)
+- `#368 <https://github.com/selfpatch/ros2_medkit/issues/368>`_
+  Optional auto-browse of the OPC-UA address space to seed the node map
+  (deferred pending validated user demand; UaExpert and ``python -m
+  asyncua.tools.uals`` are recommended for now)
+- `#366 <https://github.com/selfpatch/ros2_medkit/issues/366>`_
+  Vendor ``open62541pp`` inline so the package can be added to the
+  rosdistro release list
+
+Untracked (open the issue if you hit the pain):
+
 - Hot-reload of the node map without restarting the plugin
-- Optional auto-browse of the OPC-UA address space to seed the node map
 - Complex OPC-UA type support (structures, arrays, enums)
-- Native AlarmCondition event subscription as a complement to threshold
-  polling
+- Native ``AlarmCondition`` event subscription as a complement to
+  threshold polling
+- Vendor information model bindings (Euromap 77, Siemens DI, PA-DIM)