[mrcsin]

Problem

The OPC UA live edge (#116) needs an OPC UA server shaped like Simple-Scada's, for the integration
tests and for the demo stand. A developer machine runs the real SCADA on 49875, so the stand cannot
use that port.

What changed

• DemoScadaServer and DemoScadaNodeManager in SemiPlot.Tools.ArchiveSeeder, on the
  OPCFoundation.NetStandard.Opc.Ua.Server 2.0.1 stack. The address space follows the measured
  Simple-Scada shape:
  • namespace http://simple-scada.com/UA at index 3;
  • folder 5E4D0C1A0Broot_2, then group folders from _3;
  • node ns=3;s=5E4D0C1A0B<id>;
  • None + Anonymous with the stock token policy.
• The --follow run hosts the server. Each served value is the lattice change the archive writer
  produces (LiveTailGenerator.ChangesAt, pinned by SharedLatticeTests), stamped in true UTC. The
  first notification after a start carries the start instant.
• --opc-port is required for a follow run. --archive-lag (0 to 86400 s) holds the archive inserts
  back. FollowEdge keeps the write edge monotonic, and a graceful stop writes the held-back span.
• SemiPlot.AppHost passes --opc-port 55875.
• Packages: OPC Client and Server pinned at 2.0.1, the central Microsoft.Extensions.* pins raised to
  10.0.12, Logging.Console added.
• Tests: DemoScadaCollection in SemiPlot.Tests.Integration runs the server in process on a free
  port that is never 4840 or 49875, under Asia/Tokyo. FollowEdgeTests and the seeder command tests
  are unit tests.
• Docs: bench.md, testing-strategy.md, docs/architecture/README.md, AGENTS.md.

Measured differences from the real server, recorded in bench.md:

• The stock stack puts #None on the anonymous token only at the None endpoint; Simple-Scada puts
  it on all seven endpoints.
• The stack logs the per-session host-name line at Error.

How it was verified

• dotnet build SemiPlot.slnx: 0 errors, only the AppHost's two NU1902.
• dotnet format --verify-no-changes: exit 0. dotnet terse over the 24 touched .cs files: exit 0.
• SemiPlot.Tests.Unit: 2326/2326. SemiPlot.Tests.Integration: 216/216. The DemoScada filter
  passed 16/16 on every rerun.
• git grep -n "Opc.Ua" over UI, Core and SemiPlot.DataSource.Postgres prints nothing.
• The seeder refuses a follow run without --opc-port, --opc-port 0, and a seeding run with
  --archive-lag.
• Not run: the plan's manual stand checks (the AppHost on 55875, a browse with an external client,
  --archive-lag 60). The automated suites stand in for them in this unattended roadmap run.

Per-task commits before collapse

5901786 docs(plan): record the exec run and its checks
7b67cbd fix(seeder): address comment audit findings
f18647f fix(seeder): address review findings
83442f0 fix(seeder): address review findings
6c84be6 docs(bench): describe the OPC UA demo server
78ea497 docs(plan): verify the OPC demo server acceptance
656600c feat(apphost): serve the stand's OPC UA on 55875
b648e02 feat(seeder): host the OPC server in the follow run
7ab9cd2 feat(seeder): serve the pens and publish each change
2f9a5fb feat(seeder): start and stop the OPC UA demo server
6106b7f feat(seeder): serve the change at a lattice instant
a6b0990 feat(seeder): add the follow-only lag and OPC port
3517699 build(deps): pin the OPC UA 2.0.1 package line