Mint runtime NodeIds through a single DefaultNodeIdFactory (#4433)

# Description

Nodes created at runtime now get their NodeIds from a single
`DefaultNodeIdFactory` rather than from a `New` override per
NodeManager.
The factory derives a deterministic identifier from a canonical,
length-prefixed browse path, which is injective where the classic
`{parent}_{child}` concatenation was not — `A_B` + `C` and `A` + `B_C`
both produced `A_B_C` — and it also records the parent's identifier type
and qualifies cross-namespace segments by URI, so identifiers no longer
shift with namespace-table ordering.

A NodeManager selects its style declaratively instead of writing
assignment code:

```csharp
NodeIdFactory = NodeIdFactory.WithMode(NodeIdAssignmentMode.Counter);
```

`NodeIdAssignmentMode` offers `String` (the canonical path verbatim, the
default), `Numeric` / `Guid` / `Opaque` (that path through SHA-256),
`Counter` (sequential, for nodes whose browse paths repeat — per-session
diagnostics, inference jobs, rediscovered assets) and `None`. The
counter
starts above `0x40000000`, out of reach of any authored model, so a
long-running server cannot walk a runtime instance onto a type node.

`New` overrides are gone from every NodeManager the stack ships except
two whose identifiers are a domain scheme rather than an assignment
policy: `FileSystemNodeManager`, whose NodeIds encode the file path they
resolve back to, and `RoboticsNodeManager`, whose build coordinator
reserves identifiers across managers with ownership tracking.

**Namespace rule.** Every identifier is minted into the NodeManager's
own
namespace. Neither the parent's namespace nor the browse name's is
consulted: a parent can belong to a companion-specification model whose
NodeIds are fixed by its NodeSet (`DeviceSet` in the DI namespace), and
a
browse name only names the type that declared the child. NodeManagers
whose instance namespace is not their first one rebase with
`WithDefaultNamespaceIndex`.

**Types vs instances.** An authored NodeId on a node that stands on its
own is kept. A node hanging off a parent is re-minted, because it
reached
the factory through `AssignNodeIds` walking a subtree copied from a type
declaration. Keeping those would alias every instance onto the type's
own
nodes, and the predefined-node index takes the last writer, so the type
would quietly become an instance rather than the clash being reported.

New `ISystemContext.CreateInstance(...)` builds an instance of a
generated
type and rebases its subtree through `AssignInstanceNodeId` — the path
the
generated `CreateInstanceOf<Type>` helpers already took. The AI
NodeManager was the one place calling `NodeState.Create` directly, so
its
roots kept the NodeId their state object is born with (the type's own);
it now uses the shared path.

## Breaking changes

- `IAsyncNodeManager` extends `INodeIdFactory` and gains `AddNode` and
  `AddRootNotifier`. This lets the fluent surface mint and register
  through the interface instead of type-testing for
  `AsyncCustomNodeManager` and silently falling back to a concatenated
  identifier when the test failed — that fallback was itself a source of
  divergent NodeIds.
- `AsyncNodeManagerAdapter` delegates `New` to the wrapped NodeManager,
so
**`CustomNodeManager2` behaves exactly as before**: it mints nothing and
  a node keeps whatever NodeId it already has. Servers built on it are
  unaffected.

## Notes for reviewers

- `docs/NodeIdAssignment.md` is new and describes the whole mechanism:
the
  factory contract, identifier formats, type declarations vs instances,
  the generated helpers and their parameters, per-NodeManager behaviour,
  and an inventory of every member involved.
- The three commits are independently revertible.
- Two pieces that look redundant are deliberately kept, with the
reasoning
  recorded in the doc: `assignInstanceNodeIds` (it *suppresses* minting,
  where the rebase rule *forces* it) and the generator's
  `NodeId.Equals(TypeNodeIdConstant)` guard (it distinguishes a
  caller-assigned NodeId from a declaration's).
- Fluent builder tests previously passed only because of the removed
  fallback; they now run against a real `DefaultNodeIdFactory` through a
  shared `FluentTestNodeManager` helper.

## Related Issues

_No tracking issue yet._

## Checklist

- [ ] I have signed the
[CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf)
and read the
[CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md)
doc.
- [x] I have added tests that prove my fix is effective or that my
feature works and increased code coverage.
- [x] I have added all necessary documentation.
- [x] I have verified that my changes do not introduce (new) build or
analyzer warnings.
- [ ] I ran **all** tests locally using the **UA.slnx** solution against
at least .net **framework** and .net **10**, and all passed.
- [ ] I fixed **all** failing and flaky tests in the CI pipelines and
**all** CodeQL warnings.
- [ ] I have addressed **all** PR feedback received.

> Test runs were on **net10.0 only** — .NET Framework was not exercised
> locally. Suites run green on an idle machine: Server 4950/4955, GDS
> 1116/1170, WotCon 1225/1225, Vision 484/485, DI 424/424, AI 174/174,
> ISA95 136/136, Positioning 69/69, RobotIntent 22/22. One unrelated
> pre-existing failure remains in `Opc.Ua.Types.Tests`
> (`EveryEmbeddedExampleMatchesItsRecordedHash`) — a WoT fixture checked
> out with CRLF, fixed by
> `git add --renormalize tests/Opc.Ua.Types.Tests/Wot/Assets`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

tools/Opc.Ua.SourceGeneration.Core/Generators/FluentBuilderGenerator.cs

@@ -647,6 +647,7 @@ namespace Opc.Ua.SourceGeneration
             EmitPassThroughProperty(writer, "global::Opc.Ua.ISystemContext", "Context");
             EmitPassThroughProperty(writer, "global::Opc.Ua.Server.IAsyncNodeManager", "NodeManager");
             EmitPassThroughProperty(writer, "global::Opc.Ua.Server.Fluent.IFluentDispatcher", "Dispatcher");
+            EmitPassThroughProperty(writer, "ushort", "DefaultNamespaceIndex");
 
             writer.WriteLine();
             writer.WriteLine("    /// <inheritdoc/>");

tools/Opc.Ua.SourceGeneration.Core/Generators/NodeManagerTemplates.cs

@@ -76,7 +76,6 @@ namespace Opc.Ua.SourceGeneration
                         global::Opc.Ua.ApplicationConfiguration configuration)
                         : base(server, configuration, {{Tokens.NamespaceUri}}{{Tokens.AdditionalNamespaceUris}})
                     {
-                        SystemContext.NodeIdFactory = this;
                     }
 
                     /// <summary>