## Summary
Combines the compiled companion-model support from #4062 with the
NodeState emission fixes already in this PR. The model source generator
can now consume compiled companion `NodeSet2` models more reliably,
while generated factories consistently target base `NodeState` members
even when a generated subclass shadows them.
## Changes
### Compiled companion NodeSets
- Add `OpcUaStateTypeIndex` and wire it through `ModelSourceGenerator` /
`ModelCompilation` so standard (`ns=0`) node-state and method-state
class names are resolved from referenced `Opc.Ua.Core(.Types)` metadata.
- Add the model-generation-scoped `StandardMethodStateFallback`, which
degrades an unresolved standard typed `*MethodState` reference to
`global::Opc.Ua.MethodState` only when the type is neither available in
the compilation nor declared by the current generation pass.
- Keep declaration names outside the reference-only fallback policy,
propagate fallback state through the logical execution context, reuse
the immutable availability index, and use named incremental-generator
inputs instead of deep `Left` / `Right` chains.
- Escape generated fluent-builder XML documentation where browse names
can contain XML-sensitive characters.
### Safe NodeState factory emission
- Declare one base-typed `global::Opc.Ua.NodeState nodeState = state;`
local per generated factory.
- Use `nodeState` for base-member reads and writes to `NodeId`,
`SymbolicName`, `BrowseName`, `DisplayName`, `Description`, `WriteMask`,
`UserWriteMask`, `AccessRestrictions`, `ReleaseStatus`, `Categories`,
`Specification` and `IsPartOfTypeHierarchy`.
- Base-qualify the optional-child `previousNodeId` read, NodeId
comparison, and existing-child NodeId update.
- `global::`-qualify emitted `NodeId` / `ExpandedNodeId` namespace
prefixes to avoid namespace collisions.
### Supporting updates
- Expose `Opc.Ua.Types` internals to `Opc.Ua.Core.Encoders.Tests`.
- Update generator assertions and add focused fallback regression
coverage.
## Why
Compiled companion models can instantiate standard types whose curated
Core implementation does not expose the conventionally named typed
method-state class. The scoped fallback lets those models generate
without weakening the Stack generator or masking classes emitted by the
current model.
Separately, generated subclasses can shadow base `NodeState` properties
with strongly typed `new` properties. Routing base attributes through a
`NodeState`-typed local guarantees initialization reaches the intended
base member while keeping generated code smaller and clearer than
repeated casts.
## Validation
- Full `Opc.Ua.SourceGeneration.Core.Tests` on net10.0: **3718 passed /
8 skipped / 0 failed**.
- Combined focused generator coverage on net48: **21 passed / 0
failed**.
- Full `Opc.Ua.SourceGeneration.Tests`: **68 passed / 0 failed**.
- Full `Opc.Ua.SourceGeneration.Stack.Tests`: **90 passed / 0 failed**.
## Context
This PR supersedes #4062 and contains both source-generator change sets.
The companion-model fallback remains the scoped interim workaround
tracked by #4060; a future upstream name-resolution step can remove it.
These changes also feed the experimental data-encodings work in #4007.
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Marc Schier