WriteNodeIdUnknown called itself unconditionally as its first statement
— unbounded recursion with no base case → StackOverflowException, an
uncatchable process crash reachable by any client issuing a HistoryRead
on an unresolvable NodeId (remote DoS).
Replace the self-call with the result-slot assignment, mirroring
WriteUnsupported / WriteInternalError. The helper is now internal so the
regression test can pin the StatusCode without a server fixture.
Resolves code-review finding Server-001 (Critical).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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