Follow-up cleanup to the two-client PvP conformance drive. The class-level
ViewerId const is no longer referenced (both remaining `ViewerId:` sites are
the MsgEnvelope named ctor arg, passing `vid`/literal 1), and the Coverage
doc-comment still described "a single Scripted session" — refresh it to the
two-client PvP reality. No behavior change; tests 2/2 green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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