renderFetchOutput has no external consumer: only formatFetchOutput and
fetchMetaFromValue call it, both through the registry, which deep-freezes
the result value. Exporting it let a hypothetical caller mutate a cached
input or the returned RenderedFetch and desync the card's truncated flag
from the model text. Drop it from the barrel and document that the memo
needs no defensive copy because every caller is internal and read-only.
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