The refusal named a cause that cannot happen. `_vendor_gateway` never contacts the
network, so "unreachable" was wrong for the no-identity, failed-lookup and
not-entitled cases alike — and a guest was told it had no Nous identity when it
holds a perfectly good one.
Root of the guest case: `_error_info` dropped `account_tier`, so a guest whose
account lookup failed — precisely the state where the tier can no longer be read
from the JWT, because the token is inside its refresh window — came back looking
like a registered identity. Carry the stored tier through the error snapshot, and
both this refusal and every other tier-aware surface see it.
Pick the reason in priority order (guest / no usable identity / unreachable) in
one helper beside `fast_search_entitled`, so the predicate and its explanation
cannot drift, and phrase it as a clause for `selection_error`'s "but …" template —
the canonical `FREE_TIER_NEEDS_ACCOUNT` strings are standalone sentences and read
wrong embedded mid-sentence.
Also record why the `error` clause in `fast_search_entitled` is load-bearing
rather than defensive, so it is not removed as belt-and-braces.
The test helper now mirrors what anon_auth actually persists (the tier alongside
the token), which is what makes the failed-lookup case reproducible at all.
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