Digest, chunk-embed, and question-embed keys include fleet|restricted so
a fleet caller cannot observe a restricted cache hit. Digest.Run takes
the class from permit_restricted.
A permit_restricted caller whose keys.toml workspace is not
guardian-star is refused at Search (no Honcho request) and flagged at
serve start and keys reload.
docs: P3 restricted callers search like the fleet; cache/logs isolate.
Guard messages embed the hostname (resolve <host>, no addresses for
<host>). Restricted callers now log a coarse reason class and err=-.
Test dumps slog records and forbids the hostname anywhere in them.
docs: P3 review — fail-closed search, cache class, public dialer
kyle