docs(objectql): query-syntax states the engine's refusal of a search override naming no field

Co-authored-by: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WV4cyzHgmAWpXVdUctRKU

Author: claude

content/docs/protocol/objectql/query-syntax.mdx

@@ -1194,7 +1194,9 @@ the tolerant intersection, but not a search with nothing to scan: when no
 `searchableFields` entry names a stored field and the auto-default finds none
 (`internal: true` fields never count), the engine itself refuses a non-blank `search`
 with `400 INVALID_FIELD` (`param: 'search'`) on `find`, `findOne`, `count` and
-`aggregate` alike, rather than answering every row. Multiple whitespace-separated terms are AND-ed and
+`aggregate` alike, rather than answering every row. An override that names no field (`searchFields: []`,
+`search.fields: []`, or a comma string with no name in it) is refused there too, `400 VALIDATION_ERROR`, as
+at the ingress: leave the key out to search the default set. Multiple whitespace-separated terms are AND-ed and
 fields are OR-ed. Case sensitivity comes from the operator the expansion emits, not
 from the expansion: it emits `$icontains`, which ignores **ASCII case** by the
 rule in [Case Sensitivity](#case-sensitivity) above. So a user typing `acme` does