Caps the total serialized size of a response, as a last-resort safety net after any selection/
truncation the caller has already configured (TruncateResponseProcessor caps individual
strings/arrays, not the overall payload). Over the limit, returns a metadata wrapper with a
truncated JSON preview instead of the raw value — this intentionally does not return a
re-parseable JSON document, since a byte-accurate cut can't guarantee valid JSON either way.
Caps the total serialized size of a response, as a last-resort safety net after any selection/ truncation the caller has already configured (TruncateResponseProcessor caps individual strings/arrays, not the overall payload). Over the limit, returns a metadata wrapper with a truncated JSON preview instead of the raw value — this intentionally does not return a re-parseable JSON document, since a byte-accurate cut can't guarantee valid JSON either way.