* feat(conversation): continue reading a cut message by offset
A referenced message longer than 4,000 characters was cut, and its
suffix could not be read back. Cut messages now carry a continuation
(message_seq, offset). read_conversation(thread_id, message_seq, offset)
returns the next part of that one message, sized to the same
tool-output budget as pages. The read scans only the requested row
under the existing visibility rules and rechecks ownership. Offsets
follow the source's current text; an offset past the end is rejected.
Related to #5398.
* docs(conversation): say continuations ignore limit
A continuation always returns one part of one message, so limit does not apply there. The tool schema now says so instead of discarding it silently.
Related to #5398.
* fix(conversation): stop instead of looping when no text fits the budget
With a read_conversation tool-output budget below the envelope size, the fitted text was empty and the continuation repeated the requested offset, so an agent would repeat the identical call forever. Page and continuation reads now return output_budget_too_small with no continuation.
Related to #5398.
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Co-authored-by: Totoro-qaq <279883115+Totoro-qaq@users.noreply.github.com>
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