A paginated tool result tells the model to call the same tool again with
only _resultId/_section. The advertised schema still carried the upstream's
own `required` list, so a client that validates arguments rejected exactly
that call — "Received tool input did not match expected schema" — and the
model concluded pagination was broken and gave up
(websearch/fetch_content requires `url`; verified live on llm-model-tester).
`required` is ANDed with everything else in a schema, so no property
declaration could rescue it. It now becomes an alternation: either the
upstream's requirements (a fresh call) or `_resultId` (a re-read, which is
answered from cache and never reaches the upstream). Validators that
understand anyOf enforce that; naive ones that only read top-level
`required` now find none and accept both. Schemas that already carry a
combinator get the alternation appended to `allOf`, and a schema with no
required params is left untouched.
Covered by unit tests on a required-bearing upstream schema plus a smoke
assertion that no advertised tool keeps a drill-down-blocking `required`.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JQr5Z9gYrqBQXTGBBuemZ2
