Extends the existing _normalize_tool_input_schema to also drop top-level
union keywords that Anthropic's tool schema validator rejects with HTTP 400.
Several upstream and plugin tools ship schemas with a top-level oneOf/
allOf/anyOf (common for Pydantic discriminated unions). The existing
strip_nullable_unions pass only handles anyOf-with-null patterns; a
non-null top-level union keyword sails through and hits the API.
Salvage of #16471 — approach folded into the existing normalize helper
rather than introducing a parallel _sanitize_input_schema function, to
avoid two schema-munging code paths running against the same input.
Co-authored-by: Grey0202 <grey0202@users.noreply.github.com>
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