Anthropic MCP tools fail when input schema uses root-level anyOf/oneOf/allOf

Bug description

Anthropic rejects a tool input_schema that uses anyOf/oneOf/allOf at the root level — these combinators are only accepted nested inside properties. MCP servers commonly emit "exactly one of these fields" patterns (e.g. anyOf: [{required:["route"]}, {required:["file"]}]) as root-level combinators, which then fail Anthropic validation and take the whole tool down with a 400.

OpenCode has an existing OpenAI sanitizer (#32489) but nothing equivalent for the Anthropic family.

Steps to reproduce

1. Expose an MCP tool whose input_schema contains a root-level anyOf/oneOf/allOf (e.g. the schema in #35516 used anyOf: [{required:["route"]},{required:["file"]}]).
2. Use it with an Anthropic model (or Copilot proxying Claude, or Vertex Anthropic).

Expected behavior

Tool continues to work; the schema is folded into the root object so Anthropic accepts it.

Actual behavior

The request fails with an Anthropic validation error and the tool is unusable.

Fix

fix(opencode): sanitize MCP tool schemas for Anthropic root combinators (#47542) adds a targeted sanitizer that folds root-level combinators into the root object schema while preserving nested content verbatim.