FastMCP 4.1.0 with mcp 2.3.0: tools/call with arguments reportedly runs tools/list and list middleware

Finding: A reporter says that on fastmcp 4.1.0 with mcp 2.3.0, a 2026-07-28 Streamable HTTP tools/call carrying arguments runs a full FastMCP tools/list, including on_list_tools middleware and request logging (https://github.com/PrefectHQ/fastmcp/issues/5652). Reporter's analysis, not maintainer-confirmed: the SDK needs the tool's input schema to validate Mcp-Param headers. The reporter says python-sdk#3630, shipped in mcp 2.3.0, added an optional get_tool_input_schema keyword to the low-level Server. The reporter checked 4.1.0 and main at e2fcc4120 and says FastMCP does not pass it, so the SDK falls back to paging through tools/list. Reported design constraints for a real fix: the SDK hook is synchronous while FastMCP tool resolution is async; returning None disables validation for that call with no listing fallback, so a local-only hook could stop x-mcp-header validation for proxied or mounted tools; tool transforms may require the wire schema; and the hook needs mcp>=2.3 while fastmcp-slim allows mcp>=2.0.0. Mitigation (reporter-proposed, not verified by KFA): assigning a lambda returning None to server._mcp_server.get_tool_input_schema avoids the listing, but only when no tool declares x-mcp-header, because it disables that validation. Status: the issue is open. The supplied snapshot shows no maintainer response and no linked FastMCP fix or release; comments are partial, so maintainer and fix status are UNKNOWN. KFA did not reproduce this.