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Fix: _meta missing clientCapabilities is rejected (-32602 or -32600)

Web-audit fix skill for the mcp-modern-clientcaps check (MCP, SHOULD).

Goal

Enforce the mandatory clientCapabilities key on every modern request.

Fix

Reject a modern request whose params._meta omits io.modelcontextprotocol/clientCapabilities with a well-formed error envelope. The check accepts two codes: -32602 (Invalid params, the SDK-typed refusal) as the primary, and -32600 (Invalid Request family) from conforming non-SDK servers. The key is mandatory on every 2026-07-28 request even when the client has no capabilities to declare; an empty object is valid.

Resources

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Verify

Re-run the audit at https://anc.dev/audit or call the audit_website MCP tool; the mcp-modern-clientcaps check should report pass.