Validate every x-mcp-header annotation in a tool inputSchema against the
draft constraints (server/tools #x-mcp-header): non-empty, HTTP token
syntax, no CR/LF, primitive-only (number forbidden), and case-insensitive
uniqueness across the whole schema. Returns a human-readable reason on the
first violation, or null when every annotation is valid. Recurses to any
nesting depth.
Validate every x-mcp-header annotation in a tool inputSchema against the draft constraints (server/tools #x-mcp-header): non-empty, HTTP token syntax, no CR/LF, primitive-only (number forbidden), and case-insensitive uniqueness across the whole schema. Returns a human-readable reason on the first violation, or null when every annotation is valid. Recurses to any nesting depth.