Duplicate JSON object keys found in raw text, before a parser drops them

Overview

Scans raw JSON text (RFC 8259) for repeated object member names at any depth, including inside arrays and keys spelled differently but equal after unescaping ("a" vs "\u0061"), and reports each with its JSON pointer, UTF-8 byte offset, line, column and the value every occurrence carried, plus whether the values conflict. Also reports a leading BOM, unpaired surrogates, __proto__ keys and the exact syntax error offset. For agents that must inspect JSON before JSON.parse, json.

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