Fix JSONL Surrogates

Repairs Claude Code JSONL chat files that contain lone Unicode surrogates (U+D800-U+DFFF), which cause the Anthropic API to reject requests with "invalid high surrogate in string".

Background

Node.js internally uses UTF-16 strings. JSON.stringify() doesn't validate surrogate pairs, so lone surrogates from file reads, terminal output, or web content can end up serialized as \uD8xx without a matching low surrogate — producing invalid JSON that the API rejects.

Common triggers on Windows:

• Emoji in code comments or terminal output
• Box-drawing characters from build logs
• Web content with malformed UTF-16 encoding

Upstream issue: anthropics/claude-code#44230

How to Use