[ya-luotao]

Fixes #177

bin/rails claude_agent_sdk:install_cli failed in every Rails app with Encoding::UndefinedConversionError. Http.download_to opened the download with File::BINARY, which is 0 outside Windows, so the file was in text mode. Rails sets Encoding.default_internal to UTF-8, and every write then transcoded the binary chunks, raising on the first byte that is not valid UTF-8. The same thing happens outside Rails whenever default_internal is set.

The file is now opened with binmode: true, which also covers what File::BINARY did on Windows.

The two other installer IO paths don't need changing: Metadata.write writes ASCII only, and Metadata.read uses File.read(path, limit), which returns a binary string. Checked with external US-ASCII / internal UTF-8 (a common Docker locale), including a VERSION file containing non-UTF-8 bytes, which still gets a clean reinstall.

Tests

• New example in spec/unit/cli_installer_spec.rb: with default_internal set to UTF-8, download_to writes non-UTF-8 bytes unchanged. It fails on main and passes here.
• spec/unit/cli_installer*_spec.rb: 138 examples, 0 failures. RuboCop: no offenses.

🤖 Generated with Claude Code

https://claude.ai/code/session_016wuLhHzFb7oEoM5Qw39CBj

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[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-27T08:08:39.975364Z	d9af541	Manual request
🔒 Security Review	✅ Completed 2026-10-27T08:09:05.092464Z	d9af541	Manual request

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Reviewed commit: d9af541b0f

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