[BUG] v2.1.117 postinstall on macOS arm64 produces `claude.exe` (wrong filename), breaks `claude` command

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

After installing @anthropic-ai/claude-code@2.1.117 via npm install -g, the binary in node_modules/@anthropic-ai/claude-code/bin/ is created as claude.exe instead of claude on macOS (Apple Silicon).

Because of the .exe extension, Node's launcher fails with:

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".exe" for /Users/<me>/.nvm/versions/node/vXX/lib/node_modules/@anthropic-ai/claude-code/bin/claude.exe
at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:219:9)
...

…and claude (the wrapper) just prints error: An unknown error occurred (Unexpected) with no further detail, even with --debug.

Confirmed via file:

claude.exe: Mach-O 64-bit executable arm64

So the binary content IS the correct macOS arm64 build — it just has the wrong filename/extension applied by the postinstall script (install.cjs) at v2.1.117.

What Should Happen?

Postinstall should create the platform-correct binary as claude (no extension) on macOS/Linux, and claude.exe only on Windows.

Error Messages/Logs

Steps to Reproduce

1. macOS Apple Silicon, Node v22.14.0 via nvm, npm 11.11.0
2. Run: npm install -g @anthropic-ai/claude-code (resolves to 2.1.117)
3. Run: claude --version
4. Observe: error: An unknown error occurred (Unexpected)
5. Run directly: node $(which claude) --version
6. Observe: ERR_UNKNOWN_FILE_EXTENSION ".exe"
7. Inspect: ls /path/to/node_modules/@anthropic-ai/claude-code/bin/ → only claude.exe exists, no claude

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.117

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

• OS: macOS (Darwin 25.2.0), Apple Silicon (arm64)
• Node: v22.14.0 (via nvm)
• npm: 11.11.0
• Claude Code: 2.1.117
• Install path: ~/.nvm/versions/node/v22.14.0/lib/node_modules/@anthropic-ai/claude-code/

Workaround: rename claude.exe → claude in the bin directory, OR install via the curl-based native installer (https://claude.ai/install.sh) which bypasses npm entirely.

Possible trigger: this was reproduced after installing the deprecated happy-coder npm package, which appears to invoke npm install -g @anthropic-ai/claude-code as part of its setup. But the bug is in claude-code's own install.cjs, not happy-coder.