Fixes MCP server hanging when bd executable is not found at default path.
Problem:
- Config validation used sys.exit(1) on failure
- sys.exit() hangs in async MCP server context (doesn't properly terminate)
- Default bd path was hardcoded to ~/.local/bin/bd
Solution:
1. Use shutil.which() to find bd in PATH before falling back to default
2. Raise ConfigError instead of calling sys.exit()
3. MCP server now properly fails with error message instead of hanging
This fixes the multi-minute hang when trying to use MCP tools if bd is
installed in a non-default location (e.g., /usr/local/bin/bd).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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