Feature request: Use zsh (or login shell) for Bash tool on macOS

macOS ships bash 3.2.57 (2007) due to GPLv3 licensing, and Apple will never update it — they switched the default shell to zsh back in Catalina (2019). The Bash tool currently hardcodes bash, which means on macOS you're stuck with a 19-year-old shell that lacks features like associative arrays (declare -A), mapfile, readarray, and other bash 4+ additions.

Since virtually every macOS user's login shell is zsh, it would make sense for the Bash tool to either:

1. Use the user's configured login shell (from $SHELL or /etc/passwd), or
2. At minimum, default to zsh on macOS

Related issues: #40653 (Bash tool ignores login shell), #31437 (bash 3.2 runtime issues)

This issue was raised with AI assistance (Claude Code).