[BUG] Bash mode does not execute commands in Bash #2902

Environment

• Platform (select one):
  • Anthropic API
  • AWS Bedrock
  • Google Vertex AI
  • Other:
• Claude CLI version: 1.0.41 (Claude Code)
• Operating System: macOS 15.5
• Terminal: fish shell with iTem 2

Bug Description

The ! command trigger in Claude Code always uses /bin/zsh for command execution, even though:

1. The user's shell is fish (or bash);
2. Claude Code was launched from fish (or bash);
3. ! is called "Bash mode" in the shortcuts.

Steps to Reproduce

1. Set fish (or bash) as the default shell: chsh -s /opt/homebrew/bin/fish
2. Launch Claude Code from fish (or bash): claude
3. Use any ! command, e.g., !echo $SHELL or !echo $0
4. Observe that the output is /bin/zsh and commands are executed in zsh.

p.s. The same occurs with the Bash tool.

Expected Behavior

The ! command should execute commands in either Bash as it claims or the shell from which Claude Code was launched.

Actual Behavior

• Commands are always executed using /bin/zsh
• The SHELL environment variable is set to /bin/zsh within Claude Code
• Shell-specific features and configurations from fish are not available

Additional Context

• As mentioned in Documentation for Bash Mode #2358, I think we need better documentation for Bash mode behaviors.