feat(cli): added --force-interactive flag for non-TTY environments

[alexaustin007]

Summary

Fixes #13924

This PR adds the --force-interactive flag to allow Gemini CLI to run in interactive mode from non-TTY environments (Java, Node.js, backend services, IDE integrations).

Problem: CLI exits immediately when process.stdin.isTTY is false, preventing programmatic usage.
Solution: New flag overrides TTY detection and uses simple line-based I/O instead of full Ink UI.

Details

Implementation:

• Added --force-interactive CLI flag with yargs
• Created simpleInteractiveCli.ts for line-based I/O using Node.js readline
• Modified TTY detection to respect the flag via isInteractiveModeAllowed
• Added fork logic: Ink UI for real TTY, simple mode for non-TTY + flag

Key Features:

• Stays alive for multi-turn conversations
• Supports slash commands, @ commands, and tool execution
• Plain text output (no ANSI codes)
• Graceful EOF and signal handling

Related Issues

Fixes #13924

How to Validate

Test manually:

# Build first
npm run build

# Test with piped input
echo "hello" | node packages/cli/dist/index.js --force-interactive --prompt-interactive "test"

Expected output: "Gemini CLI ready (simple interactive mode)"

Node.js spawn test:
const { spawn } = require('child_process');
const cli = spawn('gemini', ['--force-interactive'], { stdio: ['pipe', 'pipe', 'pipe'] });
cli.stdin.write('hello\n');
// Should stay alive and respond

Pre-Merge Checklist

- Validated on required platforms/methods:
  - MacOS + npm run

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[gemini-code-assist]

Summary of Changes

Hello @alexaustin007, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the Gemini CLI's flexibility by introducing a --force-interactive flag. This flag enables the CLI to run in an interactive, line-based mode even when not connected to a traditional terminal (TTY), making it suitable for programmatic integration with other applications and services. This change resolves the issue of the CLI prematurely exiting in non-TTY environments when interactive behavior is desired, providing a robust solution for automated or embedded interactive workflows.

Highlights

• New --force-interactive flag: A new CLI flag, --force-interactive, has been introduced to enable interactive mode even when the standard input is not a TTY (terminal).
• Programmatic interactive usage: This feature allows the Gemini CLI to be used interactively from non-TTY environments such as Java, Node.js, backend services, and IDE integrations, addressing the issue of the CLI exiting prematurely in these scenarios.
• Simple line-based interactive mode: A new simpleInteractiveCli.ts file implements a line-based input/output interactive mode, which is used instead of the full Ink UI when --force-interactive is specified in a non-TTY environment.
• Enhanced interactive capabilities: The simple interactive mode supports multi-turn conversations, slash commands, @ commands, and tool execution, providing plain text output without ANSI codes.

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[gemini-code-assist]

Code Review

This pull request introduces a --force-interactive flag, a valuable feature for using the Gemini CLI in non-TTY environments. The implementation is solid, correctly forking logic between the full Ink UI and a new, simpler line-based interactive mode. The TTY checks and raw mode handling are correctly adjusted. I've found one high-severity issue in the new simple interactive mode where error messages from @ command processing are suppressed, providing a poor debugging experience for the user. My review includes a specific suggestion to fix this.