Add Gemini subagent management system via tmux

[dandye]

Summary

This PR introduces a comprehensive subagent management system for Gemini CLI, enabling parallel execution of multiple Gemini instances through tmux session orchestration.

Features

Core Commands

• spawn: Create new Gemini subagents in detached tmux sessions with configurable models and initial prompts
• send: Send messages to running subagents with intelligent handling for:
  • Regular text prompts (uses literal mode to prevent shell interpretation)
  • Shell commands (prefixed with !, executed immediately)
  • Slash commands (/help, /model, etc.)
• get-output: Retrieve subagent output with configurable line limits or full history
• list: View all active subagent sessions in simple or detailed format
• kill: Cleanly terminate subagent sessions
• attach: Provides instructions for interactive session attachment
• status: Debug and monitor subagent health and activity

Advanced Commands

• spawn-split: Create subagents in split panes for side-by-side operation
• broadcast: Send messages to multiple subagents simultaneously

Technical Implementation

• Uses tmux sessions to maintain persistent Gemini instances that survive main process exits
• Starts bash shell first, then launches Gemini to ensure session stability
• Implements 5-second initialization delay to accommodate Gemini startup sequence (banner, MCP loading, etc.)
• Intelligent message routing based on content prefix detection (! for commands, plain text for prompts)
• Uses tmux send-keys with -l flag for literal text to prevent unintended shell interpretation
• Handles Gemini's interactive input model (requires double Enter for prompt submission)

Use Cases

• Parallel research tasks with specialized agents
• Distributed analysis workflows
• Long-running background monitoring
• Multi-agent coordination for complex tasks
• Side-by-side comparison of different model outputs

Testing

All commands have been tested with:

• Basic prompt sending and response retrieval
• Shell command execution
• Multiple concurrent subagents
• Session persistence and cleanup

Example Usage

# Create a test subagent
/subagent spawn --name=test1 --prompt="Hello\! I am a test agent. Please tell me about yourself."

# Check its status
/subagent status --name=test1

# List all subagents
/subagent list

# Get the initial output
/subagent get-output --name=test1

# Send a follow-up message
/subagent send --name=test1 --message="What are your capabilities?"

# Wait a moment, then get output again
/subagent get-output --name=test1 --lines=30

# Send another message
/subagent send --name=test1 --message="Can you write a haiku about tmux?"

# Get all output
/subagent get-output --name=test1 --all=true

# Create a second subagent with a different model
/subagent spawn --name=test2 --prompt="You are a code reviewer. Say hello\!" --model=sonnet

# List all subagents with details
/subagent list --format=detailed

# Broadcast to both
/subagent broadcast --names="test1,test2" --message="What time is it?"

# Clean up
/subagent kill --name=test1
/subagent kill --name=test2

Manual tmux verification

# See all tmux sessions
tmux list-sessions

# Attach to view a subagent live
tmux attach-session -t test1

# Detach with Ctrl+B, then D