Add Antigravity (agy) subagent management system via tmux

.agents/skills/subagent/SKILL.md

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+---
+name: subagent
+description: Use when running, coordinating, monitoring, or managing parallel Antigravity (agy) subagent tasks in detached tmux sessions or split panes
+---
+
+# Antigravity (agy) Subagent Manager
+
+Orchestrates multiple parallel Antigravity (`agy`) CLI instances using `tmux` sessions. Subagents persist across exits, run background tasks or independent research, and can be queried or controlled asynchronously.
+
+## Quick Reference
+
+| Command | Action | Key Flags / Usage |
+| :--- | :--- | :--- |
+| `spawn` | Launch new subagent session | `--name=<name> --prompt="<prompt>" [--model=<model>]` |
+| `spawn-split` | Launch subagent in split pane | `--name=<name> --prompt="<prompt>" [--vertical=true] [--size=50]` |
+| `send` | Send prompt or command to subagent | `--name=<name> --message="<msg>"` |
+| `get-output` | Retrieve output from subagent | `--name=<name> [--lines=50] [--all=true]` |
+| `status` | Check session health, PID, and output | `--name=<name>` |
+| `list` | List active subagent sessions | `[--format=detailed]` |
+| `broadcast` | Send message to multiple subagents | `--names="agent1,agent2" --message="<msg>"` |
+| `attach` | View interactive session | `tmux attach-session -t <name>` |
+| `kill` | Terminate subagent session | `--name=<name>` |
+
+---
+
+## Subcommand Workflows
+
+### 1. `spawn`
+Starts a detached tmux session running `bash`, launches `agy`, waits for initialization, and submits the initial prompt.
+
+```bash
+# 1. Create detached tmux session
+tmux new-session -d -s "<name>" bash
+
+# 2. Launch agy in session
+tmux send-keys -t "<name>" "agy" C-m
+
+# 3. Wait for agy startup sequence (banner, tips, model connection)
+sleep 5
+
+# 4. Submit prompt (agy submits on single Enter)
+tmux send-keys -t "<name>" -l "<prompt>"
+tmux send-keys -t "<name>" C-m
+
+# 5. Confirm session is alive
+tmux list-sessions | grep "<name>"
+```
+
+*(If `--model` is specified, launch `agy --model <model>`)*
+
+### 2. `spawn-split`
+Spawns a subagent inside a split pane in the current tmux window using non-interactive print mode (`agy -p`).
+
+```bash
+# Horizontal (default) or Vertical (-h) split
+tmux split-window -v -p 50 "agy -p '<prompt>'"
+
+# Tag pane for identification
+tmux select-pane -T "<name>"
+```
+
+### 3. `send`
+Sends a prompt, shell command, or slash command to a running subagent session.
+
+```bash
+# For shell commands starting with '!':
+tmux send-keys -t "<name>" "<command>" C-m
+
+# For regular text prompts or slash commands:
+tmux send-keys -t "<name>" -l "<message>"
+tmux send-keys -t "<name>" C-m
+```
+
+### 4. `get-output`
+Captures text lines from the target session's scrollback buffer.
+
+```bash
+# Last N lines (default 50):
+tmux capture-pane -t "<name>" -p -S -50
+
+# Entire available buffer:
+tmux capture-pane -t "<name>" -p -S -
+```
+
+### 5. `status`
+Inspects session existence, pane PID, running command, and recent output snippet.
+
+```bash
+# Verify session exists
+tmux has-session -t "<name>" 2>/dev/null && echo "✓ Session '<name>' exists" || echo "✗ Session '<name>' not found"
+
+# Show session details
+tmux list-sessions -F "#{session_name}: #{session_windows} windows, created #{session_created_string}" | grep "<name>"
+
+# Show running process & PID
+tmux list-panes -t "<name>" -F "Pane: #{pane_current_command} (PID: #{pane_pid})" 2>/dev/null
+
+# Capture last 10 lines
+tmux capture-pane -t "<name>" -p -S -10 2>/dev/null
+```
+
+### 6. `list`
+Lists active tmux sessions.
+
+```bash
+# Simple
+tmux list-sessions 2>/dev/null || echo "No active subagents"
+
+# Detailed
+tmux list-sessions -F "Session: #{session_name} | Created: #{session_created_string} | Windows: #{session_windows} | Attached: #{session_attached}" 2>/dev/null
+```
+
+### 7. `broadcast`
+Iterates over a comma-separated list of session names and sends the message to each.
+
+```bash
+for session in $(echo "<names>" | tr "," "\n"); do
+  tmux send-keys -t "$session" -l "<message>" 2>/dev/null && tmux send-keys -t "$session" C-m 2>/dev/null && echo "Sent to $session" || echo "Failed to send to $session"
+done
+```
+
+### 8. `attach`
+Attach to view and interact with the session directly in your terminal:
+
+```bash
+tmux attach-session -t "<name>"
+```
+> **Detach Shortcut**: Press `Ctrl+B`, then `D` to detach and return to your parent terminal.
+
+### 9. `kill`
+Terminates the specified tmux session.
+
+```bash
+tmux kill-session -t "<name>" && echo "Subagent '<name>' terminated"
+```
+
+---
+
+## Tips & Operational Notes
+- Subagents run as persistent processes; always terminate unused sessions with `kill` to release system resources.
+- In Antigravity CLI (`agy`), a single Enter (`C-m`) submits prompts. Do not send double Enter (`C-m C-m`).
+- Use `-l` with `tmux send-keys` when sending prompt text to prevent tmux from interpreting special characters or key bindings.