[FEATURE]: tmux-based subagent spawning for observable parallel execution

[werkamsus]

Feature hasn't been suggested before.

• I have verified this feature I's about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem: Subagents run silently in-process. When running multiple parallel tasks, there's no way to observe them in real-time or debug a stuck agent.

Proposal: Optional tmux-based subagent spawning.

// opencode.json
{
  "subagent": {
    "spawn": "tmux"  // "inline" (default) | "tmux"
  }
}

When enabled, task tool invocations spawn in tmux panes/windows instead of inline:

• Watch multiple subagents work simultaneously in split panes
• Attach to a stuck subagent and intervene
• Sessions persist if main terminal disconnects
• Results still returned to parent via IPC (temp file, socket, etc.)

Why tmux: Battle-tested, already installed on most dev machines, handles pane layout automatically.

Open questions:

• Pane vs window per subagent?
• Layout strategy for 4+ parallel agents?
• Fallback behavior when tmux unavailable?

Happy to help prototype if there's interest.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Feature Request: Add tmux Support for Multi-Session Agent Testing #1247: Feature Request: Add tmux Support for Multi-Session Agent Testing - Proposes comprehensive tmux integration with similar goals of persistent sessions, parallel execution, and real-time monitoring
• [FEATURE]: Settings for queue execution order: sequential and parallel #6470: [FEATURE]: Settings for queue execution order: sequential and parallel - Related to managing parallel execution of multiple agents

Feel free to ignore if none of these address your specific case.