Terminal gaps for AI agent orchestration workflows (scriptability, output read-back, session persistence)

Been looking at the AI coding agent orchestration space — tools like [oh-my-claudecode](https://github.com/Yeachan-Heo/oh-my-claudecode), [oh-my-codex](https://github.com/Yeachan-Heo/oh-my-codex), [gajae-code](https://github.com/Yeachan-Heo/gajae-code). These are multi-agent orchestrators that spin up parallel agent sessions, coordinate between them, and monitor output. Every single one of them requires tmux and builds on top of it rather than VS Code terminal.

We actually already have a lot of the building blocks — `workbench.action.terminal.new` with `{ cwd }`, `split`, `renameWithArg`, `Terminal.sendText()`, `changeColor`/`changeIcon`, task `presentation.group` for split layouts. The "launch and manage" side is solid.

What's missing is the other half — reading back, controlling from outside, and surviving a window close:

**1. Output read-back** — extensions can `sendText()` into a terminal but can't read what it printed. tmux has `capture-pane -p`. Without this, an orchestrator can't check if an agent session finished, errored, or is waiting for input. Shell integration's command detection helps for structured commands but most agent CLIs are freeform output.

**2. External terminal control** — tmux lets any script do `tmux send-keys -t session:pane "command" Enter`. We don't have a `code --send-terminal ` equivalent. If you want to control a named terminal from a Python script or shell script outside VS Code, you need a running extension or the task system. Something like the existing `code --goto` / `code --diff` pattern but for terminal.

**3. Persistent/detachable terminals** — closing VS Code kills all terminal processes. tmux sessions survive disconnect. For long-running agent sessions (overnight runs, etc.), there's no way to close the editor and come back to running terminals. Could be opt-in per terminal rather than all-or-nothing.

Related issues: #90696 (tmux control mode, has 20 comments going back to 2019), #320044 (remote session persistence)

Not saying we need to replace tmux — lots of people prefer it and will keep using it. But users already inside VS Code shouldn't have to leave to an external multiplexer for these workflows, and extension authors should be able to build orchestration tools natively.