branch-out for Pi (pi-branch-out)

Fork the current Pi session into a split terminal pane or new tab with rotating layout policies, and with optional model and message queuing. Routing, split geometry, and focus behavior are all config-driven.

Install

pi install npm:pi-branch-out

From the dot314 git bundle (filtered install):

{
  "packages": [
    {
      "source": "git:github.com/w-winter/dot314",
      "extensions": ["extensions/branch-out/index.ts"],
      "skills": [],
      "themes": [],
      "prompts": []
    }
  ]
}

After installing, copy extensions/branch-out/config.json.example to extensions/branch-out/config.json and adjust to taste.

Command

/branch [--model <query>] [message]

Both arguments are optional and independent.

• --model <query> — target model for the child session. Accepts a fully qualified provider/model-id or a fuzzy query scoped to the current provider. If the query does not resolve safely the child keeps the parent's model.
• message — prefilled text in the child session's editor with a 10-second auto-submit countdown. Typing anything or pressing Esc cancels the countdown; Enter sends immediately.

Config

Config lives in extensions/branch-out/config.json next to the extension.

{
  "launchMode": "split",
  "splitDirection": "right",
  "preserveFocus": true
}

launchMode

| Value | Behavior | |-------|----------| | "split" | Open in a new split pane inside the current window (default) | | "tab" | Open in a new tab / surface |

splitDirection

Accepts a single value or a comma-separated fallback list. The first entry supported by the active backend is used; if none match, right is the final default.

"splitDirection": "counterclockwise,right"

This is useful when splitDirection is a rotating policy (unsupported by iTerm2). The fallback right kicks in automatically on that backend.

Static directions

| Value | Effect | |-------|--------| | "right" | Split to the right of the current pane | | "down" | Split below the current pane | | "left" | Split to the left of the current pane | | "up" | Split above the current pane |

Rotating layout policies (cmux and tmux only)

clockwise and counterclockwise are stateful layout policies. On the first /branch call the current pane is split in the policy's initial direction. On each subsequent call the policy picks the next queued managed leaf and splits it in that leaf's assigned direction, building a balanced recursive tree rather than a linear stack.

| Value | Pattern | |-------|--------| | "clockwise" | First split right → children split up/down → grandchildren split right/left → … | | "counterclockwise" | First split right → children split down/up → grandchildren split left/right → … |

State is persisted per backend and workspace key in /tmp/pi-branch-out-layout-state.json. Stale entries are pruned against live pane/surface lists on each call. To reset the policy entirely:

rm /tmp/pi-branch-out-layout-state.json

preserveFocus

| Value | Behavior | |-------|----------| | true | Focus stays in the pane that ran /branch (default) | | false | Focus moves to the newly created pane |

Terminal backend routing

Routing is automatic and tried in this order:

1. --branch-out-terminal flag override (always wins)
2. cmux — detected via CMUX_SOCKET_PATH
3. tmux — detected via TMUX
4. iTerm2 — detected via TERM_PROGRAM=iTerm.app
5. Terminal.app — detected via TERM_PROGRAM=Apple_Terminal
6. Ghostty — detected via GHOSTTY_RESOURCES_DIR or TERM_PROGRAM containing ghostty
7. Fallback Alacritty window

Backend capability matrix

| Backend | tab | split — static directions | split — rotating policies | |---------|-------|------------------------------|--------------------------| | cmux | ✓ | left right up down | clockwise counterclockwise | | tmux | ✓ | left right up down | clockwise counterclockwise | | iTerm2 | ✓ | right down | — (use fallback list) | | Terminal.app | ✓ | — (error) | — (error) | | Ghostty | — (new window) | — (error) | — (error) |

Backends that don't support the requested splitDirection fail fast with an explicit error rather than silently doing something else. Use a comma-separated fallback list in splitDirection to handle this gracefully (e.g. "counterclockwise,right" works on all split-capable backends).

Examples

/branch

Fork current session and open in a new pane/tab using config defaults.

/branch explore the auth edge cases

Fork with a queued message. The child session opens with "explore the auth edge cases" prefilled in the editor and a 10-second auto-submit countdown.

/branch --model flash

Fork using a fuzzy model query. If the current provider is Anthropic, flash would resolve to the closest Gemini Flash match available; if unresolvable the child keeps the parent's model.

/branch --model gemini/flash-2.5 try rewriting the parser without recursion

Fork with both a target model and a queued message.

Upstream credit

An earlier version of this extension began as an iteration on davidgasquez's branch-term.ts, MIT license.