Branch Session

Branch the current Claude Code session into a new cmux split so two divergent threads can run side-by-side. The current pane keeps running the original session; the new pane resumes a clone of the transcript.

Prerequisites

Must run inside a cmux terminal (script checks CMUX_WORKSPACE_ID). cmux CLI must be on PATH.

Process

Run the worker script shipped with this plugin:

bash "${CLAUDE_PLUGIN_DIR}/scripts/branch.sh"

The script will:

1. Locate the current session transcript under ~/.claude/projects/<cwd>/<uuid>.jsonl (most-recently-modified .jsonl in the project dir).
2. Clone the transcript to a fresh UUID and rewrite the inner sessionId field on every line.
3. Open a new cmux pane below the current one (cmux new-pane --direction down).
4. Send claude --resume <new-uuid> into the new pane.

After the script returns, report the original and branched session IDs to the user.

Caveats

• Picks the most-recently modified .jsonl in the project dir as "the current session." If multiple concurrent Claude Code sessions write to the same project dir, the heuristic can pick the wrong one.
• The new pane's surface ref is parsed from cmux new-pane stdout. If the output format changes, the script falls back to sending to the focused surface (still correct because --focus true is set on the new pane).