Jujutsu (jj) workspaces for Claude Code worktrees

2026-09-11

The Claude Code desktop app gives every session its own git worktree under .claude/worktrees/. That works fine with git, but my repos are colocated jj+git repos, and inside a plain git worktree jj is dangerous: there is no .jj in the worktree, so jj walks up, finds the .jj of the main checkout and happily treats that as the workspace root.

$ cd .claude/worktrees/some-session
$ jj workspace root
/Users/okke/projects/homelab        # <- the main checkout, not the worktree

Every jj st, jj commit or jj new that Claude runs in “its” worktree snapshots and rewrites my real working copy. So much for isolation.

The fix: WorktreeCreate / WorktreeRemove hooks

Claude Code has WorktreeCreate and WorktreeRemove hooks that replace the built-in git worktree logic entirely. The docs only show them for SVN and friends, but they fire in git repos too, and the desktop app runs them as well (it even tells you to start a new session after you add one). The hook gets {"name": ..., "cwd": ...} on stdin and prints the directory to use.

The create hook is essentially one command: jj workspace add --colocate, which makes a jj child workspace and the matching git worktree in one go. Every jj command in there then moves the worktree’s git HEAD along, exactly like the main checkout.

Required versions: --colocate is not in a jj release yet (latest is 0.45.1). You need jj from the main branch, and git 2.42 or newer because jj uses git worktree add --orphan. On a Mac:

brew unlink jj          # if you have the stable one
brew install --HEAD jj  # builds from source, takes a few minutes
brew upgrade --fetch-HEAD jj   # later, to pull in newer commits

Put these in ~/.claude/hooks/:

jj-worktree-create.sh

#!/usr/bin/env bash
# WorktreeCreate hook: one jj child workspace per Claude Code session, colocated
# with a git worktree. Requires jj > 0.45.1 (`jj workspace add --colocate`) and git >= 2.42.
# Falls back to a plain git worktree when the repo is not a jj repo.
set -euo pipefail
IFS=$'\t' read -r NAME CWD < <(jq -r '[.name, .cwd] | @tsv')
[[ "$NAME" =~ ^[A-Za-z0-9._-]+$ ]] || { echo "bad worktree name: $NAME" >&2; exit 1; }
GITDIR=$(git -C "$CWD" rev-parse --path-format=absolute --git-common-dir)
ROOT=${GITDIR%/*}
DIR="$ROOT/.claude/worktrees/$NAME"
mkdir -p "${DIR%/*}"

if [ -d "$ROOT/.jj" ]; then
  jj -R "$ROOT" workspace add --colocate "$DIR" >&2
  # Branch name == worktree name: the desktop app records branch=<name> for hook-made worktrees.
  jj -R "$DIR" --ignore-working-copy bookmark create "$NAME" -r @- >&2
else
  git -C "$ROOT" worktree add --quiet --no-track -b "$NAME" "$DIR" HEAD >&2
fi

# Claude Code skips .worktreeinclude for hook-made worktrees, so apply it here with git's own matcher.
if [ -f "$ROOT/.worktreeinclude" ]; then
  git -C "$ROOT" ls-files -z --others --ignored --exclude-from="$ROOT/.worktreeinclude" |
    rsync -a --from0 --files-from=- "$ROOT/" "$DIR/" >&2
fi
echo "$DIR"

jj-worktree-remove.sh

#!/usr/bin/env bash
set -euo pipefail
DIR=$(jq -r .worktree_path)
[ -d "$DIR" ] || exit 0
GITDIR=$(git -C "$DIR" rev-parse --path-format=absolute --git-common-dir)
ROOT=${GITDIR%/*}
NAME=${DIR##*/}
cd "$ROOT"   # the hook may be started from inside the worktree we are about to delete
git -C "$ROOT" worktree remove --force "$DIR" >&2
if [ -d "$ROOT/.jj" ]; then
  jj -R "$ROOT" --ignore-working-copy workspace forget "$NAME" >&2
  jj -R "$ROOT" --ignore-working-copy bookmark delete "$NAME" >&2   # also deletes the git branch
else
  git -C "$ROOT" branch -D "$NAME" >&2
fi

And wire them up in ~/.claude/settings.json. Use the user settings, not the repo’s .claude/settings.json: the desktop app only auto-trusts hook-made worktrees when the hook comes from user settings, otherwise every new worktree shows a trust prompt.

{
  "hooks": {
    "WorktreeCreate": [{"hooks": [{"type": "command", "command": "bash \"$HOME/.claude/hooks/jj-worktree-create.sh\""}]}],
    "WorktreeRemove": [{"hooks": [{"type": "command", "command": "bash \"$HOME/.claude/hooks/jj-worktree-remove.sh\""}]}]
  }
}

This post was written by AI (Claude), based on a session in which it investigated and set this up for me.

Python3.6 on Macbook Pro M1

2021-12-10

Installing python 3.6 on an M1 machine is possible, but it’s not trivial. The trick is to use a x86-64 version of python and install all prerequisites using a brew running under x86 too.

The following steps worked for me.

Set up ‘ibrew’, or a x86 brew

Install the x86 homebrew version. All x86-64 packages are installed in /usr/local/, while ‘normal’ brew saves packages in /opt/homebrew/

arch -x86_64 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
echo "alias ibrew=\"arch -x86_64 /usr/local/bin/brew\"" >> ~/.zshrc

Install anaconda x86-64

ibrew install anaconda
/usr/local/anaconda3/bin/conda init zsh (make sure not to use any arm conda version)

Create python 3.6 x86-64 venv

conda create --name venv_py36 python=3.6
ibrew install libpq
export PKG_CONFIG_PATH="/usr/local/opt/libpq/lib/pkgconfig"
export LDFLAGS="-L/usr/local/opt/libpq/lib"
export CPPFLAGS="-I/usr/local/opt/libpq/include"
pip install psycopg2==2.8.6 --force-reinstall --no-cache-dir
ibrew install imagemagick freetype
pip install python-magic

Blackmagic on a bluepill

2020-06-30

To flash nrfmicro chips, you can use a bluepill with blackmagic installed.

The bluepill has some issues with wrong resistors (I had to change R3 on the bluepill from 100k to 10k ohm). The blackpill with stm32f103 processor does not have this problem, and is recommended. (Black Magic is not supported on blackpill 1.2 (stm32f401) or blackpill 2.0 (stm32f411) at this time.

There’s an excellent article on flashing blackmagic firmware onto a bluepill by joric. Here are some the steps I went through to make it work on ubuntu.

Connect the usb-to-uart converter to the bluemicro and set the bluemicro boot0 jumper to 1.

Find the usb port that the converter is attached to

> dmesg | grep tty
[157210.247340] cp210x ttyUSB0: cp210x converter now disconnected from ttyUSB0
[157221.140041] usb 1-2: cp210x converter now attached to ttyUSB0

Install the dfu. Run stm32loader.py on python2 with the pySerial package installed:

python2 stm32loader.py -p /dev/ttyUSB0 -ewv blackmagic_dfu.bin

Install the blackmagic firmware:

stm32flash -w blackmagic.bin /dev/ttyUSB0 -S 0x08002000

Set the jumper back to 0, disconnect the uart adapter, connect the bluepill to usb. Check if the blackmagic probe is recognized with lsusb.

Using a trackball as scrollwheel

2020-05-27

Tiny scrollwheel on mice have a few problems. They are small and the movement to scroll is prone to RSI. I’ve been using an Elecom HUGE trackball, and I love it. Except it doesn’t have a nice scroll ring as the Kensingtons have. Today I figured out how to turn the entire trackball into a huge scrollwheel by configuring libinput.

To try it out, run a few xinput commands.

xinput list and find the device id of your mouse. In my case it’s 14.
xinput set-prop 14 "libinput Scroll Method Enabled" 0, 0, 1 to enable ‘button scrolling’
xinput set-prop 14 "libinput Button Scrolling Button" 12 to use ‘Fn3’ on the Huge as the scroll trigger. If you want to use the ‘middle mouse button’, use 2 here.

If you like it, create the file /usr/share/X11/xorg.conf.d/60-huge.conf to make these settings persist between reboots.

Section "InputClass"
    Identifier  "ELECOM TrackBall Mouse HUGE TrackBall"
    Option  "ScrollMethod" "button"
    Option  "ScrollButton" "12"
EndSection