thirdshift

A factory that turns a GitHub issue into a ready-for-review pull request by running unattended agent sessions against it. The humans are the day shift; the agents work the third shift, overnight, on any server, while you do something else.

Quality over quantity: a pull request marked ready for review is one the factory stands behind. When it can't stand behind the work, the Run is a Failed run: the work is pushed so nothing is lost, and the pull request goes back to a draft.

Terms in bold are defined in CONTEXT.md.

What a Run does

From a clone of the issue's repository, thirdshift <Issue URL>:

1. Checks that the Run makes sense, before creating anything:

   • the Origin match: the Issue URL must belong to the same GitHub repository as the origin remote of the directory you run it from;
   • the issue is open;
   • the Base branch is well defined: HEAD is not detached, the branch exists on origin, and your local copy is not ahead of it, so unpushed commits can't leak into the pull request;
   • a local Issue branch, if you have one, points at the same commit as its copy on origin, so local-only commits are never destroyed.

   Any failed check stops the Run before any work happens.

2. Picks the Issue branch (issue-<n>, or issue-<n>-branch-<k> once earlier ones are finished) and the Base branch, normally the branch you have checked out.

3. Creates a git worktree next to your clone, named <repo>-<Issue branch>, so your own checkout is never touched.

4. Runs a headless Claude Code session in that worktree with the Factory skills loaded. The agent implements the issue, reviews its work against the Base branch, addresses the Standards findings and Spec findings it agrees with, and opens a ready-for-review pull request that lists every Unaddressed finding with a reason and closes the issue.

5. Takes over deterministically: pushes the Issue branch, checks through gh that the pull request exists, is open and targets the Base branch, and marks it ready for review (gh pr ready) if the agent left it as a draft.

6. Keeps the pull request mergeable and green: merges the Base branch in and watches CI, starting a Repair session for a merge conflict or failing checks, at most 3 per Run.

7. Cleans up: removes the worktree, the local Issue branch and the temporary plugin directory, whether the Run succeeded or not.

Status

The designed behaviour described in this README is implemented. Known gaps and planned work are tracked in the open issues.

Install

curl -LsSf https://github.com/JacobStephens2/thirdshift/releases/latest/download/thirdshift-installer.sh | sh

The shell installer and the binary both come from this repository's GitHub Releases. It puts thirdshift in ~/.local/bin, where Claude Code's installer puts claude, and needs no Rust toolchain. thirdshift is a single binary with the Factory skills compiled in, so it runs without a checkout of this repository (ADR-0001, ADR-0003).

If you use Rust, you can install it from crates.io instead:

cargo install thirdshift

Updating

thirdshift update

It replaces the installed binary with the latest stable GitHub Release, or says it is already on it. Messages go to stderr and stdout stays empty. It exits 0 when it updated or was already up to date, and 1 on any failure, such as no network. Updating is safe while a Run is using the old binary, and a Run never checks for updates or updates itself.

thirdshift update only replaces a copy put in place by the shell installer (the curl command above), which leaves an install receipt in ~/.config/thirdshift/. It refuses to touch any other copy and lists the command that updates each other kind of install: cargo install thirdshift for a crates.io install, pulling and reinstalling for a build from source (see Building from source), and the curl command for a copy placed by hand.

Keep a single copy: with copies in more than one directory on your PATH (say ~/.local/bin and ~/.cargo/bin), you can end up running a stale one without noticing. type -a thirdshift lists every copy on your PATH.

Supported platforms

• Rocky Linux 9.8 and later, x86_64.
• Ubuntu 24.04.3 and later, x86_64.
• WSL2, latest release, with Ubuntu 24.04 or later, x86_64. Keep your repositories on the Linux filesystem (e.g. ~/repos), not under /mnt/c, where git is slow and file permissions misbehave. WSL1 is not supported.
• macOS Tahoe 26.5.2 and later, Apple Silicon.

One statically linked Linux binary covers the first three, so it doesn't depend on the host's glibc; macOS gets a native build.

Prerequisites

The user account that runs thirdshift needs:

• claude (Claude Code), logged in.
• gh (GitHub CLI), logged in.
• git with a global user.name and user.email, and credentials that can push to the repository (gh auth setup-git makes git use gh's login). The agents commit as this identity; without it, an agent may borrow the author of the last commit.

Auto mode

Sessions run headless in Claude Code's auto mode (claude -p --permission-mode auto), with the full permissions of that user account, including sudo if the user has it. Nobody is there to approve anything; instead, auto mode's classifier checks each action and may block ones it judges risky, such as destructive commands or actions outside the task. A blocked action the agent can't work around can end the Run as a Failed run.

What sessions leave behind

Cleanup removes only thirdshift's own worktree, local Issue branch and temporary plugin directory. Anything else an agent does as your user stays. For example, one Run downloaded a JDK to ~/.local/jdk/ because the server had no Java, installed Playwright in /tmp/pw, and left a pull request body draft in /tmp/. This is by design, but worth knowing:

• Install the target repository's toolchains up front (language runtimes, package managers, test tools), so the agents don't download their own on every Run.
• For UI work, install the headless browser dependencies, e.g. libgbm1 on Ubuntu server, which headless Chromium needs. Without it, agents can't take screenshots to check a UI change and fall back to reading the code.

Usage and cost

When claude is logged in with a claude.ai subscription, Runs use the plan's usage allowance, not API billing. The total_cost_usd in the session logs is the API-price equivalent, not a charge. An unattended Run that hits the plan's usage limit stalls or fails partway through.

Usage

cd ~/repos/widgets          # a clone of the issue's repository, on the Base branch
thirdshift https://github.com/acme/widgets/issues/7

A Run takes minutes to tens of minutes.

• stdout carries only the pull request's URL: on success, and on a Failed run that leaves a draft pull request. The exit code tells the two apart, so script it as url=$(thirdshift "$issue") && echo "ready: $url".
• stderr carries everything else: errors, cleanup problems, and progress lines while sessions run. A successful Run's last line names the pull request too.
• Exit code 0 means the Run ended with a pull request the factory stands behind. 2 means the argument is missing or isn't a GitHub Issue URL; the error and the help text go to stderr. Any other failure exits 1.

The other commands:

thirdshift update    # update to the latest release (see Updating)
thirdshift version   # print thirdshift <version>
thirdshift help      # print every form of the command, each with a one-line description

version and help print to stdout and exit 0. update follows the Run's rule: stdout stays empty, messages go to stderr.

Uncommitted changes in your clone are fine: the Run works in its own worktree from origin, so they are simply left out. Unpushed commits on the Base branch are not: push them first, or the Run stops.

Logs

Each session's full transcript, as Claude Code's stream-json output, is written to its own file under ~/.thirdshift/logs/ (created if missing):

~/.thirdshift/logs/<owner>-<repo>-issue-<n>-<timestamp>-implement.jsonl
~/.thirdshift/logs/<owner>-<repo>-issue-<n>-<timestamp>-repair-<i>.jsonl

All sessions in a Run share the Run's UTC timestamp, so a Run's logs sort together. When a Run fails, stderr ends with the path of its most recent session log, the place to start looking.

Continuation

Running thirdshift again on an issue picks up where the last Run stopped (ADR-0002). It looks at the highest-numbered Issue branch:

• No Issue branch yet: a fresh Run creates issue-<n> from the Base branch.
• The branch exists with no pull request, or an open one: the Run is a Continuation. It checks out that branch, and the agent builds on its commits instead of starting over, then creates the pull request or updates the open one. With an open pull request, that pull request's base is the Base branch, whatever you have checked out.
• The branch's pull request was merged or closed: finished work is never reopened. The Run starts fresh on the next number, issue-<n>-branch-2, -3, and so on. A number counts as used even if GitHub deleted the branch after merging.

So you can retry a Failed run with the same command, or start an issue on one server and continue it on another.

A Run is not idempotent: re-running builds on whatever is already on the branch, including a Failed run's work-in-progress commit.

Failed runs

A Failed run is one that ends, including by Ctrl-C or a closed terminal, without an open pull request from its Issue branch that targets the Base branch, is mergeable and has passing CI. Causes include the session exiting non-zero, no pull request or one with the wrong base, and running out of Repairs.

A Failed run:

1. Commits any uncommitted work as thirdshift: failed run (<reason>), with a timestamp and the hostname, and pushes the Issue branch, so nothing is lost. If the branch has no changes against the Base branch, nothing is pushed.
2. Converts its open pull request, if any, back to a draft, so a pull request only claims to be ready when the factory stands behind it. The next successful Continuation marks it ready again.
3. Cleans up as usual, prints the reason to stderr and exits non-zero.

Merges, never rebases or force-pushes: a branch worked on from several servers never loses history.

Building from source

Building needs the Rust toolchain. From a clone of this repository:

cargo install --path .

cargo install puts the binary in ~/.cargo/bin. To update it, pull and reinstall:

git checkout main && git pull
cargo install --path .

To install it system-wide instead, build it and copy it into place:

cargo build --release
sudo install -m 755 target/release/thirdshift /usr/local/bin/thirdshift

Editing a skill in skills/ has no effect until you rebuild and reinstall (ADR-0001).

Running the test suite (cargo test) also needs python3 on PATH: the integration tests swap in fake gh and claude, which are Python scripts in tests/fakes/.

Releasing

1. Bump version in Cargo.toml (and Cargo.lock) in a pull request.
2. Merge it.
3. Push a v<version> tag on the merge commit, e.g. git tag v0.2.0 && git push origin v0.2.0.

The tag starts the release workflow, generated by dist from dist-workspace.toml. It builds the Linux and macOS binaries and the installer, checks that the Linux binary starts on Rocky Linux 9 and in WSL2 with Ubuntu 24.04, and only then publishes the GitHub Release. It then publishes the same version to crates.io, skipping it if it is already there, and finally replaces the Release's body with notes generated from the merged pull requests.

Credits and license

thirdshift is released under the MIT License.

The Factory skills in skills/ are adapted from Matt Pocock's mattpocock/skills, changed to run headless with no human in the loop. They are used under the MIT License; its copyright notice is kept in skills/LICENSE and is embedded in the binary and written out with the skills on every Run. The pr skill also reproduces part of Dex Horthy's show-me skill; see skills/pr/CREDITS.md.