Add Octopus AI code review workflow

[redoh]

Summary

Adds a GitHub Actions workflow that runs Octopus, a free, open-source AI code review tool, on pull requests. Octopus indexes the codebase and posts context-aware inline review comments with severity levels. It is free and unlimited for public OSI-licensed repositories, with no API key required.

This is a follow-up to #23143 (opened by @nirs, then closed because Octopus could not post reviews — GITHUB_TOKEN is read-only on pull requests from forks).

What changed since #23143

The earlier attempt used the pull_request event, where GitHub restricts GITHUB_TOKEN to read-only for fork PRs, so the action could not post comments and failed silently. This PR resolves that:

• Uses pull_request_target, which gives the token the pull-requests: write access needed to post reviews on fork PRs.
• This is safe here because the Octopus action only reads the PR diff through the GitHub API — it never checks out or runs PR code, so no untrusted fork code executes in the privileged context. (The action also now emits a clear log message instead of failing silently if it ever lacks write access.)
• The action is pinned to a full commit SHA.
• Guarded with if: github.repository == 'kubernetes/minikube' so it does not run on forks of this repo.

Notes

• Only the workflow file is added; the flaky-test skips from Add Octopus AI code review for pull requests #23143 are intentionally left out so this PR stays focused.
• Docs, including the fork-PR security rationale: https://octopus-review.ai/docs/github-action#fork-pull-requests
• Source: https://github.com/octopusreview/octopus

Happy to adjust the trigger, permissions, or scoping to match maintainer preferences.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: redoh / name: Ferit (8ff6877)

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[minikube-bot]

Can one of the admins verify this patch?

[nirs]

@redoh Thanks for following up. I know that this can work with pull_request_target, but I'm not happy to run 3rd party code with write access in the context of pull_request_target.

What I need is a way to review pull requests with fine grain permissions allowing the reviewer to add comments. Anything else should be blocked by the system so I don't need to trust the review provider.

Ideally the reviewer will have operate as a GitHub account - any GitHub user can review minikube PRs, no special permissions are needed.

[nirs]

What is allowed by this?

[redoh]

@nirs you were right, and thanks for pushing on this. Two things you pointed out can't be solved within the Actions model:

1. GitHub Actions / GITHUB_TOKEN has no permission finer than pull-requests: write, so a workflow can't be restricted to "comment-only" — that scope also allows editing/closing PRs, labels, assignees, etc.
2. pull_request_target would mean running our (third-party) action with a writable token, which requires trusting us. Refusing that is reasonable.

So we're building the model you actually described, the reviewer operating as a plain GitHub account:

• The repo adds a zero-permission workflow (permissions: {}) that holds no token and only notifies our server which PR to review. No pull_request_target, no secrets, no third-party code running with write access in your CI.
• Our server fetches the diff and posts the review as a dedicated GitHub user account (octopus-review-bot). Because that account is not a collaborator here, GitHub itself blocks everything except submitting review comments — system-enforced comment-only, exactly what you asked for. It cannot set checks/statuses, label, or merge.
• Abuse/spam safeguards: a repo is reviewed only if we've manually approved it and it carries a maintainer-added .github/octopus.yml opt-in file (delete the file to stop, anytime).

It's actively in progress (not shipped yet):

• Server: feat(oss): server-side bot-account review mode (trigger-only, comment-only) octopusreview/octopus#536
• Action (trigger mode): feat: add trigger mode (no permissions, server posts as bot account) octopusreview/action#2

Once it's live I'll update this PR to that model. Does this approach address your concerns? Happy to adjust before we finalize.

[nirs]

So we're building the model you actually described, the reviewer operating as a plain GitHub account:

• The repo adds a zero-permission workflow (permissions: {}) that holds no token and only notifies our server which PR to review. No pull_request_target, no secrets, no third-party code running with write access in your CI.
• Our server fetches the diff and posts the review as a dedicated GitHub user account (octopus-review-bot). Because that account is not a collaborator here, GitHub itself blocks everything except submitting review comments — system-enforced comment-only, exactly what you asked for. It cannot set checks/statuses, label, or merge.

Sounds good for public projects.

• Abuse/spam safeguards: a repo is reviewed only if we've manually approved it and it carries a maintainer-added .github/octopus.yml opt-in file (delete the file to stop, anytime).

You read .github/octopus.yml from a branch in the repo, not from the PR?

Minikube does not use release branches but many projects use them and reviewing backports to release branch is very useful.

• Action (trigger mode): feat: add trigger mode (no permissions, server posts as bot account) octopusreview/action#2

If you run this in pull_request event, an attacker can trigger a review on octopus side by modifying a workflow or adding a new workflow. This should be fine if you check .github/octopus.yml` from the main branch so an attacker cannot control it.

Let's move this discussion to https://github.com/octopusreview/.