End-to-end playbook for shipping high-quality pull requests to open-source projects you don't maintain. Use whenever the user is creating, editing, or pushing a PR to a third-party GitHub repo — even if they just say "submit a PR", "open a PR", "fix this upstream", "rebase against main", "respond to the bot review", or names a target repo in the form `owner/repo`. Covers project discovery, CONTRIBUTING.md compliance, PR-size sanity check, minimal-diff implementation, isolated GUI E2E verification, PR description writing with AI-assisted disclosure, conflict resolution with fixup + autosquash, and post-submission bot/maintainer interaction. Also triggers on Chinese phrases like "提 PR"、"上游 PR"、"贡献代码"、"rebase 冲突"、"PR 描述写不好"、"回应维护者"、"AI 贡献声明".