Gstack is a production-grade AI agent skill framework and headless browser automation toolchain designed for Claude Code, Codex, Cursor, and other coding agents. It provides a structured skill system (50+ slash-command skills like `/ship`, `/review`, `/plan-ceo-review`) with a resolver pipeline that generates per-host `SKILL.md` templates from TypeScript sources. The repo also contains a fully functional headless browser daemon (`browse/`) with anti-bot stealth, multi-layer prompt injection defense (canary tokens, ML classifiers, URL blocklist, envelope sentinel), CDP escape hatch, SOCKS5 proxy bridge, and secure file I/O. Additional subsystems include markdown-to-PDF generation (`make-pdf/`), iOS QA automation (`ios-qa/`), design mockup generation (`design/`), a secret redaction engine, and a cross-session knowledge base (gbrain). The codebase is unusually well-tested with extensive unit, integration, and periodic paid E2E tests against real LLM APIs. While primarily an application, it includes data pipeline components like telemetry aggregation, eval result stores, and a brain cache specification with TTL-based entities and calibration weights, making it a hybrid with strong data engineering discipline.