Crabline is a deterministic local messaging-channel mocking framework for end-to-end testing of chat integrations. It provides a CLI tool and a TypeScript library that simulates 12+ messaging platforms (Discord, Slack, Telegram, WhatsApp, Matrix, etc.) via mock servers and provider adapters. The architecture is built around a provider adapter pattern with lazy loading, a JSONL-based event recorder with cross-process locking, and a fixture-driven test runner that supports probe, send, roundtrip, and agent modes. The system is configuration-driven via YAML manifests validated with Zod schemas, and it publishes readiness artifacts for integration with the OpenClaw QA ecosystem. The codebase demonstrates strong engineering practices: clean separation of concerns, extensive test coverage (including concurrency and edge cases), and reusable infrastructure components such as process-owned file locks, nonce generation, inbound message matchers, and webhook authentication policies. The mock servers faithfully replicate platform-specific APIs (REST, WebSocket, SSE) with configurable resource limits and admin inbound endpoints for injecting test messages. While primarily a testing tool, Crabline's components are designed for reuse: the recorder, lock system, and provider adapter base class can be extracted into other projects. The repository is actively maintained with CI/CD pipelines, dependency management, and a changelog. It is not a data research project; all data artifacts (JSONL logs) are operational evidence for test assertions, not analytical datasets.