deepseek-harness-plugin-from-scratch

Most plugin tutorials stop at how to fill in the API surface, but what actually determines whether a plugin works reliably inside a live Harness is the boundary discipline: injecting required dependencies, attaching every registration to a revocable effect, splitting replaceable capabilities into the Definition / Provider / Consumer triangle, guaranteeing that everything model-visible can be reconstructed verbatim from the Session log, and testing the real assembly path rather than mocks. This repository distills six core principles from a full upstream code audit and ships a fully installable, runnable, line-by-line readable TypeScript plugin as a reference implementation, answering not how to write apply() but how a plugin achieves correct dependency wiring, verifiable configuration, and swappable services inside a real composition root.

Five interactive chapters-minimal tool, lifecycle and effects, the capability triangle, events and persistence, testing and release-carry 51 checkpoints that reveal each line of code evolution in lockstep with the prose, with a right-hand repository snapshot that only grows and ultimately equals the chapter's canonical source. Accompanying automated scripts cover packaging, profile installation, config-layer verification, and an end-to-end greet invocation, so a green unit-test suite no longer masquerades as a working plugin.

Whether you are building or reviewing DeepSeek Harness plugins, want to internalize the plugin-service-event-Session collaboration model, or need a delivery checklist and a 17-item anti-pattern list you can paste straight into a PR description, this repository serves as both a runnable reference implementation and an audit trail where every conclusion is backed by upstream source-code evidence.