Overview

The examples use Authentication from Getting Started: the application’s request middleware.

A git host is six decisions: what serves HTTP and who may call it, where refs and objects live, how names resolve, where bulk bytes go, what verifies a push, and which refs may move. Each is a Layer, and you make them in one graph:

const GitLive = Git.ApiLive.pipe(
  Layer.provide(Git.ApiHandlersLive),
  Layer.provide(Authentication.layer),
  Layer.provide(Git.ReposDurableObject),
  Layer.provide(Git.RegistryDurableObject),
  Layer.provide(Git.HasherInline),
  Layer.provide(Git.BlobStoreR2(GitObjects)),
);

One graph, one Effect.provide. Build it with Layer.* and provide it once.

Two runtimes, one graph

A repository needs one place where a ref moves atomically. On Cloudflare that is a Durable Object, and the code that moves refs runs inside it. The graph does not know this. You write it once, the Worker builds its side of it at cold start, and each Durable Object builds its own on its first request:

                        GitLive
             ┌─────────────┴──────────────┐
         Worker                    Repo Durable Object
   wire, REST, GitHub facade      refs, objects, pull requests
   your middleware and policies         push commit, jobs
   BlobStore: clone bundles       BlobStore: packs, spilled pushes

Git.BlobStoreR2(GitObjects) appears once and serves both sides: the Worker streaming a clone bundle and the Durable Object writing a pack. Your middleware and application policies run in the Worker request. They can use the same user and database services.

The blocks

Block	Decides	Ships with
HTTP routes	the HTTP surface: every plane as one HttpApi of routes you can replace, behind your middleware	ApiHandlersLive, ApiLive, InternalApiLive
Repository	where refs and objects live, the jobs that keep a repository small	ReposDurableObject
Registry	how owner/name resolves, and listings	RegistryDurableObject, RegistryD1
Blob Store	where packs, bundles, and large pushes go	BlobStoreR2, BlobStoreS3
Hasher	what verifies a push, and on which compute	HasherInline, HasherWorkerLoader, HasherLambda
Engine	repository operations and scoped prepare/commit	EngineLive
Auth	application middleware and policy functions	native Effect HTTP middleware

Replacing a block

Every block is a Context.Service. Swap the Layer and nothing else in the graph knows:

const GitLive = Git.ApiLive.pipe(
  Layer.provide(Git.ApiHandlersLive),
  Layer.provide(Authentication.layer),
  Layer.provide(Git.ReposDurableObject),
  Layer.provide(Git.RegistryDurableObject),
  Layer.provide(Git.RegistryD1(RepoIndex)),
  Layer.provide(Git.HasherInline),
  Layer.provide(Git.BlobStoreR2(GitObjects)),
);

Leave one out and the Worker does not compile. The graph still requires the service, and the compiler says which:

const GitLive = Git.ApiLive.pipe(
  Layer.provide(Git.ApiHandlersLive),
  Layer.provide(Authentication.layer),
  Layer.provide(Git.ReposDurableObject),
  Layer.provide(Git.RegistryDurableObject),
  Layer.provide(Git.HasherInline),
);
// Layer<Server, never, BlobStore>
//                      ^ still required; providing it to the Worker is a type error

Writing your own is implementing the contract. Each block’s page shows it, and the shape is always the same:

const BlobStoreMine = Layer.effect(
  Git.BlobStore,
  Effect.gen(function* () {
    // return a Git.BlobStoreShape
  }),
);

Where next

• HTTP routes — the three planes as one HttpApi, and replacing a route.
• Recipes — which lines change for which requirements.