Practical notes for an eventual migration of `packages/opencode` server routes from the current Hono handlers to Effect `HttpApi`, either as a full replacement or as a parallel surface.
## Goal
Use Effect `HttpApi` where it gives us a better typed contract for:
- route definition
- request decoding and validation
- typed success and error responses
- OpenAPI generation
- handler composition inside Effect
This should be treated as a later-stage HTTP boundary migration, not a prerequisite for ongoing service, route-handler, or schema work.
## Core model
`HttpApi` is definition-first.
-`HttpApi` is the root API
-`HttpApiGroup` groups related endpoints
-`HttpApiEndpoint` defines a single route and its request / response schemas
- handlers are implemented separately from the contract
This is a better fit once route inputs and outputs are already moving toward Effect Schema-first models.
## Why it is relevant here
The current route-effectification work is already pushing handlers toward:
- one `AppRuntime.runPromise(Effect.gen(...))` body
- yielding services from context
- using typed Effect errors instead of Promise wrappers
That work is a good prerequisite for `HttpApi`. Once the handler body is already a composed Effect, the remaining migration is mostly about replacing the Hono route declaration and validator layer.
## What HttpApi gives us
### Contracts
Request params, query, payload, success payloads, and typed error payloads are declared in one place using Effect Schema.
### Validation and decoding
Incoming data is decoded through Effect Schema instead of hand-maintained Zod validators per route.
### OpenAPI
`HttpApi` can derive OpenAPI from the API definition, which overlaps with the current `describeRoute(...)` and `resolver(...)` pattern.
### Typed errors
`Schema.TaggedErrorClass` maps naturally to endpoint error contracts.
## Likely fit for opencode
Best fit first:
- JSON request / response endpoints
- route groups that already mostly delegate into services
- endpoints whose request and response models can be defined with Effect Schema
Harder / later fit:
- SSE endpoints
- websocket endpoints
- streaming handlers
- routes with heavy Hono-specific middleware assumptions
## Current blockers and gaps
### Schema split
Many route boundaries still use Zod-first validators. That does not block all experimentation, but full `HttpApi` adoption is easier after the domain and boundary types are more consistently Schema-first with `.zod` compatibility only where needed.
### Mixed handler styles
Many current `server/instance/*.ts` handlers still call async facades directly. Migrating those to composed `Effect.gen(...)` handlers is the low-risk step to do first.
### Non-JSON routes
The server currently includes SSE, websocket, and streaming-style endpoints. Those should not be the first `HttpApi` targets.
### Existing Hono integration
The current server composition, middleware, and docs flow are Hono-centered today. That suggests a parallel or incremental adoption plan is safer than a flag day rewrite.
## Recommended strategy
### 1. Finish the prerequisites first
- continue route-handler effectification in `server/instance/*.ts`
- continue schema migration toward Effect Schema-first DTOs and errors
- keep removing service facades
### 2. Start with one parallel group
Introduce one small `HttpApi` group for plain JSON endpoints only. Good initial candidates are the least stateful endpoints in:
-`server/instance/question.ts`
-`server/instance/provider.ts`
-`server/instance/permission.ts`
Avoid `session.ts`, SSE, websocket, and TUI-facing routes first.
Do not re-architect business logic during the HTTP migration. `HttpApi` handlers should call the same Effect services already used by the Hono handlers.
The `HttpApi` implementation lives under `src/server/instance/httpapi/` as a standalone Effect HTTP server. It is **not mounted into the Hono app**. There is no `toWebHandler` bridge, no Hono `Handler` export, and no `.route()` call wiring it into `experimental.ts`.
The standalone server (`httpapi/server.ts`) can be started independently and proves the routes work. Tests exercise it via `HttpRouter.serve` with `NodeHttpServer.layerTest`.
The goal is to build enough route coverage in the Effect server that the Hono server can eventually be replaced entirely. Until then, the two implementations exist side by side but are completely separate processes.
If the parallel slice works well, migrate additional JSON route groups one at a time. Leave streaming-style endpoints on Hono until there is a clear reason to move them.
Every `HttpApi` slice should follow `specs/effect/schema.md` and the Schema -> Zod interop rule in `specs/effect/migration.md`.
Default rule:
- Effect Schema owns the type
-`.zod` exists only as a compatibility surface
- do not introduce a new hand-written Zod schema for a type that is already migrating to Effect Schema
Practical implication for `HttpApi` migration:
- if a route boundary already depends on a shared DTO, ID, input, output, or tagged error, migrate that model to Effect Schema first or in the same change
- if an existing Hono route or tool still needs Zod, derive it with `@/util/effect-zod`
- avoid maintaining parallel Zod and Effect definitions for the same request or response type
Ordering for a route-group migration:
1. move implicated shared `schema.ts` leaf types to Effect Schema first
3. move tagged route-facing errors to `Schema.TaggedErrorClass` where needed
4. switch existing Zod boundary validators to derived `.zod`
5. define the `HttpApi` contract from the canonical Effect schemas
Temporary exception:
- it is acceptable to keep a route-local Zod schema for the first spike only when the type is boundary-local and migrating it would create unrelated churn
- if that happens, leave a short note so the type does not become a permanent second source of truth
## First vertical slice
The first `HttpApi` spike should be intentionally small and repeatable.
Chosen slice:
- group: `question`
- endpoints: `GET /question` and `POST /question/:requestID/reply`
Non-goals:
- no `session` routes
- no SSE or websocket routes
- no auth redesign
- no broad service refactor
Behavior rule:
- preserve current runtime behavior first
- treat semantic changes such as introducing new `404` behavior as a separate follow-up unless they are required to make the contract honest
Add `POST /question/:requestID/reject` only after the first two endpoints work cleanly.
## Repeatable slice template
Use the same sequence for each route group.
1. Pick one JSON-only route group that already mostly delegates into services.
2. Identify the shared DTOs, IDs, and errors implicated by that slice.
3. Apply the schema migration ordering above so those types are Effect Schema-first.
4. Define the `HttpApi` contract separately from the handlers.
5. Implement handlers by yielding the existing service from context.
6. Mount the new surface in parallel under an experimental prefix.
7. Add one end-to-end test and one OpenAPI-focused test.
8. Compare ergonomics before migrating the next endpoint.
Rule of thumb:
- migrate one route group at a time
- migrate one or two endpoints first, not the whole file
- keep business logic in the existing service
- keep the first spike easy to delete if the experiment is not worth continuing
## Example structure
Placement rule:
- keep `HttpApi` code under `src/server`, not `src/effect`
-`src/effect` should stay focused on runtimes, layers, instance state, and shared Effect plumbing
- place each `HttpApi` slice next to the HTTP boundary it serves
- for instance-scoped routes, prefer `src/server/instance/httpapi/*`
- if control-plane routes ever migrate, prefer `src/server/control/httpapi/*`
- the standalone server resolves instance context via an `HttpRouter.middleware` that reads `x-opencode-directory` headers and `directory` query params
- this is the Effect equivalent of the Hono `WorkspaceRouterMiddleware`
-`HttpApi` handlers yield services from context and assume the correct instance has already been provided
- request decoding and response shapes are schema-defined from canonical Effect schemas
- any remaining Zod boundary usage is derived from `.zod` or clearly temporary
- OpenAPI is generated from the `HttpApi` contract
- the tests are straightforward enough that the next slice feels mechanical
## Learnings from the question slice
The first parallel `question` spike gave us a concrete pattern to reuse.
-`Schema.Class` works well for route DTOs such as `Question.Request`, `Question.Info`, and `Question.Reply`.
- scalar or collection schemas such as `Question.Answer` should stay as schemas and use helpers like `withStatics(...)` instead of being forced into classes.
- if an `HttpApi` success schema uses `Schema.Class`, the handler or underlying service needs to return real schema instances rather than plain objects.
- internal event payloads can stay anonymous when we want to avoid adding extra named OpenAPI component churn for non-route shapes.
- [ ] decide after the spike whether `HttpApi` should stay parallel, replace only some groups, or become the long-term default
## Rule of thumb
Do not start with the hardest route file.
If `HttpApi` is adopted here, it should arrive after the handler body is already Effect-native and after the relevant request / response models have moved to Effect Schema.
