feat(sdk): add Effect HttpApi codegen

Author: kitlangton

bun.lock

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+# @opencode-ai/httpapi-codegen
+
+Build-time source generation for domain-oriented Effect APIs derived from `HttpApi` and Effect Schema contracts.
+
+The package is private while its API is explored. Its tests are the executable specification for the generator. It must remain independent of OpenCode Core and use synthetic `HttpApi` fixtures.
+
+## Settled rules
+
+- Flatten path, query, header, and payload fields into one input object.
+- Reject duplicate field names across input channels.
+- Emit no method argument for zero fields, an optional object when every field is optional, and a required object when any field is required.
+- Unwrap exact `{ data: A }` success envelopes.
+- Map no-content success to `void`.
+- Preserve other single success values.
+- Reject ambiguous multiple-success contracts.
+- Expose streaming success as `Stream`, not `Effect<Stream>`.
+- Reject schemas whose wire/domain transformation cannot be generated exactly.
+- Map transport, unexpected-status, and response-decoding failures to one stable generated `ClientError`.
+- Generate only the Effect API initially; Promise runtime ownership, cancellation, and stream adaptation are deferred.
+- Commit generated source for review; CI regenerates and fails when the worktree changes.
+- Track generated files in `.httpapi-codegen.json` so regeneration removes only stale files previously owned by the generator.
+
+## Boundary
+
+This package generates only the remote API derived from `HttpApi`. It does not generate embedded implementations or embedded-only capabilities. The OpenCode integration composes two distinct total objects:
+
+- A remote object containing the generated HTTP capabilities.
+- An embedded object implementing the shared shape against local services and adding embedded-only capabilities.
+
+The embedded object may be a structural superset of the remote object, but the constructors and concrete result types remain distinct.
+
+Codegen generates every endpoint in the `HttpApi` it receives. OpenCode owns the product decision by composing the exact remote API before invoking the generator; the generic package has no endpoint filtering policy.
+
+The public `generate(Api, { directory })` operation is an Effect requiring `FileSystem`. Internally it composes a pure `compile(Api)` phase with `write(output, directory)`. Compiler tests inspect virtual files directly; writer tests use `FileSystem.makeNoop`.
+
+Generation formats TypeScript with Prettier before writing. Output paths are flat, unique, and checked against traversal, reserved manifest names, and existing symbolic links.
+
+Generated source starts with one self-contained module per `HttpApiGroup`, plus root client and index modules. Schema dependencies may be duplicated across group modules. Cross-group schema partitioning is deferred until measured output or bundle cost requires it.
+
+Codegen preserves group and endpoint identifiers exactly. The composed remote `HttpApi` owns public names such as `session` and `get`; the generator performs no prefix stripping, casing conversion, or public-name annotation mapping.

packages/httpapi-codegen/README.md

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+{
+  "$schema": "https://json.schemastore.org/package.json",
+  "name": "@opencode-ai/httpapi-codegen",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "test": "bun test --timeout 5000 --only-failures",
+    "typecheck": "tsgo --noEmit"
+  },
+  "dependencies": {
+    "effect": "catalog:",
+    "prettier": "3.6.2"
+  },
+  "devDependencies": {
+    "@tsconfig/bun": "catalog:",
+    "@types/bun": "catalog:",
+    "@typescript/native-preview": "catalog:"
+  }
+}