feat(core): flatten provider config and load native packages (#35563)

Co-authored-by: Dax Raad <d@ironbay.co>

packages/schema/test/contract-hygiene.test.ts

@@ -4,6 +4,7 @@ import { Agent } from "../src/agent.js"
 import { FileSystem } from "../src/filesystem.js"
 import { Model } from "../src/model.js"
 import { Project } from "../src/project.js"
+import { Provider } from "../src/provider.js"
 import { Pty } from "../src/pty.js"
 import { Question } from "../src/question.js"
 import { Session } from "../src/session.js"
@@ -18,6 +19,19 @@ describe("contract hygiene", () => {
     expect(Schema.encodeSync(Value)({ value: undefined })).toEqual({})
   })
 
+  test("model defaults and provider overlays preserve public invariants", () => {
+    const id = Model.ID.make("model")
+    expect(Model.Info.empty(Provider.ID.make("provider"), id)).toMatchObject({ modelID: id, variants: [] })
+    expect(() =>
+      Schema.decodeUnknownSync(Provider.Info)({
+        id: "provider",
+        name: "Provider",
+        package: "native",
+        settings: { invalid: 1n },
+      }),
+    ).toThrow()
+  })
+
   test("todo status and priority preserve arbitrary strings", () => {
     const decode = Schema.decodeUnknownSync(SessionTodo.Info)
     expect(decode({ content: "ship", status: "waiting", priority: "urgent" })).toEqual({
@@ -39,7 +53,7 @@ describe("contract hygiene", () => {
       Model.Ref,
       Model.Capabilities,
       Model.Cost,
-      Model.Api,
+      Model.Variant,
       Project.Current,
       Project.Directory,
       Project.DirectoriesInput,