feat(core): honor default session models (#30982)

packages/core/test/config/config.test.ts

@@ -52,6 +52,20 @@ const provider = {
 }
 
 describe("Config", () => {
+  it.effect("returns the latest defined scalar from priority-ordered documents", () =>
+    Effect.sync(() => {
+      const entries = [
+        new Config.Document({ type: "document", info: new Config.Info({ model: "openrouter/openai/gpt-5" }) }),
+        new Config.Directory({ type: "directory", path: AbsolutePath.make("/skills") }),
+        new Config.Document({ type: "document", info: new Config.Info({}) }),
+        new Config.Document({ type: "document", info: new Config.Info({ model: "openrouter/openai/gpt-5.5" }) }),
+      ]
+
+      expect(Config.latest(entries, "model")).toBe("openrouter/openai/gpt-5.5")
+      expect(Config.latest(entries, "default_agent")).toBeUndefined()
+    }),
+  )
+
   it.effect("detects v1 configuration from any v1-only top-level key", () =>
     Effect.sync(() => {
       expect(ConfigMigrateV1.isV1({ snapshot: false })).toBe(true)

packages/core/test/config/provider.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect } from "bun:test"
-import { Effect, Schema } from "effect"
+import { Effect, Option, Schema } from "effect"
 import { Catalog } from "@opencode-ai/core/catalog"
 import { Config } from "@opencode-ai/core/config"
 import { ConfigProviderPlugin } from "@opencode-ai/core/config/plugin/provider"
@@ -30,6 +30,7 @@ describe("ConfigProviderPlugin.Plugin", () => {
             new Config.Document({
               type: "document",
               info: decode({
+                model: "custom/first",
                 providers: {
                   custom: {
                     name: "Configured",
@@ -59,11 +60,15 @@ describe("ConfigProviderPlugin.Plugin", () => {
             new Config.Document({
               type: "document",
               info: decode({
+                model: "custom/default",
                 providers: {
                   custom: {
                     api: { type: "aisdk", package: "custom-sdk", url: "https://example.test" },
                     request: request({ last: "last", shared: "last" }),
                     models: {
+                      default: {
+                        name: "Default",
+                      },
                       chat: {
                         api: { id: "api-chat" },
                         name: "Last",
@@ -106,6 +111,7 @@ describe("ConfigProviderPlugin.Plugin", () => {
 
       const provider = yield* catalog.provider.get(providerID)
       const model = yield* catalog.model.get(providerID, modelID)
+      expect(Option.getOrUndefined(yield* catalog.model.default())?.id).toBe(ModelV2.ID.make("default"))
       expect(provider.name).toBe("Renamed")
       expect(provider.env).toEqual(["CUSTOM_API_KEY"])
       expect(provider.enabled).toEqual({ via: "custom", data: {} })

packages/core/test/session-create.test.ts

@@ -337,14 +337,50 @@ describe("SessionV2.create", () => {
       expect(yield* unavailable(session.shell({ sessionID: created.id, command: "pwd" }))).toBe("shell")
       expect(yield* unavailable(session.skill({ sessionID: created.id, skill: "review" }))).toBe("skill")
       expect(yield* unavailable(session.switchAgent({ sessionID: created.id, agent: "build" }))).toBe("switchAgent")
+    }),
+  )
+
+  it.effect("switches the selected model through the durable Session event", () =>
+    Effect.gen(function* () {
+      const session = yield* SessionV2.Service
+      const created = yield* session.create({ location })
+      const model = ModelV2.Ref.make({
+        id: ModelV2.ID.make("sonnet"),
+        providerID: ProviderV2.ID.anthropic,
+        variant: ModelV2.VariantID.make("high"),
+      })
+
+      yield* session.switchModel({ sessionID: created.id, model })
+
+      expect(yield* session.get(created.id)).toMatchObject({ model })
       expect(
-        yield* unavailable(
-          session.switchModel({
-            sessionID: created.id,
+        Array.from(yield* session.events({ sessionID: created.id }).pipe(Stream.take(1), Stream.runCollect)),
+      ).toMatchObject([{ event: { type: "session.next.model.switched", data: { model } } }])
+
+      yield* session.switchModel({ sessionID: created.id, model })
+      const { db } = yield* Database.Service
+      expect(
+        yield* db.select().from(EventTable).where(eq(EventTable.aggregate_id, created.id)).all().pipe(Effect.orDie),
+      ).toHaveLength(2)
+    }),
+  )
+
+  it.effect("rejects a model switch for a missing Session", () =>
+    Effect.gen(function* () {
+      const session = yield* SessionV2.Service
+      const missing = SessionV2.ID.make("ses_missing_model_switch")
+
+      expect(
+        yield* session
+          .switchModel({
+            sessionID: missing,
             model: ModelV2.Ref.make({ id: ModelV2.ID.make("sonnet"), providerID: ProviderV2.ID.anthropic }),
-          }),
-        ),
-      ).toBe("switchModel")
+          })
+          .pipe(
+            Effect.flip,
+            Effect.map((error) => error._tag),
+          ),
+      ).toBe("Session.NotFoundError")
     }),
   )
 })