fix(core): validate public session model switches (#31012)

packages/core/src/public/opencode.ts

@@ -1,9 +1,11 @@
 export * as OpenCode from "./opencode"
 
 import { Context, Effect, Layer } from "effect"
+import { Catalog } from "../catalog"
 import { Database } from "../database/database"
 import { EventV2 } from "../event"
 import { LocationServiceMap } from "../location-layer"
+import { PluginBoot } from "../plugin/boot"
 import { ProjectV2 } from "../project"
 import { SessionV2 } from "../session"
 import * as SessionExecutionLocal from "../session/execution/local"
@@ -21,16 +23,61 @@ export interface Interface {
 /** Intentional public native API for Effect applications embedding OpenCode. */
 export class Service extends Context.Service<Service, Interface>()("@opencode/public/OpenCode") {}
 
-const SessionsLayer = SessionV2.layer.pipe(
-  Layer.provide(SessionProjector.layer),
-  Layer.provide(SessionExecutionLocal.layer),
-  Layer.provide(LocationServiceMap.layer),
-  Layer.provide(SessionStore.layer),
-  Layer.provide(EventV2.layer),
-  Layer.provide(Database.defaultLayer),
-  Layer.provide(ProjectV2.defaultLayer),
-  Layer.orDie,
+class SessionModelValidation extends Context.Service<
+  SessionModelValidation,
+  {
+    readonly validate: (
+      input: Session.SwitchModelInput & { readonly location: Session.Info["location"] },
+    ) => Effect.Effect<void, Session.ModelUnavailableError | Session.VariantUnavailableError>
+  }
+>()("@opencode/public/OpenCode/SessionModelValidation") {}
+
+const LocationServicesLayer = LocationServiceMap.layer
+const SessionModelValidationLayer = Layer.effect(
+  SessionModelValidation,
+  Effect.gen(function* () {
+    const locations = yield* LocationServiceMap
+    return SessionModelValidation.of({
+      validate: Effect.fn("OpenCode.sessions.validateModel")(function* (input) {
+        yield* Effect.gen(function* () {
+          yield* (yield* PluginBoot.Service).wait()
+          const catalog = yield* Catalog.Service
+          const model = (yield* catalog.model.available()).find(
+            (model) => model.providerID === input.model.providerID && model.id === input.model.id,
+          )
+          if (!model)
+            return yield* new Session.ModelUnavailableError({
+              providerID: input.model.providerID,
+              modelID: input.model.id,
+            })
+          if (
+            input.model.variant !== undefined &&
+            input.model.variant !== "default" &&
+            !model.variants.some((variant) => variant.id === input.model.variant)
+          )
+            return yield* new Session.VariantUnavailableError({
+              providerID: input.model.providerID,
+              modelID: input.model.id,
+              variant: input.model.variant,
+            })
+        }).pipe(Effect.provide(locations.get(input.location)))
+      }),
+    })
+  }),
 )
+
+const SessionsLayer = Layer.merge(
+  SessionV2.layer.pipe(
+    Layer.provide(SessionProjector.layer),
+    Layer.provide(SessionExecutionLocal.layer),
+    Layer.provide(SessionStore.layer),
+    Layer.provide(EventV2.layer),
+    Layer.provide(Database.defaultLayer),
+    Layer.provide(ProjectV2.defaultLayer),
+    Layer.orDie,
+  ),
+  SessionModelValidationLayer,
+).pipe(Layer.provide(LocationServicesLayer))
 const ApplicationToolsLayer = ApplicationTools.layer
 
 // TODO: Accept explicit storage so tests and embeddings can select disposable or application-owned persistence.
@@ -39,6 +86,7 @@ export const layer = Layer.effect(
   Effect.gen(function* () {
     const sessions = yield* SessionV2.Service
     const tools = yield* ApplicationTools.Service
+    const validation = yield* SessionModelValidation
     return Service.of({
       tools: { attach: tools.attach },
       sessions: {
@@ -51,7 +99,11 @@ export const layer = Layer.effect(
           }),
         get: sessions.get,
         list: sessions.list,
-        switchModel: sessions.switchModel,
+        switchModel: Effect.fn("OpenCode.sessions.switchModel")(function* (input) {
+          const session = yield* sessions.get(input.sessionID)
+          yield* validation.validate({ ...input, location: session.location })
+          yield* sessions.switchModel(input)
+        }),
         interrupt: sessions.interrupt,
         prompt: (input) =>
           sessions.prompt({