fix(core): respect v2 default agents (#30969)

packages/core/src/agent.ts

@@ -44,11 +44,13 @@ export class Info extends Schema.Class<Info>("AgentV2.Info")({
 
 type Data = {
   agents: Map<ID, Info>
+  default?: ID
 }
 
 export type Editor = {
   list: () => readonly Info[]
   get: (id: ID) => Info | undefined
+  default: (id: ID | undefined) => void
   update: (id: ID, fn: (agent: Draft<Info>) => void) => void
   remove: (id: ID) => void
 }
@@ -57,6 +59,8 @@ export interface Interface {
   readonly transform: State.Interface<Data, Editor>["transform"]
   readonly update: (update: State.Transform<Editor>) => Effect.Effect<void, never, Scope.Scope>
   readonly get: (id: ID) => Effect.Effect<Info | undefined>
+  readonly default: () => Effect.Effect<Info | undefined>
+  readonly resolve: (id?: ID | string) => Effect.Effect<Info | undefined>
   readonly all: () => Effect.Effect<Info[]>
 }
 
@@ -72,6 +76,9 @@ export const layer = Layer.effect(
       editor: (draft) => ({
         list: () => Array.fromIterable(draft.agents.values()) as Info[],
         get: (id) => draft.agents.get(id),
+        default: (id) => {
+          draft.default = id
+        },
         update: (id, fn) => {
           const current = draft.agents.get(id) ?? castDraft(Info.empty(id))
           if (!draft.agents.has(id)) draft.agents.set(id, current)
@@ -83,6 +90,19 @@ export const layer = Layer.effect(
         },
       }),
     })
+    const selectable = (agent: Info | undefined) =>
+      agent && agent.mode !== "subagent" && !agent.hidden ? agent : undefined
+    const selectedDefault = () => {
+      const data = state.get()
+      const configured = data.default ? selectable(data.agents.get(data.default)) : undefined
+      if (configured) return configured
+      const build = selectable(data.agents.get(ID.make("build")))
+      if (build) return build
+      for (const agent of data.agents.values()) {
+        const fallback = selectable(agent)
+        if (fallback) return fallback
+      }
+    }
 
     return Service.of({
       transform: state.transform,
@@ -93,6 +113,13 @@ export const layer = Layer.effect(
       get: Effect.fn("AgentV2.get")(function* (id) {
         return state.get().agents.get(id)
       }),
+      default: Effect.fn("AgentV2.default")(function* () {
+        return selectedDefault()
+      }),
+      resolve: Effect.fn("AgentV2.resolve")(function* (id) {
+        if (id !== undefined) return state.get().agents.get(ID.make(id))
+        return selectedDefault()
+      }),
       all: Effect.fn("AgentV2.all")(function* () {
         return Array.fromIterable(state.get().agents.values())
       }),

packages/core/src/config.ts

@@ -35,6 +35,9 @@ export class Info extends Schema.Class<Info>("Config.Info")({
   model: Schema.String.pipe(Schema.optional).annotate({
     description: "Default model to use when no session or agent model is selected",
   }),
+  default_agent: Schema.String.pipe(Schema.optional).annotate({
+    description: "Default primary agent to use when no session agent is selected",
+  }),
   autoupdate: Schema.Union([Schema.Boolean, Schema.Literal("notify")])
     .pipe(Schema.optional)
     .annotate({
@@ -130,6 +133,9 @@ export const layer = Layer.effect(
     const location = yield* Location.Service
     const policy = yield* Policy.Service
     const names = ["config.json", "opencode.json", "opencode.jsonc"]
+    const decodeOptions = { errors: "all", onExcessProperty: "ignore", propertyOrder: "original" } as const
+    const decodeInfo = Schema.decodeUnknownOption(Info, decodeOptions)
+    const decodeV1Info = Schema.decodeUnknownOption(ConfigV1.Info, decodeOptions)
 
     const loadFile = Effect.fnUntraced(function* (filepath: string) {
       const text = yield* fs.readFileStringSafe(filepath)
@@ -139,21 +145,10 @@ export const layer = Layer.effect(
       const input: unknown = parse(text, errors, { allowTrailingComma: true })
       if (errors.length) return
 
-      const decoded = ConfigMigrateV1.isV1(input)
-        ? Option.map(
-            Schema.decodeUnknownOption(ConfigV1.Info)(input, {
-              errors: "all",
-              onExcessProperty: "ignore",
-              propertyOrder: "original",
-            }),
-            ConfigMigrateV1.migrate,
-          )
-        : Option.some(input)
       const info = Option.getOrUndefined(
-        Option.flatMap(
-          decoded,
-          Schema.decodeUnknownOption(Info, { errors: "all", onExcessProperty: "ignore", propertyOrder: "original" }),
-        ),
+        ConfigMigrateV1.isV1(input)
+          ? decodeV1Info(input).pipe(Option.map(ConfigMigrateV1.migrate), Option.flatMap(decodeInfo))
+          : decodeInfo(input),
       )
       if (!info) return
       return new Document({ type: "document", path: filepath, info })

packages/core/src/config/plugin/agent.ts

@@ -58,6 +58,8 @@ export const Plugin = PluginV2.define({
 
     yield* agent.update((editor) => {
       const global = documents.flatMap((document) => document.info.permissions ?? [])
+      const configuredDefault = documents.findLast((document) => document.info.default_agent !== undefined)?.info.default_agent
+      if (configuredDefault !== undefined) editor.default(AgentV2.ID.make(configuredDefault))
       for (const current of editor.list()) {
         editor.update(current.id, (agent) => agent.permissions.push(...global))
       }

packages/core/src/permission.ts

@@ -16,6 +16,7 @@ export { Effect, Rule, Ruleset } from "./permission/schema"
 type Effect = PermissionSchema.Effect
 type Rule = PermissionSchema.Rule
 type Ruleset = PermissionSchema.Ruleset
+const missingAgentPermissions: Ruleset = [{ action: "*", resource: "*", effect: "deny" }]
 
 export const ID = Schema.String.check(Schema.isStartsWith("per")).pipe(
   Schema.brand("PermissionV2.ID"),
@@ -161,7 +162,7 @@ export const layer = Layer.effect(
     const configured = EffectRuntime.fn("PermissionV2.configured")(function* (sessionID: SessionV2.ID) {
       const session = yield* sessions.get(sessionID)
       if (!session) return yield* new SessionV2.NotFoundError({ sessionID })
-      return (yield* agents.get(AgentV2.ID.make(session.agent ?? "build")))?.permissions ?? []
+      return (yield* agents.resolve(session.agent))?.permissions ?? missingAgentPermissions
     })
 
     function denied(input: AssertInput, rules: Ruleset) {

packages/core/src/plugin/agent.ts

@@ -9,6 +9,8 @@ import { PermissionV2 } from "../permission"
 import { PluginV2 } from "../plugin"
 
 const TRUNCATION_GLOB = path.join(Global.Path.data, "tool-output", "*")
+const BUILD_SYSTEM =
+  "You are an AI coding agent. Help the user accomplish software engineering tasks by inspecting the workspace, making targeted changes, and using tools according to the configured permissions."
 
 const PROMPT_EXPLORE = `You are a file search specialist. You excel at thoroughly navigating and exploring codebases.
 
@@ -123,6 +125,7 @@ export const Plugin = PluginV2.define({
     yield* agent.update((editor) => {
       editor.update(AgentV2.ID.make("build"), (item) => {
         item.description = "The default agent. Executes tools based on configured permissions."
+        item.system ??= BUILD_SYSTEM
         item.mode = "primary"
         item.permissions.push(
           ...PermissionV2.merge(defaults, [

packages/core/src/session/runner/llm.ts

@@ -16,6 +16,7 @@ import { SessionInput } from "../input"
 import { QuestionV2 } from "../../question"
 import { SystemContextRegistry } from "../../system-context-registry"
 import { SessionContextEpoch } from "../context-epoch"
+import { AgentV2 } from "../../agent"
 
 /**
  * Runs one durable coding-agent Session until it settles.
@@ -84,6 +85,7 @@ export const layer = Layer.effect(
   Effect.gen(function* () {
     const events = yield* EventV2.Service
     const llm = yield* LLMClient.Service
+    const agents = yield* AgentV2.Service
     const tools = yield* ToolRegistry.Service
     const models = yield* SessionRunnerModel.Service
     const store = yield* SessionStore.Service
@@ -134,6 +136,7 @@ export const layer = Layer.effect(
       const session = yield* getSession(sessionID)
       const initialized = yield* SessionContextEpoch.initialize(db, systemContext, session.id, session.location)
       const model = yield* models.resolve(session)
+      const agent = yield* agents.resolve(session.agent)
       const toolFibers = yield* FiberSet.make<void, never>()
       let needsContinuation = false
       if (promotion) {
@@ -149,13 +152,13 @@ export const layer = Layer.effect(
       const context = yield* store.runnerContext(session.id, system.baselineSeq)
       const request = LLM.request({
         model,
-        system: system.baseline.length > 0 ? [SystemPart.make(system.baseline)] : [],
+        system: [agent?.system, system.baseline].filter((part): part is string => part !== undefined && part.length > 0).map(SystemPart.make),
         messages: toLLMMessages(context, model),
         tools: yield* tools.definitions(),
       })
       const publisher = createLLMEventPublisher(events, {
         sessionID: session.id,
-        agent: session.agent ?? "build",
+        agent: agent?.id ?? "build",
         model: {
           id: ModelV2.ID.make(model.id),
           providerID: ProviderV2.ID.make(model.provider),

packages/core/src/v1/config/migrate.ts

@@ -18,7 +18,6 @@ const keys = new Set([
   "disabled_providers",
   "enabled_providers",
   "small_model",
-  "default_agent",
   "mode",
   "agent",
   "provider",
@@ -38,6 +37,7 @@ export function migrate(info: typeof ConfigV1.Info.Type) {
     $schema: info.$schema,
     shell: info.shell,
     model: info.model,
+    default_agent: info.default_agent,
     autoupdate: info.autoupdate,
     share: info.share ?? (info.autoshare ? "auto" : undefined),
     enterprise: info.enterprise,