refactor(opencode): separate deferred MCP prompt

packages/opencode/src/session/mcp-tools.ts

@@ -43,16 +43,19 @@ export const DEFERRED_TOOL_SYSTEM_PROMPT = `Deferred tools are separate from dir
 - Use \`call_deferred_tool\` only with a \`tool_id\` copied from \`search_deferred_tools\` results.
 - Never use deferred tools for direct tools already listed in the current tool list, including shell, file, search, edit, web, task, LSP, question, or apply_patch tools.`
 
-interface Input {
+interface Input extends DeferredInput {
-  agent: Agent.Info
   model: Provider.Model
-  session: Session.Info
   processor: Pick<SessionProcessor.Handle, "message" | "updateToolCall" | "completeToolCall">
   bypassAgentCheck: boolean
-  messages: SessionV1.WithParts[]
   promptOps: TaskPromptOps
 }
 
+interface DeferredInput {
+  agent: Agent.Info
+  session: Session.Info
+  messages: SessionV1.WithParts[]
+}
+
 interface DeferredToolDescriptor {
   id: string
   description: string
@@ -60,11 +63,6 @@ interface DeferredToolDescriptor {
   searchText: string
 }
 
-interface Output {
-  tools: Record<string, Tool>
-  deferredSystemPrompt?: string
-}
-
 const SearchDeferredToolsParameters = Schema.Struct({
   query: Schema.String.annotate({
     description:
@@ -104,7 +102,6 @@ export const resolve = Effect.fn("SessionMcpTools.resolve")(function* (input: In
   const permission = yield* Permission.Service
   const mcp = yield* MCP.Service
   const truncate = yield* Truncate.Service
-  const flags = yield* RuntimeFlags.Service
 
   const context = (args: Record<string, unknown>, options: ToolExecutionOptions): Context => ({
     sessionID: input.session.id,
@@ -238,36 +235,20 @@ export const resolve = Effect.fn("SessionMcpTools.resolve")(function* (input: In
   if (hasMcpResourceServer) addResourceTools(tools, { input, run, mcp, plugin, truncate, context })
 
   const mcpTools = yield* mcp.tools()
-  const mcpDisabled = Permission.disabled(
+  const deferred = yield* deferredState(input, mcpTools)
-    Object.keys(mcpTools),
-    Permission.merge(input.agent.permission, input.session.permission ?? []),
-  )
-  const userTools = currentUserToolOverrides(input.messages)
-  const allowedMcpTools = Object.fromEntries(
-    Object.entries(mcpTools).filter(([key]) => userTools?.[key] !== false && !mcpDisabled.has(key)),
-  )
-  const deferredDescriptors =
-    flags.experimentalToolSearch && Object.keys(allowedMcpTools).length > 0
-      ? yield* deferredToolDescriptors(allowedMcpTools)
-      : []
-  const deferMcpTools =
-    deferredDescriptors.length > 0 && deferredToolSchemaTokens(deferredDescriptors) >= MIN_DEFERRED_MCP_SCHEMA_TOKENS
 
-  if (deferMcpTools) {
+  if (deferred) {
     addDeferredTools(tools, {
       input,
       run,
       plugin,
       truncate,
       context,
-      deferredDescriptors,
+      deferredDescriptors: deferred.descriptors,
-      allowedMcpTools,
+      allowedMcpTools: deferred.allowedMcpTools,
       executeMcpTool,
     })
-    return {
+    return tools
-      tools,
-      deferredSystemPrompt: deferredSystemPrompt(allowedMcpTools, clients),
-    } satisfies Output
   }
 
   for (const [key, item] of Object.entries(mcpTools)) {
@@ -281,9 +262,37 @@ export const resolve = Effect.fn("SessionMcpTools.resolve")(function* (input: In
     tools[key] = item
   }
 
-  return { tools } satisfies Output
+  return tools
 })
 
+export const systemPrompt = Effect.fn("SessionMcpTools.systemPrompt")(function* (input: DeferredInput) {
+  const mcp = yield* MCP.Service
+  const deferred = yield* deferredState(input, yield* mcp.tools())
+  if (!deferred) return undefined
+  return deferredSystemPrompt(deferred.allowedMcpTools, yield* mcp.clients())
+})
+
+function deferredState(input: DeferredInput, mcpTools: Record<string, Tool>) {
+  return Effect.gen(function* () {
+    const flags = yield* RuntimeFlags.Service
+    if (!flags.experimentalToolSearch) return undefined
+
+    const mcpDisabled = Permission.disabled(
+      Object.keys(mcpTools),
+      Permission.merge(input.agent.permission, input.session.permission ?? []),
+    )
+    const userTools = currentUserToolOverrides(input.messages)
+    const allowedMcpTools = Object.fromEntries(
+      Object.entries(mcpTools).filter(([key]) => userTools?.[key] !== false && !mcpDisabled.has(key)),
+    )
+    if (Object.keys(allowedMcpTools).length === 0) return undefined
+
+    const descriptors = yield* deferredToolDescriptors(allowedMcpTools)
+    if (deferredToolSchemaTokens(descriptors) < MIN_DEFERRED_MCP_SCHEMA_TOKENS) return undefined
+    return { allowedMcpTools, descriptors }
+  })
+}
+
 function deferredSystemPrompt(allowedMcpTools: Record<string, Tool>, clients: Record<string, unknown>) {
   const servers = deferredServerSummaries(Object.keys(allowedMcpTools), Object.keys(clients))
   return [

packages/opencode/src/session/prompt.ts

@@ -55,6 +55,7 @@ import { eq } from "drizzle-orm"
 import { SessionTable } from "@opencode-ai/core/session/sql"
 import { SessionReminders } from "./reminders"
 import { SessionTools } from "./tools"
+import { SessionMcpTools } from "./mcp-tools"
 import { LLMEvent } from "@opencode-ai/llm"
 
 // @ts-ignore
@@ -1223,7 +1224,7 @@ export const layer = Layer.effect(
             const bypassAgentCheck = lastUserMsg?.parts.some((p) => p.type === "agent") ?? false
             const promptOps = yield* ops()
 
-            const resolvedTools = yield* SessionTools.resolve({
+            const tools = yield* SessionTools.resolve({
               agent,
               session,
               model,
@@ -1239,7 +1240,6 @@ export const layer = Layer.effect(
               Effect.provideService(Truncate.Service, truncate),
               Effect.provideService(RuntimeFlags.Service, flags),
             )
-            const tools = resolvedTools.tools
 
             if (lastUser.format?.type === "json_schema") {
               tools["StructuredOutput"] = createStructuredOutputTool({
@@ -1260,7 +1260,10 @@ export const layer = Layer.effect(
               sys.environment(model),
               instruction.system().pipe(Effect.orDie),
               sys.mcp(agent, session.permission),
-              Effect.succeed(resolvedTools.deferredSystemPrompt),
+              SessionMcpTools.systemPrompt({ agent, session, messages: msgs }).pipe(
+                Effect.provideService(MCP.Service, mcp),
+                Effect.provideService(RuntimeFlags.Service, flags),
+              ),
               MessageV2.toModelMessagesEffect(msgs, model),
             ])
             const system = [

packages/opencode/src/session/tools.ts

@@ -108,12 +108,8 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
     })
   }
 
-  const mcp = yield* SessionMcpTools.resolve(input)
+  Object.assign(tools, yield* SessionMcpTools.resolve(input))
-  Object.assign(tools, mcp.tools)
+  return tools
-  return {
-    tools,
-    deferredSystemPrompt: mcp.deferredSystemPrompt,
-  }
 })
 
 export * as SessionTools from "./tools"

packages/opencode/test/session/tools.test.ts

@@ -11,6 +11,7 @@ import { MCP } from "@/mcp"
 import { Permission } from "@/permission"
 import { RuntimeFlags } from "@/effect/runtime-flags"
 import { SessionTools } from "@/session/tools"
+import { SessionMcpTools } from "@/session/mcp-tools"
 import { MessageID, SessionID } from "@/session/schema"
 import { Session } from "@/session/session"
 import { Plugin } from "@/plugin"
@@ -132,7 +133,7 @@ const belowThresholdIt = makeIt({
   queryDescription: "Natural language analytics query",
 })
 
-function resolveToolResult(input: { messages?: SessionV1.WithParts[] } = {}) {
+function resolveTools(input: { messages?: SessionV1.WithParts[] } = {}) {
   return SessionTools.resolve({
     agent,
     model,
@@ -144,10 +145,6 @@ function resolveToolResult(input: { messages?: SessionV1.WithParts[] } = {}) {
   })
 }
 
-function resolveTools(input: { messages?: SessionV1.WithParts[] } = {}) {
-  return resolveToolResult(input).pipe(Effect.map((result) => result.tools))
-}
-
 describe("session.tools", () => {
   deferredIt.instance("defers MCP tools behind fixed search and call tools", () =>
     Effect.gen(function* () {
@@ -184,7 +181,7 @@ describe("session.tools", () => {
 
   deferredIt.instance("lists deferred MCP servers in the system prompt", () =>
     Effect.gen(function* () {
-      const prompt = (yield* resolveToolResult()).deferredSystemPrompt
+      const prompt = yield* SessionMcpTools.systemPrompt({ agent, session, messages: [] })
 
       expect(prompt).toContain("Deferred MCP servers available through `search_deferred_tools`:")
       expect(prompt).toContain("- posthog: 2 tools")