feat: add plan mode with enter/exit tools (#8281)

packages/opencode/src/tool/plan-enter.txt

@@ -0,0 +1,14 @@
+Use this tool to suggest switching to plan agent when the user's request would benefit from planning before implementation.
+
+If they explicitly mention wanting to create a plan ALWAYS call this tool first.
+
+This tool will ask the user if they want to switch to plan agent.
+
+Call this tool when:
+- The user's request is complex and would benefit from planning first
+- You want to research and design before making changes
+- The task involves multiple files or significant architectural decisions
+
+Do NOT call this tool:
+- For simple, straightforward tasks
+- When the user explicitly wants immediate implementation

packages/opencode/src/tool/plan-exit.txt

@@ -0,0 +1,13 @@
+Use this tool when you have completed the planning phase and are ready to exit plan agent.
+
+This tool will ask the user if they want to switch to build agent to start implementing the plan.
+
+Call this tool:
+- After you have written a complete plan to the plan file
+- After you have clarified any questions with the user
+- When you are confident the plan is ready for implementation
+
+Do NOT call this tool:
+- Before you have created or finalized the plan
+- If you still have unanswered questions about the implementation
+- If the user has indicated they want to continue planning

packages/opencode/src/tool/plan.ts

@@ -0,0 +1,130 @@
+import z from "zod"
+import path from "path"
+import { Tool } from "./tool"
+import { Question } from "../question"
+import { Session } from "../session"
+import { MessageV2 } from "../session/message-v2"
+import { Identifier } from "../id/id"
+import { Provider } from "../provider/provider"
+import { Instance } from "../project/instance"
+import EXIT_DESCRIPTION from "./plan-exit.txt"
+import ENTER_DESCRIPTION from "./plan-enter.txt"
+
+async function getLastModel(sessionID: string) {
+  for await (const item of MessageV2.stream(sessionID)) {
+    if (item.info.role === "user" && item.info.model) return item.info.model
+  }
+  return Provider.defaultModel()
+}
+
+export const PlanExitTool = Tool.define("plan_exit", {
+  description: EXIT_DESCRIPTION,
+  parameters: z.object({}),
+  async execute(_params, ctx) {
+    const session = await Session.get(ctx.sessionID)
+    const plan = path.relative(Instance.worktree, Session.plan(session))
+    const answers = await Question.ask({
+      sessionID: ctx.sessionID,
+      questions: [
+        {
+          question: `Plan at ${plan} is complete. Would you like to switch to the build agent and start implementing?`,
+          header: "Build Agent",
+          custom: false,
+          options: [
+            { label: "Yes", description: "Switch to build agent and start implementing the plan" },
+            { label: "No", description: "Stay with plan agent to continue refining the plan" },
+          ],
+        },
+      ],
+      tool: ctx.callID ? { messageID: ctx.messageID, callID: ctx.callID } : undefined,
+    })
+
+    const answer = answers[0]?.[0]
+    if (answer === "No") throw new Question.RejectedError()
+
+    const model = await getLastModel(ctx.sessionID)
+
+    const userMsg: MessageV2.User = {
+      id: Identifier.ascending("message"),
+      sessionID: ctx.sessionID,
+      role: "user",
+      time: {
+        created: Date.now(),
+      },
+      agent: "build",
+      model,
+    }
+    await Session.updateMessage(userMsg)
+    await Session.updatePart({
+      id: Identifier.ascending("part"),
+      messageID: userMsg.id,
+      sessionID: ctx.sessionID,
+      type: "text",
+      text: `The plan at ${plan} has been approved, you can now edit files. Execute the plan`,
+      synthetic: true,
+    } satisfies MessageV2.TextPart)
+
+    return {
+      title: "Switching to build agent",
+      output: "User approved switching to build agent. Wait for further instructions.",
+      metadata: {},
+    }
+  },
+})
+
+export const PlanEnterTool = Tool.define("plan_enter", {
+  description: ENTER_DESCRIPTION,
+  parameters: z.object({}),
+  async execute(_params, ctx) {
+    const session = await Session.get(ctx.sessionID)
+    const plan = path.relative(Instance.worktree, Session.plan(session))
+
+    const answers = await Question.ask({
+      sessionID: ctx.sessionID,
+      questions: [
+        {
+          question: `Would you like to switch to the plan agent and create a plan saved to ${plan}?`,
+          header: "Plan Mode",
+          custom: false,
+          options: [
+            { label: "Yes", description: "Switch to plan agent for research and planning" },
+            { label: "No", description: "Stay with build agent to continue making changes" },
+          ],
+        },
+      ],
+      tool: ctx.callID ? { messageID: ctx.messageID, callID: ctx.callID } : undefined,
+    })
+
+    const answer = answers[0]?.[0]
+
+    if (answer === "No") throw new Question.RejectedError()
+
+    const model = await getLastModel(ctx.sessionID)
+
+    const userMsg: MessageV2.User = {
+      id: Identifier.ascending("message"),
+      sessionID: ctx.sessionID,
+      role: "user",
+      time: {
+        created: Date.now(),
+      },
+      agent: "plan",
+      model,
+    }
+    await Session.updateMessage(userMsg)
+    await Session.updatePart({
+      id: Identifier.ascending("part"),
+      messageID: userMsg.id,
+      sessionID: ctx.sessionID,
+      type: "text",
+      text: "User has requested to enter plan mode. Switch to plan mode and begin planning.",
+      synthetic: true,
+    } satisfies MessageV2.TextPart)
+
+    return {
+      title: "Switching to plan agent",
+      output: `User confirmed to switch to plan mode. A new message has been created to switch you to plan mode. The plan file will be at ${plan}. Begin planning.`,
+      metadata: {},
+    }
+  },
+})

packages/opencode/src/tool/registry.ts

@@ -25,6 +25,7 @@ import { Flag } from "@/flag/flag"
 import { Log } from "@/util/log"
 import { LspTool } from "./lsp"
 import { Truncate } from "./truncation"
+import { PlanExitTool, PlanEnterTool } from "./plan"
 
 export namespace ToolRegistry {
   const log = Log.create({ service: "tool.registry" })
@@ -109,6 +110,7 @@ export namespace ToolRegistry {
       SkillTool,
       ...(Flag.OPENCODE_EXPERIMENTAL_LSP_TOOL ? [LspTool] : []),
       ...(config.experimental?.batch_tool === true ? [BatchTool] : []),
+      ...(Flag.OPENCODE_EXPERIMENTAL_PLAN_MODE && Flag.OPENCODE_CLIENT === "cli" ? [PlanExitTool, PlanEnterTool] : []),
       ...custom,
     ]
   }