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

packages/opencode/src/session/index.ts

@@ -1,3 +1,5 @@
+import { Slug } from "@opencode-ai/util/slug"
+import pat from "path"
 import { BusEvent } from "@/bus/bus-event"
 import { Bus } from "@/bus"
 import { Decimal } from "decimal.js"
@@ -19,6 +21,7 @@ import { Snapshot } from "@/snapshot"
 
 import type { Provider } from "@/provider/provider"
 import { PermissionNext } from "@/permission/next"
+import path from "path"
 
 export namespace Session {
   const log = Log.create({ service: "session" })
@@ -39,6 +42,7 @@ export namespace Session {
   export const Info = z
     .object({
       id: Identifier.schema("session"),
+      slug: z.string(),
       projectID: z.string(),
       directory: z.string(),
       parentID: Identifier.schema("session").optional(),
@@ -194,6 +198,7 @@ export namespace Session {
   }) {
     const result: Info = {
       id: Identifier.descending("session", input.id),
+      slug: Slug.create(),
       version: Installation.VERSION,
       projectID: Instance.project.id,
       directory: input.directory,
@@ -227,6 +232,10 @@ export namespace Session {
     return result
   }
 
+  export function plan(input: { slug: string; time: { created: number } }) {
+    return path.join(Instance.worktree, ".opencode", "plans", [input.time.created, input.slug].join("-") + ".md")
+  }
+
   export const get = fn(Identifier.schema("session"), async (id) => {
     const read = await Storage.read<Info>(["session", Instance.project.id, id])
     return read as Info

packages/opencode/src/session/prompt.ts

@@ -510,9 +510,10 @@ export namespace SessionPrompt {
       const agent = await Agent.get(lastUser.agent)
       const maxSteps = agent.steps ?? Infinity
       const isLastStep = step >= maxSteps
-      msgs = insertReminders({
+      msgs = await insertReminders({
         messages: msgs,
         agent,
+        session,
       })
 
       const processor = SessionProcessor.create({
@@ -1185,30 +1186,140 @@ export namespace SessionPrompt {
     }
   }
 
-  function insertReminders(input: { messages: MessageV2.WithParts[]; agent: Agent.Info }) {
+  async function insertReminders(input: { messages: MessageV2.WithParts[]; agent: Agent.Info; session: Session.Info }) {
     const userMessage = input.messages.findLast((msg) => msg.info.role === "user")
     if (!userMessage) return input.messages
-    if (input.agent.name === "plan") {
-      userMessage.parts.push({
-        id: Identifier.ascending("part"),
-        messageID: userMessage.info.id,
-        sessionID: userMessage.info.sessionID,
-        type: "text",
-        // TODO (for mr dax): update to use the anthropic full fledged one (see plan-reminder-anthropic.txt)
-        text: PROMPT_PLAN,
-        synthetic: true,
-      })
+
+    // Original logic when experimental plan mode is disabled
+    if (!Flag.OPENCODE_EXPERIMENTAL_PLAN_MODE) {
+      if (input.agent.name === "plan") {
+        userMessage.parts.push({
+          id: Identifier.ascending("part"),
+          messageID: userMessage.info.id,
+          sessionID: userMessage.info.sessionID,
+          type: "text",
+          text: PROMPT_PLAN,
+          synthetic: true,
+        })
+      }
+      const wasPlan = input.messages.some((msg) => msg.info.role === "assistant" && msg.info.agent === "plan")
+      if (wasPlan && input.agent.name === "build") {
+        userMessage.parts.push({
+          id: Identifier.ascending("part"),
+          messageID: userMessage.info.id,
+          sessionID: userMessage.info.sessionID,
+          type: "text",
+          text: BUILD_SWITCH,
+          synthetic: true,
+        })
+      }
+      return input.messages
     }
-    const wasPlan = input.messages.some((msg) => msg.info.role === "assistant" && msg.info.agent === "plan")
-    if (wasPlan && input.agent.name === "build") {
-      userMessage.parts.push({
+
+    // New plan mode logic when flag is enabled
+    const assistantMessage = input.messages.findLast((msg) => msg.info.role === "assistant")
+
+    // Switching from plan mode to build mode
+    if (input.agent.name !== "plan" && assistantMessage?.info.agent === "plan") {
+      const plan = Session.plan(input.session)
+      const exists = await Bun.file(plan).exists()
+      if (exists) {
+        const part = await Session.updatePart({
+          id: Identifier.ascending("part"),
+          messageID: userMessage.info.id,
+          sessionID: userMessage.info.sessionID,
+          type: "text",
+          text: BUILD_SWITCH.replace("{{plan}}", plan),
+          synthetic: true,
+        })
+        userMessage.parts.push(part)
+      }
+    }
+
+    // Entering plan mode
+    if (input.agent.name === "plan" && assistantMessage?.info.agent !== "plan") {
+      const plan = Session.plan(input.session)
+      const exists = await Bun.file(plan).exists()
+      if (!exists) await fs.mkdir(path.dirname(plan), { recursive: true })
+      const part = await Session.updatePart({
         id: Identifier.ascending("part"),
         messageID: userMessage.info.id,
         sessionID: userMessage.info.sessionID,
         type: "text",
-        text: BUILD_SWITCH,
+        text: `<system-reminder>
+Plan mode is active. The user indicated that they do not want you to execute yet -- you MUST NOT make any edits (with the exception of the plan file mentioned below), run any non-readonly tools (including changing configs or making commits), or otherwise make any changes to the system. This supercedes any other instructions you have received.
+
+## Plan File Info:
+${exists ? `A plan file already exists at ${plan}. You can read it and make incremental edits using the edit tool.` : `No plan file exists yet. You should create your plan at ${plan} using the write tool.`}
+You should build your plan incrementally by writing to or editing this file. NOTE that this is the only file you are allowed to edit - other than this you are only allowed to take READ-ONLY actions.
+
+## Plan Workflow
+
+### Phase 1: Initial Understanding
+Goal: Gain a comprehensive understanding of the user's request by reading through code and asking them questions. Critical: In this phase you should only use the explore subagent type.
+
+1. Focus on understanding the user's request and the code associated with their request
+
+2. **Launch up to 3 explore agents IN PARALLEL** (single message, multiple tool calls) to efficiently explore the codebase.
+   - Use 1 agent when the task is isolated to known files, the user provided specific file paths, or you're making a small targeted change.
+   - Use multiple agents when: the scope is uncertain, multiple areas of the codebase are involved, or you need to understand existing patterns before planning.
+   - Quality over quantity - 3 agents maximum, but you should try to use the minimum number of agents necessary (usually just 1)
+   - If using multiple agents: Provide each agent with a specific search focus or area to explore. Example: One agent searches for existing implementations, another explores related components, a third investigates testing patterns
+
+3. After exploring the code, use the question tool to clarify ambiguities in the user request up front.
+
+### Phase 2: Design
+Goal: Design an implementation approach.
+
+Launch general agent(s) to design the implementation based on the user's intent and your exploration results from Phase 1.
+
+You can launch up to 1 agent(s) in parallel.
+
+**Guidelines:**
+- **Default**: Launch at least 1 Plan agent for most tasks - it helps validate your understanding and consider alternatives
+- **Skip agents**: Only for truly trivial tasks (typo fixes, single-line changes, simple renames)
+
+Examples of when to use multiple agents:
+- The task touches multiple parts of the codebase
+- It's a large refactor or architectural change
+- There are many edge cases to consider
+- You'd benefit from exploring different approaches
+
+Example perspectives by task type:
+- New feature: simplicity vs performance vs maintainability
+- Bug fix: root cause vs workaround vs prevention
+- Refactoring: minimal change vs clean architecture
+
+In the agent prompt:
+- Provide comprehensive background context from Phase 1 exploration including filenames and code path traces
+- Describe requirements and constraints
+- Request a detailed implementation plan
+
+### Phase 3: Review
+Goal: Review the plan(s) from Phase 2 and ensure alignment with the user's intentions.
+1. Read the critical files identified by agents to deepen your understanding
+2. Ensure that the plans align with the user's original request
+3. Use question tool to clarify any remaining questions with the user
+
+### Phase 4: Final Plan
+Goal: Write your final plan to the plan file (the only file you can edit).
+- Include only your recommended approach, not all alternatives
+- Ensure that the plan file is concise enough to scan quickly, but detailed enough to execute effectively
+- Include the paths of critical files to be modified
+- Include a verification section describing how to test the changes end-to-end (run the code, use MCP tools, run tests)
+
+### Phase 5: Call plan_exit tool
+At the very end of your turn, once you have asked the user questions and are happy with your final plan file - you should always call plan_exit to indicate to the user that you are done planning.
+This is critical - your turn should only end with either asking the user a question or calling plan_exit. Do not stop unless it's for these 2 reasons.
+
+**Important:** Use question tool to clarify requirements/approach, use plan_exit to request plan approval. Do NOT use question tool to ask "Is this plan okay?" - that's what plan_exit does.
+
+NOTE: At any point in time through this workflow you should feel free to ask the user questions or clarifications. Don't make large assumptions about user intent. The goal is to present a well researched plan to the user, and tie any loose ends before implementation begins.
+</system-reminder>`,
         synthetic: true,
       })
+      userMessage.parts.push(part)
+      return input.messages
     }
     return input.messages
   }

packages/opencode/src/session/prompt/build-switch.txt

@@ -2,4 +2,6 @@
 Your operational mode has changed from plan to build.
 You are no longer in read-only mode.
 You are permitted to make file changes, run shell commands, and utilize your arsenal of tools as needed.
+
+A plan file exists at {{plan}}. You should read this file and execute on the plan defined within it.
 </system-reminder>