compaction: preserve todo list across context compaction

esrehmki · ESRE-dev · commit 17645bfb8f8e · 2026-04-17T17:56:05.000+02:00
* after compaction the agent lost track of its task list
      and failed to resume work where it left off

ADD

    * inject current todo state into the summarizer prompt so
      the post-compaction agent sees the full task list and
      can continue from the correct point
    * formatTodos helper renders persisted todos as a markdown
      section appended to the compaction template

TEST

    * unit tests for formatTodos covering empty input, entry
      formatting, prompt concatenation, persistence note, and
      special characters
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
@@ -16,6 +16,7 @@ import { ModelID, ProviderID } from "@/provider/schema"
 import { Effect, Layer, Context } from "effect"
 import { InstanceState } from "@/effect"
 import { isOverflow as overflow } from "./overflow"
+import { Todo } from "./todo"
 
 const log = Log.create({ service: "session.compaction" })
 
@@ -28,6 +29,12 @@ export const Event = {
   ),
 }
 
+export function formatTodos(todos: Todo.Info[]): string | undefined {
+  if (todos.length === 0) return undefined
+  const items = todos.map((t) => `- [${t.status}] (${t.priority}) ${t.content}`).join("\n")
+  return `\n\n## Current Task List\nThe agent is tracking the following tasks (persisted in the database — these survive compaction):\n${items}`
+}
+
 export const PRUNE_MINIMUM = 20_000
 export const PRUNE_PROTECT = 40_000
 const PRUNE_PROTECTED_TOOLS = ["skill"]
@@ -66,6 +73,7 @@ export const layer: Layer.Layer<
   | Plugin.Service
   | SessionProcessor.Service
   | Provider.Service
+  | Todo.Service
 > = Layer.effect(
   Service,
   Effect.gen(function* () {
@@ -76,6 +84,7 @@ export const layer: Layer.Layer<
     const plugin = yield* Plugin.Service
     const processors = yield* SessionProcessor.Service
     const provider = yield* Provider.Service
+    const todo = yield* Todo.Service
 
     const isOverflow = Effect.fn("SessionCompaction.isOverflow")(function* (input: {
       tokens: MessageV2.Assistant["tokens"]
@@ -182,7 +191,7 @@ export const layer: Layer.Layer<
         { sessionID: input.sessionID },
         { context: [], prompt: undefined },
       )
-      const defaultPrompt = `Provide a detailed prompt for continuing our conversation above.
+      let defaultPrompt = `Provide a detailed prompt for continuing our conversation above.
 Focus on information that would be helpful for continuing the conversation, including what we did, what we're doing, which files we're working on, and what we're going to do next.
 The summary that you construct will be used so that another agent can read it and continue the work.
 Do not call any tools. Respond only with the summary text.
@@ -212,6 +221,12 @@ When constructing the summary, try to stick to this template:
 [Construct a structured list of relevant files that have been read, edited, or created that pertain to the task at hand. If all the files in a directory are relevant, include the path to the directory.]
 ---`
 
+      const todos = yield* todo.get(input.sessionID)
+      const section = formatTodos(todos)
+      if (section) {
+        defaultPrompt += section
+      }
+
       const prompt = compacting.prompt ?? [defaultPrompt, ...compacting.context].join("\n\n")
       const msgs = structuredClone(messages)
       yield* plugin.trigger("experimental.chat.messages.transform", {}, { messages: msgs })
@@ -404,6 +419,7 @@ export const defaultLayer = Layer.suspend(() =>
     Layer.provide(SessionProcessor.defaultLayer),
     Layer.provide(Agent.defaultLayer),
     Layer.provide(Plugin.defaultLayer),
+    Layer.provide(Todo.defaultLayer),
     Layer.provide(Bus.layer),
     Layer.provide(Config.defaultLayer),
   ),
diff --git a/packages/opencode/test/session/compaction-todo.test.ts b/packages/opencode/test/session/compaction-todo.test.ts
@@ -0,0 +1,65 @@
+import { describe, expect, test } from "bun:test"
+import { SessionCompaction } from "../../src/session/compaction"
+
+describe("SessionCompaction.formatTodos", () => {
+  test("returns undefined for empty array", () => {
+    expect(SessionCompaction.formatTodos([])).toBeUndefined()
+  })
+
+  test("returns section with header for non-empty list", () => {
+    const result = SessionCompaction.formatTodos([{ content: "Fix bug", status: "pending", priority: "high" }])
+    expect(result).toContain("## Current Task List")
+  })
+
+  test("includes one entry per item", () => {
+    const todos = [
+      { content: "Fix bug", status: "pending", priority: "high" },
+      { content: "Write tests", status: "in_progress", priority: "medium" },
+      { content: "Deploy", status: "completed", priority: "low" },
+    ]
+    const result = SessionCompaction.formatTodos(todos)!
+    expect(result).toContain("- [pending] (high) Fix bug")
+    expect(result).toContain("- [in_progress] (medium) Write tests")
+    expect(result).toContain("- [completed] (low) Deploy")
+  })
+
+  test("formats status, priority, and content in markdown", () => {
+    const result = SessionCompaction.formatTodos([{ content: "Task A", status: "open", priority: "low" }])!
+    expect(result).toContain("- [open] (low) Task A")
+  })
+
+  test("entry count matches input length", () => {
+    const todos = Array.from({ length: 5 }, (_, i) => ({
+      content: `Task ${i}`,
+      status: "pending",
+      priority: "medium",
+    }))
+    const result = SessionCompaction.formatTodos(todos)!
+    const entries = result.split("\n").filter((line) => line.startsWith("- ["))
+    expect(entries).toHaveLength(5)
+  })
+
+  test("section starts with double newline for prompt concatenation", () => {
+    const result = SessionCompaction.formatTodos([{ content: "Task", status: "pending", priority: "high" }])!
+    expect(result.startsWith("\n\n")).toBe(true)
+  })
+
+  test("includes persistence note for agent context", () => {
+    const result = SessionCompaction.formatTodos([{ content: "Task", status: "pending", priority: "high" }])!
+    expect(result).toContain("persisted in the database")
+    expect(result).toContain("survive compaction")
+  })
+
+  test("no section header in empty result", () => {
+    const result = SessionCompaction.formatTodos([])
+    expect(result).toBeUndefined()
+    expect(result ?? "").not.toContain("## Current Task List")
+  })
+
+  test("handles special characters in content", () => {
+    const result = SessionCompaction.formatTodos([
+      { content: "Fix `code` in **bold** & <html>", status: "pending", priority: "high" },
+    ])!
+    expect(result).toContain("Fix `code` in **bold** & <html>")
+  })
+})
