fix: add compaction todo preserver hook

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/compaction-todo-preserver/index.test.ts

@@ -0,0 +1,74 @@
+import { describe, expect, it, mock } from "bun:test"
+import type { PluginInput } from "@opencode-ai/plugin"
+import { createCompactionTodoPreserverHook } from "./index"
+
+const updateMock = mock(async () => {})
+
+mock.module("opencode/session/todo", () => ({
+  Todo: {
+    update: updateMock,
+  },
+}))
+
+type TodoSnapshot = {
+  id: string
+  content: string
+  status: "pending" | "in_progress" | "completed" | "cancelled"
+  priority?: "low" | "medium" | "high"
+}
+
+function createMockContext(todoResponses: TodoSnapshot[][]): PluginInput {
+  let callIndex = 0
+  return {
+    client: {
+      session: {
+        todo: async () => {
+          const current = todoResponses[Math.min(callIndex, todoResponses.length - 1)] ?? []
+          callIndex += 1
+          return { data: current }
+        },
+      },
+    },
+    directory: "/tmp/test",
+  } as PluginInput
+}
+
+describe("compaction-todo-preserver", () => {
+  it("restores todos after compaction when missing", async () => {
+    //#given
+    updateMock.mockClear()
+    const sessionID = "session-compaction-missing"
+    const todos = [
+      { id: "1", content: "Task 1", status: "pending", priority: "high" },
+      { id: "2", content: "Task 2", status: "in_progress", priority: "medium" },
+    ]
+    const ctx = createMockContext([todos, []])
+    const hook = createCompactionTodoPreserverHook(ctx)
+
+    //#when
+    await hook.capture(sessionID)
+    await hook.event({ event: { type: "session.compacted", properties: { sessionID } } })
+
+    //#then
+    expect(updateMock).toHaveBeenCalledTimes(1)
+    expect(updateMock).toHaveBeenCalledWith({ sessionID, todos })
+  })
+
+  it("skips restore when todos already present", async () => {
+    //#given
+    updateMock.mockClear()
+    const sessionID = "session-compaction-present"
+    const todos = [
+      { id: "1", content: "Task 1", status: "pending", priority: "high" },
+    ]
+    const ctx = createMockContext([todos, todos])
+    const hook = createCompactionTodoPreserverHook(ctx)
+
+    //#when
+    await hook.capture(sessionID)
+    await hook.event({ event: { type: "session.compacted", properties: { sessionID } } })
+
+    //#then
+    expect(updateMock).not.toHaveBeenCalled()
+  })
+})

src/hooks/compaction-todo-preserver/index.ts

@@ -0,0 +1,127 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { log } from "../../shared/logger"
+
+interface TodoSnapshot {
+  id: string
+  content: string
+  status: "pending" | "in_progress" | "completed" | "cancelled"
+  priority?: "low" | "medium" | "high"
+}
+
+type TodoWriter = (input: { sessionID: string; todos: TodoSnapshot[] }) => Promise<void>
+
+const HOOK_NAME = "compaction-todo-preserver"
+
+function extractTodos(response: unknown): TodoSnapshot[] {
+  const payload = response as { data?: unknown }
+  if (Array.isArray(payload?.data)) {
+    return payload.data as TodoSnapshot[]
+  }
+  if (Array.isArray(response)) {
+    return response as TodoSnapshot[]
+  }
+  return []
+}
+
+async function resolveTodoWriter(): Promise<TodoWriter | null> {
+  try {
+    const loader = "opencode/session/todo"
+    const mod = (await import(loader)) as {
+      Todo?: { update?: TodoWriter }
+    }
+    const update = mod.Todo?.update
+    if (typeof update === "function") {
+      return update
+    }
+  } catch (err) {
+    log(`[${HOOK_NAME}] Failed to resolve Todo.update`, { error: String(err) })
+  }
+  return null
+}
+
+function resolveSessionID(props?: Record<string, unknown>): string | undefined {
+  return (props?.sessionID ??
+    (props?.info as { id?: string } | undefined)?.id) as string | undefined
+}
+
+export interface CompactionTodoPreserver {
+  capture: (sessionID: string) => Promise<void>
+  event: (input: { event: { type: string; properties?: unknown } }) => Promise<void>
+}
+
+export function createCompactionTodoPreserverHook(
+  ctx: PluginInput,
+): CompactionTodoPreserver {
+  const snapshots = new Map<string, TodoSnapshot[]>()
+
+  const capture = async (sessionID: string): Promise<void> => {
+    if (!sessionID) return
+    try {
+      const response = await ctx.client.session.todo({ path: { id: sessionID } })
+      const todos = extractTodos(response)
+      if (todos.length === 0) return
+      snapshots.set(sessionID, todos)
+      log(`[${HOOK_NAME}] Captured todo snapshot`, { sessionID, count: todos.length })
+    } catch (err) {
+      log(`[${HOOK_NAME}] Failed to capture todos`, { sessionID, error: String(err) })
+    }
+  }
+
+  const restore = async (sessionID: string): Promise<void> => {
+    const snapshot = snapshots.get(sessionID)
+    if (!snapshot || snapshot.length === 0) return
+
+    let hasCurrent = false
+    let currentTodos: TodoSnapshot[] = []
+    try {
+      const response = await ctx.client.session.todo({ path: { id: sessionID } })
+      currentTodos = extractTodos(response)
+      hasCurrent = true
+    } catch (err) {
+      log(`[${HOOK_NAME}] Failed to fetch todos post-compaction`, { sessionID, error: String(err) })
+    }
+
+    if (hasCurrent && currentTodos.length > 0) {
+      snapshots.delete(sessionID)
+      log(`[${HOOK_NAME}] Skipped restore (todos already present)`, { sessionID, count: currentTodos.length })
+      return
+    }
+
+    const writer = await resolveTodoWriter()
+    if (!writer) {
+      log(`[${HOOK_NAME}] Skipped restore (Todo.update unavailable)`, { sessionID })
+      return
+    }
+
+    try {
+      await writer({ sessionID, todos: snapshot })
+      log(`[${HOOK_NAME}] Restored todos after compaction`, { sessionID, count: snapshot.length })
+    } catch (err) {
+      log(`[${HOOK_NAME}] Failed to restore todos`, { sessionID, error: String(err) })
+    } finally {
+      snapshots.delete(sessionID)
+    }
+  }
+
+  const event = async ({ event }: { event: { type: string; properties?: unknown } }): Promise<void> => {
+    const props = event.properties as Record<string, unknown> | undefined
+
+    if (event.type === "session.deleted") {
+      const sessionID = resolveSessionID(props)
+      if (sessionID) {
+        snapshots.delete(sessionID)
+      }
+      return
+    }
+
+    if (event.type === "session.compacted") {
+      const sessionID = resolveSessionID(props)
+      if (sessionID) {
+        await restore(sessionID)
+      }
+      return
+    }
+  }
+
+  return { capture, event }
+}

src/hooks/index.ts

@@ -35,6 +35,7 @@ export { createQuestionLabelTruncatorHook } from "./question-label-truncator";
 export { createSubagentQuestionBlockerHook } from "./subagent-question-blocker";
 export { createStopContinuationGuardHook, type StopContinuationGuard } from "./stop-continuation-guard";
 export { createCompactionContextInjector } from "./compaction-context-injector";
+export { createCompactionTodoPreserverHook } from "./compaction-todo-preserver";
 export { createUnstableAgentBabysitterHook } from "./unstable-agent-babysitter";
 export { createPreemptiveCompactionHook } from "./preemptive-compaction";
 export { createTasksTodowriteDisablerHook } from "./tasks-todowrite-disabler";