fix(hooks): respect previous message's agent mode in message sending hooks

Message hooks like todo-continuation-enforcer and background-notification
now preserve the agent mode from the previous message when sending follow-up
prompts. This ensures that continuation messages and task completion
notifications use the same agent that was active in the conversation.

- Export findNearestMessageWithFields and MESSAGE_STORAGE from hook-message-injector
- Add getMessageDir helper to locate session message directories
- Pass agent field to session.prompt in todo-continuation-enforcer
- Pass agent field to session.prompt in BackgroundManager.notifyParentSession

Closes #59

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/features/background-agent/manager.ts

@@ -1,9 +1,15 @@
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
 import type { PluginInput } from "@opencode-ai/plugin"
 import type {
   BackgroundTask,
   LaunchInput,
 } from "./types"
 import { log } from "../../shared/logger"
+import {
+  findNearestMessageWithFields,
+  MESSAGE_STORAGE,
+} from "../hook-message-injector"
 
 type OpencodeClient = PluginInput["client"]
 
@@ -24,6 +30,20 @@ interface Event {
   properties?: EventProperties
 }
 
+function getMessageDir(sessionID: string): string | null {
+  if (!existsSync(MESSAGE_STORAGE)) return null
+
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) return directPath
+
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) return sessionPath
+  }
+
+  return null
+}
+
 export class BackgroundManager {
   private tasks: Map<string, BackgroundTask>
   private notifications: Map<string, BackgroundTask[]>
@@ -253,9 +273,13 @@ export class BackgroundManager {
 
     setTimeout(async () => {
       try {
+        const messageDir = getMessageDir(task.parentSessionID)
+        const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+
         await this.client.session.prompt({
           path: { id: task.parentSessionID },
           body: {
+            agent: prevMessage?.agent,
             parts: [{ type: "text", text: message }],
           },
           query: { directory: this.directory },

src/features/hook-message-injector/index.ts

@@ -1,2 +1,4 @@
-export { injectHookMessage } from "./injector"
+export { injectHookMessage, findNearestMessageWithFields } from "./injector"
+export type { StoredMessage } from "./injector"
 export type { MessageMeta, OriginalMessageContext, TextPart } from "./types"
+export { MESSAGE_STORAGE } from "./constants"

src/features/hook-message-injector/injector.ts

@@ -3,13 +3,13 @@ import { join } from "node:path"
 import { MESSAGE_STORAGE, PART_STORAGE } from "./constants"
 import type { MessageMeta, OriginalMessageContext, TextPart } from "./types"
 
-interface StoredMessage {
+export interface StoredMessage {
   agent?: string
   model?: { providerID?: string; modelID?: string }
   tools?: Record<string, boolean>
 }
 
-function findNearestMessageWithFields(messageDir: string): StoredMessage | null {
+export function findNearestMessageWithFields(messageDir: string): StoredMessage | null {
   try {
     const files = readdirSync(messageDir)
       .filter((f) => f.endsWith(".json"))