refactor(shared): consolidate 13+ getMessageDir copies into single shared function

src/features/background-agent/message-dir.ts

@@ -1 +1 @@
-export { getMessageDir } from "./message-storage-locator"
+export { getMessageDir } from "../../shared"

src/features/background-agent/message-storage-locator.ts

@@ -1,17 +1 @@
-import { existsSync, readdirSync } from "node:fs"
-import { join } from "node:path"
-import { MESSAGE_STORAGE } from "../hook-message-injector"
-
-export 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
-}
+import { getMessageDir } from "../../shared"

src/features/background-agent/parent-session-context-resolver.ts

@@ -1,7 +1,7 @@
 import type { OpencodeClient } from "./constants"
 import type { BackgroundTask } from "./types"
 import { findNearestMessageWithFields } from "../hook-message-injector"
-import { getMessageDir } from "./message-storage-locator"
+import { getMessageDir } from "../../shared"
 
 type AgentModel = { providerID: string; modelID: string }
 

src/features/background-agent/result-handler.ts

@@ -1,6 +1,6 @@
 export type { ResultHandlerContext } from "./result-handler-context"
 export { formatDuration } from "./duration-formatter"
-export { getMessageDir } from "./message-storage-locator"
+export { getMessageDir } from "../../shared"
 export { checkSessionTodos } from "./session-todo-checker"
 export { validateSessionHasOutput } from "./session-output-validator"
 export { tryCompleteTask } from "./background-task-completer"