refactor(tools/background-task): split tools.ts into focused modules under 200 LOC

- Create modules/ directory with 6 focused modules:
  - background-task.ts: task creation logic
  - background-output.ts: output retrieval logic
  - background-cancel.ts: cancellation logic
  - formatters.ts: message formatting utilities
  - message-processing.ts: message extraction utilities
  - utils.ts: shared utility functions
- Reduce tools.ts from ~798 to ~30 lines (barrel pattern)
- Add new types to types.ts for module interfaces
- Update index.ts for clean re-exports
- Follow modular code architecture (200 LOC limit)

🤖 Generated with assistance of OhMyOpenCode

src/tools/background-task/modules/utils.ts

@@ -0,0 +1,65 @@
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
+import { MESSAGE_STORAGE } from "../../../features/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
+}
+
+export function formatDuration(start: Date, end?: Date): string {
+  const duration = (end ?? new Date()).getTime() - start.getTime()
+  const seconds = Math.floor(duration / 1000)
+  const minutes = Math.floor(seconds / 60)
+  const hours = Math.floor(minutes / 60)
+
+  if (hours > 0) {
+    return `${hours}h ${minutes % 60}m ${seconds % 60}s`
+  } else if (minutes > 0) {
+    return `${minutes}m ${seconds % 60}s`
+  } else {
+    return `${seconds}s`
+  }
+}
+
+export function truncateText(text: string, maxLength: number): string {
+  if (text.length <= maxLength) return text
+  return text.slice(0, maxLength) + "..."
+}
+
+export function delay(ms: number): Promise<void> {
+  return new Promise(resolve => setTimeout(resolve, ms))
+}
+
+export function formatMessageTime(value: unknown): string {
+  if (typeof value === "string") {
+    const date = new Date(value)
+    return Number.isNaN(date.getTime()) ? value : date.toISOString()
+  }
+  if (typeof value === "object" && value !== null) {
+    if ("created" in value) {
+      const created = (value as { created?: number }).created
+      if (typeof created === "number") {
+        return new Date(created).toISOString()
+      }
+    }
+  }
+  return "Unknown time"
+}
+
+export type ToolContextWithMetadata = {
+  sessionID: string
+  messageID: string
+  agent: string
+  abort: AbortSignal
+  metadata?: (input: { title?: string; metadata?: Record<string, unknown> }) => void
+}