refactor(background-agent): split manager.ts into focused modules

Extract 30+ single-responsibility modules from manager.ts (1556 LOC):
- task lifecycle: task-starter, task-completer, task-canceller, task-resumer
- task queries: task-queries, task-poller, task-queue-processor
- notifications: notification-builder, notification-tracker, parent-session-notifier
- session handling: session-validator, session-output-validator, session-todo-checker
- spawner: spawner/ directory with focused spawn modules
- utilities: duration-formatter, error-classifier, message-storage-locator
- result handling: result-handler-context, background-task-completer
- shutdown: background-manager-shutdown, process-signal

src/features/background-agent/parent-session-notifier.ts

@@ -0,0 +1,102 @@
+import type { BackgroundTask } from "./types"
+import type { ResultHandlerContext } from "./result-handler-context"
+import { TASK_CLEANUP_DELAY_MS } from "./constants"
+import { log } from "../../shared"
+import { getTaskToastManager } from "../task-toast-manager"
+import { formatDuration } from "./duration-formatter"
+import { buildBackgroundTaskNotificationText } from "./background-task-notification-template"
+import { resolveParentSessionAgentAndModel } from "./parent-session-context-resolver"
+
+export async function notifyParentSession(
+  task: BackgroundTask,
+  ctx: ResultHandlerContext
+): Promise<void> {
+  const { client, state } = ctx
+
+  const duration = formatDuration(task.startedAt ?? new Date(), task.completedAt)
+  log("[background-agent] notifyParentSession called for task:", task.id)
+
+  const toastManager = getTaskToastManager()
+  if (toastManager) {
+    toastManager.showCompletionToast({
+      id: task.id,
+      description: task.description,
+      duration,
+    })
+  }
+
+  const pendingSet = state.pendingByParent.get(task.parentSessionID)
+  if (pendingSet) {
+    pendingSet.delete(task.id)
+    if (pendingSet.size === 0) {
+      state.pendingByParent.delete(task.parentSessionID)
+    }
+  }
+
+  const allComplete = !pendingSet || pendingSet.size === 0
+  const remainingCount = pendingSet?.size ?? 0
+
+  const statusText = task.status === "completed" ? "COMPLETED" : "CANCELLED"
+
+  const completedTasks = allComplete
+    ? Array.from(state.tasks.values()).filter(
+        (t) =>
+          t.parentSessionID === task.parentSessionID &&
+          t.status !== "running" &&
+          t.status !== "pending"
+      )
+    : []
+
+  const notification = buildBackgroundTaskNotificationText({
+    task,
+    duration,
+    statusText,
+    allComplete,
+    remainingCount,
+    completedTasks,
+  })
+
+  const { agent, model } = await resolveParentSessionAgentAndModel({ client, task })
+
+  log("[background-agent] notifyParentSession context:", {
+    taskId: task.id,
+    resolvedAgent: agent,
+    resolvedModel: model,
+  })
+
+  try {
+    await client.session.promptAsync({
+      path: { id: task.parentSessionID },
+      body: {
+        noReply: !allComplete,
+        ...(agent !== undefined ? { agent } : {}),
+        ...(model !== undefined ? { model } : {}),
+        parts: [{ type: "text", text: notification }],
+      },
+    })
+
+    log("[background-agent] Sent notification to parent session:", {
+      taskId: task.id,
+      allComplete,
+      noReply: !allComplete,
+    })
+  } catch (error) {
+    log("[background-agent] Failed to send notification:", error)
+  }
+
+  if (!allComplete) return
+
+  for (const completedTask of completedTasks) {
+    const taskId = completedTask.id
+    state.clearCompletionTimer(taskId)
+    const timer = setTimeout(() => {
+      state.completionTimers.delete(taskId)
+      if (state.tasks.has(taskId)) {
+        state.clearNotificationsForTask(taskId)
+        state.tasks.delete(taskId)
+        log("[background-agent] Removed completed task from memory:", taskId)
+      }
+    }, TASK_CLEANUP_DELAY_MS)
+    state.setCompletionTimer(taskId, timer)
+  }
+}