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
2026-02-08 16:20:52 +09:00
parent c7122b4127
commit e3bd43ff64
43 changed files with 2753 additions and 2071 deletions
--- a/src/features/background-agent/background-event-handler.ts
+++ b/src/features/background-agent/background-event-handler.ts
@@ -0,0 +1,199 @@
+import { log } from "../../shared"
+import { MIN_IDLE_TIME_MS } from "./constants"
+import { subagentSessions } from "../claude-code-session-state"
+import type { BackgroundTask } from "./types"
+
+type Event = { type: string; properties?: Record<string, unknown> }
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function getString(obj: Record<string, unknown>, key: string): string | undefined {
+  const value = obj[key]
+  return typeof value === "string" ? value : undefined
+}
+
+export function handleBackgroundEvent(args: {
+  event: Event
+  findBySession: (sessionID: string) => BackgroundTask | undefined
+  getAllDescendantTasks: (sessionID: string) => BackgroundTask[]
+  cancelTask: (
+    taskId: string,
+    options: { source: string; reason: string; skipNotification: true }
+  ) => Promise<boolean>
+  tryCompleteTask: (task: BackgroundTask, source: string) => Promise<boolean>
+  validateSessionHasOutput: (sessionID: string) => Promise<boolean>
+  checkSessionTodos: (sessionID: string) => Promise<boolean>
+  idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>>
+  completionTimers: Map<string, ReturnType<typeof setTimeout>>
+  tasks: Map<string, BackgroundTask>
+  cleanupPendingByParent: (task: BackgroundTask) => void
+  clearNotificationsForTask: (taskId: string) => void
+  emitIdleEvent: (sessionID: string) => void
+}): void {
+  const {
+    event,
+    findBySession,
+    getAllDescendantTasks,
+    cancelTask,
+    tryCompleteTask,
+    validateSessionHasOutput,
+    checkSessionTodos,
+    idleDeferralTimers,
+    completionTimers,
+    tasks,
+    cleanupPendingByParent,
+    clearNotificationsForTask,
+    emitIdleEvent,
+  } = args
+
+  const props = event.properties
+
+  if (event.type === "message.part.updated") {
+    if (!props || !isRecord(props)) return
+    const sessionID = getString(props, "sessionID")
+    if (!sessionID) return
+
+    const task = findBySession(sessionID)
+    if (!task) return
+
+    const existingTimer = idleDeferralTimers.get(task.id)
+    if (existingTimer) {
+      clearTimeout(existingTimer)
+      idleDeferralTimers.delete(task.id)
+    }
+
+    const type = getString(props, "type")
+    const tool = getString(props, "tool")
+
+    if (type === "tool" || tool) {
+      if (!task.progress) {
+        task.progress = { toolCalls: 0, lastUpdate: new Date() }
+      }
+      task.progress.toolCalls += 1
+      task.progress.lastTool = tool
+      task.progress.lastUpdate = new Date()
+    }
+  }
+
+  if (event.type === "session.idle") {
+    if (!props || !isRecord(props)) return
+    const sessionID = getString(props, "sessionID")
+    if (!sessionID) return
+
+    const task = findBySession(sessionID)
+    if (!task || task.status !== "running") return
+
+    const startedAt = task.startedAt
+    if (!startedAt) return
+
+    const elapsedMs = Date.now() - startedAt.getTime()
+    if (elapsedMs < MIN_IDLE_TIME_MS) {
+      const remainingMs = MIN_IDLE_TIME_MS - elapsedMs
+      if (!idleDeferralTimers.has(task.id)) {
+        log("[background-agent] Deferring early session.idle:", {
+          elapsedMs,
+          remainingMs,
+          taskId: task.id,
+        })
+        const timer = setTimeout(() => {
+          idleDeferralTimers.delete(task.id)
+          emitIdleEvent(sessionID)
+        }, remainingMs)
+        idleDeferralTimers.set(task.id, timer)
+      } else {
+        log("[background-agent] session.idle already deferred:", { elapsedMs, taskId: task.id })
+      }
+      return
+    }
+
+    validateSessionHasOutput(sessionID)
+      .then(async (hasValidOutput) => {
+        if (task.status !== "running") {
+          log("[background-agent] Task status changed during validation, skipping:", {
+            taskId: task.id,
+            status: task.status,
+          })
+          return
+        }
+
+        if (!hasValidOutput) {
+          log("[background-agent] Session.idle but no valid output yet, waiting:", task.id)
+          return
+        }
+
+        const hasIncompleteTodos = await checkSessionTodos(sessionID)
+
+        if (task.status !== "running") {
+          log("[background-agent] Task status changed during todo check, skipping:", {
+            taskId: task.id,
+            status: task.status,
+          })
+          return
+        }
+
+        if (hasIncompleteTodos) {
+          log("[background-agent] Task has incomplete todos, waiting for todo-continuation:", task.id)
+          return
+        }
+
+        await tryCompleteTask(task, "session.idle event")
+      })
+      .catch((err) => {
+        log("[background-agent] Error in session.idle handler:", err)
+      })
+  }
+
+  if (event.type === "session.deleted") {
+    if (!props || !isRecord(props)) return
+    const infoRaw = props["info"]
+    if (!isRecord(infoRaw)) return
+    const sessionID = getString(infoRaw, "id")
+    if (!sessionID) return
+
+    const tasksToCancel = new Map<string, BackgroundTask>()
+    const directTask = findBySession(sessionID)
+    if (directTask) {
+      tasksToCancel.set(directTask.id, directTask)
+    }
+    for (const descendant of getAllDescendantTasks(sessionID)) {
+      tasksToCancel.set(descendant.id, descendant)
+    }
+    if (tasksToCancel.size === 0) return
+
+    for (const task of tasksToCancel.values()) {
+      if (task.status === "running" || task.status === "pending") {
+        void cancelTask(task.id, {
+          source: "session.deleted",
+          reason: "Session deleted",
+          skipNotification: true,
+        }).catch((err) => {
+          log("[background-agent] Failed to cancel task on session.deleted:", {
+            taskId: task.id,
+            error: err,
+          })
+        })
+      }
+
+      const completionTimer = completionTimers.get(task.id)
+      if (completionTimer) {
+        clearTimeout(completionTimer)
+        completionTimers.delete(task.id)
+      }
+
+      const idleTimer = idleDeferralTimers.get(task.id)
+      if (idleTimer) {
+        clearTimeout(idleTimer)
+        idleDeferralTimers.delete(task.id)
+      }
+
+      cleanupPendingByParent(task)
+      tasks.delete(task.id)
+      clearNotificationsForTask(task.id)
+      if (task.sessionID) {
+        subagentSessions.delete(task.sessionID)
+      }
+    }
+  }
+}
--- a/src/features/background-agent/background-manager-shutdown.ts
+++ b/src/features/background-agent/background-manager-shutdown.ts
@@ -0,0 +1,82 @@
+import { log } from "../../shared"
+
+import type { BackgroundTask, LaunchInput } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+import type { PluginInput } from "@opencode-ai/plugin"
+
+type QueueItem = { task: BackgroundTask; input: LaunchInput }
+
+export function shutdownBackgroundManager(args: {
+  shutdownTriggered: { value: boolean }
+  stopPolling: () => void
+  tasks: Map<string, BackgroundTask>
+  client: PluginInput["client"]
+  onShutdown?: () => void
+  concurrencyManager: ConcurrencyManager
+  completionTimers: Map<string, ReturnType<typeof setTimeout>>
+  idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>>
+  notifications: Map<string, BackgroundTask[]>
+  pendingByParent: Map<string, Set<string>>
+  queuesByKey: Map<string, QueueItem[]>
+  processingKeys: Set<string>
+  unregisterProcessCleanup: () => void
+}): void {
+  const {
+    shutdownTriggered,
+    stopPolling,
+    tasks,
+    client,
+    onShutdown,
+    concurrencyManager,
+    completionTimers,
+    idleDeferralTimers,
+    notifications,
+    pendingByParent,
+    queuesByKey,
+    processingKeys,
+    unregisterProcessCleanup,
+  } = args
+
+  if (shutdownTriggered.value) return
+  shutdownTriggered.value = true
+
+  log("[background-agent] Shutting down BackgroundManager")
+  stopPolling()
+
+  for (const task of tasks.values()) {
+    if (task.status === "running" && task.sessionID) {
+      client.session.abort({ path: { id: task.sessionID } }).catch(() => {})
+    }
+  }
+
+  if (onShutdown) {
+    try {
+      onShutdown()
+    } catch (error) {
+      log("[background-agent] Error in onShutdown callback:", error)
+    }
+  }
+
+  for (const task of tasks.values()) {
+    if (task.concurrencyKey) {
+      concurrencyManager.release(task.concurrencyKey)
+      task.concurrencyKey = undefined
+    }
+  }
+
+  for (const timer of completionTimers.values()) clearTimeout(timer)
+  completionTimers.clear()
+
+  for (const timer of idleDeferralTimers.values()) clearTimeout(timer)
+  idleDeferralTimers.clear()
+
+  concurrencyManager.clear()
+  tasks.clear()
+  notifications.clear()
+  pendingByParent.clear()
+  queuesByKey.clear()
+  processingKeys.clear()
+  unregisterProcessCleanup()
+
+  log("[background-agent] Shutdown complete")
+}
--- a/src/features/background-agent/background-task-completer.ts
+++ b/src/features/background-agent/background-task-completer.ts
@@ -0,0 +1,40 @@
+import type { BackgroundTask } from "./types"
+import type { ResultHandlerContext } from "./result-handler-context"
+import { log } from "../../shared"
+import { notifyParentSession } from "./parent-session-notifier"
+
+export async function tryCompleteTask(
+  task: BackgroundTask,
+  source: string,
+  ctx: ResultHandlerContext
+): Promise<boolean> {
+  const { concurrencyManager, state } = ctx
+
+  if (task.status !== "running") {
+    log("[background-agent] Task already completed, skipping:", {
+      taskId: task.id,
+      status: task.status,
+      source,
+    })
+    return false
+  }
+
+  task.status = "completed"
+  task.completedAt = new Date()
+
+  if (task.concurrencyKey) {
+    concurrencyManager.release(task.concurrencyKey)
+    task.concurrencyKey = undefined
+  }
+
+  state.markForNotification(task)
+
+  try {
+    await notifyParentSession(task, ctx)
+    log(`[background-agent] Task completed via ${source}:`, task.id)
+  } catch (error) {
+    log("[background-agent] Error in notifyParentSession:", { taskId: task.id, error })
+  }
+
+  return true
+}
--- a/src/features/background-agent/background-task-notification-template.ts
+++ b/src/features/background-agent/background-task-notification-template.ts
@@ -0,0 +1,46 @@
+import type { BackgroundTask } from "./types"
+
+export type BackgroundTaskNotificationStatus = "COMPLETED" | "CANCELLED"
+
+export function buildBackgroundTaskNotificationText(input: {
+  task: BackgroundTask
+  duration: string
+  statusText: BackgroundTaskNotificationStatus
+  allComplete: boolean
+  remainingCount: number
+  completedTasks: BackgroundTask[]
+}): string {
+  const { task, duration, statusText, allComplete, remainingCount, completedTasks } = input
+
+  const errorInfo = task.error ? `\n**Error:** ${task.error}` : ""
+
+  if (allComplete) {
+    const completedTasksText = completedTasks
+      .map((t) => `- \`${t.id}\`: ${t.description}`)
+      .join("\n")
+
+    return `<system-reminder>
+[ALL BACKGROUND TASKS COMPLETE]
+
+**Completed:**
+${completedTasksText || `- \`${task.id}\`: ${task.description}`}
+
+Use \`background_output(task_id="<id>")\` to retrieve each result.
+</system-reminder>`
+  }
+
+  const agentInfo = task.category ? `${task.agent} (${task.category})` : task.agent
+
+  return `<system-reminder>
+[BACKGROUND TASK ${statusText}]
+**ID:** \`${task.id}\`
+**Description:** ${task.description}
+**Agent:** ${agentInfo}
+**Duration:** ${duration}${errorInfo}
+
+**${remainingCount} task${remainingCount === 1 ? "" : "s"} still in progress.** You WILL be notified when ALL complete.
+Do NOT poll - continue productive work.
+
+Use \`background_output(task_id="${task.id}")\` to retrieve this result when ready.
+</system-reminder>`
+}
--- a/src/features/background-agent/duration-formatter.ts
+++ b/src/features/background-agent/duration-formatter.ts
@@ -0,0 +1,14 @@
+export function formatDuration(start: Date, end?: Date): string {
+  const duration = (end ?? new Date()).getTime() - start.getTime()
+  const seconds = Math.floor(duration / 1000)
+  const minutes = Math.floor(seconds / 60)
+  const hours = Math.floor(minutes / 60)
+
+  if (hours > 0) {
+    return `${hours}h ${minutes % 60}m ${seconds % 60}s`
+  }
+  if (minutes > 0) {
+    return `${minutes}m ${seconds % 60}s`
+  }
+  return `${seconds}s`
+}
--- a/src/features/background-agent/error-classifier.ts
+++ b/src/features/background-agent/error-classifier.ts
@@ -0,0 +1,21 @@
+export function isAbortedSessionError(error: unknown): boolean {
+  const message = getErrorText(error)
+  return message.toLowerCase().includes("aborted")
+}
+
+export function getErrorText(error: unknown): string {
+  if (!error) return ""
+  if (typeof error === "string") return error
+  if (error instanceof Error) {
+    return `${error.name}: ${error.message}`
+  }
+  if (typeof error === "object" && error !== null) {
+    if ("message" in error && typeof error.message === "string") {
+      return error.message
+    }
+    if ("name" in error && typeof error.name === "string") {
+      return error.name
+    }
+  }
+  return ""
+}
--- a/src/features/background-agent/format-duration.ts
+++ b/src/features/background-agent/format-duration.ts
@@ -0,0 +1,14 @@
+export function formatDuration(start: Date, end?: Date): string {
+  const duration = (end ?? new Date()).getTime() - start.getTime()
+  const seconds = Math.floor(duration / 1000)
+  const minutes = Math.floor(seconds / 60)
+  const hours = Math.floor(minutes / 60)
+
+  if (hours > 0) {
+    return `${hours}h ${minutes % 60}m ${seconds % 60}s`
+  }
+  if (minutes > 0) {
+    return `${minutes}m ${seconds % 60}s`
+  }
+  return `${seconds}s`
+}
--- a/src/features/background-agent/manager.ts
+++ b/src/features/background-agent/manager.ts
--- a/src/features/background-agent/message-dir.ts
+++ b/src/features/background-agent/message-dir.ts
@@ -0,0 +1,18 @@
+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
+}
--- a/src/features/background-agent/message-storage-locator.ts
+++ b/src/features/background-agent/message-storage-locator.ts
@@ -0,0 +1,17 @@
+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
+}
--- a/src/features/background-agent/notification-builder.ts
+++ b/src/features/background-agent/notification-builder.ts
@@ -0,0 +1,40 @@
+import type { BackgroundTask } from "./types"
+
+export function buildBackgroundTaskNotificationText(args: {
+  task: BackgroundTask
+  duration: string
+  allComplete: boolean
+  remainingCount: number
+  completedTasks: BackgroundTask[]
+}): string {
+  const { task, duration, allComplete, remainingCount, completedTasks } = args
+  const statusText = task.status === "completed" ? "COMPLETED" : "CANCELLED"
+  const errorInfo = task.error ? `\n**Error:** ${task.error}` : ""
+
+  if (allComplete) {
+    const completedTasksText = completedTasks
+      .map((t) => `- \`${t.id}\`: ${t.description}`)
+      .join("\n")
+
+    return `<system-reminder>
+[ALL BACKGROUND TASKS COMPLETE]
+
+**Completed:**
+${completedTasksText || `- \`${task.id}\`: ${task.description}`}
+
+Use \`background_output(task_id="<id>")\` to retrieve each result.
+</system-reminder>`
+  }
+
+  return `<system-reminder>
+[BACKGROUND TASK ${statusText}]
+**ID:** \`${task.id}\`
+**Description:** ${task.description}
+**Duration:** ${duration}${errorInfo}
+
+**${remainingCount} task${remainingCount === 1 ? "" : "s"} still in progress.** You WILL be notified when ALL complete.
+Do NOT poll - continue productive work.
+
+Use \`background_output(task_id="${task.id}")\` to retrieve this result when ready.
+</system-reminder>`
+}
--- a/src/features/background-agent/notification-tracker.ts
+++ b/src/features/background-agent/notification-tracker.ts
@@ -0,0 +1,52 @@
+import type { BackgroundTask } from "./types"
+
+export function markForNotification(
+  notifications: Map<string, BackgroundTask[]>,
+  task: BackgroundTask
+): void {
+  const queue = notifications.get(task.parentSessionID) ?? []
+  queue.push(task)
+  notifications.set(task.parentSessionID, queue)
+}
+
+export function getPendingNotifications(
+  notifications: Map<string, BackgroundTask[]>,
+  sessionID: string
+): BackgroundTask[] {
+  return notifications.get(sessionID) ?? []
+}
+
+export function clearNotifications(
+  notifications: Map<string, BackgroundTask[]>,
+  sessionID: string
+): void {
+  notifications.delete(sessionID)
+}
+
+export function clearNotificationsForTask(
+  notifications: Map<string, BackgroundTask[]>,
+  taskId: string
+): void {
+  for (const [sessionID, tasks] of notifications.entries()) {
+    const filtered = tasks.filter((t) => t.id !== taskId)
+    if (filtered.length === 0) {
+      notifications.delete(sessionID)
+    } else {
+      notifications.set(sessionID, filtered)
+    }
+  }
+}
+
+export function cleanupPendingByParent(
+  pendingByParent: Map<string, Set<string>>,
+  task: BackgroundTask
+): void {
+  if (!task.parentSessionID) return
+  const pending = pendingByParent.get(task.parentSessionID)
+  if (!pending) return
+
+  pending.delete(task.id)
+  if (pending.size === 0) {
+    pendingByParent.delete(task.parentSessionID)
+  }
+}
--- a/src/features/background-agent/notify-parent-session.ts
+++ b/src/features/background-agent/notify-parent-session.ts
@@ -0,0 +1,192 @@
+import { log } from "../../shared"
+
+import { findNearestMessageWithFields } from "../hook-message-injector"
+import { getTaskToastManager } from "../task-toast-manager"
+
+import { TASK_CLEANUP_DELAY_MS } from "./constants"
+import { formatDuration } from "./format-duration"
+import { isAbortedSessionError } from "./error-classifier"
+import { getMessageDir } from "./message-dir"
+import { buildBackgroundTaskNotificationText } from "./notification-builder"
+
+import type { BackgroundTask } from "./types"
+import type { OpencodeClient } from "./opencode-client"
+
+type AgentModel = { providerID: string; modelID: string }
+
+type MessageInfo = {
+  agent?: string
+  model?: AgentModel
+  providerID?: string
+  modelID?: string
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function extractMessageInfo(message: unknown): MessageInfo {
+  if (!isRecord(message)) return {}
+  const info = message["info"]
+  if (!isRecord(info)) return {}
+
+  const agent = typeof info["agent"] === "string" ? info["agent"] : undefined
+  const modelObj = info["model"]
+  if (isRecord(modelObj)) {
+    const providerID = modelObj["providerID"]
+    const modelID = modelObj["modelID"]
+    if (typeof providerID === "string" && typeof modelID === "string") {
+      return { agent, model: { providerID, modelID } }
+    }
+  }
+
+  const providerID = info["providerID"]
+  const modelID = info["modelID"]
+  if (typeof providerID === "string" && typeof modelID === "string") {
+    return { agent, model: { providerID, modelID } }
+  }
+
+  return { agent }
+}
+
+export async function notifyParentSession(args: {
+  task: BackgroundTask
+  tasks: Map<string, BackgroundTask>
+  pendingByParent: Map<string, Set<string>>
+  completionTimers: Map<string, ReturnType<typeof setTimeout>>
+  clearNotificationsForTask: (taskId: string) => void
+  client: OpencodeClient
+}): Promise<void> {
+  const { task, tasks, pendingByParent, completionTimers, clearNotificationsForTask, client } = args
+
+  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 = pendingByParent.get(task.parentSessionID)
+  if (pendingSet) {
+    pendingSet.delete(task.id)
+    if (pendingSet.size === 0) {
+      pendingByParent.delete(task.parentSessionID)
+    }
+  }
+
+  const allComplete = !pendingSet || pendingSet.size === 0
+  const remainingCount = pendingSet?.size ?? 0
+
+  const completedTasks = allComplete
+    ? Array.from(tasks.values()).filter(
+        (t) =>
+          t.parentSessionID === task.parentSessionID &&
+          t.status !== "running" &&
+          t.status !== "pending"
+      )
+    : []
+
+  const notification = buildBackgroundTaskNotificationText({
+    task,
+    duration,
+    allComplete,
+    remainingCount,
+    completedTasks,
+  })
+
+  let agent: string | undefined = task.parentAgent
+  let model: AgentModel | undefined
+
+  try {
+    const messagesResp = await client.session.messages({
+      path: { id: task.parentSessionID },
+    })
+    const raw = (messagesResp as { data?: unknown }).data ?? []
+    const messages = Array.isArray(raw) ? raw : []
+
+    for (let i = messages.length - 1; i >= 0; i--) {
+      const extracted = extractMessageInfo(messages[i])
+      if (extracted.agent || extracted.model) {
+        agent = extracted.agent ?? task.parentAgent
+        model = extracted.model
+        break
+      }
+    }
+  } catch (error) {
+    if (isAbortedSessionError(error)) {
+      log("[background-agent] Parent session aborted, skipping notification:", {
+        taskId: task.id,
+        parentSessionID: task.parentSessionID,
+      })
+      return
+    }
+
+    const messageDir = getMessageDir(task.parentSessionID)
+    const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+    agent = currentMessage?.agent ?? task.parentAgent
+    model =
+      currentMessage?.model?.providerID && currentMessage?.model?.modelID
+        ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+        : undefined
+  }
+
+  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) {
+    if (isAbortedSessionError(error)) {
+      log("[background-agent] Parent session aborted, skipping notification:", {
+        taskId: task.id,
+        parentSessionID: task.parentSessionID,
+      })
+      return
+    }
+    log("[background-agent] Failed to send notification:", error)
+  }
+
+  if (!allComplete) return
+
+  for (const completedTask of completedTasks) {
+    const taskId = completedTask.id
+    const existingTimer = completionTimers.get(taskId)
+    if (existingTimer) {
+      clearTimeout(existingTimer)
+      completionTimers.delete(taskId)
+    }
+
+    const timer = setTimeout(() => {
+      completionTimers.delete(taskId)
+      if (tasks.has(taskId)) {
+        clearNotificationsForTask(taskId)
+        tasks.delete(taskId)
+        log("[background-agent] Removed completed task from memory:", taskId)
+      }
+    }, TASK_CLEANUP_DELAY_MS)
+
+    completionTimers.set(taskId, timer)
+  }
+}
--- a/src/features/background-agent/opencode-client.ts
+++ b/src/features/background-agent/opencode-client.ts
@@ -0,0 +1,3 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+
+export type OpencodeClient = PluginInput["client"]
--- a/src/features/background-agent/parent-session-context-resolver.ts
+++ b/src/features/background-agent/parent-session-context-resolver.ts
@@ -0,0 +1,75 @@
+import type { OpencodeClient } from "./constants"
+import type { BackgroundTask } from "./types"
+import { findNearestMessageWithFields } from "../hook-message-injector"
+import { getMessageDir } from "./message-storage-locator"
+
+type AgentModel = { providerID: string; modelID: string }
+
+function isObject(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function extractAgentAndModelFromMessage(message: unknown): {
+  agent?: string
+  model?: AgentModel
+} {
+  if (!isObject(message)) return {}
+  const info = message["info"]
+  if (!isObject(info)) return {}
+
+  const agent = typeof info["agent"] === "string" ? info["agent"] : undefined
+  const modelObj = info["model"]
+  if (isObject(modelObj)) {
+    const providerID = modelObj["providerID"]
+    const modelID = modelObj["modelID"]
+    if (typeof providerID === "string" && typeof modelID === "string") {
+      return { agent, model: { providerID, modelID } }
+    }
+  }
+
+  const providerID = info["providerID"]
+  const modelID = info["modelID"]
+  if (typeof providerID === "string" && typeof modelID === "string") {
+    return { agent, model: { providerID, modelID } }
+  }
+
+  return { agent }
+}
+
+export async function resolveParentSessionAgentAndModel(input: {
+  client: OpencodeClient
+  task: BackgroundTask
+}): Promise<{ agent?: string; model?: AgentModel }> {
+  const { client, task } = input
+
+  let agent: string | undefined = task.parentAgent
+  let model: AgentModel | undefined
+
+  try {
+    const messagesResp = await client.session.messages({
+      path: { id: task.parentSessionID },
+    })
+
+    const messagesRaw = "data" in messagesResp ? messagesResp.data : []
+    const messages = Array.isArray(messagesRaw) ? messagesRaw : []
+
+    for (let i = messages.length - 1; i >= 0; i--) {
+      const extracted = extractAgentAndModelFromMessage(messages[i])
+      if (extracted.agent || extracted.model) {
+        agent = extracted.agent ?? task.parentAgent
+        model = extracted.model
+        break
+      }
+    }
+  } catch {
+    const messageDir = getMessageDir(task.parentSessionID)
+    const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+    agent = currentMessage?.agent ?? task.parentAgent
+    model =
+      currentMessage?.model?.providerID && currentMessage?.model?.modelID
+        ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+        : undefined
+  }
+
+  return { agent, model }
+}
--- a/src/features/background-agent/parent-session-notifier.ts
+++ b/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)
+  }
+}
--- a/src/features/background-agent/poll-running-tasks.ts
+++ b/src/features/background-agent/poll-running-tasks.ts
@@ -0,0 +1,178 @@
+import { log } from "../../shared"
+
+import {
+  MIN_STABILITY_TIME_MS,
+} from "./constants"
+
+import type { BackgroundTask } from "./types"
+import type { OpencodeClient } from "./opencode-client"
+
+type SessionStatusMap = Record<string, { type: string }>
+
+type MessagePart = {
+  type?: string
+  tool?: string
+  name?: string
+  text?: string
+}
+
+type SessionMessage = {
+  info?: { role?: string }
+  parts?: MessagePart[]
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function asSessionMessages(value: unknown): SessionMessage[] {
+  if (!Array.isArray(value)) return []
+  return value.filter(isRecord) as SessionMessage[]
+}
+
+export async function pollRunningTasks(args: {
+  tasks: Iterable<BackgroundTask>
+  client: OpencodeClient
+  pruneStaleTasksAndNotifications: () => void
+  checkAndInterruptStaleTasks: () => Promise<void>
+  validateSessionHasOutput: (sessionID: string) => Promise<boolean>
+  checkSessionTodos: (sessionID: string) => Promise<boolean>
+  tryCompleteTask: (task: BackgroundTask, source: string) => Promise<boolean>
+  hasRunningTasks: () => boolean
+  stopPolling: () => void
+}): Promise<void> {
+  const {
+    tasks,
+    client,
+    pruneStaleTasksAndNotifications,
+    checkAndInterruptStaleTasks,
+    validateSessionHasOutput,
+    checkSessionTodos,
+    tryCompleteTask,
+    hasRunningTasks,
+    stopPolling,
+  } = args
+
+  pruneStaleTasksAndNotifications()
+  await checkAndInterruptStaleTasks()
+
+  const statusResult = await client.session.status()
+  const allStatuses = ((statusResult as { data?: unknown }).data ?? {}) as SessionStatusMap
+
+  for (const task of tasks) {
+    if (task.status !== "running") continue
+
+    const sessionID = task.sessionID
+    if (!sessionID) continue
+
+    try {
+      const sessionStatus = allStatuses[sessionID]
+      if (sessionStatus?.type === "idle") {
+        const hasValidOutput = await validateSessionHasOutput(sessionID)
+        if (!hasValidOutput) {
+          log("[background-agent] Polling idle but no valid output yet, waiting:", task.id)
+          continue
+        }
+
+        if (task.status !== "running") continue
+
+        const hasIncompleteTodos = await checkSessionTodos(sessionID)
+        if (hasIncompleteTodos) {
+          log("[background-agent] Task has incomplete todos via polling, waiting:", task.id)
+          continue
+        }
+
+        await tryCompleteTask(task, "polling (idle status)")
+        continue
+      }
+
+      const messagesResult = await client.session.messages({
+        path: { id: sessionID },
+      })
+
+      if ((messagesResult as { error?: unknown }).error) {
+        continue
+      }
+
+      const messages = asSessionMessages((messagesResult as { data?: unknown }).data)
+      const assistantMsgs = messages.filter((m) => m.info?.role === "assistant")
+
+      let toolCalls = 0
+      let lastTool: string | undefined
+      let lastMessage: string | undefined
+
+      for (const msg of assistantMsgs) {
+        const parts = msg.parts ?? []
+        for (const part of parts) {
+          if (part.type === "tool_use" || part.tool) {
+            toolCalls += 1
+            lastTool = part.tool || part.name || "unknown"
+          }
+          if (part.type === "text" && part.text) {
+            lastMessage = part.text
+          }
+        }
+      }
+
+      if (!task.progress) {
+        task.progress = { toolCalls: 0, lastUpdate: new Date() }
+      }
+      task.progress.toolCalls = toolCalls
+      task.progress.lastTool = lastTool
+      task.progress.lastUpdate = new Date()
+      if (lastMessage) {
+        task.progress.lastMessage = lastMessage
+        task.progress.lastMessageAt = new Date()
+      }
+
+      const currentMsgCount = messages.length
+      const startedAt = task.startedAt
+      if (!startedAt) continue
+
+      const elapsedMs = Date.now() - startedAt.getTime()
+      if (elapsedMs >= MIN_STABILITY_TIME_MS) {
+        if (task.lastMsgCount === currentMsgCount) {
+          task.stablePolls = (task.stablePolls ?? 0) + 1
+          if (task.stablePolls >= 3) {
+            const recheckStatus = await client.session.status()
+            const recheckData = ((recheckStatus as { data?: unknown }).data ?? {}) as SessionStatusMap
+            const currentStatus = recheckData[sessionID]
+
+            if (currentStatus?.type !== "idle") {
+              log("[background-agent] Stability reached but session not idle, resetting:", {
+                taskId: task.id,
+                sessionStatus: currentStatus?.type ?? "not_in_status",
+              })
+              task.stablePolls = 0
+              continue
+            }
+
+            const hasValidOutput = await validateSessionHasOutput(sessionID)
+            if (!hasValidOutput) {
+              log("[background-agent] Stability reached but no valid output, waiting:", task.id)
+              continue
+            }
+
+            if (task.status !== "running") continue
+
+            const hasIncompleteTodos = await checkSessionTodos(sessionID)
+            if (!hasIncompleteTodos) {
+              await tryCompleteTask(task, "stability detection")
+              continue
+            }
+          }
+        } else {
+          task.stablePolls = 0
+        }
+      }
+
+      task.lastMsgCount = currentMsgCount
+    } catch (error) {
+      log("[background-agent] Poll error for task:", { taskId: task.id, error })
+    }
+  }
+
+  if (!hasRunningTasks()) {
+    stopPolling()
+  }
+}
--- a/src/features/background-agent/process-signal.ts
+++ b/src/features/background-agent/process-signal.ts
@@ -0,0 +1,19 @@
+export type ProcessCleanupEvent = NodeJS.Signals | "beforeExit" | "exit"
+
+export function registerProcessSignal(
+  signal: ProcessCleanupEvent,
+  handler: () => void,
+  exitAfter: boolean
+): () => void {
+  const listener = () => {
+    handler()
+    if (exitAfter) {
+      // Set exitCode and schedule exit after delay to allow other handlers to complete async cleanup
+      // Use 6s delay to accommodate LSP cleanup (5s timeout + 1s SIGKILL wait)
+      process.exitCode = 0
+      setTimeout(() => process.exit(), 6000)
+    }
+  }
+  process.on(signal, listener)
+  return listener
+}
--- a/src/features/background-agent/result-handler-context.ts
+++ b/src/features/background-agent/result-handler-context.ts
@@ -0,0 +1,9 @@
+import type { OpencodeClient } from "./constants"
+import type { ConcurrencyManager } from "./concurrency"
+import type { TaskStateManager } from "./state"
+
+export interface ResultHandlerContext {
+  client: OpencodeClient
+  concurrencyManager: ConcurrencyManager
+  state: TaskStateManager
+}
--- a/src/features/background-agent/result-handler.ts
+++ b/src/features/background-agent/result-handler.ts
@@ -1,276 +1,7 @@
-import type { BackgroundTask } from "./types"
-import type { OpencodeClient, Todo } from "./constants"
-import { TASK_CLEANUP_DELAY_MS } from "./constants"
-import { log } from "../../shared"
-import { getTaskToastManager } from "../task-toast-manager"
-import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../hook-message-injector"
-import { existsSync, readdirSync } from "node:fs"
-import { join } from "node:path"
-import type { ConcurrencyManager } from "./concurrency"
-import type { TaskStateManager } from "./state"
-
-export interface ResultHandlerContext {
-  client: OpencodeClient
-  concurrencyManager: ConcurrencyManager
-  state: TaskStateManager
-}
-
-export async function checkSessionTodos(
-  client: OpencodeClient,
-  sessionID: string
-): Promise<boolean> {
-  try {
-    const response = await client.session.todo({
-      path: { id: sessionID },
-    })
-    const todos = (response.data ?? response) as Todo[]
-    if (!todos || todos.length === 0) return false
-
-    const incomplete = todos.filter(
-      (t) => t.status !== "completed" && t.status !== "cancelled"
-    )
-    return incomplete.length > 0
-  } catch {
-    return false
-  }
-}
-
-export async function validateSessionHasOutput(
-  client: OpencodeClient,
-  sessionID: string
-): Promise<boolean> {
-  try {
-    const response = await client.session.messages({
-      path: { id: sessionID },
-    })
-
-    const messages = response.data ?? []
-    
-    const hasAssistantOrToolMessage = messages.some(
-      (m: { info?: { role?: string } }) => 
-        m.info?.role === "assistant" || m.info?.role === "tool"
-    )
-
-    if (!hasAssistantOrToolMessage) {
-      log("[background-agent] No assistant/tool messages found in session:", sessionID)
-      return false
-    }
-
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    const hasContent = messages.some((m: any) => {
-      if (m.info?.role !== "assistant" && m.info?.role !== "tool") return false
-      const parts = m.parts ?? []
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      return parts.some((p: any) => 
-        (p.type === "text" && p.text && p.text.trim().length > 0) ||
-        (p.type === "reasoning" && p.text && p.text.trim().length > 0) ||
-        p.type === "tool" ||
-        (p.type === "tool_result" && p.content && 
-          (typeof p.content === "string" ? p.content.trim().length > 0 : p.content.length > 0))
-      )
-    })
-
-    if (!hasContent) {
-      log("[background-agent] Messages exist but no content found in session:", sessionID)
-      return false
-    }
-
-    return true
-  } catch (error) {
-    log("[background-agent] Error validating session output:", error)
-    return true
-  }
-}
-
-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 ${seconds % 60}s`
-  }
-  return `${seconds}s`
-}
-
-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 async function tryCompleteTask(
-  task: BackgroundTask,
-  source: string,
-  ctx: ResultHandlerContext
-): Promise<boolean> {
-  const { concurrencyManager, state } = ctx
-
-  if (task.status !== "running") {
-    log("[background-agent] Task already completed, skipping:", { taskId: task.id, status: task.status, source })
-    return false
-  }
-
-  task.status = "completed"
-  task.completedAt = new Date()
-
-  if (task.concurrencyKey) {
-    concurrencyManager.release(task.concurrencyKey)
-    task.concurrencyKey = undefined
-  }
-
-  state.markForNotification(task)
-
-  try {
-    await notifyParentSession(task, ctx)
-    log(`[background-agent] Task completed via ${source}:`, task.id)
-  } catch (err) {
-    log("[background-agent] Error in notifyParentSession:", { taskId: task.id, error: err })
-  }
-
-  return true
-}
-
-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 errorInfo = task.error ? `\n**Error:** ${task.error}` : ""
-  
-  let notification: string
-  let completedTasks: BackgroundTask[] = []
-  if (allComplete) {
-    completedTasks = Array.from(state.tasks.values())
-      .filter(t => t.parentSessionID === task.parentSessionID && t.status !== "running" && t.status !== "pending")
-    const completedTasksText = completedTasks
-      .map(t => `- \`${t.id}\`: ${t.description}`)
-      .join("\n")
-
-    notification = `<system-reminder>
-[ALL BACKGROUND TASKS COMPLETE]
-
-**Completed:**
-${completedTasksText || `- \`${task.id}\`: ${task.description}`}
-
-Use \`background_output(task_id="<id>")\` to retrieve each result.
-</system-reminder>`
-  } else {
-    const agentInfo = task.category 
-      ? `${task.agent} (${task.category})`
-      : task.agent
-    notification = `<system-reminder>
-[BACKGROUND TASK ${statusText}]
-**ID:** \`${task.id}\`
-**Description:** ${task.description}
-**Agent:** ${agentInfo}
-**Duration:** ${duration}${errorInfo}
-
-**${remainingCount} task${remainingCount === 1 ? "" : "s"} still in progress.** You WILL be notified when ALL complete.
-Do NOT poll - continue productive work.
-
-Use \`background_output(task_id="${task.id}")\` to retrieve this result when ready.
-</system-reminder>`
-  }
-
-  let agent: string | undefined = task.parentAgent
-  let model: { providerID: string; modelID: string } | undefined
-
-  try {
-    const messagesResp = await client.session.messages({ path: { id: task.parentSessionID } })
-    const messages = (messagesResp.data ?? []) as Array<{
-      info?: { agent?: string; model?: { providerID: string; modelID: string }; modelID?: string; providerID?: string }
-    }>
-    for (let i = messages.length - 1; i >= 0; i--) {
-      const info = messages[i].info
-      if (info?.agent || info?.model || (info?.modelID && info?.providerID)) {
-        agent = info.agent ?? task.parentAgent
-        model = info.model ?? (info.providerID && info.modelID ? { providerID: info.providerID, modelID: info.modelID } : undefined)
-        break
-      }
-    }
-  } catch {
-    const messageDir = getMessageDir(task.parentSessionID)
-    const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
-    agent = currentMessage?.agent ?? task.parentAgent
-    model = currentMessage?.model?.providerID && currentMessage?.model?.modelID
-      ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
-      : undefined
-  }
-
-  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) {
-    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)
-    }
-  }
-}
+export type { ResultHandlerContext } from "./result-handler-context"
+export { formatDuration } from "./duration-formatter"
+export { getMessageDir } from "./message-storage-locator"
+export { checkSessionTodos } from "./session-todo-checker"
+export { validateSessionHasOutput } from "./session-output-validator"
+export { tryCompleteTask } from "./background-task-completer"
+export { notifyParentSession } from "./parent-session-notifier"
--- a/src/features/background-agent/session-output-validator.ts
+++ b/src/features/background-agent/session-output-validator.ts
@@ -0,0 +1,88 @@
+import type { OpencodeClient } from "./constants"
+import { log } from "../../shared"
+
+type SessionMessagePart = {
+  type?: string
+  text?: string
+  content?: unknown
+}
+
+function isObject(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function getMessageRole(message: unknown): string | undefined {
+  if (!isObject(message)) return undefined
+  const info = message["info"]
+  if (!isObject(info)) return undefined
+  const role = info["role"]
+  return typeof role === "string" ? role : undefined
+}
+
+function getMessageParts(message: unknown): SessionMessagePart[] {
+  if (!isObject(message)) return []
+  const parts = message["parts"]
+  if (!Array.isArray(parts)) return []
+
+  return parts
+    .filter((part): part is SessionMessagePart => isObject(part))
+    .map((part) => ({
+      type: typeof part["type"] === "string" ? part["type"] : undefined,
+      text: typeof part["text"] === "string" ? part["text"] : undefined,
+      content: part["content"],
+    }))
+}
+
+function partHasContent(part: SessionMessagePart): boolean {
+  if (part.type === "text" || part.type === "reasoning") {
+    return Boolean(part.text && part.text.trim().length > 0)
+  }
+  if (part.type === "tool") return true
+  if (part.type === "tool_result") {
+    if (typeof part.content === "string") return part.content.trim().length > 0
+    if (Array.isArray(part.content)) return part.content.length > 0
+    return Boolean(part.content)
+  }
+  return false
+}
+
+export async function validateSessionHasOutput(
+  client: OpencodeClient,
+  sessionID: string
+): Promise<boolean> {
+  try {
+    const response = await client.session.messages({
+      path: { id: sessionID },
+    })
+
+    const messagesRaw = "data" in response ? response.data : []
+    const messages = Array.isArray(messagesRaw) ? messagesRaw : []
+
+    const hasAssistantOrToolMessage = messages.some((message) => {
+      const role = getMessageRole(message)
+      return role === "assistant" || role === "tool"
+    })
+
+    if (!hasAssistantOrToolMessage) {
+      log("[background-agent] No assistant/tool messages found in session:", sessionID)
+      return false
+    }
+
+    const hasContent = messages.some((message) => {
+      const role = getMessageRole(message)
+      if (role !== "assistant" && role !== "tool") return false
+      const parts = getMessageParts(message)
+      return parts.some(partHasContent)
+    })
+
+    if (!hasContent) {
+      log("[background-agent] Messages exist but no content found in session:", sessionID)
+      return false
+    }
+
+    return true
+  } catch (error) {
+    log("[background-agent] Error validating session output:", error)
+    return true
+  }
+}
--- a/src/features/background-agent/session-todo-checker.ts
+++ b/src/features/background-agent/session-todo-checker.ts
@@ -0,0 +1,33 @@
+import type { OpencodeClient, Todo } from "./constants"
+
+function isTodo(value: unknown): value is Todo {
+  if (typeof value !== "object" || value === null) return false
+  const todo = value as Record<string, unknown>
+  return (
+    typeof todo["id"] === "string" &&
+    typeof todo["content"] === "string" &&
+    typeof todo["status"] === "string" &&
+    typeof todo["priority"] === "string"
+  )
+}
+
+export async function checkSessionTodos(
+  client: OpencodeClient,
+  sessionID: string
+): Promise<boolean> {
+  try {
+    const response = await client.session.todo({
+      path: { id: sessionID },
+    })
+
+    const todosRaw = "data" in response ? response.data : response
+    if (!Array.isArray(todosRaw) || todosRaw.length === 0) return false
+
+    const incomplete = todosRaw
+      .filter(isTodo)
+      .filter((todo) => todo.status !== "completed" && todo.status !== "cancelled")
+    return incomplete.length > 0
+  } catch {
+    return false
+  }
+}
--- a/src/features/background-agent/session-validator.ts
+++ b/src/features/background-agent/session-validator.ts
@@ -0,0 +1,111 @@
+import { log } from "../../shared"
+
+import type { OpencodeClient } from "./opencode-client"
+
+type Todo = {
+  content: string
+  status: string
+  priority: string
+  id: string
+}
+
+type SessionMessage = {
+  info?: { role?: string }
+  parts?: unknown
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function asSessionMessages(value: unknown): SessionMessage[] {
+  if (!Array.isArray(value)) return []
+  return value as SessionMessage[]
+}
+
+function asParts(value: unknown): Array<Record<string, unknown>> {
+  if (!Array.isArray(value)) return []
+  return value.filter(isRecord)
+}
+
+function hasNonEmptyText(value: unknown): boolean {
+  return typeof value === "string" && value.trim().length > 0
+}
+
+function isToolResultContentNonEmpty(content: unknown): boolean {
+  if (typeof content === "string") return content.trim().length > 0
+  if (Array.isArray(content)) return content.length > 0
+  return false
+}
+
+/**
+ * Validates that a session has actual assistant/tool output before marking complete.
+ * Prevents premature completion when session.idle fires before agent responds.
+ */
+export async function validateSessionHasOutput(
+  client: OpencodeClient,
+  sessionID: string
+): Promise<boolean> {
+  try {
+    const response = await client.session.messages({
+      path: { id: sessionID },
+    })
+
+    const messages = asSessionMessages((response as { data?: unknown }).data ?? response)
+
+    const hasAssistantOrToolMessage = messages.some(
+      (m) => m.info?.role === "assistant" || m.info?.role === "tool"
+    )
+    if (!hasAssistantOrToolMessage) {
+      log("[background-agent] No assistant/tool messages found in session:", sessionID)
+      return false
+    }
+
+    const hasContent = messages.some((m) => {
+      if (m.info?.role !== "assistant" && m.info?.role !== "tool") return false
+
+      const parts = asParts(m.parts)
+      return parts.some((part) => {
+        const type = part.type
+        if (type === "tool") return true
+        if (type === "text" && hasNonEmptyText(part.text)) return true
+        if (type === "reasoning" && hasNonEmptyText(part.text)) return true
+        if (type === "tool_result" && isToolResultContentNonEmpty(part.content)) return true
+        return false
+      })
+    })
+
+    if (!hasContent) {
+      log("[background-agent] Messages exist but no content found in session:", sessionID)
+      return false
+    }
+
+    return true
+  } catch (error) {
+    log("[background-agent] Error validating session output:", error)
+    // On error, allow completion to proceed (don't block indefinitely)
+    return true
+  }
+}
+
+export async function checkSessionTodos(
+  client: OpencodeClient,
+  sessionID: string
+): Promise<boolean> {
+  try {
+    const response = await client.session.todo({
+      path: { id: sessionID },
+    })
+
+    const raw = (response as { data?: unknown }).data ?? response
+    const todos = Array.isArray(raw) ? (raw as Todo[]) : []
+    if (todos.length === 0) return false
+
+    const incomplete = todos.filter(
+      (t) => t.status !== "completed" && t.status !== "cancelled"
+    )
+    return incomplete.length > 0
+  } catch {
+    return false
+  }
+}
--- a/src/features/background-agent/spawner.ts
+++ b/src/features/background-agent/spawner.ts
@@ -1,242 +1,4 @@
-import type { BackgroundTask, LaunchInput, ResumeInput } from "./types"
-import type { OpencodeClient, OnSubagentSessionCreated, QueueItem } from "./constants"
-import { TMUX_CALLBACK_DELAY_MS } from "./constants"
-import { log, getAgentToolRestrictions, promptWithModelSuggestionRetry } from "../../shared"
-import { subagentSessions } from "../claude-code-session-state"
-import { getTaskToastManager } from "../task-toast-manager"
-import { isInsideTmux } from "../../shared/tmux"
-import type { ConcurrencyManager } from "./concurrency"
-
-export interface SpawnerContext {
-  client: OpencodeClient
-  directory: string
-  concurrencyManager: ConcurrencyManager
-  tmuxEnabled: boolean
-  onSubagentSessionCreated?: OnSubagentSessionCreated
-  onTaskError: (task: BackgroundTask, error: Error) => void
-}
-
-export function createTask(input: LaunchInput): BackgroundTask {
-  return {
-    id: `bg_${crypto.randomUUID().slice(0, 8)}`,
-    status: "pending",
-    queuedAt: new Date(),
-    description: input.description,
-    prompt: input.prompt,
-    agent: input.agent,
-    parentSessionID: input.parentSessionID,
-    parentMessageID: input.parentMessageID,
-    parentModel: input.parentModel,
-    parentAgent: input.parentAgent,
-    model: input.model,
-  }
-}
-
-export async function startTask(
-  item: QueueItem,
-  ctx: SpawnerContext
-): Promise<void> {
-  const { task, input } = item
-  const { client, directory, concurrencyManager, tmuxEnabled, onSubagentSessionCreated, onTaskError } = ctx
-
-  log("[background-agent] Starting task:", {
-    taskId: task.id,
-    agent: input.agent,
-    model: input.model,
-  })
-
-  const concurrencyKey = input.model
-    ? `${input.model.providerID}/${input.model.modelID}`
-    : input.agent
-
-  const parentSession = await client.session.get({
-    path: { id: input.parentSessionID },
-  }).catch((err) => {
-    log(`[background-agent] Failed to get parent session: ${err}`)
-    return null
-  })
-  const parentDirectory = parentSession?.data?.directory ?? directory
-  log(`[background-agent] Parent dir: ${parentSession?.data?.directory}, using: ${parentDirectory}`)
-
-  const createResult = await client.session.create({
-    body: {
-      parentID: input.parentSessionID,
-      title: `Background: ${input.description}`,
-      permission: [
-        { permission: "question", action: "deny" as const, pattern: "*" },
-      ],
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    } as any,
-    query: {
-      directory: parentDirectory,
-    },
-  }).catch((error) => {
-    concurrencyManager.release(concurrencyKey)
-    throw error
-  })
-
-  if (createResult.error) {
-    concurrencyManager.release(concurrencyKey)
-    throw new Error(`Failed to create background session: ${createResult.error}`)
-  }
-
-  const sessionID = createResult.data.id
-  subagentSessions.add(sessionID)
-
-  log("[background-agent] tmux callback check", {
-    hasCallback: !!onSubagentSessionCreated,
-    tmuxEnabled,
-    isInsideTmux: isInsideTmux(),
-    sessionID,
-    parentID: input.parentSessionID,
-  })
-
-  if (onSubagentSessionCreated && tmuxEnabled && isInsideTmux()) {
-    log("[background-agent] Invoking tmux callback NOW", { sessionID })
-    await onSubagentSessionCreated({
-      sessionID,
-      parentID: input.parentSessionID,
-      title: input.description,
-    }).catch((err) => {
-      log("[background-agent] Failed to spawn tmux pane:", err)
-    })
-    log("[background-agent] tmux callback completed, waiting")
-    await new Promise(r => setTimeout(r, TMUX_CALLBACK_DELAY_MS))
-  } else {
-    log("[background-agent] SKIP tmux callback - conditions not met")
-  }
-
-  task.status = "running"
-  task.startedAt = new Date()
-  task.sessionID = sessionID
-  task.progress = {
-    toolCalls: 0,
-    lastUpdate: new Date(),
-  }
-  task.concurrencyKey = concurrencyKey
-  task.concurrencyGroup = concurrencyKey
-
-  log("[background-agent] Launching task:", { taskId: task.id, sessionID, agent: input.agent })
-
-  const toastManager = getTaskToastManager()
-  if (toastManager) {
-    toastManager.updateTask(task.id, "running")
-  }
-
-  log("[background-agent] Calling prompt (fire-and-forget) for launch with:", {
-    sessionID,
-    agent: input.agent,
-    model: input.model,
-    hasSkillContent: !!input.skillContent,
-    promptLength: input.prompt.length,
-  })
-
-  const launchModel = input.model
-    ? { providerID: input.model.providerID, modelID: input.model.modelID }
-    : undefined
-  const launchVariant = input.model?.variant
-
-  promptWithModelSuggestionRetry(client, {
-    path: { id: sessionID },
-    body: {
-      agent: input.agent,
-      ...(launchModel ? { model: launchModel } : {}),
-      ...(launchVariant ? { variant: launchVariant } : {}),
-      system: input.skillContent,
-      tools: {
-        ...getAgentToolRestrictions(input.agent),
-        task: false,
-        call_omo_agent: true,
-        question: false,
-      },
-      parts: [{ type: "text", text: input.prompt }],
-    },
-  }).catch((error) => {
-    log("[background-agent] promptAsync error:", error)
-    onTaskError(task, error instanceof Error ? error : new Error(String(error)))
-  })
-}
-
-export async function resumeTask(
-  task: BackgroundTask,
-  input: ResumeInput,
-  ctx: Pick<SpawnerContext, "client" | "concurrencyManager" | "onTaskError">
-): Promise<void> {
-  const { client, concurrencyManager, onTaskError } = ctx
-
-  if (!task.sessionID) {
-    throw new Error(`Task has no sessionID: ${task.id}`)
-  }
-
-  if (task.status === "running") {
-    log("[background-agent] Resume skipped - task already running:", {
-      taskId: task.id,
-      sessionID: task.sessionID,
-    })
-    return
-  }
-
-  const concurrencyKey = task.concurrencyGroup ?? task.agent
-  await concurrencyManager.acquire(concurrencyKey)
-  task.concurrencyKey = concurrencyKey
-  task.concurrencyGroup = concurrencyKey
-
-  task.status = "running"
-  task.completedAt = undefined
-  task.error = undefined
-  task.parentSessionID = input.parentSessionID
-  task.parentMessageID = input.parentMessageID
-  task.parentModel = input.parentModel
-  task.parentAgent = input.parentAgent
-  task.startedAt = new Date()
-
-  task.progress = {
-    toolCalls: task.progress?.toolCalls ?? 0,
-    lastUpdate: new Date(),
-  }
-
-  subagentSessions.add(task.sessionID)
-
-  const toastManager = getTaskToastManager()
-  if (toastManager) {
-    toastManager.addTask({
-      id: task.id,
-      description: task.description,
-      agent: task.agent,
-      isBackground: true,
-    })
-  }
-
-  log("[background-agent] Resuming task:", { taskId: task.id, sessionID: task.sessionID })
-
-  log("[background-agent] Resuming task - calling prompt (fire-and-forget) with:", {
-    sessionID: task.sessionID,
-    agent: task.agent,
-    model: task.model,
-    promptLength: input.prompt.length,
-  })
-
-  const resumeModel = task.model
-    ? { providerID: task.model.providerID, modelID: task.model.modelID }
-    : undefined
-  const resumeVariant = task.model?.variant
-
-  client.session.promptAsync({
-    path: { id: task.sessionID },
-    body: {
-      agent: task.agent,
-      ...(resumeModel ? { model: resumeModel } : {}),
-      ...(resumeVariant ? { variant: resumeVariant } : {}),
-      tools: {
-        ...getAgentToolRestrictions(task.agent),
-        task: false,
-        call_omo_agent: true,
-        question: false,
-      },
-      parts: [{ type: "text", text: input.prompt }],
-    },
-  }).catch((error) => {
-    log("[background-agent] resume prompt error:", error)
-    onTaskError(task, error instanceof Error ? error : new Error(String(error)))
-  })
-}
+export type { SpawnerContext } from "./spawner/spawner-context"
+export { createTask } from "./spawner/task-factory"
+export { startTask } from "./spawner/task-starter"
+export { resumeTask } from "./spawner/task-resumer"
--- a/src/features/background-agent/spawner/background-session-creator.ts
+++ b/src/features/background-agent/spawner/background-session-creator.ts
@@ -0,0 +1,45 @@
+import type { OpencodeClient } from "../constants"
+import type { ConcurrencyManager } from "../concurrency"
+import type { LaunchInput } from "../types"
+import { log } from "../../../shared"
+
+export async function createBackgroundSession(options: {
+  client: OpencodeClient
+  input: LaunchInput
+  parentDirectory: string
+  concurrencyManager: ConcurrencyManager
+  concurrencyKey: string
+}): Promise<string> {
+  const { client, input, parentDirectory, concurrencyManager, concurrencyKey } = options
+
+  const body = {
+    parentID: input.parentSessionID,
+    title: `Background: ${input.description}`,
+  }
+
+  const createResult = await client.session
+    .create({
+      body,
+      query: {
+        directory: parentDirectory,
+      },
+    })
+    .catch((error: unknown) => {
+      concurrencyManager.release(concurrencyKey)
+      throw error
+    })
+
+  if (createResult.error) {
+    concurrencyManager.release(concurrencyKey)
+    throw new Error(`Failed to create background session: ${createResult.error}`)
+  }
+
+  if (!createResult.data?.id) {
+    concurrencyManager.release(concurrencyKey)
+    throw new Error("Failed to create background session: API returned no session ID")
+  }
+
+  const sessionID = createResult.data.id
+  log("[background-agent] Background session created", { sessionID })
+  return sessionID
+}
--- a/src/features/background-agent/spawner/concurrency-key-from-launch-input.ts
+++ b/src/features/background-agent/spawner/concurrency-key-from-launch-input.ts
@@ -0,0 +1,7 @@
+import type { LaunchInput } from "../types"
+
+export function getConcurrencyKeyFromLaunchInput(input: LaunchInput): string {
+  return input.model
+    ? `${input.model.providerID}/${input.model.modelID}`
+    : input.agent
+}
--- a/src/features/background-agent/spawner/parent-directory-resolver.ts
+++ b/src/features/background-agent/spawner/parent-directory-resolver.ts
@@ -0,0 +1,21 @@
+import type { OpencodeClient } from "../constants"
+import { log } from "../../../shared"
+
+export async function resolveParentDirectory(options: {
+  client: OpencodeClient
+  parentSessionID: string
+  defaultDirectory: string
+}): Promise<string> {
+  const { client, parentSessionID, defaultDirectory } = options
+
+  const parentSession = await client.session
+    .get({ path: { id: parentSessionID } })
+    .catch((error: unknown) => {
+      log(`[background-agent] Failed to get parent session: ${error}`)
+      return null
+    })
+
+  const parentDirectory = parentSession?.data?.directory ?? defaultDirectory
+  log(`[background-agent] Parent dir: ${parentSession?.data?.directory}, using: ${parentDirectory}`)
+  return parentDirectory
+}
--- a/src/features/background-agent/spawner/spawner-context.ts
+++ b/src/features/background-agent/spawner/spawner-context.ts
@@ -0,0 +1,12 @@
+import type { BackgroundTask } from "../types"
+import type { ConcurrencyManager } from "../concurrency"
+import type { OpencodeClient, OnSubagentSessionCreated } from "../constants"
+
+export interface SpawnerContext {
+  client: OpencodeClient
+  directory: string
+  concurrencyManager: ConcurrencyManager
+  tmuxEnabled: boolean
+  onSubagentSessionCreated?: OnSubagentSessionCreated
+  onTaskError: (task: BackgroundTask, error: Error) => void
+}
--- a/src/features/background-agent/spawner/task-factory.ts
+++ b/src/features/background-agent/spawner/task-factory.ts
@@ -0,0 +1,18 @@
+import { randomUUID } from "crypto"
+import type { BackgroundTask, LaunchInput } from "../types"
+
+export function createTask(input: LaunchInput): BackgroundTask {
+  return {
+    id: `bg_${randomUUID().slice(0, 8)}`,
+    status: "pending",
+    queuedAt: new Date(),
+    description: input.description,
+    prompt: input.prompt,
+    agent: input.agent,
+    parentSessionID: input.parentSessionID,
+    parentMessageID: input.parentMessageID,
+    parentModel: input.parentModel,
+    parentAgent: input.parentAgent,
+    model: input.model,
+  }
+}
--- a/src/features/background-agent/spawner/task-resumer.ts
+++ b/src/features/background-agent/spawner/task-resumer.ts
@@ -0,0 +1,91 @@
+import type { BackgroundTask, ResumeInput } from "../types"
+import { log, getAgentToolRestrictions } from "../../../shared"
+import type { SpawnerContext } from "./spawner-context"
+import { subagentSessions } from "../../claude-code-session-state"
+import { getTaskToastManager } from "../../task-toast-manager"
+
+export async function resumeTask(
+  task: BackgroundTask,
+  input: ResumeInput,
+  ctx: Pick<SpawnerContext, "client" | "concurrencyManager" | "onTaskError">
+): Promise<void> {
+  const { client, concurrencyManager, onTaskError } = ctx
+
+  if (!task.sessionID) {
+    throw new Error(`Task has no sessionID: ${task.id}`)
+  }
+
+  if (task.status === "running") {
+    log("[background-agent] Resume skipped - task already running:", {
+      taskId: task.id,
+      sessionID: task.sessionID,
+    })
+    return
+  }
+
+  const concurrencyKey = task.concurrencyGroup ?? task.agent
+  await concurrencyManager.acquire(concurrencyKey)
+  task.concurrencyKey = concurrencyKey
+  task.concurrencyGroup = concurrencyKey
+
+  task.status = "running"
+  task.completedAt = undefined
+  task.error = undefined
+  task.parentSessionID = input.parentSessionID
+  task.parentMessageID = input.parentMessageID
+  task.parentModel = input.parentModel
+  task.parentAgent = input.parentAgent
+  task.startedAt = new Date()
+
+  task.progress = {
+    toolCalls: task.progress?.toolCalls ?? 0,
+    lastUpdate: new Date(),
+  }
+
+  subagentSessions.add(task.sessionID)
+
+  const toastManager = getTaskToastManager()
+  if (toastManager) {
+    toastManager.addTask({
+      id: task.id,
+      description: task.description,
+      agent: task.agent,
+      isBackground: true,
+    })
+  }
+
+  log("[background-agent] Resuming task:", { taskId: task.id, sessionID: task.sessionID })
+
+  log("[background-agent] Resuming task - calling prompt (fire-and-forget) with:", {
+    sessionID: task.sessionID,
+    agent: task.agent,
+    model: task.model,
+    promptLength: input.prompt.length,
+  })
+
+  const resumeModel = task.model
+    ? { providerID: task.model.providerID, modelID: task.model.modelID }
+    : undefined
+  const resumeVariant = task.model?.variant
+
+  client.session
+    .promptAsync({
+      path: { id: task.sessionID },
+      body: {
+        agent: task.agent,
+        ...(resumeModel ? { model: resumeModel } : {}),
+        ...(resumeVariant ? { variant: resumeVariant } : {}),
+        tools: {
+          ...getAgentToolRestrictions(task.agent),
+          task: false,
+          call_omo_agent: true,
+          question: false,
+        },
+        parts: [{ type: "text", text: input.prompt }],
+      },
+    })
+    .catch((error: unknown) => {
+      log("[background-agent] resume prompt error:", error)
+      onTaskError(task, error instanceof Error ? error : new Error(String(error)))
+    })
+}
--- a/src/features/background-agent/spawner/task-starter.ts
+++ b/src/features/background-agent/spawner/task-starter.ts
@@ -0,0 +1,94 @@
+import type { QueueItem } from "../constants"
+import { log, getAgentToolRestrictions, promptWithModelSuggestionRetry } from "../../../shared"
+import { subagentSessions } from "../../claude-code-session-state"
+import { getTaskToastManager } from "../../task-toast-manager"
+import { createBackgroundSession } from "./background-session-creator"
+import { getConcurrencyKeyFromLaunchInput } from "./concurrency-key-from-launch-input"
+import { resolveParentDirectory } from "./parent-directory-resolver"
+import type { SpawnerContext } from "./spawner-context"
+import { maybeInvokeTmuxCallback } from "./tmux-callback-invoker"
+
+export async function startTask(item: QueueItem, ctx: SpawnerContext): Promise<void> {
+  const { task, input } = item
+  const { client, directory, concurrencyManager, tmuxEnabled, onSubagentSessionCreated, onTaskError } = ctx
+
+  log("[background-agent] Starting task:", {
+    taskId: task.id,
+    agent: input.agent,
+    model: input.model,
+  })
+
+  const concurrencyKey = getConcurrencyKeyFromLaunchInput(input)
+  const parentDirectory = await resolveParentDirectory({
+    client,
+    parentSessionID: input.parentSessionID,
+    defaultDirectory: directory,
+  })
+
+  const sessionID = await createBackgroundSession({
+    client,
+    input,
+    parentDirectory,
+    concurrencyManager,
+    concurrencyKey,
+  })
+  subagentSessions.add(sessionID)
+
+  await maybeInvokeTmuxCallback({
+    onSubagentSessionCreated,
+    tmuxEnabled,
+    sessionID,
+    parentID: input.parentSessionID,
+    title: input.description,
+  })
+
+  task.status = "running"
+  task.startedAt = new Date()
+  task.sessionID = sessionID
+  task.progress = {
+    toolCalls: 0,
+    lastUpdate: new Date(),
+  }
+  task.concurrencyKey = concurrencyKey
+  task.concurrencyGroup = concurrencyKey
+
+  log("[background-agent] Launching task:", { taskId: task.id, sessionID, agent: input.agent })
+
+  const toastManager = getTaskToastManager()
+  if (toastManager) {
+    toastManager.updateTask(task.id, "running")
+  }
+
+  log("[background-agent] Calling prompt (fire-and-forget) for launch with:", {
+    sessionID,
+    agent: input.agent,
+    model: input.model,
+    hasSkillContent: !!input.skillContent,
+    promptLength: input.prompt.length,
+  })
+
+  const launchModel = input.model
+    ? { providerID: input.model.providerID, modelID: input.model.modelID }
+    : undefined
+  const launchVariant = input.model?.variant
+
+  promptWithModelSuggestionRetry(client, {
+    path: { id: sessionID },
+    body: {
+      agent: input.agent,
+      ...(launchModel ? { model: launchModel } : {}),
+      ...(launchVariant ? { variant: launchVariant } : {}),
+      system: input.skillContent,
+      tools: {
+        ...getAgentToolRestrictions(input.agent),
+        task: false,
+        call_omo_agent: true,
+        question: false,
+      },
+      parts: [{ type: "text", text: input.prompt }],
+    },
+  }).catch((error: unknown) => {
+    log("[background-agent] promptAsync error:", error)
+    onTaskError(task, error instanceof Error ? error : new Error(String(error)))
+  })
+}
--- a/src/features/background-agent/spawner/tmux-callback-invoker.ts
+++ b/src/features/background-agent/spawner/tmux-callback-invoker.ts
@@ -0,0 +1,40 @@
+import { setTimeout } from "timers/promises"
+import type { OnSubagentSessionCreated } from "../constants"
+import { TMUX_CALLBACK_DELAY_MS } from "../constants"
+import { log } from "../../../shared"
+import { isInsideTmux } from "../../../shared/tmux"
+
+export async function maybeInvokeTmuxCallback(options: {
+  onSubagentSessionCreated?: OnSubagentSessionCreated
+  tmuxEnabled: boolean
+  sessionID: string
+  parentID: string
+  title: string
+}): Promise<void> {
+  const { onSubagentSessionCreated, tmuxEnabled, sessionID, parentID, title } = options
+
+  log("[background-agent] tmux callback check", {
+    hasCallback: !!onSubagentSessionCreated,
+    tmuxEnabled,
+    isInsideTmux: isInsideTmux(),
+    sessionID,
+    parentID,
+  })
+
+  if (!onSubagentSessionCreated || !tmuxEnabled || !isInsideTmux()) {
+    log("[background-agent] SKIP tmux callback - conditions not met")
+    return
+  }
+
+  log("[background-agent] Invoking tmux callback NOW", { sessionID })
+  await onSubagentSessionCreated({
+    sessionID,
+    parentID,
+    title,
+  }).catch((error: unknown) => {
+    log("[background-agent] Failed to spawn tmux pane:", error)
+  })
+
+  log("[background-agent] tmux callback completed, waiting")
+  await setTimeout(TMUX_CALLBACK_DELAY_MS)
+}
--- a/src/features/background-agent/stale-task-pruner.ts
+++ b/src/features/background-agent/stale-task-pruner.ts
@@ -0,0 +1,57 @@
+import { log } from "../../shared"
+
+import { TASK_TTL_MS } from "./constants"
+import { subagentSessions } from "../claude-code-session-state"
+import { pruneStaleTasksAndNotifications } from "./task-poller"
+
+import type { BackgroundTask } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+
+export function pruneStaleState(args: {
+  tasks: Map<string, BackgroundTask>
+  notifications: Map<string, BackgroundTask[]>
+  concurrencyManager: ConcurrencyManager
+  cleanupPendingByParent: (task: BackgroundTask) => void
+  clearNotificationsForTask: (taskId: string) => void
+}): void {
+  const {
+    tasks,
+    notifications,
+    concurrencyManager,
+    cleanupPendingByParent,
+    clearNotificationsForTask,
+  } = args
+
+  pruneStaleTasksAndNotifications({
+    tasks,
+    notifications,
+    onTaskPruned: (taskId, task, errorMessage) => {
+      const now = Date.now()
+      const timestamp = task.status === "pending"
+        ? task.queuedAt?.getTime()
+        : task.startedAt?.getTime()
+      const age = timestamp ? now - timestamp : TASK_TTL_MS
+
+      log("[background-agent] Pruning stale task:", {
+        taskId,
+        status: task.status,
+        age: Math.round(age / 1000) + "s",
+      })
+
+      task.status = "error"
+      task.error = errorMessage
+      task.completedAt = new Date()
+      if (task.concurrencyKey) {
+        concurrencyManager.release(task.concurrencyKey)
+        task.concurrencyKey = undefined
+      }
+
+      cleanupPendingByParent(task)
+      clearNotificationsForTask(taskId)
+      tasks.delete(taskId)
+      if (task.sessionID) {
+        subagentSessions.delete(task.sessionID)
+      }
+    },
+  })
+}
--- a/src/features/background-agent/state.ts
+++ b/src/features/background-agent/state.ts
@@ -2,7 +2,6 @@ import type { BackgroundTask, LaunchInput } from "./types"
 import type { QueueItem } from "./constants"
 import { log } from "../../shared"
 import { subagentSessions } from "../claude-code-session-state"
-
 export class TaskStateManager {
  readonly tasks: Map<string, BackgroundTask> = new Map()
  readonly notifications: Map<string, BackgroundTask[]> = new Map()
@@ -10,11 +9,9 @@ export class TaskStateManager {
  readonly queuesByKey: Map<string, QueueItem[]> = new Map()
  readonly processingKeys: Set<string> = new Set()
  readonly completionTimers: Map<string, ReturnType<typeof setTimeout>> = new Map()
-
  getTask(id: string): BackgroundTask | undefined {
    return this.tasks.get(id)
  }
-
  findBySession(sessionID: string): BackgroundTask | undefined {
    for (const task of this.tasks.values()) {
      if (task.sessionID === sessionID) {
@@ -23,7 +20,6 @@ export class TaskStateManager {
    }
    return undefined
  }
-
  getTasksByParentSession(sessionID: string): BackgroundTask[] {
    const result: BackgroundTask[] = []
    for (const task of this.tasks.values()) {
@@ -52,7 +48,6 @@ export class TaskStateManager {
  getRunningTasks(): BackgroundTask[] {
    return Array.from(this.tasks.values()).filter(t => t.status === "running")
  }
-
  getCompletedTasks(): BackgroundTask[] {
    return Array.from(this.tasks.values()).filter(t => t.status !== "running")
  }
--- a/src/features/background-agent/task-canceller.ts
+++ b/src/features/background-agent/task-canceller.ts
@@ -0,0 +1,117 @@
+import { log } from "../../shared"
+
+import type { BackgroundTask } from "./types"
+import type { LaunchInput } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+import type { OpencodeClient } from "./opencode-client"
+
+type QueueItem = { task: BackgroundTask; input: LaunchInput }
+
+export async function cancelBackgroundTask(args: {
+  taskId: string
+  options?: {
+    source?: string
+    reason?: string
+    abortSession?: boolean
+    skipNotification?: boolean
+  }
+  tasks: Map<string, BackgroundTask>
+  queuesByKey: Map<string, QueueItem[]>
+  completionTimers: Map<string, ReturnType<typeof setTimeout>>
+  idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>>
+  concurrencyManager: ConcurrencyManager
+  client: OpencodeClient
+  cleanupPendingByParent: (task: BackgroundTask) => void
+  markForNotification: (task: BackgroundTask) => void
+  notifyParentSession: (task: BackgroundTask) => Promise<void>
+}): Promise<boolean> {
+  const {
+    taskId,
+    options,
+    tasks,
+    queuesByKey,
+    completionTimers,
+    idleDeferralTimers,
+    concurrencyManager,
+    client,
+    cleanupPendingByParent,
+    markForNotification,
+    notifyParentSession,
+  } = args
+
+  const task = tasks.get(taskId)
+  if (!task || (task.status !== "running" && task.status !== "pending")) {
+    return false
+  }
+
+  const source = options?.source ?? "cancel"
+  const abortSession = options?.abortSession !== false
+  const reason = options?.reason
+
+  if (task.status === "pending") {
+    const key = task.model
+      ? `${task.model.providerID}/${task.model.modelID}`
+      : task.agent
+    const queue = queuesByKey.get(key)
+    if (queue) {
+      const index = queue.findIndex((item) => item.task.id === taskId)
+      if (index !== -1) {
+        queue.splice(index, 1)
+        if (queue.length === 0) {
+          queuesByKey.delete(key)
+        }
+      }
+    }
+    log("[background-agent] Cancelled pending task:", { taskId, key })
+  }
+
+  task.status = "cancelled"
+  task.completedAt = new Date()
+  if (reason) {
+    task.error = reason
+  }
+
+  if (task.concurrencyKey) {
+    concurrencyManager.release(task.concurrencyKey)
+    task.concurrencyKey = undefined
+  }
+
+  const completionTimer = completionTimers.get(task.id)
+  if (completionTimer) {
+    clearTimeout(completionTimer)
+    completionTimers.delete(task.id)
+  }
+
+  const idleTimer = idleDeferralTimers.get(task.id)
+  if (idleTimer) {
+    clearTimeout(idleTimer)
+    idleDeferralTimers.delete(task.id)
+  }
+
+  cleanupPendingByParent(task)
+
+  if (abortSession && task.sessionID) {
+    client.session.abort({
+      path: { id: task.sessionID },
+    }).catch(() => {})
+  }
+
+  if (options?.skipNotification) {
+    log(`[background-agent] Task cancelled via ${source} (notification skipped):`, task.id)
+    return true
+  }
+
+  markForNotification(task)
+
+  try {
+    await notifyParentSession(task)
+    log(`[background-agent] Task cancelled via ${source}:`, task.id)
+  } catch (err) {
+    log("[background-agent] Error in notifyParentSession for cancelled task:", {
+      taskId: task.id,
+      error: err,
+    })
+  }
+
+  return true
+}
--- a/src/features/background-agent/task-completer.ts
+++ b/src/features/background-agent/task-completer.ts
@@ -0,0 +1,68 @@
+import { log } from "../../shared"
+
+import type { BackgroundTask } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+import type { OpencodeClient } from "./opencode-client"
+
+export async function tryCompleteBackgroundTask(args: {
+  task: BackgroundTask
+  source: string
+  concurrencyManager: ConcurrencyManager
+  idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>>
+  client: OpencodeClient
+  markForNotification: (task: BackgroundTask) => void
+  cleanupPendingByParent: (task: BackgroundTask) => void
+  notifyParentSession: (task: BackgroundTask) => Promise<void>
+}): Promise<boolean> {
+  const {
+    task,
+    source,
+    concurrencyManager,
+    idleDeferralTimers,
+    client,
+    markForNotification,
+    cleanupPendingByParent,
+    notifyParentSession,
+  } = args
+
+  if (task.status !== "running") {
+    log("[background-agent] Task already completed, skipping:", {
+      taskId: task.id,
+      status: task.status,
+      source,
+    })
+    return false
+  }
+
+  task.status = "completed"
+  task.completedAt = new Date()
+
+  if (task.concurrencyKey) {
+    concurrencyManager.release(task.concurrencyKey)
+    task.concurrencyKey = undefined
+  }
+
+  markForNotification(task)
+  cleanupPendingByParent(task)
+
+  const idleTimer = idleDeferralTimers.get(task.id)
+  if (idleTimer) {
+    clearTimeout(idleTimer)
+    idleDeferralTimers.delete(task.id)
+  }
+
+  if (task.sessionID) {
+    client.session.abort({
+      path: { id: task.sessionID },
+    }).catch(() => {})
+  }
+
+  try {
+    await notifyParentSession(task)
+    log(`[background-agent] Task completed via ${source}:`, task.id)
+  } catch (err) {
+    log("[background-agent] Error in notifyParentSession:", { taskId: task.id, error: err })
+  }
+
+  return true
+}
--- a/src/features/background-agent/task-launch.ts
+++ b/src/features/background-agent/task-launch.ts
@@ -0,0 +1,77 @@
+import { getTaskToastManager } from "../task-toast-manager"
+import { log } from "../../shared"
+
+import type { BackgroundTask } from "./types"
+import type { LaunchInput } from "./types"
+
+type QueueItem = {
+  task: BackgroundTask
+  input: LaunchInput
+}
+
+export function launchBackgroundTask(args: {
+  input: LaunchInput
+  tasks: Map<string, BackgroundTask>
+  pendingByParent: Map<string, Set<string>>
+  queuesByKey: Map<string, QueueItem[]>
+  getConcurrencyKeyFromInput: (input: LaunchInput) => string
+  processKey: (key: string) => void
+}): BackgroundTask {
+  const { input, tasks, pendingByParent, queuesByKey, getConcurrencyKeyFromInput, processKey } = args
+
+  log("[background-agent] launch() called with:", {
+    agent: input.agent,
+    model: input.model,
+    description: input.description,
+    parentSessionID: input.parentSessionID,
+  })
+
+  if (!input.agent || input.agent.trim() === "") {
+    throw new Error("Agent parameter is required")
+  }
+
+  const task: BackgroundTask = {
+    id: `bg_${crypto.randomUUID().slice(0, 8)}`,
+    status: "pending",
+    queuedAt: new Date(),
+    description: input.description,
+    prompt: input.prompt,
+    agent: input.agent,
+    parentSessionID: input.parentSessionID,
+    parentMessageID: input.parentMessageID,
+    parentModel: input.parentModel,
+    parentAgent: input.parentAgent,
+    model: input.model,
+    category: input.category,
+  }
+
+  tasks.set(task.id, task)
+
+  if (input.parentSessionID) {
+    const pending = pendingByParent.get(input.parentSessionID) ?? new Set<string>()
+    pending.add(task.id)
+    pendingByParent.set(input.parentSessionID, pending)
+  }
+
+  const key = getConcurrencyKeyFromInput(input)
+  const queue = queuesByKey.get(key) ?? []
+  queue.push({ task, input })
+  queuesByKey.set(key, queue)
+
+  log("[background-agent] Task queued:", { taskId: task.id, key, queueLength: queue.length })
+
+  const toastManager = getTaskToastManager()
+  if (toastManager) {
+    toastManager.addTask({
+      id: task.id,
+      description: input.description,
+      agent: input.agent,
+      isBackground: true,
+      status: "queued",
+      skills: input.skills,
+    })
+  }
+
+  processKey(key)
+  return task
+}
--- a/src/features/background-agent/task-poller.ts
+++ b/src/features/background-agent/task-poller.ts
@@ -0,0 +1,107 @@
+import { log } from "../../shared"
+
+import type { BackgroundTaskConfig } from "../../config/schema"
+import type { BackgroundTask } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+import type { OpencodeClient } from "./opencode-client"
+
+import {
+  DEFAULT_STALE_TIMEOUT_MS,
+  MIN_RUNTIME_BEFORE_STALE_MS,
+  TASK_TTL_MS,
+} from "./constants"
+
+export function pruneStaleTasksAndNotifications(args: {
+  tasks: Map<string, BackgroundTask>
+  notifications: Map<string, BackgroundTask[]>
+  onTaskPruned: (taskId: string, task: BackgroundTask, errorMessage: string) => void
+}): void {
+  const { tasks, notifications, onTaskPruned } = args
+  const now = Date.now()
+
+  for (const [taskId, task] of tasks.entries()) {
+    const timestamp = task.status === "pending"
+      ? task.queuedAt?.getTime()
+      : task.startedAt?.getTime()
+
+    if (!timestamp) continue
+
+    const age = now - timestamp
+    if (age <= TASK_TTL_MS) continue
+
+    const errorMessage = task.status === "pending"
+      ? "Task timed out while queued (30 minutes)"
+      : "Task timed out after 30 minutes"
+
+    onTaskPruned(taskId, task, errorMessage)
+  }
+
+  for (const [sessionID, queued] of notifications.entries()) {
+    if (queued.length === 0) {
+      notifications.delete(sessionID)
+      continue
+    }
+
+    const validNotifications = queued.filter((task) => {
+      if (!task.startedAt) return false
+      const age = now - task.startedAt.getTime()
+      return age <= TASK_TTL_MS
+    })
+
+    if (validNotifications.length === 0) {
+      notifications.delete(sessionID)
+    } else if (validNotifications.length !== queued.length) {
+      notifications.set(sessionID, validNotifications)
+    }
+  }
+}
+
+export async function checkAndInterruptStaleTasks(args: {
+  tasks: Iterable<BackgroundTask>
+  client: OpencodeClient
+  config: BackgroundTaskConfig | undefined
+  concurrencyManager: ConcurrencyManager
+  notifyParentSession: (task: BackgroundTask) => Promise<void>
+}): Promise<void> {
+  const { tasks, client, config, concurrencyManager, notifyParentSession } = args
+  const staleTimeoutMs = config?.staleTimeoutMs ?? DEFAULT_STALE_TIMEOUT_MS
+  const now = Date.now()
+
+  for (const task of tasks) {
+    if (task.status !== "running") continue
+    if (!task.progress?.lastUpdate) continue
+
+    const startedAt = task.startedAt
+    const sessionID = task.sessionID
+    if (!startedAt || !sessionID) continue
+
+    const runtime = now - startedAt.getTime()
+    if (runtime < MIN_RUNTIME_BEFORE_STALE_MS) continue
+
+    const timeSinceLastUpdate = now - task.progress.lastUpdate.getTime()
+    if (timeSinceLastUpdate <= staleTimeoutMs) continue
+    if (task.status !== "running") continue
+
+    const staleMinutes = Math.round(timeSinceLastUpdate / 60000)
+    task.status = "cancelled"
+    task.error = `Stale timeout (no activity for ${staleMinutes}min)`
+    task.completedAt = new Date()
+
+    if (task.concurrencyKey) {
+      concurrencyManager.release(task.concurrencyKey)
+      task.concurrencyKey = undefined
+    }
+
+    client.session.abort({
+      path: { id: sessionID },
+    }).catch(() => {})
+
+    log(`[background-agent] Task ${task.id} interrupted: stale timeout`)
+
+    try {
+      await notifyParentSession(task)
+    } catch (err) {
+      log("[background-agent] Error in notifyParentSession for stale task:", { taskId: task.id, error: err })
+    }
+  }
+}
--- a/src/features/background-agent/task-queries.ts
+++ b/src/features/background-agent/task-queries.ts
@@ -0,0 +1,56 @@
+import type { BackgroundTask } from "./types"
+
+export function getTasksByParentSession(
+  tasks: Iterable<BackgroundTask>,
+  sessionID: string
+): BackgroundTask[] {
+  const result: BackgroundTask[] = []
+  for (const task of tasks) {
+    if (task.parentSessionID === sessionID) {
+      result.push(task)
+    }
+  }
+  return result
+}
+
+export function getAllDescendantTasks(
+  tasksByParent: (sessionID: string) => BackgroundTask[],
+  sessionID: string
+): BackgroundTask[] {
+  const result: BackgroundTask[] = []
+  const directChildren = tasksByParent(sessionID)
+
+  for (const child of directChildren) {
+    result.push(child)
+    if (child.sessionID) {
+      result.push(...getAllDescendantTasks(tasksByParent, child.sessionID))
+    }
+  }
+
+  return result
+}
+
+export function findTaskBySession(
+  tasks: Iterable<BackgroundTask>,
+  sessionID: string
+): BackgroundTask | undefined {
+  for (const task of tasks) {
+    if (task.sessionID === sessionID) return task
+  }
+  return undefined
+}
+
+export function getRunningTasks(tasks: Iterable<BackgroundTask>): BackgroundTask[] {
+  return Array.from(tasks).filter((t) => t.status === "running")
+}
+
+export function getCompletedTasks(tasks: Iterable<BackgroundTask>): BackgroundTask[] {
+  return Array.from(tasks).filter((t) => t.status !== "running")
+}
+
+export function hasRunningTasks(tasks: Iterable<BackgroundTask>): boolean {
+  for (const task of tasks) {
+    if (task.status === "running") return true
+  }
+  return false
+}
--- a/src/features/background-agent/task-queue-processor.ts
+++ b/src/features/background-agent/task-queue-processor.ts
@@ -0,0 +1,52 @@
+import { log } from "../../shared"
+
+import type { BackgroundTask } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+
+type QueueItem = {
+  task: BackgroundTask
+  input: import("./types").LaunchInput
+}
+
+export async function processConcurrencyKeyQueue(args: {
+  key: string
+  queuesByKey: Map<string, QueueItem[]>
+  processingKeys: Set<string>
+  concurrencyManager: ConcurrencyManager
+  startTask: (item: QueueItem) => Promise<void>
+}): Promise<void> {
+  const { key, queuesByKey, processingKeys, concurrencyManager, startTask } = args
+
+  if (processingKeys.has(key)) return
+  processingKeys.add(key)
+
+  try {
+    const queue = queuesByKey.get(key)
+    while (queue && queue.length > 0) {
+      const item = queue[0]
+
+      await concurrencyManager.acquire(key)
+
+      if (item.task.status === "cancelled") {
+        concurrencyManager.release(key)
+        queue.shift()
+        continue
+      }
+
+      try {
+        await startTask(item)
+      } catch (error) {
+        log("[background-agent] Error starting task:", error)
+        // Release concurrency slot if startTask failed and didn't release it itself
+        // This prevents slot leaks when errors occur after acquire but before task.concurrencyKey is set
+        if (!item.task.concurrencyKey) {
+          concurrencyManager.release(key)
+        }
+      }
+
+      queue.shift()
+    }
+  } finally {
+    processingKeys.delete(key)
+  }
+}
--- a/src/features/background-agent/task-resumer.ts
+++ b/src/features/background-agent/task-resumer.ts
@@ -0,0 +1,144 @@
+import { log, getAgentToolRestrictions } from "../../shared"
+import { subagentSessions } from "../claude-code-session-state"
+import { getTaskToastManager } from "../task-toast-manager"
+
+import type { BackgroundTask, ResumeInput } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+import type { OpencodeClient } from "./opencode-client"
+
+type ModelRef = { providerID: string; modelID: string }
+
+export async function resumeBackgroundTask(args: {
+  input: ResumeInput
+  findBySession: (sessionID: string) => BackgroundTask | undefined
+  client: OpencodeClient
+  concurrencyManager: ConcurrencyManager
+  pendingByParent: Map<string, Set<string>>
+  startPolling: () => void
+  markForNotification: (task: BackgroundTask) => void
+  cleanupPendingByParent: (task: BackgroundTask) => void
+  notifyParentSession: (task: BackgroundTask) => Promise<void>
+}): Promise<BackgroundTask> {
+  const {
+    input,
+    findBySession,
+    client,
+    concurrencyManager,
+    pendingByParent,
+    startPolling,
+    markForNotification,
+    cleanupPendingByParent,
+    notifyParentSession,
+  } = args
+
+  const existingTask = findBySession(input.sessionId)
+  if (!existingTask) {
+    throw new Error(`Task not found for session: ${input.sessionId}`)
+  }
+
+  if (!existingTask.sessionID) {
+    throw new Error(`Task has no sessionID: ${existingTask.id}`)
+  }
+
+  if (existingTask.status === "running") {
+    log("[background-agent] Resume skipped - task already running:", {
+      taskId: existingTask.id,
+      sessionID: existingTask.sessionID,
+    })
+    return existingTask
+  }
+
+  const concurrencyKey = existingTask.concurrencyGroup ?? existingTask.agent
+  await concurrencyManager.acquire(concurrencyKey)
+  existingTask.concurrencyKey = concurrencyKey
+  existingTask.concurrencyGroup = concurrencyKey
+
+  existingTask.status = "running"
+  existingTask.completedAt = undefined
+  existingTask.error = undefined
+  existingTask.parentSessionID = input.parentSessionID
+  existingTask.parentMessageID = input.parentMessageID
+  existingTask.parentModel = input.parentModel
+  existingTask.parentAgent = input.parentAgent
+  existingTask.startedAt = new Date()
+
+  existingTask.progress = {
+    toolCalls: existingTask.progress?.toolCalls ?? 0,
+    lastUpdate: new Date(),
+  }
+
+  startPolling()
+  if (existingTask.sessionID) {
+    subagentSessions.add(existingTask.sessionID)
+  }
+
+  if (input.parentSessionID) {
+    const pending = pendingByParent.get(input.parentSessionID) ?? new Set<string>()
+    pending.add(existingTask.id)
+    pendingByParent.set(input.parentSessionID, pending)
+  }
+
+  const toastManager = getTaskToastManager()
+  if (toastManager) {
+    toastManager.addTask({
+      id: existingTask.id,
+      description: existingTask.description,
+      agent: existingTask.agent,
+      isBackground: true,
+    })
+  }
+
+  log("[background-agent] Resuming task:", { taskId: existingTask.id, sessionID: existingTask.sessionID })
+  log("[background-agent] Resuming task - calling prompt (fire-and-forget) with:", {
+    sessionID: existingTask.sessionID,
+    agent: existingTask.agent,
+    model: existingTask.model,
+    promptLength: input.prompt.length,
+  })
+
+  const resumeModel: ModelRef | undefined = existingTask.model
+    ? { providerID: existingTask.model.providerID, modelID: existingTask.model.modelID }
+    : undefined
+  const resumeVariant = existingTask.model?.variant
+
+  client.session.promptAsync({
+    path: { id: existingTask.sessionID },
+    body: {
+      agent: existingTask.agent,
+      ...(resumeModel ? { model: resumeModel } : {}),
+      ...(resumeVariant ? { variant: resumeVariant } : {}),
+      tools: {
+        ...getAgentToolRestrictions(existingTask.agent),
+        task: false,
+        call_omo_agent: true,
+        question: false,
+      },
+      parts: [{ type: "text", text: input.prompt }],
+    },
+  }).catch((error) => {
+    log("[background-agent] resume prompt error:", error)
+    existingTask.status = "error"
+    const errorMessage = error instanceof Error ? error.message : String(error)
+    existingTask.error = errorMessage
+    existingTask.completedAt = new Date()
+
+    if (existingTask.concurrencyKey) {
+      concurrencyManager.release(existingTask.concurrencyKey)
+      existingTask.concurrencyKey = undefined
+    }
+
+    if (existingTask.sessionID) {
+      client.session.abort({
+        path: { id: existingTask.sessionID },
+      }).catch(() => {})
+    }
+
+    markForNotification(existingTask)
+    cleanupPendingByParent(existingTask)
+    notifyParentSession(existingTask).catch((err) => {
+      log("[background-agent] Failed to notify on resume error:", err)
+    })
+  })
+
+  return existingTask
+}
--- a/src/features/background-agent/task-starter.ts
+++ b/src/features/background-agent/task-starter.ts
@@ -0,0 +1,190 @@
+import { log, getAgentToolRestrictions, promptWithModelSuggestionRetry } from "../../shared"
+import { isInsideTmux } from "../../shared/tmux"
+
+import { subagentSessions } from "../claude-code-session-state"
+import { getTaskToastManager } from "../task-toast-manager"
+
+import type { BackgroundTask } from "./types"
+import type { LaunchInput } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+import type { OpencodeClient } from "./opencode-client"
+
+type QueueItem = {
+  task: BackgroundTask
+  input: LaunchInput
+}
+
+type ModelRef = { providerID: string; modelID: string }
+
+export async function startQueuedTask(args: {
+  item: QueueItem
+  client: OpencodeClient
+  defaultDirectory: string
+  tmuxEnabled: boolean
+  onSubagentSessionCreated?: (event: { sessionID: string; parentID: string; title: string }) => Promise<void>
+  startPolling: () => void
+  getConcurrencyKeyFromInput: (input: LaunchInput) => string
+  concurrencyManager: ConcurrencyManager
+  findBySession: (sessionID: string) => BackgroundTask | undefined
+  markForNotification: (task: BackgroundTask) => void
+  cleanupPendingByParent: (task: BackgroundTask) => void
+  notifyParentSession: (task: BackgroundTask) => Promise<void>
+}): Promise<void> {
+  const {
+    item,
+    client,
+    defaultDirectory,
+    tmuxEnabled,
+    onSubagentSessionCreated,
+    startPolling,
+    getConcurrencyKeyFromInput,
+    concurrencyManager,
+    findBySession,
+    markForNotification,
+    cleanupPendingByParent,
+    notifyParentSession,
+  } = args
+
+  const { task, input } = item
+
+  log("[background-agent] Starting task:", {
+    taskId: task.id,
+    agent: input.agent,
+    model: input.model,
+  })
+
+  const concurrencyKey = getConcurrencyKeyFromInput(input)
+
+  const parentSession = await client.session.get({
+    path: { id: input.parentSessionID },
+  }).catch((err) => {
+    log(`[background-agent] Failed to get parent session: ${err}`)
+    return null
+  })
+
+  const parentDirectory = parentSession?.data?.directory ?? defaultDirectory
+  log(`[background-agent] Parent dir: ${parentSession?.data?.directory}, using: ${parentDirectory}`)
+
+  const createResult = await client.session.create({
+    body: {
+      parentID: input.parentSessionID,
+      title: `${input.description} (@${input.agent} subagent)`,
+    },
+    query: {
+      directory: parentDirectory,
+    },
+  })
+
+  if (createResult.error) {
+    throw new Error(`Failed to create background session: ${createResult.error}`)
+  }
+
+  if (!createResult.data?.id) {
+    throw new Error("Failed to create background session: API returned no session ID")
+  }
+
+  const sessionID = createResult.data.id
+  subagentSessions.add(sessionID)
+
+  log("[background-agent] tmux callback check", {
+    hasCallback: !!onSubagentSessionCreated,
+    tmuxEnabled,
+    isInsideTmux: isInsideTmux(),
+    sessionID,
+    parentID: input.parentSessionID,
+  })
+
+  if (onSubagentSessionCreated && tmuxEnabled && isInsideTmux()) {
+    log("[background-agent] Invoking tmux callback NOW", { sessionID })
+    await onSubagentSessionCreated({
+      sessionID,
+      parentID: input.parentSessionID,
+      title: input.description,
+    }).catch((err) => {
+      log("[background-agent] Failed to spawn tmux pane:", err)
+    })
+    log("[background-agent] tmux callback completed, waiting 200ms")
+    await new Promise<void>((resolve) => {
+      setTimeout(() => resolve(), 200)
+    })
+  } else {
+    log("[background-agent] SKIP tmux callback - conditions not met")
+  }
+
+  task.status = "running"
+  task.startedAt = new Date()
+  task.sessionID = sessionID
+  task.progress = {
+    toolCalls: 0,
+    lastUpdate: new Date(),
+  }
+  task.concurrencyKey = concurrencyKey
+  task.concurrencyGroup = concurrencyKey
+
+  startPolling()
+
+  log("[background-agent] Launching task:", { taskId: task.id, sessionID, agent: input.agent })
+
+  const toastManager = getTaskToastManager()
+  if (toastManager) {
+    toastManager.updateTask(task.id, "running")
+  }
+
+  log("[background-agent] Calling prompt (fire-and-forget) for launch with:", {
+    sessionID,
+    agent: input.agent,
+    model: input.model,
+    hasSkillContent: !!input.skillContent,
+    promptLength: input.prompt.length,
+  })
+
+  const launchModel: ModelRef | undefined = input.model
+    ? { providerID: input.model.providerID, modelID: input.model.modelID }
+    : undefined
+  const launchVariant = input.model?.variant
+
+  promptWithModelSuggestionRetry(client, {
+    path: { id: sessionID },
+    body: {
+      agent: input.agent,
+      ...(launchModel ? { model: launchModel } : {}),
+      ...(launchVariant ? { variant: launchVariant } : {}),
+      system: input.skillContent,
+      tools: {
+        ...getAgentToolRestrictions(input.agent),
+        task: false,
+        call_omo_agent: true,
+        question: false,
+      },
+      parts: [{ type: "text", text: input.prompt }],
+    },
+  }).catch((error) => {
+    log("[background-agent] promptAsync error:", error)
+    const existingTask = findBySession(sessionID)
+    if (!existingTask) return
+
+    existingTask.status = "error"
+    const errorMessage = error instanceof Error ? error.message : String(error)
+    if (errorMessage.includes("agent.name") || errorMessage.includes("undefined")) {
+      existingTask.error = `Agent "${input.agent}" not found. Make sure the agent is registered in your opencode.json or provided by a plugin.`
+    } else {
+      existingTask.error = errorMessage
+    }
+    existingTask.completedAt = new Date()
+
+    if (existingTask.concurrencyKey) {
+      concurrencyManager.release(existingTask.concurrencyKey)
+      existingTask.concurrencyKey = undefined
+    }
+
+    client.session.abort({
+      path: { id: sessionID },
+    }).catch(() => {})
+
+    markForNotification(existingTask)
+    cleanupPendingByParent(existingTask)
+    notifyParentSession(existingTask).catch((err) => {
+      log("[background-agent] Failed to notify on error:", err)
+    })
+  })
+}
--- a/src/features/background-agent/task-tracker.ts
+++ b/src/features/background-agent/task-tracker.ts
@@ -0,0 +1,97 @@
+import { log } from "../../shared"
+import { subagentSessions } from "../claude-code-session-state"
+
+import type { BackgroundTask } from "./types"
+import type { ConcurrencyManager } from "./concurrency"
+
+export async function trackExternalTask(args: {
+  input: {
+    taskId: string
+    sessionID: string
+    parentSessionID: string
+    description: string
+    agent?: string
+    parentAgent?: string
+    concurrencyKey?: string
+  }
+  tasks: Map<string, BackgroundTask>
+  pendingByParent: Map<string, Set<string>>
+  concurrencyManager: ConcurrencyManager
+  startPolling: () => void
+  cleanupPendingByParent: (task: BackgroundTask) => void
+}): Promise<BackgroundTask> {
+  const { input, tasks, pendingByParent, concurrencyManager, startPolling, cleanupPendingByParent } = args
+
+  const existingTask = tasks.get(input.taskId)
+  if (existingTask) {
+    const parentChanged = input.parentSessionID !== existingTask.parentSessionID
+    if (parentChanged) {
+      cleanupPendingByParent(existingTask)
+      existingTask.parentSessionID = input.parentSessionID
+    }
+    if (input.parentAgent !== undefined) {
+      existingTask.parentAgent = input.parentAgent
+    }
+    if (!existingTask.concurrencyGroup) {
+      existingTask.concurrencyGroup = input.concurrencyKey ?? existingTask.agent
+    }
+
+    if (existingTask.sessionID) {
+      subagentSessions.add(existingTask.sessionID)
+    }
+    startPolling()
+
+    if (existingTask.status === "pending" || existingTask.status === "running") {
+      const pending = pendingByParent.get(input.parentSessionID) ?? new Set<string>()
+      pending.add(existingTask.id)
+      pendingByParent.set(input.parentSessionID, pending)
+    } else if (!parentChanged) {
+      cleanupPendingByParent(existingTask)
+    }
+
+    log("[background-agent] External task already registered:", {
+      taskId: existingTask.id,
+      sessionID: existingTask.sessionID,
+      status: existingTask.status,
+    })
+
+    return existingTask
+  }
+
+  const concurrencyGroup = input.concurrencyKey ?? input.agent ?? "task"
+  if (input.concurrencyKey) {
+    await concurrencyManager.acquire(input.concurrencyKey)
+  }
+
+  const task: BackgroundTask = {
+    id: input.taskId,
+    sessionID: input.sessionID,
+    parentSessionID: input.parentSessionID,
+    parentMessageID: "",
+    description: input.description,
+    prompt: "",
+    agent: input.agent || "task",
+    status: "running",
+    startedAt: new Date(),
+    progress: {
+      toolCalls: 0,
+      lastUpdate: new Date(),
+    },
+    parentAgent: input.parentAgent,
+    concurrencyKey: input.concurrencyKey,
+    concurrencyGroup,
+  }
+
+  tasks.set(task.id, task)
+  subagentSessions.add(input.sessionID)
+  startPolling()
+
+  if (input.parentSessionID) {
+    const pending = pendingByParent.get(input.parentSessionID) ?? new Set<string>()
+    pending.add(task.id)
+    pendingByParent.set(input.parentSessionID, pending)
+  }
+
+  log("[background-agent] Registered external task:", { taskId: task.id, sessionID: input.sessionID })
+  return task
+}