diff --git a/src/features/background-agent/cancel-task-cleanup.test.ts b/src/features/background-agent/cancel-task-cleanup.test.ts
index d8e43f95b..19bb03351 100644
--- a/src/features/background-agent/cancel-task-cleanup.test.ts
+++ b/src/features/background-agent/cancel-task-cleanup.test.ts
@@ -107,7 +107,8 @@ describe("BackgroundManager.cancelTask cleanup", () => {
     expect(cancelled).toBe(true)
     expect(getPendingByParent(manager).get(task.parentSessionId)).toBeUndefined()
     runScheduledCleanup(manager, task.id)
-    expect(manager.getTask(task.id)).toBeUndefined()
+    expect(getTaskMap(manager).has(task.id)).toBe(false)
+    expect(manager.getTask(task.id)?.sessionId).toBe(task.sessionId)
   })
 
   test("#given a running task #when cancelTask called with skipNotification=false #then task is also eventually removed", async () => {
@@ -131,7 +132,8 @@ describe("BackgroundManager.cancelTask cleanup", () => {
     // then
     expect(cancelled).toBe(true)
     runScheduledCleanup(manager, task.id)
-    expect(manager.getTask(task.id)).toBeUndefined()
+    expect(getTaskMap(manager).has(task.id)).toBe(false)
+    expect(manager.getTask(task.id)?.sessionId).toBe(task.sessionId)
   })
 
   test("#given a running task #when cancelTask called with skipNotification=true #then concurrency slot is freed and pending tasks can start", async () => {
diff --git a/src/features/background-agent/manager.test.ts b/src/features/background-agent/manager.test.ts
index 5f622466b..6c92398ad 100644
--- a/src/features/background-agent/manager.test.ts
+++ b/src/features/background-agent/manager.test.ts
@@ -5991,6 +5991,68 @@ describe("BackgroundManager regression fixes - resume and aborted notification",
 
     manager.shutdown()
   })
+
+  test("should keep completed task retrievable after scheduled removal", () => {
+    //#given
+    const manager = createBackgroundManager()
+    const task: BackgroundTask = {
+      id: "task-archive-regression",
+      sessionId: "session-archive-regression",
+      parentSessionId: "parent-session",
+      parentMessageId: "msg-1",
+      description: "archive regression",
+      prompt: "test",
+      agent: "explore",
+      status: "completed",
+      startedAt: new Date(),
+      completedAt: new Date(),
+    }
+    getTaskMap(manager).set(task.id, task)
+
+    //#when
+    ;(cast<{ removeTask: (task: BackgroundTask) => void }>(manager)).removeTask(task)
+
+    //#then
+    expect(getTaskMap(manager).has(task.id)).toBe(false)
+    const archivedTask = manager.getTask(task.id)
+    expect(archivedTask?.sessionId).toBe(task.sessionId)
+    expect(archivedTask?.prompt).toBe("[redacted]")
+    expect(archivedTask?.startedAt).toEqual(task.startedAt)
+
+    manager.shutdown()
+  })
+
+  test("should cap completed task archive size at 100 entries", () => {
+    //#given
+    const manager = createBackgroundManager()
+
+    //#when
+    for (let index = 0; index < 120; index += 1) {
+      const task: BackgroundTask = {
+        id: `task-archive-${index}`,
+        sessionId: `session-archive-${index}`,
+        parentSessionId: "parent-session",
+        parentMessageId: "msg-1",
+        description: "archive cap regression",
+        prompt: `sensitive-${index}`,
+        agent: "explore",
+        status: "completed",
+        startedAt: new Date(),
+        completedAt: new Date(),
+      }
+      ;(cast<{ removeTask: (task: BackgroundTask) => void }>(manager)).removeTask(task)
+    }
+
+    //#then
+    const archive = cast<Map<string, unknown>>(Reflect.get(manager, "completedTaskArchive"))
+    expect(archive.size).toBe(100)
+    expect(archive.has("task-archive-0")).toBe(false)
+    expect(archive.has("task-archive-19")).toBe(false)
+    expect(archive.has("task-archive-20")).toBe(true)
+    expect(archive.has("task-archive-119")).toBe(true)
+
+    manager.shutdown()
+  })
 })
 
 describe("BackgroundManager - tool permission spread order", () => {
diff --git a/src/features/background-agent/manager.ts b/src/features/background-agent/manager.ts
index 85df81f1a..540c65d58 100644
--- a/src/features/background-agent/manager.ts
+++ b/src/features/background-agent/manager.ts
@@ -188,6 +188,7 @@ export interface SubagentSessionCreatedEvent {
 export type OnSubagentSessionCreated = (event: SubagentSessionCreatedEvent) => Promise<void>
 
 const MAX_TASK_REMOVAL_RESCHEDULES = 6
+const MAX_COMPLETED_TASK_ARCHIVE_SIZE = 100
 
 export interface BackgroundManagerConfig {
   pluginContext: PluginInput
@@ -222,6 +223,7 @@ export class BackgroundManager {
   private queuesByKey: Map<string, QueueItem[]> = new Map()
   private processingKeys: Set<string> = new Set()
   private completionTimers: Map<string, ReturnType<typeof setTimeout>> = new Map()
+  private completedTaskArchive: Map<string, BackgroundTask> = new Map()
   private completedTaskSummaries: Map<string, BackgroundTaskNotificationTask[]> = new Map()
   private idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>> = new Map()
   private notificationQueueByParent: Map<string, Promise<void>> = new Map()
@@ -347,6 +349,7 @@ export class BackgroundManager {
   }
 
   private addTask(task: BackgroundTask): void {
+    this.completedTaskArchive.delete(task.id)
     this.tasks.set(task.id, task)
     if (!task.parentSessionId) {
       return
@@ -358,10 +361,47 @@ export class BackgroundManager {
   }
 
   private removeTask(task: BackgroundTask): void {
+    this.archiveCompletedTask(task)
     this.tasks.delete(task.id)
     this.removeTaskFromParentIndex(task.id, task.parentSessionId)
   }
 
+  private archiveCompletedTask(task: BackgroundTask): void {
+    if (!task.sessionId) {
+      return
+    }
+    if (task.status === "running" || task.status === "pending") {
+      return
+    }
+
+    const archivedTask: BackgroundTask = {
+      id: task.id,
+      parentSessionId: task.parentSessionId,
+      parentMessageId: task.parentMessageId,
+      description: task.description,
+      prompt: "[redacted]",
+      agent: task.agent,
+      sessionId: task.sessionId,
+      status: task.status,
+      queuedAt: task.queuedAt,
+      startedAt: task.startedAt,
+      completedAt: task.completedAt,
+      model: task.model,
+      error: task.error,
+      category: task.category,
+    }
+
+    this.completedTaskArchive.set(task.id, archivedTask)
+    if (this.completedTaskArchive.size <= MAX_COMPLETED_TASK_ARCHIVE_SIZE) {
+      return
+    }
+
+    const oldestTaskID = this.completedTaskArchive.keys().next().value
+    if (typeof oldestTaskID === "string") {
+      this.completedTaskArchive.delete(oldestTaskID)
+    }
+  }
+
   private updateTaskParent(task: BackgroundTask, parentSessionID: string): void {
     if (task.parentSessionId === parentSessionID) {
       return
@@ -830,7 +870,7 @@ The fallback retry session is now created and can be inspected directly.
   }
 
   getTask(id: string): BackgroundTask | undefined {
-    return this.tasks.get(id)
+    return this.tasks.get(id) ?? this.completedTaskArchive.get(id)
   }
 
   getTasksByParentSession(sessionID: string): BackgroundTask[] {