diff --git a/apps/web/components/task/task-page-content-helpers.test.ts b/apps/web/components/task/task-page-content-helpers.test.ts
index ad0ef00ace..d1b477f3fc 100644
--- a/apps/web/components/task/task-page-content-helpers.test.ts
+++ b/apps/web/components/task/task-page-content-helpers.test.ts
@@ -1,13 +1,48 @@
 import { describe, expect, it, vi } from "vitest";
 import type { Task } from "@/lib/types/http";
+import type { KanbanState } from "@/lib/state/slices";
 import {
+  buildArchivedValue,
   buildDebugEntries,
   hasResolvedTaskDetails,
+  resolveEffectiveTask,
   resolveTaskContentState,
   resolveTaskProps,
   syncActiveTaskSession,
 } from "./task-page-content-helpers";
 
+type KanbanTask = KanbanState["tasks"][number];
+
+function makeArchivedTaskDetails(overrides: Partial<Task> = {}): Task {
+  return {
+    id: "task-1",
+    title: "Archived task",
+    description: "",
+    workflow_step_id: "step-1",
+    position: 0,
+    state: "TODO",
+    workspace_id: "ws-1",
+    workflow_id: "wf-1",
+    priority: 0,
+    repositories: [],
+    created_at: "",
+    updated_at: "2026-07-19T00:00:00Z",
+    archived_at: "2026-07-19T00:00:00Z",
+    ...overrides,
+  } as Task;
+}
+
+function makeKanbanTask(overrides: Partial<KanbanTask> = {}): KanbanTask {
+  return {
+    id: "task-1",
+    title: "Restored task",
+    workflowStepId: "step-1",
+    position: 0,
+    state: "TODO",
+    ...overrides,
+  } as KanbanTask;
+}
+
 function baseParams(overrides: Partial<Parameters<typeof buildDebugEntries>[0]> = {}) {
   return {
     connectionStatus: "connected",
@@ -185,3 +220,41 @@ describe("syncActiveTaskSession", () => {
     expect(setActiveSessionAuto).not.toHaveBeenCalled();
   });
 });
+
+describe("resolveEffectiveTask archived state", () => {
+  // Regression: unarchiving from the detail top bar publishes
+  // task.updated(archived_at=null) which re-adds the task to the kanban, but
+  // the one-shot fetchTask details still carry the old archived_at. The
+  // resolved task must reflect the live kanban entry so the top bar stops
+  // showing the archived UI / Unarchive button — otherwise the task "never
+  // comes back" after a successful unarchive.
+  it("clears a stale archived_at when the task is present in the kanban", () => {
+    const taskDetails = makeArchivedTaskDetails();
+    const kanbanTask = makeKanbanTask();
+
+    const resolved = resolveEffectiveTask(taskDetails, null, kanbanTask, "task-1");
+
+    expect(resolved?.archived_at).toBeNull();
+    expect(buildArchivedValue(resolved, null).isArchived).toBe(false);
+  });
+
+  it("keeps archived_at when the task is absent from the kanban (still archived)", () => {
+    const taskDetails = makeArchivedTaskDetails();
+
+    const resolved = resolveEffectiveTask(taskDetails, null, null, "task-1");
+
+    expect(resolved?.archived_at).toBe("2026-07-19T00:00:00Z");
+    expect(buildArchivedValue(resolved, null).isArchived).toBe(true);
+  });
+
+  it("prefers live kanban title/state while preserving base-only fields", () => {
+    const taskDetails = makeArchivedTaskDetails({ archived_at: null });
+    const kanbanTask = makeKanbanTask({ title: "Live title", state: "IN_PROGRESS" });
+
+    const resolved = resolveEffectiveTask(taskDetails, null, kanbanTask, "task-1");
+
+    expect(resolved?.title).toBe("Live title");
+    expect(resolved?.state).toBe("IN_PROGRESS");
+    expect(resolved?.workspace_id).toBe("ws-1");
+  });
+});
diff --git a/apps/web/components/task/task-page-content-helpers.ts b/apps/web/components/task/task-page-content-helpers.ts
index 7faabfbdc9..e172d97866 100644
--- a/apps/web/components/task/task-page-content-helpers.ts
+++ b/apps/web/components/task/task-page-content-helpers.ts
@@ -1,4 +1,11 @@
-import type { Repository, Task } from "@/lib/types/http";
+import {
+  taskId as toTaskId,
+  workflowId as toWorkflowId,
+  workspaceId as toWorkspaceId,
+  type Repository,
+  type Task,
+} from "@/lib/types/http";
+import type { KanbanState } from "@/lib/state/slices";
 import { issueFieldsFromMetadata } from "@/lib/metadata-utils";
 
 type ACPDebugInfo = {
@@ -93,6 +100,77 @@ export function deriveIsAgentWorking(
   return isAgentRunning && (taskState === "IN_PROGRESS" || taskState === "SCHEDULING");
 }
 
+/**
+ * Resolve the task the detail view should render, layering the freshest of
+ * three sources: the one-shot `fetchTask` details, the SSR/`initialTask`, and
+ * the live kanban entry. The base (details/initial) carries fields the kanban
+ * doesn't (repositories, timestamps); the kanban carries live board state.
+ */
+export function resolveEffectiveTask(
+  taskDetails: Task | null,
+  initialTask: Task | null,
+  kanbanTask: KanbanState["tasks"][number] | null,
+  effectiveTaskId: string | null,
+): Task | null {
+  const matchingTaskDetails = taskDetails?.id === effectiveTaskId ? taskDetails : null;
+  const matchingInitialTask = initialTask?.id === effectiveTaskId ? initialTask : null;
+  const baseTask = matchingTaskDetails ?? matchingInitialTask;
+
+  if (!baseTask && !kanbanTask) return null;
+  if (baseTask) return mergeBaseWithKanban(baseTask, kanbanTask);
+  if (kanbanTask) return buildTaskFromKanban(kanbanTask, taskDetails, initialTask);
+  return null;
+}
+
+export function mergeBaseWithKanban(
+  baseTask: Task,
+  kanbanTask: KanbanState["tasks"][number] | null,
+): Task {
+  if (!kanbanTask) return baseTask;
+  return {
+    ...baseTask,
+    title: kanbanTask.title ?? baseTask.title,
+    description: kanbanTask.description ?? baseTask.description,
+    workflow_step_id:
+      (kanbanTask.workflowStepId as string | undefined) ?? baseTask.workflow_step_id,
+    position: kanbanTask.position ?? baseTask.position,
+    state: (kanbanTask.state as Task["state"] | undefined) ?? baseTask.state,
+    repositories: baseTask.repositories,
+    // A task present in the kanban board is by definition not archived: the
+    // board never holds archived tasks, and unarchive re-adds it via
+    // task.updated(archived_at=null). The one-shot `fetchTask` that seeds
+    // baseTask only refetches on task-id change, so it keeps a stale
+    // archived_at after an in-place unarchive from the detail top bar —
+    // trust the live kanban entry instead. Without this the top bar keeps
+    // showing the Unarchive button / archived banner and the task "never
+    // comes back" even though the backend restored it.
+    archived_at: null,
+  };
+}
+
+export function buildTaskFromKanban(
+  kanbanTask: KanbanState["tasks"][number],
+  taskDetails: Task | null,
+  initialTask: Task | null,
+): Task {
+  const prevWorkspaceId = taskDetails?.workspace_id ?? initialTask?.workspace_id;
+  const prevBoardId = taskDetails?.workflow_id ?? initialTask?.workflow_id;
+  return {
+    id: toTaskId(kanbanTask.id),
+    title: kanbanTask.title,
+    description: kanbanTask.description ?? "",
+    workflow_step_id: kanbanTask.workflowStepId,
+    position: kanbanTask.position,
+    state: kanbanTask.state ?? "CREATED",
+    workspace_id: prevWorkspaceId ?? toWorkspaceId(""),
+    workflow_id: prevBoardId ?? toWorkflowId(""),
+    priority: 0,
+    repositories: [],
+    created_at: "",
+    updated_at: kanbanTask.updatedAt ?? "",
+  };
+}
+
 export function buildArchivedValue(task: Task | null, repository: Repository | null) {
   const isArchived = !!task?.archived_at;
   return {
diff --git a/apps/web/components/task/task-page-content.tsx b/apps/web/components/task/task-page-content.tsx
index d3209c0199..66f9122ab1 100644
--- a/apps/web/components/task/task-page-content.tsx
+++ b/apps/web/components/task/task-page-content.tsx
@@ -2,14 +2,7 @@
 
 import { useEffect, useMemo, useState } from "react";
 import { IconAlertTriangle } from "@tabler/icons-react";
-import {
-  taskId as toTaskId,
-  workflowId as toWorkflowId,
-  workspaceId as toWorkspaceId,
-  type Repository,
-  type RepositoryScript,
-  type Task,
-} from "@/lib/types/http";
+import type { Repository, RepositoryScript, Task } from "@/lib/types/http";
 import type { Terminal } from "@/hooks/domains/session/use-terminals";
 import type { KanbanState } from "@/lib/state/slices";
 import { useRepositories } from "@/hooks/domains/workspace/use-repositories";
@@ -27,6 +20,7 @@ import {
   deriveIsAgentWorking,
   buildArchivedValue,
   hasResolvedTaskDetails,
+  resolveEffectiveTask,
   resolveTaskContentState,
   syncActiveTaskSession,
 } from "@/components/task/task-page-content-helpers";
@@ -45,62 +39,6 @@ type TaskPageContentProps = {
   officeTaskHref?: string | null;
 };
 
-function resolveEffectiveTask(
-  taskDetails: Task | null,
-  initialTask: Task | null,
-  kanbanTask: KanbanState["tasks"][number] | null,
-  effectiveTaskId: string | null,
-): Task | null {
-  const matchingTaskDetails = taskDetails?.id === effectiveTaskId ? taskDetails : null;
-  const matchingInitialTask = initialTask?.id === effectiveTaskId ? initialTask : null;
-  const baseTask = matchingTaskDetails ?? matchingInitialTask;
-
-  if (!baseTask && !kanbanTask) return null;
-  if (baseTask) return mergeBaseWithKanban(baseTask, kanbanTask);
-  if (kanbanTask) return buildTaskFromKanban(kanbanTask, taskDetails, initialTask);
-  return null;
-}
-
-function mergeBaseWithKanban(
-  baseTask: Task,
-  kanbanTask: KanbanState["tasks"][number] | null,
-): Task {
-  if (!kanbanTask) return baseTask;
-  return {
-    ...baseTask,
-    title: kanbanTask.title ?? baseTask.title,
-    description: kanbanTask.description ?? baseTask.description,
-    workflow_step_id:
-      (kanbanTask.workflowStepId as string | undefined) ?? baseTask.workflow_step_id,
-    position: kanbanTask.position ?? baseTask.position,
-    state: (kanbanTask.state as Task["state"] | undefined) ?? baseTask.state,
-    repositories: baseTask.repositories,
-  };
-}
-
-function buildTaskFromKanban(
-  kanbanTask: KanbanState["tasks"][number],
-  taskDetails: Task | null,
-  initialTask: Task | null,
-): Task {
-  const prevWorkspaceId = taskDetails?.workspace_id ?? initialTask?.workspace_id;
-  const prevBoardId = taskDetails?.workflow_id ?? initialTask?.workflow_id;
-  return {
-    id: toTaskId(kanbanTask.id),
-    title: kanbanTask.title,
-    description: kanbanTask.description ?? "",
-    workflow_step_id: kanbanTask.workflowStepId,
-    position: kanbanTask.position,
-    state: kanbanTask.state ?? "CREATED",
-    workspace_id: prevWorkspaceId ?? toWorkspaceId(""),
-    workflow_id: prevBoardId ?? toWorkflowId(""),
-    priority: 0,
-    repositories: [],
-    created_at: "",
-    updated_at: kanbanTask.updatedAt ?? "",
-  };
-}
-
 export function useWorkflowStepsMapped() {
   const kanbanSteps = useAppStore((state) => state.kanban.steps);
   return useMemo(
diff --git a/apps/web/e2e/tests/task/unarchive-detail-topbar.spec.ts b/apps/web/e2e/tests/task/unarchive-detail-topbar.spec.ts
new file mode 100644
index 0000000000..a17e937a1b
--- /dev/null
+++ b/apps/web/e2e/tests/task/unarchive-detail-topbar.spec.ts
@@ -0,0 +1,39 @@
+import { test, expect } from "../../fixtures/test-base";
+
+// Regression: unarchiving from the task-detail top bar must clear the archived
+// UI *in place*. The detail view seeds `archived_at` from a one-shot fetchTask
+// that only re-fetches when the task id changes. Unarchive publishes
+// task.updated(archived_at=null), which re-adds the task to the kanban, and the
+// task resolver must trust that live entry over the stale fetch. Before the fix
+// the merge kept the stale archived_at, so the Unarchive button stayed and the
+// task "never came back" even though the backend restored it and the toast said
+// success.
+test("unarchiving from the detail top bar clears the archived UI in place", async ({
+  testPage,
+  apiClient,
+  seedData,
+}) => {
+  const task = await apiClient.createTask(seedData.workspaceId, "Unarchive in place", {
+    workflow_id: seedData.workflowId,
+    workflow_step_id: seedData.startStepId,
+  });
+  await apiClient.archiveTask(task.id);
+
+  await testPage.goto(`/t/${task.id}`);
+
+  const unarchiveButton = testPage.getByTestId("task-unarchive-button");
+  await expect(unarchiveButton).toBeVisible();
+
+  const responsePromise = testPage.waitForResponse((response) =>
+    response.url().endsWith(`/api/v1/tasks/${task.id}/unarchive`),
+  );
+  await unarchiveButton.click();
+  await responsePromise;
+
+  await expect(testPage.getByText("Task unarchived")).toBeVisible();
+  // The Unarchive button only renders while isArchived is true, so its removal
+  // proves the detail view observed the unarchive without a navigation/refetch.
+  await expect(unarchiveButton).toHaveCount(0);
+  // No redirect away — unarchive keeps the user on the same task route.
+  await expect(testPage).toHaveURL(new RegExp(`/t/${task.id}`));
+});