diff --git a/canvas/src/components/mobile/__tests__/MobileDetail.test.tsx b/canvas/src/components/mobile/__tests__/MobileDetail.test.tsx
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+++ b/canvas/src/components/mobile/__tests__/MobileDetail.test.tsx
@@ -0,0 +1,367 @@
+// @vitest-environment jsdom
+/**
+ * MobileDetail — agent detail page with tabbed content (Overview/Activity/Config/Memory).
+ *
+ * Per spec §03: tabbed agent detail page. MobileChat (MR !717) was also tested here.
+ *
+ * NOTE: No @testing-library/jest-dom — use DOM APIs.
+ */
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { cleanup, render } from "@testing-library/react";
+import React from "react";
+
+import { MobileDetail } from "../MobileDetail";
+
+// ─── Mock store ───────────────────────────────────────────────────────────────
+
+const mockNodeId = "ws-detail-test";
+const mockOnBack = vi.fn();
+const mockOnChat = vi.fn();
+
+// Module-level mutable state for the mock store.
+// Tests mutate this between cases to control what the component sees.
+const mockStoreState = {
+  nodes: [] as Array<{
+    id: string;
+    position: { x: number; y: number };
+    data: Record<string, unknown>;
+    width?: number;
+    height?: number;
+  }>,
+};
+
+vi.mock("@/store/canvas", () => ({
+  useCanvasStore: Object.assign(
+    vi.fn((sel) => sel(mockStoreState)),
+    { getState: () => mockStoreState },
+  ),
+  summarizeWorkspaceCapabilities: vi.fn((data: Record<string, unknown>) => {
+    const agentCard = data.agentCard as Record<string, unknown> | null;
+    const skills = Array.isArray(agentCard?.skills)
+      ? (agentCard.skills as Array<Record<string, unknown>>).map(
+          (s) => String(s.name || s.id || ""),
+        ).filter(Boolean)
+      : [];
+    return {
+      runtime: (typeof data.runtime === "string" && data.runtime)
+        ? data.runtime
+        : (typeof agentCard?.runtime === "string" ? String(agentCard.runtime) : null),
+      skills,
+      skillCount: skills.length,
+      currentTask: String(data.currentTask ?? ""),
+      hasActiveTask: String(data.currentTask ?? "").trim().length > 0,
+    };
+  }),
+}));
+
+// Stub the API so DetailActivity doesn't attempt real network calls.
+vi.mock("@/lib/api", () => ({ api: { get: vi.fn().mockResolvedValue([]) } }));
+
+// ─── Fixtures ────────────────────────────────────────────────────────────────
+
+const onlineNode = {
+  id: mockNodeId,
+  position: { x: 100, y: 200 },
+  data: {
+    name: "Test Agent",
+    status: "online",
+    tier: 2,
+    agentCard: {
+      runtime: "claude-code",
+      skills: [
+        { name: "web-search", id: "skill-1" },
+        { name: "code-review", id: "skill-2" },
+        { name: "file-ops", id: "skill-3" },
+      ],
+    },
+    currentTask: "Reviewing PR #717",
+    activeTasks: 3,
+    collapsed: false,
+    role: "agent",
+    lastErrorRate: 0,
+    lastSampleError: "",
+    url: "",
+    parentId: null,
+    runtime: "claude-code",
+    needsRestart: false,
+  },
+  width: 240,
+  height: 130,
+};
+
+const failedNode = {
+  id: "ws-failed",
+  position: { x: 0, y: 0 },
+  data: {
+    name: "Failed Worker",
+    status: "failed",
+    tier: 4,
+    agentCard: null,
+    currentTask: "",
+    activeTasks: 0,
+    collapsed: false,
+    role: "agent",
+    lastErrorRate: 0.8,
+    lastSampleError: "Connection refused",
+    url: "",
+    parentId: null,
+    runtime: "external",
+    needsRestart: false,
+  },
+};
+
+const offlineNode = {
+  id: "ws-offline",
+  position: { x: 0, y: 0 },
+  data: {
+    name: "Offline Bot",
+    status: "offline",
+    tier: 1,
+    agentCard: null,
+    currentTask: "",
+    activeTasks: 0,
+    collapsed: false,
+    role: "agent",
+    lastErrorRate: 0,
+    lastSampleError: "",
+    url: "",
+    parentId: null,
+    runtime: "claude-code",
+    needsRestart: false,
+  },
+};
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+function renderDetail(agentId: string, dark = false) {
+  return render(
+    <MobileDetail
+      agentId={agentId}
+      dark={dark}
+      onBack={mockOnBack}
+      onChat={mockOnChat}
+    />,
+  );
+}
+
+// ─── Setup / teardown ─────────────────────────────────────────────────────────
+
+beforeEach(() => {
+  mockOnBack.mockClear();
+  mockOnChat.mockClear();
+  mockStoreState.nodes = [];
+});
+
+afterEach(() => {
+  cleanup();
+  vi.clearAllMocks();
+});
+
+// ─── Not found ────────────────────────────────────────────────────────────────
+
+describe("MobileDetail — agent not found", () => {
+  it('renders "Agent not found." when no node matches agentId', () => {
+    mockStoreState.nodes = [onlineNode];
+    const { container } = renderDetail("nonexistent-id");
+    expect(container.textContent ?? "").toContain("Agent not found.");
+  });
+
+  it("does not render any tab buttons when agent not found", () => {
+    mockStoreState.nodes = [];
+    const { container } = renderDetail("ghost-agent");
+    expect(container.querySelectorAll("button").length).toBe(0);
+  });
+});
+
+// ─── Hero render ─────────────────────────────────────────────────────────────
+
+describe("MobileDetail — hero section", () => {
+  beforeEach(() => {
+    mockStoreState.nodes = [onlineNode];
+  });
+
+  it("renders the agent name as an h1", () => {
+    const { container } = renderDetail(mockNodeId);
+    const h1 = container.querySelector("h1");
+    expect(h1).toBeTruthy();
+    expect(h1!.textContent).toBe("Test Agent");
+  });
+
+  it("renders agent tag below the name", () => {
+    const { container } = renderDetail(mockNodeId);
+    // Tag appears in the hero section, styled differently from the name
+    expect(container.textContent ?? "").toContain("claude-code");
+  });
+
+  it("renders a Back button with aria-label", () => {
+    const { container } = renderDetail(mockNodeId);
+    const backBtn = container.querySelector('[aria-label="Back"]');
+    expect(backBtn).toBeTruthy();
+  });
+
+  it("Back button calls onBack", () => {
+    const { container } = renderDetail(mockNodeId);
+    const backBtn = container.querySelector('[aria-label="Back"]') as HTMLButtonElement;
+    backBtn.click();
+    expect(mockOnBack).toHaveBeenCalledTimes(1);
+  });
+
+  it("renders a More button", () => {
+    const { container } = renderDetail(mockNodeId);
+    const moreBtn = container.querySelector('[aria-label="More"]');
+    expect(moreBtn).toBeTruthy();
+  });
+
+  it("renders Chat CTA with icon text", () => {
+    const { container } = renderDetail(mockNodeId);
+    expect(container.textContent ?? "").toContain("Open chat");
+  });
+
+  it("Chat CTA calls onChat", () => {
+    const { container } = renderDetail(mockNodeId);
+    const chatBtn = Array.from(container.querySelectorAll("button")).find(
+      (b) => b.textContent?.includes("Open chat"),
+    );
+    expect(chatBtn).toBeTruthy();
+    (chatBtn as HTMLButtonElement).click();
+    expect(mockOnChat).toHaveBeenCalledTimes(1);
+  });
+});
+
+// ─── Pill stats ───────────────────────────────────────────────────────────────
+
+describe("MobileDetail — pill stats", () => {
+  beforeEach(() => {
+    mockStoreState.nodes = [onlineNode];
+  });
+
+  it("renders TIER pill with the agent tier", () => {
+    const { container } = renderDetail(mockNodeId);
+    expect(container.textContent ?? "").toContain("TIER");
+  });
+
+  it("renders RUNTIME pill", () => {
+    const { container } = renderDetail(mockNodeId);
+    expect(container.textContent ?? "").toContain("RUNTIME");
+  });
+
+  it("renders SKILLS pill with count", () => {
+    const { container } = renderDetail(mockNodeId);
+    // 3 skills in the agentCard fixture
+    expect(container.textContent ?? "").toContain("SKILLS");
+  });
+
+  it("renders STATUS pill", () => {
+    const { container } = renderDetail(mockNodeId);
+    expect(container.textContent ?? "").toContain("STATUS");
+  });
+
+  it("STATUS pill shows agent status value", () => {
+    const { container } = renderDetail(mockNodeId);
+    // online status from the fixture
+    expect(container.textContent ?? "").toContain("online");
+  });
+
+  it("renders all 4 pills for online agent", () => {
+    const { container } = renderDetail(mockNodeId);
+    // Count the pill container divs — each PillStat is a div with specific inline styles
+    // We verify by content: TIER, RUNTIME, SKILLS, STATUS should all be present
+    const text = container.textContent ?? "";
+    expect(text).toContain("TIER");
+    expect(text).toContain("RUNTIME");
+    expect(text).toContain("SKILLS");
+    expect(text).toContain("STATUS");
+  });
+});
+
+// ─── Tabs ─────────────────────────────────────────────────────────────────────
+
+describe("MobileDetail — tab switching", () => {
+  beforeEach(() => {
+    mockStoreState.nodes = [onlineNode];
+  });
+
+  it("renders all 4 tab buttons", () => {
+    const { container } = renderDetail(mockNodeId);
+    const text = container.textContent ?? "";
+    expect(text).toContain("Overview");
+    expect(text).toContain("Activity");
+    expect(text).toContain("Config");
+    expect(text).toContain("Memory");
+  });
+
+  it("defaults to Overview tab", () => {
+    const { container } = renderDetail(mockNodeId);
+    // DetailOverview renders ID, Tier, Runtime, Active tasks, Skills, Origin rows
+    expect(container.textContent ?? "").toContain("ID");
+    expect(container.textContent ?? "").toContain("Tier");
+  });
+
+  it("Overview tab shows agent ID", () => {
+    const { container } = renderDetail(mockNodeId);
+    expect(container.textContent ?? "").toContain(mockNodeId);
+  });
+
+  it("Overview tab shows active tasks count", () => {
+    const { container } = renderDetail(mockNodeId);
+    // onlineNode has activeTasks: 3
+    expect(container.textContent ?? "").toContain("Active tasks");
+    expect(container.textContent ?? "").toContain("3");
+  });
+
+  it("Overview tab shows skill count", () => {
+    const { container } = renderDetail(mockNodeId);
+    // 3 skills in agentCard
+    expect(container.textContent ?? "").toContain("Skills");
+    expect(container.textContent ?? "").toContain("3 loaded");
+  });
+
+  it("Config tab button is findable and is a button element", () => {
+    const { container } = renderDetail(mockNodeId);
+    const configTab = Array.from(container.querySelectorAll("button")).find(
+      (b) => b.textContent?.trim() === "Config",
+    );
+    expect(configTab).toBeTruthy();
+    expect((configTab as HTMLButtonElement).type).toBe("button");
+  });
+
+  it("Memory tab button is findable and is a button element", () => {
+    const { container } = renderDetail(mockNodeId);
+    const memoryTab = Array.from(container.querySelectorAll("button")).find(
+      (b) => b.textContent?.trim() === "Memory",
+    );
+    expect(memoryTab).toBeTruthy();
+    expect((memoryTab as HTMLButtonElement).type).toBe("button");
+  });
+});
+
+// ─── Status rendering ─────────────────────────────────────────────────────────
+
+describe("MobileDetail — status rendering", () => {
+  it("renders failed status for failed agent", () => {
+    mockStoreState.nodes = [failedNode];
+    const { container } = renderDetail("ws-failed");
+    expect(container.textContent ?? "").toContain("Failed Worker");
+    expect(container.textContent ?? "").toContain("failed");
+  });
+
+  it("renders offline status for offline agent", () => {
+    mockStoreState.nodes = [offlineNode];
+    const { container } = renderDetail("ws-offline");
+    expect(container.textContent ?? "").toContain("Offline Bot");
+    expect(container.textContent ?? "").toContain("offline");
+  });
+});
+
+// ─── Dark mode ───────────────────────────────────────────────────────────────
+
+describe("MobileDetail — dark mode", () => {
+  beforeEach(() => {
+    mockStoreState.nodes = [onlineNode];
+  });
+
+  it("renders without crashing in dark mode", () => {
+    const { container } = renderDetail(mockNodeId, true);
+    expect(container.querySelector("h1")?.textContent).toBe("Test Agent");
+  });
+});