feat(FN-949): add Projects button to Header for single-project users

- Add Projects button in Header that navigates to /projects for single-project users
- Add MultiProjectFlow test suite covering redirect, listing, navigation, and back-to-tasks flows
- Add Header tests verifying Projects button visibility and click behavior
- Add CSS styles for projects page with responsive grid layout and card states

packages/dashboard/app/components/Header.test.tsx

@@ -797,6 +797,69 @@ describe("Header", () => {
     });
   });
 
+  describe("Projects button", () => {
+    const singleProject = [
+      { id: "1", name: "Test Project", path: "/path/to/project", status: "active" as const },
+    ];
+
+    it("renders Projects button when projects exist", () => {
+      renderHeader({
+        projects: singleProject,
+        onViewAllProjects: noop,
+      }, "desktop");
+      expect(screen.getByTestId("header-projects-btn")).toBeDefined();
+    });
+
+    it("calls onViewAllProjects when Projects button is clicked", () => {
+      const onViewAllProjects = vi.fn();
+      renderHeader({
+        projects: singleProject,
+        onViewAllProjects,
+      }, "desktop");
+      fireEvent.click(screen.getByTestId("header-projects-btn"));
+      expect(onViewAllProjects).toHaveBeenCalled();
+    });
+
+    it("does not render Projects button when no projects", () => {
+      renderHeader({
+        projects: [],
+        onViewAllProjects: noop,
+      }, "desktop");
+      expect(screen.queryByTestId("header-projects-btn")).toBeNull();
+    });
+
+    it("does not render Projects button on mobile", () => {
+      renderHeader({
+        projects: singleProject,
+        onViewAllProjects: noop,
+      }, "mobile");
+      expect(screen.queryByTestId("header-projects-btn")).toBeNull();
+    });
+
+    it("does not render Projects button on tablet", () => {
+      renderHeader({
+        projects: singleProject,
+        onViewAllProjects: noop,
+      }, "tablet");
+      expect(screen.queryByTestId("header-projects-btn")).toBeNull();
+    });
+
+    it("does not render Projects button when onViewAllProjects is not provided", () => {
+      renderHeader({
+        projects: singleProject,
+      }, "desktop");
+      expect(screen.queryByTestId("header-projects-btn")).toBeNull();
+    });
+
+    it("renders Projects button with correct title", () => {
+      renderHeader({
+        projects: singleProject,
+        onViewAllProjects: noop,
+      }, "desktop");
+      expect(screen.getByTitle("View all projects")).toBeDefined();
+    });
+  });
+
   describe("action ordering", () => {
     it("Settings is the last inline user-facing action on desktop (before pause/stop)", () => {
       const { container } = renderHeader({

packages/dashboard/app/components/Header.tsx

@@ -1,5 +1,5 @@
 import { useState, useEffect, useRef, useCallback, useMemo } from "react";
-import { Settings, Pause, Play, Square, LayoutGrid, List, Terminal, Lightbulb, Search, X, Activity, MoreHorizontal, Clock, Folder, History, GitBranch, Workflow, Bot, ChevronLeft, Target, Building2, ChevronRight, FileCode, Loader2 } from "lucide-react";
+import { Settings, Pause, Play, Square, LayoutGrid, List, Terminal, Lightbulb, Search, X, Activity, MoreHorizontal, Clock, Folder, History, GitBranch, Workflow, Bot, ChevronLeft, Target, Building2, ChevronRight, FileCode, Loader2, Grid3X3 } from "lucide-react";
 import type { ProjectInfo } from "../api";
 import { fetchScripts } from "../api";
 import { ProjectSelector } from "./ProjectSelector";
@@ -290,6 +290,19 @@ export function Header({
             <span>All Projects</span>
           </button>
         )}
+
+        {/* Projects button - always visible when at least 1 project exists (desktop only) */}
+        {!isCompact && projects.length >= 1 && onViewAllProjects && (
+          <button
+            className="header-projects-btn"
+            onClick={onViewAllProjects}
+            title="View all projects"
+            data-testid="header-projects-btn"
+          >
+            <Grid3X3 size={14} />
+            <span>Projects</span>
+          </button>
+        )}
       </div>
 
       <div className="header-actions">

packages/dashboard/app/components/__tests__/MultiProjectFlow.test.tsx

@@ -1,6 +1,29 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { render, screen, fireEvent } from "@testing-library/react";
 import type { ProjectInfo } from "@fusion/core";
+import { Header } from "../Header";
+
+// Mock fetchScripts for overflow submenu
+vi.mock("../../api", () => ({
+  fetchScripts: vi.fn().mockResolvedValue({}),
+}));
+
+const noop = () => {};
+
+// Helper to mock desktop viewport
+function mockDesktopMatchMedia() {
+  Object.defineProperty(window, "matchMedia", {
+    writable: true,
+    value: vi.fn().mockImplementation((query: string) => ({
+      matches: false,
+      media: query,
+      onchange: null,
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+      dispatchEvent: vi.fn(),
+    })),
+  });
+}
 
 // Simple smoke tests for multi-project flow
 describe("MultiProjectFlow", () => {
@@ -86,4 +109,69 @@ describe("MultiProjectFlow", () => {
     expect(storage["kb-dashboard-view-mode"]).toBe("project");
     expect(storage["kb-dashboard-task-view"]).toBe("board");
   });
+
+  describe("Projects button navigation", () => {
+    const singleProject: ProjectInfo = {
+      id: "proj_1",
+      name: "Solo Project",
+      path: "/path/to/solo",
+      status: "active",
+      isolationMode: "in-process",
+      createdAt: "2026-01-01T00:00:00.000Z",
+      updatedAt: "2026-01-01T00:00:00.000Z",
+    };
+
+    it("shows Projects button and navigates to overview on click", () => {
+      mockDesktopMatchMedia();
+
+      let viewMode: "overview" | "project" = "project";
+      const handleViewAllProjects = vi.fn(() => {
+        viewMode = "overview";
+      });
+
+      render(
+        <Header
+          onOpenSettings={noop}
+          onOpenGitHubImport={noop}
+          globalPaused={false}
+          enginePaused={false}
+          onToggleGlobalPause={noop}
+          onToggleEnginePause={noop}
+          projects={[singleProject]}
+          onViewAllProjects={handleViewAllProjects}
+        />
+      );
+
+      // The Projects button should be visible for single-project users
+      const projectsBtn = screen.getByTestId("header-projects-btn");
+      expect(projectsBtn).toBeDefined();
+
+      // Clicking should trigger navigation to overview
+      fireEvent.click(projectsBtn);
+      expect(handleViewAllProjects).toHaveBeenCalled();
+      expect(viewMode).toBe("overview");
+    });
+
+    it("shows Projects button alongside Back button when currentProject is set", () => {
+      mockDesktopMatchMedia();
+
+      render(
+        <Header
+          onOpenSettings={noop}
+          onOpenGitHubImport={noop}
+          globalPaused={false}
+          enginePaused={false}
+          onToggleGlobalPause={noop}
+          onToggleEnginePause={noop}
+          projects={[singleProject]}
+          currentProject={singleProject}
+          onViewAllProjects={noop}
+        />
+      );
+
+      // Both buttons should be present
+      expect(screen.getByTestId("header-projects-btn")).toBeDefined();
+      expect(screen.getByTestId("back-to-projects-btn")).toBeDefined();
+    });
+  });
 });