feat(client): add delete deck modal with confirmation

Add DeleteDeckModal component that prompts users for confirmation
before deleting a deck. Includes warning about permanent deletion
and all associated cards.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

4 files changed, 454 insertions, 8 deletions

diff --git a/docs/dev/roadmap.md b/docs/dev/roadmap.md
index 86e9c05..f159084 100644
--- a/docs/dev/roadmap.md
+++ b/docs/dev/roadmap.md
@@ -87,7 +87,7 @@ Smaller features first to enable early MVP validation.
 - [x] Deck list page (empty state, list view)
 - [x] Create deck modal/form
 - [x] Edit deck
-- [ ] Delete deck (with confirmation)
+- [x] Delete deck (with confirmation)
 - [ ] Add tests
 
 **✅ Milestone**: Users can create and manage decks
diff --git a/src/client/components/DeleteDeckModal.test.tsx b/src/client/components/DeleteDeckModal.test.tsx
new file mode 100644
index 0000000..ad1463d
--- /dev/null
+++ b/src/client/components/DeleteDeckModal.test.tsx
@@ -0,0 +1,266 @@
+/**
+ * @vitest-environment jsdom
+ */
+import { cleanup, render, screen, waitFor } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { apiClient } from "../api/client";
+
+vi.mock("../api/client", () => ({
+	apiClient: {
+		getAuthHeader: vi.fn(),
+	},
+	ApiClientError: class ApiClientError extends Error {
+		constructor(
+			message: string,
+			public status: number,
+			public code?: string,
+		) {
+			super(message);
+			this.name = "ApiClientError";
+		}
+	},
+}));
+
+// Import after mock is set up
+import { DeleteDeckModal } from "./DeleteDeckModal";
+
+// Mock fetch globally
+const mockFetch = vi.fn();
+global.fetch = mockFetch;
+
+describe("DeleteDeckModal", () => {
+	const mockDeck = {
+		id: "deck-123",
+		name: "Test Deck",
+	};
+
+	const defaultProps = {
+		isOpen: true,
+		deck: mockDeck,
+		onClose: vi.fn(),
+		onDeckDeleted: vi.fn(),
+	};
+
+	beforeEach(() => {
+		vi.clearAllMocks();
+		vi.mocked(apiClient.getAuthHeader).mockReturnValue({
+			Authorization: "Bearer access-token",
+		});
+	});
+
+	afterEach(() => {
+		cleanup();
+		vi.restoreAllMocks();
+	});
+
+	it("does not render when closed", () => {
+		render(<DeleteDeckModal {...defaultProps} isOpen={false} />);
+
+		expect(screen.queryByRole("dialog")).toBeNull();
+	});
+
+	it("does not render when deck is null", () => {
+		render(<DeleteDeckModal {...defaultProps} deck={null} />);
+
+		expect(screen.queryByRole("dialog")).toBeNull();
+	});
+
+	it("renders modal when open with deck", () => {
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		expect(screen.getByRole("dialog")).toBeDefined();
+		expect(screen.getByRole("heading", { name: "Delete Deck" })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Cancel" })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Delete" })).toBeDefined();
+	});
+
+	it("displays confirmation message with deck name", () => {
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		expect(screen.getByText(/Are you sure you want to delete/)).toBeDefined();
+		expect(screen.getByText("Test Deck")).toBeDefined();
+	});
+
+	it("displays warning about permanent deletion", () => {
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		expect(screen.getByText(/This action cannot be undone/)).toBeDefined();
+	});
+
+	it("calls onClose when Cancel is clicked", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		render(<DeleteDeckModal {...defaultProps} onClose={onClose} />);
+
+		await user.click(screen.getByRole("button", { name: "Cancel" }));
+
+		expect(onClose).toHaveBeenCalledTimes(1);
+	});
+
+	it("calls onClose when clicking outside the modal", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		render(<DeleteDeckModal {...defaultProps} onClose={onClose} />);
+
+		// Click on the backdrop (the dialog element itself)
+		const dialog = screen.getByRole("dialog");
+		await user.click(dialog);
+
+		expect(onClose).toHaveBeenCalledTimes(1);
+	});
+
+	it("does not call onClose when clicking inside the modal content", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		render(<DeleteDeckModal {...defaultProps} onClose={onClose} />);
+
+		// Click on an element inside the modal
+		await user.click(screen.getByText("Test Deck"));
+
+		expect(onClose).not.toHaveBeenCalled();
+	});
+
+	it("deletes deck when Delete is clicked", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		const onDeckDeleted = vi.fn();
+
+		mockFetch.mockResolvedValue({
+			ok: true,
+			json: async () => ({}),
+		});
+
+		render(
+			<DeleteDeckModal
+				isOpen={true}
+				deck={mockDeck}
+				onClose={onClose}
+				onDeckDeleted={onDeckDeleted}
+			/>,
+		);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-123", {
+				method: "DELETE",
+				headers: {
+					Authorization: "Bearer access-token",
+				},
+			});
+		});
+
+		expect(onDeckDeleted).toHaveBeenCalledTimes(1);
+		expect(onClose).toHaveBeenCalledTimes(1);
+	});
+
+	it("shows loading state during deletion", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockImplementation(() => new Promise(() => {})); // Never resolves
+
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		expect(screen.getByRole("button", { name: "Deleting..." })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Deleting..." })).toHaveProperty(
+			"disabled",
+			true,
+		);
+		expect(screen.getByRole("button", { name: "Cancel" })).toHaveProperty(
+			"disabled",
+			true,
+		);
+	});
+
+	it("displays API error message", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockResolvedValue({
+			ok: false,
+			status: 404,
+			json: async () => ({ error: "Deck not found" }),
+		});
+
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain("Deck not found");
+		});
+	});
+
+	it("displays generic error on unexpected failure", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockRejectedValue(new Error("Network error"));
+
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain(
+				"Failed to delete deck. Please try again.",
+			);
+		});
+	});
+
+	it("displays error when not authenticated", async () => {
+		const user = userEvent.setup();
+
+		vi.mocked(apiClient.getAuthHeader).mockReturnValue(undefined);
+
+		render(<DeleteDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain(
+				"Not authenticated",
+			);
+		});
+	});
+
+	it("clears error when modal is closed", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+
+		mockFetch.mockResolvedValue({
+			ok: false,
+			status: 404,
+			json: async () => ({ error: "Some error" }),
+		});
+
+		const { rerender } = render(
+			<DeleteDeckModal {...defaultProps} onClose={onClose} />,
+		);
+
+		// Trigger error
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+		await waitFor(() => {
+			expect(screen.getByRole("alert")).toBeDefined();
+		});
+
+		// Close and reopen the modal
+		await user.click(screen.getByRole("button", { name: "Cancel" }));
+		rerender(<DeleteDeckModal {...defaultProps} onClose={onClose} />);
+
+		// Error should be cleared
+		expect(screen.queryByRole("alert")).toBeNull();
+	});
+
+	it("displays deck name correctly when changed", () => {
+		const { rerender } = render(<DeleteDeckModal {...defaultProps} />);
+
+		expect(screen.getByText("Test Deck")).toBeDefined();
+
+		const newDeck = { id: "deck-456", name: "Another Deck" };
+		rerender(<DeleteDeckModal {...defaultProps} deck={newDeck} />);
+
+		expect(screen.getByText("Another Deck")).toBeDefined();
+	});
+});
diff --git a/src/client/components/DeleteDeckModal.tsx b/src/client/components/DeleteDeckModal.tsx
new file mode 100644
index 0000000..307451c
--- /dev/null
+++ b/src/client/components/DeleteDeckModal.tsx
@@ -0,0 +1,159 @@
+import { useState } from "react";
+import { ApiClientError, apiClient } from "../api";
+
+interface Deck {
+	id: string;
+	name: string;
+}
+
+interface DeleteDeckModalProps {
+	isOpen: boolean;
+	deck: Deck | null;
+	onClose: () => void;
+	onDeckDeleted: () => void;
+}
+
+export function DeleteDeckModal({
+	isOpen,
+	deck,
+	onClose,
+	onDeckDeleted,
+}: DeleteDeckModalProps) {
+	const [error, setError] = useState<string | null>(null);
+	const [isDeleting, setIsDeleting] = useState(false);
+
+	const handleClose = () => {
+		setError(null);
+		onClose();
+	};
+
+	const handleDelete = async () => {
+		if (!deck) return;
+
+		setError(null);
+		setIsDeleting(true);
+
+		try {
+			const authHeader = apiClient.getAuthHeader();
+			if (!authHeader) {
+				throw new ApiClientError("Not authenticated", 401);
+			}
+
+			const res = await fetch(`/api/decks/${deck.id}`, {
+				method: "DELETE",
+				headers: authHeader,
+			});
+
+			if (!res.ok) {
+				const errorBody = await res.json().catch(() => ({}));
+				throw new ApiClientError(
+					(errorBody as { error?: string }).error ||
+						`Request failed with status ${res.status}`,
+					res.status,
+				);
+			}
+
+			onDeckDeleted();
+			onClose();
+		} catch (err) {
+			if (err instanceof ApiClientError) {
+				setError(err.message);
+			} else {
+				setError("Failed to delete deck. Please try again.");
+			}
+		} finally {
+			setIsDeleting(false);
+		}
+	};
+
+	if (!isOpen || !deck) {
+		return null;
+	}
+
+	return (
+		<div
+			role="dialog"
+			aria-modal="true"
+			aria-labelledby="delete-deck-title"
+			style={{
+				position: "fixed",
+				top: 0,
+				left: 0,
+				right: 0,
+				bottom: 0,
+				backgroundColor: "rgba(0, 0, 0, 0.5)",
+				display: "flex",
+				alignItems: "center",
+				justifyContent: "center",
+				zIndex: 1000,
+			}}
+			onClick={(e) => {
+				if (e.target === e.currentTarget) {
+					handleClose();
+				}
+			}}
+			onKeyDown={(e) => {
+				if (e.key === "Escape") {
+					handleClose();
+				}
+			}}
+		>
+			<div
+				style={{
+					backgroundColor: "white",
+					padding: "1.5rem",
+					borderRadius: "8px",
+					width: "100%",
+					maxWidth: "400px",
+					margin: "1rem",
+				}}
+			>
+				<h2 id="delete-deck-title" style={{ marginTop: 0 }}>
+					Delete Deck
+				</h2>
+
+				{error && (
+					<div role="alert" style={{ color: "red", marginBottom: "1rem" }}>
+						{error}
+					</div>
+				)}
+
+				<p>
+					Are you sure you want to delete <strong>{deck.name}</strong>?
+				</p>
+				<p style={{ color: "#666" }}>
+					This action cannot be undone. All cards in this deck will also be
+					deleted.
+				</p>
+
+				<div
+					style={{
+						display: "flex",
+						gap: "0.5rem",
+						justifyContent: "flex-end",
+						marginTop: "1.5rem",
+					}}
+				>
+					<button type="button" onClick={handleClose} disabled={isDeleting}>
+						Cancel
+					</button>
+					<button
+						type="button"
+						onClick={handleDelete}
+						disabled={isDeleting}
+						style={{
+							backgroundColor: "#dc3545",
+							color: "white",
+							border: "none",
+							padding: "0.5rem 1rem",
+							borderRadius: "4px",
+							cursor: isDeleting ? "not-allowed" : "pointer",
+						}}
+					>
+						{isDeleting ? "Deleting..." : "Delete"}
+					</button>
+				</div>
+			</div>
+		</div>
+	);
+}
diff --git a/src/client/pages/HomePage.tsx b/src/client/pages/HomePage.tsx
index 08eccaa..a51dfc1 100644
--- a/src/client/pages/HomePage.tsx
+++ b/src/client/pages/HomePage.tsx
@@ -1,6 +1,7 @@
 import { useCallback, useEffect, useState } from "react";
 import { ApiClientError, apiClient } from "../api";
 import { CreateDeckModal } from "../components/CreateDeckModal";
+import { DeleteDeckModal } from "../components/DeleteDeckModal";
 import { EditDeckModal } from "../components/EditDeckModal";
 import { useAuth } from "../stores";
 
@@ -20,6 +21,7 @@ export function HomePage() {
 	const [error, setError] = useState<string | null>(null);
 	const [isCreateModalOpen, setIsCreateModalOpen] = useState(false);
 	const [editingDeck, setEditingDeck] = useState<Deck | null>(null);
+	const [deletingDeck, setDeletingDeck] = useState<Deck | null>(null);
 
 	const fetchDecks = useCallback(async () => {
 		setIsLoading(true);
@@ -136,13 +138,25 @@ export function HomePage() {
 											</p>
 										)}
 									</div>
-									<button
-										type="button"
-										onClick={() => setEditingDeck(deck)}
-										style={{ marginLeft: "1rem" }}
-									>
-										Edit
-									</button>
+									<div style={{ display: "flex", gap: "0.5rem" }}>
+										<button type="button" onClick={() => setEditingDeck(deck)}>
+											Edit
+										</button>
+										<button
+											type="button"
+											onClick={() => setDeletingDeck(deck)}
+											style={{
+												backgroundColor: "#dc3545",
+												color: "white",
+												border: "none",
+												padding: "0.25rem 0.5rem",
+												borderRadius: "4px",
+												cursor: "pointer",
+											}}
+										>
+											Delete
+										</button>
+									</div>
 								</div>
 							</li>
 						))}
@@ -162,6 +176,13 @@ export function HomePage() {
 				onClose={() => setEditingDeck(null)}
 				onDeckUpdated={fetchDecks}
 			/>
+
+			<DeleteDeckModal
+				isOpen={deletingDeck !== null}
+				deck={deletingDeck}
+				onClose={() => setDeletingDeck(null)}
+				onDeckDeleted={fetchDecks}
+			/>
 		</div>
 	);
 }