feat(client): add delete card modal with confirmation

Completes Phase 5 card management by adding the ability to delete cards
with a confirmation dialog. Includes unit tests for the modal component
and integration tests for the delete flow in DeckDetailPage.

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

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

5 files changed, 691 insertions, 8 deletions

diff --git a/docs/dev/roadmap.md b/docs/dev/roadmap.md
index 7552761..76e016a 100644
--- a/docs/dev/roadmap.md
+++ b/docs/dev/roadmap.md
@@ -106,8 +106,8 @@ Smaller features first to enable early MVP validation.
 - [x] Card list view (in deck detail page)
 - [x] Create card form (front/back)
 - [x] Edit card
-- [ ] Delete card
-- [ ] Add tests
+- [x] Delete card
+- [x] Add tests
 
 **✅ Milestone**: Users can create and manage cards
 
diff --git a/src/client/components/DeleteCardModal.test.tsx b/src/client/components/DeleteCardModal.test.tsx
new file mode 100644
index 0000000..4178ee8
--- /dev/null
+++ b/src/client/components/DeleteCardModal.test.tsx
@@ -0,0 +1,286 @@
+/**
+ * @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 { DeleteCardModal } from "./DeleteCardModal";
+
+// Mock fetch globally
+const mockFetch = vi.fn();
+global.fetch = mockFetch;
+
+describe("DeleteCardModal", () => {
+	const mockCard = {
+		id: "card-123",
+		front: "Test Question",
+	};
+
+	const defaultProps = {
+		isOpen: true,
+		deckId: "deck-456",
+		card: mockCard,
+		onClose: vi.fn(),
+		onCardDeleted: 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(<DeleteCardModal {...defaultProps} isOpen={false} />);
+
+		expect(screen.queryByRole("dialog")).toBeNull();
+	});
+
+	it("does not render when card is null", () => {
+		render(<DeleteCardModal {...defaultProps} card={null} />);
+
+		expect(screen.queryByRole("dialog")).toBeNull();
+	});
+
+	it("renders modal when open with card", () => {
+		render(<DeleteCardModal {...defaultProps} />);
+
+		expect(screen.getByRole("dialog")).toBeDefined();
+		expect(screen.getByRole("heading", { name: "Delete Card" })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Cancel" })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Delete" })).toBeDefined();
+	});
+
+	it("displays confirmation message with card front text", () => {
+		render(<DeleteCardModal {...defaultProps} />);
+
+		expect(screen.getByText(/Are you sure you want to delete/)).toBeDefined();
+		expect(screen.getByText(/"Test Question"/)).toBeDefined();
+	});
+
+	it("truncates long front text in confirmation message", () => {
+		const longFrontCard = {
+			id: "card-123",
+			front:
+				"This is a very long question that should be truncated when displayed in the confirmation modal",
+		};
+		render(<DeleteCardModal {...defaultProps} card={longFrontCard} />);
+
+		expect(
+			screen.getByText(
+				/"This is a very long question that should be trunca.../,
+			),
+		).toBeDefined();
+	});
+
+	it("displays warning about permanent deletion", () => {
+		render(<DeleteCardModal {...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(<DeleteCardModal {...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(<DeleteCardModal {...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(<DeleteCardModal {...defaultProps} onClose={onClose} />);
+
+		// Click on the heading inside the modal
+		await user.click(screen.getByRole("heading", { name: "Delete Card" }));
+
+		expect(onClose).not.toHaveBeenCalled();
+	});
+
+	it("deletes card when Delete is clicked", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		const onCardDeleted = vi.fn();
+
+		mockFetch.mockResolvedValue({
+			ok: true,
+			json: async () => ({}),
+		});
+
+		render(
+			<DeleteCardModal
+				isOpen={true}
+				deckId="deck-456"
+				card={mockCard}
+				onClose={onClose}
+				onCardDeleted={onCardDeleted}
+			/>,
+		);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(mockFetch).toHaveBeenCalledWith(
+				"/api/decks/deck-456/cards/card-123",
+				{
+					method: "DELETE",
+					headers: {
+						Authorization: "Bearer access-token",
+					},
+				},
+			);
+		});
+
+		expect(onCardDeleted).toHaveBeenCalledTimes(1);
+		expect(onClose).toHaveBeenCalledTimes(1);
+	});
+
+	it("shows loading state during deletion", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockImplementation(() => new Promise(() => {})); // Never resolves
+
+		render(<DeleteCardModal {...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: "Card not found" }),
+		});
+
+		render(<DeleteCardModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain("Card not found");
+		});
+	});
+
+	it("displays generic error on unexpected failure", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockRejectedValue(new Error("Network error"));
+
+		render(<DeleteCardModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Delete" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain(
+				"Failed to delete card. Please try again.",
+			);
+		});
+	});
+
+	it("displays error when not authenticated", async () => {
+		const user = userEvent.setup();
+
+		vi.mocked(apiClient.getAuthHeader).mockReturnValue(undefined);
+
+		render(<DeleteCardModal {...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(
+			<DeleteCardModal {...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(<DeleteCardModal {...defaultProps} onClose={onClose} />);
+
+		// Error should be cleared
+		expect(screen.queryByRole("alert")).toBeNull();
+	});
+
+	it("displays card front correctly when card changes", () => {
+		const { rerender } = render(<DeleteCardModal {...defaultProps} />);
+
+		expect(screen.getByText(/"Test Question"/)).toBeDefined();
+
+		const newCard = { id: "card-789", front: "Another Question" };
+		rerender(<DeleteCardModal {...defaultProps} card={newCard} />);
+
+		expect(screen.getByText(/"Another Question"/)).toBeDefined();
+	});
+});
diff --git a/src/client/components/DeleteCardModal.tsx b/src/client/components/DeleteCardModal.tsx
new file mode 100644
index 0000000..99abbd0
--- /dev/null
+++ b/src/client/components/DeleteCardModal.tsx
@@ -0,0 +1,161 @@
+import { useState } from "react";
+import { ApiClientError, apiClient } from "../api";
+
+interface Card {
+	id: string;
+	front: string;
+}
+
+interface DeleteCardModalProps {
+	isOpen: boolean;
+	deckId: string;
+	card: Card | null;
+	onClose: () => void;
+	onCardDeleted: () => void;
+}
+
+export function DeleteCardModal({
+	isOpen,
+	deckId,
+	card,
+	onClose,
+	onCardDeleted,
+}: DeleteCardModalProps) {
+	const [error, setError] = useState<string | null>(null);
+	const [isDeleting, setIsDeleting] = useState(false);
+
+	const handleClose = () => {
+		setError(null);
+		onClose();
+	};
+
+	const handleDelete = async () => {
+		if (!card) return;
+
+		setError(null);
+		setIsDeleting(true);
+
+		try {
+			const authHeader = apiClient.getAuthHeader();
+			if (!authHeader) {
+				throw new ApiClientError("Not authenticated", 401);
+			}
+
+			const res = await fetch(`/api/decks/${deckId}/cards/${card.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 ${res.status}`,
+					res.status,
+				);
+			}
+
+			onCardDeleted();
+			onClose();
+		} catch (err) {
+			if (err instanceof ApiClientError) {
+				setError(err.message);
+			} else {
+				setError("Failed to delete card. Please try again.");
+			}
+		} finally {
+			setIsDeleting(false);
+		}
+	};
+
+	if (!isOpen || !card) {
+		return null;
+	}
+
+	// Truncate front text for display if too long
+	const displayFront =
+		card.front.length > 50 ? `${card.front.slice(0, 50)}...` : card.front;
+
+	return (
+		<div
+			role="dialog"
+			aria-modal="true"
+			aria-labelledby="delete-card-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-card-title" style={{ marginTop: 0 }}>
+					Delete Card
+				</h2>
+
+				{error && (
+					<div role="alert" style={{ color: "red", marginBottom: "1rem" }}>
+						{error}
+					</div>
+				)}
+
+				<p>Are you sure you want to delete this card?</p>
+				<p style={{ color: "#666", fontStyle: "italic" }}>"{displayFront}"</p>
+				<p style={{ color: "#666" }}>This action cannot be undone.</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/DeckDetailPage.test.tsx b/src/client/pages/DeckDetailPage.test.tsx
index de22b08..0589073 100644
--- a/src/client/pages/DeckDetailPage.test.tsx
+++ b/src/client/pages/DeckDetailPage.test.tsx
@@ -372,4 +372,207 @@ describe("DeckDetailPage", () => {
 		// No description should be shown
 		expect(screen.queryByText("Common Japanese words")).toBeNull();
 	});
+
+	describe("Delete Card", () => {
+		it("shows Delete button for each card", async () => {
+			mockFetch
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ deck: mockDeck }),
+				})
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ cards: mockCards }),
+				});
+
+			renderWithProviders();
+
+			await waitFor(() => {
+				expect(screen.getByText("Hello")).toBeDefined();
+			});
+
+			const deleteButtons = screen.getAllByRole("button", { name: "Delete" });
+			expect(deleteButtons.length).toBe(2);
+		});
+
+		it("opens delete confirmation modal when Delete button is clicked", async () => {
+			const user = userEvent.setup();
+
+			mockFetch
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ deck: mockDeck }),
+				})
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ cards: mockCards }),
+				});
+
+			renderWithProviders();
+
+			await waitFor(() => {
+				expect(screen.getByText("Hello")).toBeDefined();
+			});
+
+			const deleteButtons = screen.getAllByRole("button", { name: "Delete" });
+			const firstDeleteButton = deleteButtons[0];
+			if (firstDeleteButton) {
+				await user.click(firstDeleteButton);
+			}
+
+			expect(screen.getByRole("dialog")).toBeDefined();
+			expect(
+				screen.getByRole("heading", { name: "Delete Card" }),
+			).toBeDefined();
+		});
+
+		it("closes delete modal when Cancel is clicked", async () => {
+			const user = userEvent.setup();
+
+			mockFetch
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ deck: mockDeck }),
+				})
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ cards: mockCards }),
+				});
+
+			renderWithProviders();
+
+			await waitFor(() => {
+				expect(screen.getByText("Hello")).toBeDefined();
+			});
+
+			const deleteButtons = screen.getAllByRole("button", { name: "Delete" });
+			const firstDeleteButton = deleteButtons[0];
+			if (firstDeleteButton) {
+				await user.click(firstDeleteButton);
+			}
+
+			expect(screen.getByRole("dialog")).toBeDefined();
+
+			await user.click(screen.getByRole("button", { name: "Cancel" }));
+
+			expect(screen.queryByRole("dialog")).toBeNull();
+		});
+
+		it("deletes card and refreshes list on confirmation", async () => {
+			const user = userEvent.setup();
+
+			mockFetch
+				// Initial load
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ deck: mockDeck }),
+				})
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ cards: mockCards }),
+				})
+				// Delete request
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({}),
+				})
+				// Refresh cards after deletion
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ cards: [mockCards[1]] }),
+				});
+
+			renderWithProviders();
+
+			await waitFor(() => {
+				expect(screen.getByText("Hello")).toBeDefined();
+			});
+
+			const deleteButtons = screen.getAllByRole("button", { name: "Delete" });
+			const firstDeleteButton = deleteButtons[0];
+			if (firstDeleteButton) {
+				await user.click(firstDeleteButton);
+			}
+
+			// Find the Delete button in the modal (not the card list)
+			const modalDeleteButtons = screen.getAllByRole("button", {
+				name: "Delete",
+			});
+			const confirmDeleteButton = modalDeleteButtons.find((btn) =>
+				btn.closest('[role="dialog"]'),
+			);
+			if (confirmDeleteButton) {
+				await user.click(confirmDeleteButton);
+			}
+
+			// Wait for modal to close and list to refresh
+			await waitFor(() => {
+				expect(screen.queryByRole("dialog")).toBeNull();
+			});
+
+			// Verify DELETE request was made
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-1/cards/card-1", {
+				method: "DELETE",
+				headers: { Authorization: "Bearer access-token" },
+			});
+
+			// Verify card count updated
+			await waitFor(() => {
+				expect(
+					screen.getByRole("heading", { name: "Cards (1)" }),
+				).toBeDefined();
+			});
+		});
+
+		it("displays error when delete fails", async () => {
+			const user = userEvent.setup();
+
+			mockFetch
+				// Initial load
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ deck: mockDeck }),
+				})
+				.mockResolvedValueOnce({
+					ok: true,
+					json: async () => ({ cards: mockCards }),
+				})
+				// Delete request fails
+				.mockResolvedValueOnce({
+					ok: false,
+					status: 500,
+					json: async () => ({ error: "Failed to delete card" }),
+				});
+
+			renderWithProviders();
+
+			await waitFor(() => {
+				expect(screen.getByText("Hello")).toBeDefined();
+			});
+
+			const deleteButtons = screen.getAllByRole("button", { name: "Delete" });
+			const firstDeleteButton = deleteButtons[0];
+			if (firstDeleteButton) {
+				await user.click(firstDeleteButton);
+			}
+
+			// Find the Delete button in the modal
+			const modalDeleteButtons = screen.getAllByRole("button", {
+				name: "Delete",
+			});
+			const confirmDeleteButton = modalDeleteButtons.find((btn) =>
+				btn.closest('[role="dialog"]'),
+			);
+			if (confirmDeleteButton) {
+				await user.click(confirmDeleteButton);
+			}
+
+			// Error should be displayed in the modal
+			await waitFor(() => {
+				expect(screen.getByRole("alert").textContent).toContain(
+					"Failed to delete card",
+				);
+			});
+		});
+	});
 });
diff --git a/src/client/pages/DeckDetailPage.tsx b/src/client/pages/DeckDetailPage.tsx
index 57e4af9..cdc216a 100644
--- a/src/client/pages/DeckDetailPage.tsx
+++ b/src/client/pages/DeckDetailPage.tsx
@@ -2,6 +2,7 @@ import { useCallback, useEffect, useState } from "react";
 import { Link, useParams } from "wouter";
 import { ApiClientError, apiClient } from "../api";
 import { CreateCardModal } from "../components/CreateCardModal";
+import { DeleteCardModal } from "../components/DeleteCardModal";
 import { EditCardModal } from "../components/EditCardModal";
 
 interface Card {
@@ -38,6 +39,7 @@ export function DeckDetailPage() {
 	const [error, setError] = useState<string | null>(null);
 	const [isCreateModalOpen, setIsCreateModalOpen] = useState(false);
 	const [editingCard, setEditingCard] = useState<Card | null>(null);
+	const [deletingCard, setDeletingCard] = useState<Card | null>(null);
 
 	const fetchDeck = useCallback(async () => {
 		if (!deckId) return;
@@ -241,13 +243,34 @@ export function DeckDetailPage() {
 												<span>Lapses: {card.lapses}</span>
 											</div>
 										</div>
-										<button
-											type="button"
-											onClick={() => setEditingCard(card)}
-											style={{ marginLeft: "1rem" }}
+										<div
+											style={{
+												display: "flex",
+												gap: "0.5rem",
+												marginLeft: "1rem",
+											}}
 										>
-											Edit
-										</button>
+											<button
+												type="button"
+												onClick={() => setEditingCard(card)}
+											>
+												Edit
+											</button>
+											<button
+												type="button"
+												onClick={() => setDeletingCard(card)}
+												style={{
+													backgroundColor: "#dc3545",
+													color: "white",
+													border: "none",
+													padding: "0.5rem 1rem",
+													borderRadius: "4px",
+													cursor: "pointer",
+												}}
+											>
+												Delete
+											</button>
+										</div>
 									</div>
 								</li>
 							))}
@@ -274,6 +297,16 @@ export function DeckDetailPage() {
 					onCardUpdated={fetchCards}
 				/>
 			)}
+
+			{deckId && (
+				<DeleteCardModal
+					isOpen={deletingCard !== null}
+					deckId={deckId}
+					card={deletingCard}
+					onClose={() => setDeletingCard(null)}
+					onCardDeleted={fetchCards}
+				/>
+			)}
 		</div>
 	);
 }