feat(client): add edit deck modal with form validation

Add EditDeckModal component that allows users to edit existing decks.
The modal pre-populates with current deck values and supports updating
name and description fields with proper validation and error handling.

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

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

4 files changed, 680 insertions, 7 deletions

diff --git a/docs/dev/roadmap.md b/docs/dev/roadmap.md
index bcddb38..86e9c05 100644
--- a/docs/dev/roadmap.md
+++ b/docs/dev/roadmap.md
@@ -86,7 +86,7 @@ Smaller features first to enable early MVP validation.
 ### Frontend
 - [x] Deck list page (empty state, list view)
 - [x] Create deck modal/form
-- [ ] Edit deck
+- [x] Edit deck
 - [ ] Delete deck (with confirmation)
 - [ ] Add tests
 
diff --git a/src/client/components/EditDeckModal.test.tsx b/src/client/components/EditDeckModal.test.tsx
new file mode 100644
index 0000000..e4c997e
--- /dev/null
+++ b/src/client/components/EditDeckModal.test.tsx
@@ -0,0 +1,445 @@
+/**
+ * @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 { EditDeckModal } from "./EditDeckModal";
+
+// Mock fetch globally
+const mockFetch = vi.fn();
+global.fetch = mockFetch;
+
+describe("EditDeckModal", () => {
+	const mockDeck = {
+		id: "deck-123",
+		name: "Test Deck",
+		description: "Test description",
+		newCardsPerDay: 20,
+	};
+
+	const defaultProps = {
+		isOpen: true,
+		deck: mockDeck,
+		onClose: vi.fn(),
+		onDeckUpdated: 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(<EditDeckModal {...defaultProps} isOpen={false} />);
+
+		expect(screen.queryByRole("dialog")).toBeNull();
+	});
+
+	it("does not render when deck is null", () => {
+		render(<EditDeckModal {...defaultProps} deck={null} />);
+
+		expect(screen.queryByRole("dialog")).toBeNull();
+	});
+
+	it("renders modal when open with deck", () => {
+		render(<EditDeckModal {...defaultProps} />);
+
+		expect(screen.getByRole("dialog")).toBeDefined();
+		expect(screen.getByRole("heading", { name: "Edit Deck" })).toBeDefined();
+		expect(screen.getByLabelText("Name")).toBeDefined();
+		expect(screen.getByLabelText("Description (optional)")).toBeDefined();
+		expect(screen.getByRole("button", { name: "Cancel" })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Save" })).toBeDefined();
+	});
+
+	it("populates form with deck values", () => {
+		render(<EditDeckModal {...defaultProps} />);
+
+		expect(screen.getByLabelText("Name")).toHaveProperty("value", "Test Deck");
+		expect(screen.getByLabelText("Description (optional)")).toHaveProperty(
+			"value",
+			"Test description",
+		);
+	});
+
+	it("populates form with empty description when deck description is null", () => {
+		const deckWithNullDesc = { ...mockDeck, description: null };
+		render(<EditDeckModal {...defaultProps} deck={deckWithNullDesc} />);
+
+		expect(screen.getByLabelText("Description (optional)")).toHaveProperty(
+			"value",
+			"",
+		);
+	});
+
+	it("disables save button when name is empty", async () => {
+		const user = userEvent.setup();
+		render(<EditDeckModal {...defaultProps} />);
+
+		const nameInput = screen.getByLabelText("Name");
+		await user.clear(nameInput);
+
+		const saveButton = screen.getByRole("button", { name: "Save" });
+		expect(saveButton).toHaveProperty("disabled", true);
+	});
+
+	it("enables save button when name has content", () => {
+		render(<EditDeckModal {...defaultProps} />);
+
+		const saveButton = screen.getByRole("button", { name: "Save" });
+		expect(saveButton).toHaveProperty("disabled", false);
+	});
+
+	it("calls onClose when Cancel is clicked", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		render(<EditDeckModal {...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(<EditDeckModal {...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(<EditDeckModal {...defaultProps} onClose={onClose} />);
+
+		// Click on an element inside the modal
+		await user.click(screen.getByLabelText("Name"));
+
+		expect(onClose).not.toHaveBeenCalled();
+	});
+
+	it("updates deck with new name", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		const onDeckUpdated = vi.fn();
+
+		mockFetch.mockResolvedValue({
+			ok: true,
+			json: async () => ({
+				deck: {
+					id: "deck-123",
+					name: "Updated Deck",
+					description: "Test description",
+					newCardsPerDay: 20,
+				},
+			}),
+		});
+
+		render(
+			<EditDeckModal
+				isOpen={true}
+				deck={mockDeck}
+				onClose={onClose}
+				onDeckUpdated={onDeckUpdated}
+			/>,
+		);
+
+		const nameInput = screen.getByLabelText("Name");
+		await user.clear(nameInput);
+		await user.type(nameInput, "Updated Deck");
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-123", {
+				method: "PUT",
+				headers: {
+					"Content-Type": "application/json",
+					Authorization: "Bearer access-token",
+				},
+				body: JSON.stringify({
+					name: "Updated Deck",
+					description: "Test description",
+				}),
+			});
+		});
+
+		expect(onDeckUpdated).toHaveBeenCalledTimes(1);
+		expect(onClose).toHaveBeenCalledTimes(1);
+	});
+
+	it("updates deck with new description", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+		const onDeckUpdated = vi.fn();
+
+		mockFetch.mockResolvedValue({
+			ok: true,
+			json: async () => ({
+				deck: {
+					id: "deck-123",
+					name: "Test Deck",
+					description: "New description",
+					newCardsPerDay: 20,
+				},
+			}),
+		});
+
+		render(
+			<EditDeckModal
+				isOpen={true}
+				deck={mockDeck}
+				onClose={onClose}
+				onDeckUpdated={onDeckUpdated}
+			/>,
+		);
+
+		const descInput = screen.getByLabelText("Description (optional)");
+		await user.clear(descInput);
+		await user.type(descInput, "New description");
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-123", {
+				method: "PUT",
+				headers: {
+					"Content-Type": "application/json",
+					Authorization: "Bearer access-token",
+				},
+				body: JSON.stringify({
+					name: "Test Deck",
+					description: "New description",
+				}),
+			});
+		});
+
+		expect(onDeckUpdated).toHaveBeenCalledTimes(1);
+		expect(onClose).toHaveBeenCalledTimes(1);
+	});
+
+	it("clears description when input is emptied", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockResolvedValue({
+			ok: true,
+			json: async () => ({
+				deck: {
+					id: "deck-123",
+					name: "Test Deck",
+					description: null,
+					newCardsPerDay: 20,
+				},
+			}),
+		});
+
+		render(<EditDeckModal {...defaultProps} />);
+
+		const descInput = screen.getByLabelText("Description (optional)");
+		await user.clear(descInput);
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-123", {
+				method: "PUT",
+				headers: {
+					"Content-Type": "application/json",
+					Authorization: "Bearer access-token",
+				},
+				body: JSON.stringify({
+					name: "Test Deck",
+					description: null,
+				}),
+			});
+		});
+	});
+
+	it("trims whitespace from name and description", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockResolvedValue({
+			ok: true,
+			json: async () => ({ deck: { id: "deck-123" } }),
+		});
+
+		const deckWithWhitespace = {
+			...mockDeck,
+			name: "  Deck  ",
+			description: "  Description  ",
+		};
+		render(<EditDeckModal {...defaultProps} deck={deckWithWhitespace} />);
+
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-123", {
+				method: "PUT",
+				headers: {
+					"Content-Type": "application/json",
+					Authorization: "Bearer access-token",
+				},
+				body: JSON.stringify({
+					name: "Deck",
+					description: "Description",
+				}),
+			});
+		});
+	});
+
+	it("shows loading state during submission", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockImplementation(() => new Promise(() => {})); // Never resolves
+
+		render(<EditDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		expect(screen.getByRole("button", { name: "Saving..." })).toBeDefined();
+		expect(screen.getByRole("button", { name: "Saving..." })).toHaveProperty(
+			"disabled",
+			true,
+		);
+		expect(screen.getByRole("button", { name: "Cancel" })).toHaveProperty(
+			"disabled",
+			true,
+		);
+		expect(screen.getByLabelText("Name")).toHaveProperty("disabled", true);
+		expect(screen.getByLabelText("Description (optional)")).toHaveProperty(
+			"disabled",
+			true,
+		);
+	});
+
+	it("displays API error message", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockResolvedValue({
+			ok: false,
+			status: 400,
+			json: async () => ({ error: "Deck name already exists" }),
+		});
+
+		render(<EditDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain(
+				"Deck name already exists",
+			);
+		});
+	});
+
+	it("displays generic error on unexpected failure", async () => {
+		const user = userEvent.setup();
+
+		mockFetch.mockRejectedValue(new Error("Network error"));
+
+		render(<EditDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain(
+				"Failed to update deck. Please try again.",
+			);
+		});
+	});
+
+	it("displays error when not authenticated", async () => {
+		const user = userEvent.setup();
+
+		vi.mocked(apiClient.getAuthHeader).mockReturnValue(undefined);
+
+		render(<EditDeckModal {...defaultProps} />);
+
+		await user.click(screen.getByRole("button", { name: "Save" }));
+
+		await waitFor(() => {
+			expect(screen.getByRole("alert").textContent).toContain(
+				"Not authenticated",
+			);
+		});
+	});
+
+	it("updates form when deck prop changes", () => {
+		const { rerender } = render(<EditDeckModal {...defaultProps} />);
+
+		expect(screen.getByLabelText("Name")).toHaveProperty("value", "Test Deck");
+
+		const newDeck = {
+			...mockDeck,
+			name: "New Deck Name",
+			description: "New description",
+		};
+		rerender(<EditDeckModal {...defaultProps} deck={newDeck} />);
+
+		expect(screen.getByLabelText("Name")).toHaveProperty(
+			"value",
+			"New Deck Name",
+		);
+		expect(screen.getByLabelText("Description (optional)")).toHaveProperty(
+			"value",
+			"New description",
+		);
+	});
+
+	it("clears error when modal is closed", async () => {
+		const user = userEvent.setup();
+		const onClose = vi.fn();
+
+		mockFetch.mockResolvedValue({
+			ok: false,
+			status: 400,
+			json: async () => ({ error: "Some error" }),
+		});
+
+		const { rerender } = render(
+			<EditDeckModal {...defaultProps} onClose={onClose} />,
+		);
+
+		// Trigger error
+		await user.click(screen.getByRole("button", { name: "Save" }));
+		await waitFor(() => {
+			expect(screen.getByRole("alert")).toBeDefined();
+		});
+
+		// Close and reopen the modal
+		await user.click(screen.getByRole("button", { name: "Cancel" }));
+		rerender(<EditDeckModal {...defaultProps} onClose={onClose} />);
+
+		// Error should be cleared
+		expect(screen.queryByRole("alert")).toBeNull();
+	});
+});
diff --git a/src/client/components/EditDeckModal.tsx b/src/client/components/EditDeckModal.tsx
new file mode 100644
index 0000000..46f1d4b
--- /dev/null
+++ b/src/client/components/EditDeckModal.tsx
@@ -0,0 +1,202 @@
+import { type FormEvent, useEffect, useState } from "react";
+import { ApiClientError, apiClient } from "../api";
+
+interface Deck {
+	id: string;
+	name: string;
+	description: string | null;
+	newCardsPerDay: number;
+}
+
+interface EditDeckModalProps {
+	isOpen: boolean;
+	deck: Deck | null;
+	onClose: () => void;
+	onDeckUpdated: () => void;
+}
+
+export function EditDeckModal({
+	isOpen,
+	deck,
+	onClose,
+	onDeckUpdated,
+}: EditDeckModalProps) {
+	const [name, setName] = useState("");
+	const [description, setDescription] = useState("");
+	const [error, setError] = useState<string | null>(null);
+	const [isSubmitting, setIsSubmitting] = useState(false);
+
+	// Sync form state when deck changes
+	useEffect(() => {
+		if (deck) {
+			setName(deck.name);
+			setDescription(deck.description ?? "");
+			setError(null);
+		}
+	}, [deck]);
+
+	const handleClose = () => {
+		setError(null);
+		onClose();
+	};
+
+	const handleSubmit = async (e: FormEvent) => {
+		e.preventDefault();
+		if (!deck) return;
+
+		setError(null);
+		setIsSubmitting(true);
+
+		try {
+			const authHeader = apiClient.getAuthHeader();
+			if (!authHeader) {
+				throw new ApiClientError("Not authenticated", 401);
+			}
+
+			const res = await fetch(`/api/decks/${deck.id}`, {
+				method: "PUT",
+				headers: {
+					"Content-Type": "application/json",
+					...authHeader,
+				},
+				body: JSON.stringify({
+					name: name.trim(),
+					description: description.trim() || null,
+				}),
+			});
+
+			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,
+				);
+			}
+
+			onDeckUpdated();
+			onClose();
+		} catch (err) {
+			if (err instanceof ApiClientError) {
+				setError(err.message);
+			} else {
+				setError("Failed to update deck. Please try again.");
+			}
+		} finally {
+			setIsSubmitting(false);
+		}
+	};
+
+	if (!isOpen || !deck) {
+		return null;
+	}
+
+	return (
+		<div
+			role="dialog"
+			aria-modal="true"
+			aria-labelledby="edit-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="edit-deck-title" style={{ marginTop: 0 }}>
+					Edit Deck
+				</h2>
+
+				<form onSubmit={handleSubmit}>
+					{error && (
+						<div role="alert" style={{ color: "red", marginBottom: "1rem" }}>
+							{error}
+						</div>
+					)}
+
+					<div style={{ marginBottom: "1rem" }}>
+						<label
+							htmlFor="edit-deck-name"
+							style={{ display: "block", marginBottom: "0.25rem" }}
+						>
+							Name
+						</label>
+						<input
+							id="edit-deck-name"
+							type="text"
+							value={name}
+							onChange={(e) => setName(e.target.value)}
+							required
+							maxLength={255}
+							disabled={isSubmitting}
+							style={{ width: "100%", boxSizing: "border-box" }}
+						/>
+					</div>
+
+					<div style={{ marginBottom: "1rem" }}>
+						<label
+							htmlFor="edit-deck-description"
+							style={{ display: "block", marginBottom: "0.25rem" }}
+						>
+							Description (optional)
+						</label>
+						<textarea
+							id="edit-deck-description"
+							value={description}
+							onChange={(e) => setDescription(e.target.value)}
+							maxLength={1000}
+							disabled={isSubmitting}
+							rows={3}
+							style={{
+								width: "100%",
+								boxSizing: "border-box",
+								resize: "vertical",
+							}}
+						/>
+					</div>
+
+					<div
+						style={{
+							display: "flex",
+							gap: "0.5rem",
+							justifyContent: "flex-end",
+						}}
+					>
+						<button type="button" onClick={handleClose} disabled={isSubmitting}>
+							Cancel
+						</button>
+						<button type="submit" disabled={isSubmitting || !name.trim()}>
+							{isSubmitting ? "Saving..." : "Save"}
+						</button>
+					</div>
+				</form>
+			</div>
+		</div>
+	);
+}
diff --git a/src/client/pages/HomePage.tsx b/src/client/pages/HomePage.tsx
index d753aa1..08eccaa 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 { EditDeckModal } from "../components/EditDeckModal";
 import { useAuth } from "../stores";
 
 interface Deck {
@@ -18,6 +19,7 @@ export function HomePage() {
 	const [isLoading, setIsLoading] = useState(true);
 	const [error, setError] = useState<string | null>(null);
 	const [isCreateModalOpen, setIsCreateModalOpen] = useState(false);
+	const [editingDeck, setEditingDeck] = useState<Deck | null>(null);
 
 	const fetchDecks = useCallback(async () => {
 		setIsLoading(true);
@@ -119,12 +121,29 @@ export function HomePage() {
 									borderRadius: "4px",
 								}}
 							>
-								<h3 style={{ margin: 0 }}>{deck.name}</h3>
-								{deck.description && (
-									<p style={{ margin: "0.5rem 0 0 0", color: "#666" }}>
-										{deck.description}
-									</p>
-								)}
+								<div
+									style={{
+										display: "flex",
+										justifyContent: "space-between",
+										alignItems: "flex-start",
+									}}
+								>
+									<div>
+										<h3 style={{ margin: 0 }}>{deck.name}</h3>
+										{deck.description && (
+											<p style={{ margin: "0.5rem 0 0 0", color: "#666" }}>
+												{deck.description}
+											</p>
+										)}
+									</div>
+									<button
+										type="button"
+										onClick={() => setEditingDeck(deck)}
+										style={{ marginLeft: "1rem" }}
+									>
+										Edit
+									</button>
+								</div>
 							</li>
 						))}
 					</ul>
@@ -136,6 +155,13 @@ export function HomePage() {
 				onClose={() => setIsCreateModalOpen(false)}
 				onDeckCreated={fetchDecks}
 			/>
+
+			<EditDeckModal
+				isOpen={editingDeck !== null}
+				deck={editingDeck}
+				onClose={() => setEditingDeck(null)}
+				onDeckUpdated={fetchDecks}
+			/>
 		</div>
 	);
 }