story-kit: create 174_story_matrix_chatbot_interface_for_story_kit

frontend/src/hooks/useChatHistory.test.ts

@@ -5,12 +5,20 @@ import { useChatHistory } from "./useChatHistory";
 
 const PROJECT = "/tmp/test-project";
 const STORAGE_KEY = `storykit-chat-history:${PROJECT}`;
+const LIMIT_KEY = `storykit-chat-history-limit:${PROJECT}`;
 
 const sampleMessages: Message[] = [
 	{ role: "user", content: "Hello" },
 	{ role: "assistant", content: "Hi there!" },
 ];
 
+function makeMessages(count: number): Message[] {
+	return Array.from({ length: count }, (_, i) => ({
+		role: "user" as const,
+		content: `Message ${i + 1}`,
+	}));
+}
+
 describe("useChatHistory", () => {
 	beforeEach(() => {
 		localStorage.clear();
@@ -143,4 +151,125 @@ describe("useChatHistory", () => {
 
 		expect(localStorage.getItem(STORAGE_KEY)).toBeNull();
 	});
+
+	// --- Story 179: Chat history pruning tests ---
+
+	it("S179: default limit of 200 is applied when saving to localStorage", () => {
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+
+		expect(result.current.maxMessages).toBe(200);
+	});
+
+	it("S179: messages are pruned from the front when exceeding the limit", () => {
+		// Set a small limit to make testing practical
+		localStorage.setItem(LIMIT_KEY, "3");
+
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+		const fiveMessages = makeMessages(5);
+
+		act(() => {
+			result.current.setMessages(fiveMessages);
+		});
+
+		// localStorage should contain only the last 3 messages
+		const stored: Message[] = JSON.parse(
+			localStorage.getItem(STORAGE_KEY) ?? "[]",
+		);
+		expect(stored).toEqual(fiveMessages.slice(-3));
+		expect(stored).toHaveLength(3);
+		expect(stored[0].content).toBe("Message 3");
+	});
+
+	it("S179: messages under the limit are not pruned", () => {
+		localStorage.setItem(LIMIT_KEY, "10");
+
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+		const threeMessages = makeMessages(3);
+
+		act(() => {
+			result.current.setMessages(threeMessages);
+		});
+
+		const stored: Message[] = JSON.parse(
+			localStorage.getItem(STORAGE_KEY) ?? "[]",
+		);
+		expect(stored).toEqual(threeMessages);
+		expect(stored).toHaveLength(3);
+	});
+
+	it("S179: limit is configurable via localStorage key", () => {
+		localStorage.setItem(LIMIT_KEY, "5");
+
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+
+		expect(result.current.maxMessages).toBe(5);
+	});
+
+	it("S179: setMaxMessages updates the limit and persists it", () => {
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+
+		act(() => {
+			result.current.setMaxMessages(50);
+		});
+
+		expect(result.current.maxMessages).toBe(50);
+		expect(localStorage.getItem(LIMIT_KEY)).toBe("50");
+	});
+
+	it("S179: a limit of 0 means unlimited (no pruning)", () => {
+		localStorage.setItem(LIMIT_KEY, "0");
+
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+		const manyMessages = makeMessages(500);
+
+		act(() => {
+			result.current.setMessages(manyMessages);
+		});
+
+		const stored: Message[] = JSON.parse(
+			localStorage.getItem(STORAGE_KEY) ?? "[]",
+		);
+		expect(stored).toHaveLength(500);
+		expect(stored).toEqual(manyMessages);
+	});
+
+	it("S179: changing the limit re-prunes messages on next save", () => {
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+		const tenMessages = makeMessages(10);
+
+		act(() => {
+			result.current.setMessages(tenMessages);
+		});
+
+		// All 10 saved (default limit 200 > 10)
+		let stored: Message[] = JSON.parse(
+			localStorage.getItem(STORAGE_KEY) ?? "[]",
+		);
+		expect(stored).toHaveLength(10);
+
+		// Now lower the limit — the effect re-runs and prunes
+		act(() => {
+			result.current.setMaxMessages(3);
+		});
+
+		stored = JSON.parse(localStorage.getItem(STORAGE_KEY) ?? "[]");
+		expect(stored).toHaveLength(3);
+		expect(stored[0].content).toBe("Message 8");
+	});
+
+	it("S179: invalid limit in localStorage falls back to default", () => {
+		localStorage.setItem(LIMIT_KEY, "not-a-number");
+
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+
+		expect(result.current.maxMessages).toBe(200);
+	});
+
+	it("S179: negative limit in localStorage falls back to default", () => {
+		localStorage.setItem(LIMIT_KEY, "-5");
+
+		const { result } = renderHook(() => useChatHistory(PROJECT));
+
+		expect(result.current.maxMessages).toBe(200);
+	});
 });

frontend/src/hooks/useChatHistory.ts

@@ -2,11 +2,37 @@ import { useCallback, useEffect, useRef, useState } from "react";
 import type { Message } from "../types";
 
 const STORAGE_KEY_PREFIX = "storykit-chat-history:";
+const LIMIT_KEY_PREFIX = "storykit-chat-history-limit:";
+const DEFAULT_LIMIT = 200;
 
 function storageKey(projectPath: string): string {
 	return `${STORAGE_KEY_PREFIX}${projectPath}`;
 }
 
+function limitKey(projectPath: string): string {
+	return `${LIMIT_KEY_PREFIX}${projectPath}`;
+}
+
+function loadLimit(projectPath: string): number {
+	try {
+		const raw = localStorage.getItem(limitKey(projectPath));
+		if (raw === null) return DEFAULT_LIMIT;
+		const parsed = Number(raw);
+		if (!Number.isFinite(parsed) || parsed < 0) return DEFAULT_LIMIT;
+		return Math.floor(parsed);
+	} catch {
+		return DEFAULT_LIMIT;
+	}
+}
+
+function saveLimit(projectPath: string, limit: number): void {
+	try {
+		localStorage.setItem(limitKey(projectPath), String(limit));
+	} catch {
+		// Ignore — quota or security errors.
+	}
+}
+
 function loadMessages(projectPath: string): Message[] {
 	try {
 		const raw = localStorage.getItem(storageKey(projectPath));
@@ -19,12 +45,22 @@ function loadMessages(projectPath: string): Message[] {
 	}
 }
 
-function saveMessages(projectPath: string, messages: Message[]): void {
+function pruneMessages(messages: Message[], limit: number): Message[] {
+	if (limit === 0 || messages.length <= limit) return messages;
+	return messages.slice(-limit);
+}
+
+function saveMessages(
+	projectPath: string,
+	messages: Message[],
+	limit: number,
+): void {
 	try {
-		if (messages.length === 0) {
+		const pruned = pruneMessages(messages, limit);
+		if (pruned.length === 0) {
 			localStorage.removeItem(storageKey(projectPath));
 		} else {
-			localStorage.setItem(storageKey(projectPath), JSON.stringify(messages));
+			localStorage.setItem(storageKey(projectPath), JSON.stringify(pruned));
 		}
 	} catch (e) {
 		console.warn("Failed to persist chat history to localStorage:", e);
@@ -35,15 +71,18 @@ export function useChatHistory(projectPath: string) {
 	const [messages, setMessagesState] = useState<Message[]>(() =>
 		loadMessages(projectPath),
 	);
+	const [maxMessages, setMaxMessagesState] = useState<number>(() =>
+		loadLimit(projectPath),
+	);
 	const projectPathRef = useRef(projectPath);
 
 	// Keep the ref in sync so the effect closure always has the latest path.
 	projectPathRef.current = projectPath;
 
-	// Persist whenever messages change.
+	// Persist whenever messages or limit change.
 	useEffect(() => {
-		saveMessages(projectPathRef.current, messages);
-	}, [messages]);
+		saveMessages(projectPathRef.current, messages, maxMessages);
+	}, [messages, maxMessages]);
 
 	const setMessages = useCallback(
 		(update: Message[] | ((prev: Message[]) => Message[])) => {
@@ -52,6 +91,11 @@ export function useChatHistory(projectPath: string) {
 		[],
 	);
 
+	const setMaxMessages = useCallback((limit: number) => {
+		setMaxMessagesState(limit);
+		saveLimit(projectPathRef.current, limit);
+	}, []);
+
 	const clearMessages = useCallback(() => {
 		setMessagesState([]);
 		// Eagerly remove from storage so clearSession doesn't depend on the
@@ -63,5 +107,11 @@ export function useChatHistory(projectPath: string) {
 		}
 	}, []);
 
-	return { messages, setMessages, clearMessages } as const;
+	return {
+		messages,
+		setMessages,
+		clearMessages,
+		maxMessages,
+		setMaxMessages,
+	} as const;
 }