fix(feed): stop refreshes from re-sorting the updated list

Two fixes to refresh order stability (My Shows / Feed sort by
lastUpdated):

- A refresh that fetches identical episodes no longer bumps
  lastUpdated (id-set comparison via sameEpisodes), so unchanged
  feeds keep their position instead of reordering every cycle.
- refreshAllFeeds now fetches in parallel and applies ONE atomic
  update instead of a per-feed setFeeds, which re-sorted the list
  once per completion and made order flap until the batch finished.

Adds feed-refresh regression tests with mocked clock.

tests/feed-refresh.test.ts

@@ -0,0 +1,155 @@
+/**
+ * Feed refresh order-stability regression test.
+ *
+ * My Shows / Feed sort by `lastUpdated` ("updated") by default, and every
+ * refresh bumped it unconditionally — so a startup refresh-all re-sorted the
+ * list once per feed as each fetch landed (order flapping until the batch
+ * finished). These tests pin the contract:
+ *
+ *   1. A refresh that fetches identical episodes does NOT bump lastUpdated —
+ *      the feed object is untouched, so the list cannot reorder.
+ *   2. A refresh that fetches genuinely new episodes DOES bump lastUpdated.
+ *   3. refreshAllFeeds applies one atomic update: unchanged feeds keep their
+ *      order and timestamps after a full refresh.
+ *
+ * The clock is mocked (fake timers) so the "did lastUpdated advance?" checks
+ * are deterministic — no real sleeps that would race under load.
+ */
+
+import { test, expect, beforeAll, afterAll, beforeEach, vi } from "bun:test";
+import { mkdtempSync, rmSync } from "fs";
+import { tmpdir } from "os";
+import { join } from "path";
+
+// Point the config dir at a throwaway directory BEFORE importing the stores
+// (their module-level init reads it).
+const configHome = mkdtempSync(join(tmpdir(), "podtui-refresh-"));
+process.env.XDG_CONFIG_HOME = configHome;
+
+import { useFeedStore } from "../src/stores/feed";
+import type { Podcast } from "../src/types/podcast";
+
+interface ServedEpisode {
+	title: string;
+	date: string;
+}
+
+let server: ReturnType<typeof Bun.serve> | null = null;
+let servedEpisodes: ServedEpisode[] = [];
+let feedAId = "";
+
+/** XML for the current served episode list (episode ids = feedUrl#index). */
+function feedXml(episodes: ServedEpisode[], origin: string): string {
+	const items = episodes
+		.map(
+			(ep, i) => `<item>
+	<title>${ep.title}</title>
+	<pubDate>${ep.date}</pubDate>
+	<enclosure url="${origin}/audio-${i}.mp3" length="12345" type="audio/mpeg"/>
+</item>`,
+		)
+		.join("\n");
+	return `<?xml version="1.0" encoding="UTF-8"?>
+<rss version="2.0"><channel>
+<title>Test Show</title>
+<description>Regression test feed</description>
+${items}
+</channel></rss>`;
+}
+
+const makePodcast = (feedUrl: string): Podcast => ({
+	id: feedUrl,
+	title: "Test Show",
+	description: "Regression test feed",
+	author: "tester",
+	feedUrl,
+	lastUpdated: new Date(),
+	isSubscribed: true,
+});
+
+beforeAll(() => {
+	server = Bun.serve({
+		port: 0,
+		fetch(req) {
+			const url = new URL(req.url);
+			if (url.pathname.endsWith(".xml")) {
+				return new Response(feedXml(servedEpisodes, url.origin), {
+					headers: { "Content-Type": "application/rss+xml" },
+				});
+			}
+			return new Response("not found", { status: 404 });
+		},
+	});
+});
+
+beforeEach(() => {
+	vi.useFakeTimers();
+});
+
+afterAll(() => {
+	vi.useRealTimers();
+	server?.stop(true);
+	rmSync(configHome, { recursive: true, force: true });
+});
+
+test("refresh with identical episodes does not bump lastUpdated", async () => {
+	const store = useFeedStore();
+	servedEpisodes = [
+		{ title: "Ep 3", date: "2026-08-03T00:00:00Z" },
+		{ title: "Ep 2", date: "2026-08-02T00:00:00Z" },
+		{ title: "Ep 1", date: "2026-08-01T00:00:00Z" },
+	];
+	const feedUrl = `http://127.0.0.1:${server!.port}/show-a.xml`;
+	const feed = await store.addFeed(makePodcast(feedUrl), "test-source");
+	expect(feed).not.toBeNull();
+	feedAId = feed!.id;
+
+	const before = store.getFeed(feedAId)!;
+	const beforeUpdated = before.lastUpdated.getTime();
+
+	// Advance the (mocked) clock, then refresh with identical content.
+	vi.advanceTimersByTime(60_000);
+	await store.refreshFeed(feedAId);
+
+	const after = store.getFeed(feedAId)!;
+	expect(after).toBe(before); // same object: no update applied at all
+	expect(after.lastUpdated.getTime()).toBe(beforeUpdated);
+	expect(after.episodes.length).toBe(3);
+});
+
+test("refresh with a genuinely new episode bumps lastUpdated", async () => {
+	const store = useFeedStore();
+	servedEpisodes.push({ title: "Ep 0 (new)", date: "2026-08-04T00:00:00Z" });
+
+	const before = store.getFeed(feedAId)!.lastUpdated.getTime();
+	vi.advanceTimersByTime(60_000);
+	await store.refreshFeed(feedAId);
+
+	const after = store.getFeed(feedAId)!;
+	expect(after.lastUpdated.getTime()).toBeGreaterThan(before);
+	expect(after.episodes.length).toBe(4);
+});
+
+test("refreshAllFeeds keeps unchanged feeds' order and timestamps", async () => {
+	const store = useFeedStore();
+	// Feed B: distinct URL, identical served content, so refreshing it is a
+	// no-op too.
+	const feedBUrl = `http://127.0.0.1:${server!.port}/show-b.xml`;
+	const feedB = await store.addFeed(makePodcast(feedBUrl), "test-source");
+	expect(feedB).not.toBeNull();
+	const feedBId = feedB!.id;
+
+	const orderBefore = store.getFilteredFeeds().map((f) => f.id);
+	const tsBefore: Record<string, number> = {};
+	for (const id of [feedAId, feedBId]) {
+		tsBefore[id] = store.getFeed(id)!.lastUpdated.getTime();
+	}
+
+	vi.advanceTimersByTime(60_000);
+	await store.refreshAllFeeds();
+
+	expect(store.getFilteredFeeds().map((f) => f.id)).toEqual(orderBefore);
+	for (const id of [feedAId, feedBId]) {
+		expect(store.getFeed(id)!.lastUpdated.getTime()).toBe(tsBefore[id]);
+	}
+});