refactor(feed): port refresh batch to Effect for concurrency and timeout

Replace the hand-rolled worker pool (mapWithConcurrency) with an Effect
program (src/effects/feed-refresh.ts): Effect.forEach bounds in-flight
fetches, Effect.timeout bounds each feed via the Clock service, and
failures fold to null so a bad feed never fails the batch. Per-feed
apply-as-it-lands is preserved — the apply callback runs inside each
feed's own fiber, so there is no Promise.all barrier.

Store boundary unchanged: refreshAllFeeds runs the program through
Effect.runPromise, keeping runAutoDownload + flushPendingSave after the
batch and isLoadingFeeds around it.

Adds TestClock-driven tests (tests/feed-refresh-effect.test.ts) that pin
concurrency, per-feed apply, timeout, and failure isolation without real
20s waits. Pins effect@^3 (V4 is in beta).

package.json

@@ -24,6 +24,7 @@
     "@opentui/core": "^0.1.77",
     "@opentui/solid": "^0.1.77",
     "date-fns": "^4.1.0",
+    "effect": "^3",
     "solid-js": "^1.9.9"
   }
 }

src/effects/feed-refresh.ts

@@ -0,0 +1,85 @@
+/**
+ * Feed-refresh batch as an Effect program.
+ *
+ * Replaces the hand-rolled worker pool (mapWithConcurrency) + per-feed
+ * fetch/apply plumbing in stores/feed.ts with Effect's structured
+ * concurrency:
+ *   - `Effect.forEach(..., { concurrency })` bounds in-flight fetches to
+ *     `concurrency` (starts exactly that many fibers; each completion pulls
+ *     the next feed — identical semantics to the old shared-counter pool).
+ *   - `Effect.timeout` bounds each feed's fetch to `timeoutMs`. It runs
+ *     through the `Clock` service, so under `TestContext` the TestClock
+ *     drives it deterministically (no real 20s wait in tests).
+ *   - Failures are folded to a null result: a failed or timed-out feed is
+ *     left untouched instead of failing the batch.
+ *   - The apply callback runs inside each feed's own fiber, so a feed's
+ *     refreshed episodes land AS ITS OWN FETCH COMPLETES — the
+ *     per-feed-apply-as-it-lands contract, no Promise.all barrier.
+ *
+ * The store boundary (stores/feed.ts) supplies the real fetch and apply
+ * closures and runs the program with Effect.runPromise.
+ */
+
+import { Duration, Effect } from "effect"
+import type { Episode } from "../types/episode"
+import type { Feed } from "../types/feed"
+
+/** Result of fetching one feed's RSS. `episodes: null` means the fetch
+ *  failed or timed out — callers must leave that feed untouched. */
+export interface RefreshFetchResult {
+  episodes: Episode[] | null
+  coverUrl: string | undefined
+}
+
+/** Result guaranteed to have parsed episodes (the apply path only). */
+export interface RefreshSuccess {
+  episodes: Episode[]
+  coverUrl: string | undefined
+}
+
+export interface RefreshBatchOptions {
+  /** Max simultaneous in-flight fetches. */
+  concurrency: number
+  /** Per-feed fetch timeout in milliseconds. */
+  timeoutMs: number
+}
+
+/** Fold any failure (network error, timeout, rejection) to a null result so
+ *  one bad feed can never fail the batch. */
+const failedResult: RefreshFetchResult = { episodes: null, coverUrl: undefined }
+
+/** Fetch one feed with a timeout, applying its result as its own fetch
+ *  lands. A failed or timed-out fetch yields null — the feed is untouched. */
+const refreshOne = (
+  feed: Feed,
+  fetchOne: (feed: Feed) => Promise<RefreshFetchResult>,
+  applyOne: (feed: Feed, result: RefreshSuccess) => void,
+  timeoutMs: number,
+): Effect.Effect<void> =>
+  Effect.tryPromise(() => fetchOne(feed)).pipe(
+    Effect.timeout(Duration.millis(timeoutMs)),
+    Effect.catchAll(() => Effect.succeed(failedResult)),
+    Effect.flatMap((result) => {
+      if (result.episodes === null) return Effect.void
+      // Capture the narrowed array before the closure — TS drops the
+      // `episodes !== null` narrowing inside Effect.sync's callback.
+      const episodes = result.episodes
+      return Effect.sync(() => applyOne(feed, { episodes, coverUrl: result.coverUrl }))
+    }),
+  )
+
+/** Refresh every feed with bounded concurrency. Each feed's refreshed
+ *  episodes are applied as its own fetch lands (no barrier); a failed or
+ *  timed-out feed is left untouched. The program never fails — failures
+ *  are folded to per-feed no-ops. */
+export const refreshFeedsBatch = (
+  feeds: readonly Feed[],
+  fetchOne: (feed: Feed) => Promise<RefreshFetchResult>,
+  applyOne: (feed: Feed, result: RefreshSuccess) => void,
+  options: RefreshBatchOptions,
+): Effect.Effect<void> =>
+  Effect.forEach(
+    feeds,
+    (feed) => refreshOne(feed, fetchOne, applyOne, options.timeoutMs),
+    { concurrency: options.concurrency, discard: true },
+  )

src/stores/feed.ts

@@ -4,6 +4,8 @@
  */
 
 import { createSignal } from "solid-js";
+import { Effect } from "effect";
+import { refreshFeedsBatch } from "../effects/feed-refresh";
 import { FeedVisibility } from "../types/feed";
 import type { Feed, FeedFilter, FeedSortField } from "../types/feed";
 import type { Podcast } from "../types/podcast";
@@ -249,31 +251,6 @@ export function sameRefreshWindow(
 	return fetched.every((e) => signatures.has(episodeSignature(e)));
 }
 
-/** Run `fn` over every item with at most `limit` executions in flight — a
- *  classic worker pool. Workers pull indexes from a shared counter, so the
- *  first `limit` calls start immediately and each completion frees its slot
- *  for the next item; results are assembled in INPUT order regardless of
- *  completion order. A hung `fn` holds at most one slot. */
-async function mapWithConcurrency<T, R>(
-	items: T[],
-	limit: number,
-	fn: (item: T) => Promise<R>,
-): Promise<R[]> {
-	const results = new Array<R>(items.length);
-	let nextIndex = 0;
-	const workers = Array.from(
-		{ length: Math.min(limit, items.length) },
-		async () => {
-			let i: number;
-			while ((i = nextIndex++) < items.length) {
-				results[i] = await fn(items[i]);
-			}
-		},
-	);
-	await Promise.all(workers);
-	return results;
-}
-
 function createFeedStore() {
 	const [feeds, setFeeds] = createSignal<Feed[]>([]);
 	const [sources, setSources] = createSignal<PodcastSource[]>([
@@ -644,27 +621,25 @@ function createFeedStore() {
 		})(), "Refreshing");
 	};
 
-	/** Refresh all feeds — bounded concurrency (at most FETCH_CONCURRENCY
-	 *  in-flight requests), and each feed's refreshed episodes are applied
-	 *  AS ITS OWN FETCH LANDS (no Promise.all barrier). Per-feed apply is
-	 *  safe because applyRefreshedEpisodes keeps unchanged feeds' object
-	 *  identity and lastUpdated (union merge), so each feed's refreshed
-	 *  episodes render as its own fetch resolves — the order flapping the
-	 *  old atomic barrier existed to hide can no longer happen. */
+	/** Refresh all feeds via the Effect batch program (effects/feed-refresh):
+	 *  bounded concurrency (at most FETCH_CONCURRENCY in-flight requests)
+	 *  and each feed's refreshed episodes applied AS ITS OWN FETCH LANDS
+	 *  (no barrier — the apply runs inside the feed's own fiber). Per-feed
+	 *  apply is safe because applyRefreshedEpisodes keeps unchanged feeds'
+	 *  object identity and lastUpdated (union merge), so each feed's
+	 *  refreshed episodes render as its own fetch resolves — the order
+	 *  flapping the old atomic barrier existed to hide can no longer
+	 *  happen. A failed or timed-out fetch (null episodes) leaves that
+	 *  feed untouched. */
 	const refreshAllFeeds = async () => {
 		setIsLoadingFeeds(true);
 		try {
-			await mapWithConcurrency(
+			await Effect.runPromise(
+				refreshFeedsBatch(
 					feeds(),
-				FETCH_CONCURRENCY,
-				async (feed) => {
-					const { episodes, coverUrl } = await fetchEpisodes(
-						feed.podcast.feedUrl,
-						MAX_EPISODES_REFRESH,
-						feed.id,
-					);
-					// A failed fetch (null) leaves that feed untouched.
-					if (!episodes) return;
+					(feed) =>
+						fetchEpisodes(feed.podcast.feedUrl, MAX_EPISODES_REFRESH, feed.id),
+					(feed, { episodes, coverUrl }) => {
 						setFeeds((prev) => {
 							let updated = applyRefreshedEpisodes(prev, feed.id, episodes);
 							if (coverUrl) {
@@ -678,6 +653,8 @@ function createFeedStore() {
 							return updated;
 						});
 					},
+					{ concurrency: FETCH_CONCURRENCY, timeoutMs: FETCH_TIMEOUT_MS },
+				),
 			);
 			// Global auto-download: one idempotent pass after the batch.
 			runAutoDownload();

tests/feed-refresh-effect.test.ts

@@ -0,0 +1,230 @@
+/**
+ * Feed-refresh Effect program tests (src/effects/feed-refresh.ts).
+ *
+ * These test the Effect program in isolation — no store singleton, no
+ * network, no fake timers. The fetch/apply closures are injected, and the
+ * `Clock` service comes from TestContext's TestClock, so timeouts are driven
+ * deterministically with TestClock.adjust instead of real 20s waits.
+ *
+ * Contracts pinned here (mirrored at the store level by
+ * feed-nonblocking.test.ts / feed-refresh.test.ts against a real Bun.serve):
+ *   1. Bounded concurrency — never more than `concurrency` fetches in
+ *      flight, and the pool pulls the next feed as one completes.
+ *   2. Per-feed apply as its own fetch lands (no barrier).
+ *   3. A timed-out fetch leaves that feed untouched and does not stall the
+ *      batch (TestClock.adjust fires the timeout deterministically).
+ *   4. A rejecting fetch leaves that feed untouched and does not fail the
+ *      batch.
+ */
+
+import { test, expect } from "bun:test"
+import { Duration, Effect, Fiber, TestClock, TestContext } from "effect"
+import {
+	refreshFeedsBatch,
+	type RefreshFetchResult,
+} from "../src/effects/feed-refresh"
+import type { Feed } from "../src/types/feed"
+import type { Podcast } from "../src/types/podcast"
+import type { Episode } from "../src/types/episode"
+
+const makePodcast = (id: string): Podcast => ({
+	id,
+	title: `Show ${id}`,
+	description: `Show ${id} description`,
+	feedUrl: `http://example.com/${id}.xml`,
+	lastUpdated: new Date(0),
+	isSubscribed: true,
+})
+
+const makeFeed = (id: string): Feed => ({
+	id,
+	podcast: makePodcast(id),
+	episodes: [],
+	visibility: "public" as Feed["visibility"],
+	sourceId: "test",
+	lastUpdated: new Date(0),
+	isPinned: false,
+})
+
+const makeEpisode = (id: string): Episode => ({
+	id,
+	podcastId: "pod",
+	title: `Ep ${id}`,
+	description: "",
+	audioUrl: `https://example.com/${id}.mp3`,
+	duration: 60,
+	pubDate: new Date(0),
+})
+
+/** Resolve an episode result without dragging in the full RSS shape. */
+const ok = (episodeIds: string[]): RefreshFetchResult => ({
+	episodes: episodeIds.map(makeEpisode),
+	coverUrl: undefined,
+})
+
+/** One macrotask turn — lets microtask-scheduled Effect fibers run. */
+const tick = (): Promise<void> => {
+	const { promise, resolve } = Promise.withResolvers<void>()
+	setImmediate(resolve)
+	return promise
+}
+
+/** A resolvable fetch gate: the pool parks on `promise` until the test
+ *  resolves it. (Promise.withResolvers's return type is not in tsconfig's
+ *  ES2015.Promise lib, hence the explicit shape.) */
+interface Gate {
+	promise: Promise<RefreshFetchResult>
+	resolve: (value: RefreshFetchResult) => void
+}
+
+/** Poll `cond` across up to `iterations` event-loop turns. */
+async function pollUntil(
+	cond: () => boolean,
+	iterations = 500,
+): Promise<boolean> {
+	for (let i = 0; i < iterations; i++) {
+		if (cond()) return true
+		await tick()
+	}
+	return cond()
+}
+
+test("bounds in-flight fetches to the configured concurrency", async () => {
+	const feeds = Array.from({ length: 10 }, (_, i) => makeFeed(`feed-${i}`))
+	let inFlight = 0
+	let maxInFlight = 0
+	const gates: Gate[] = []
+	const applied: string[] = []
+
+	const program = refreshFeedsBatch(
+		feeds,
+		(feed) => {
+			inFlight++
+			if (inFlight > maxInFlight) maxInFlight = inFlight
+			const gate = Promise.withResolvers<RefreshFetchResult>()
+			gates.push(gate)
+			return gate.promise.finally(() => {
+				inFlight--
+			})
+		},
+		(feed) => {
+			applied.push(feed.id)
+		},
+		{ concurrency: 4, timeoutMs: 60_000 },
+	)
+
+	// Run the batch in flight (NOT awaited) and observe the pool from
+	// outside via the gate side effects.
+	const done = Effect.runPromise(program)
+	// The pool starts exactly `concurrency` fetches up front.
+	const sawStart = await pollUntil(() => gates.length >= 4)
+	expect(sawStart).toBe(true)
+	expect(maxInFlight).toBe(4)
+	expect(gates.length).toBe(4)
+
+	// Resolve one gate: the pool pulls the next feed, still bounded at 4.
+	gates[0].resolve(ok(["a"]))
+	const sawPull = await pollUntil(() => gates.length >= 5)
+	expect(sawPull).toBe(true)
+	expect(maxInFlight).toBeLessThanOrEqual(4)
+
+	// Release everything, re-draining as the pool pulls new gates, until
+	// every feed has been fetched and applied.
+	while (applied.length < 10) {
+		for (const gate of gates.splice(0)) gate.resolve(ok(["x"]))
+		await tick()
+	}
+	await done
+	expect(maxInFlight).toBeLessThanOrEqual(4)
+	expect(applied).toHaveLength(10)
+})
+
+test("applies each feed as its own fetch lands (no barrier)", async () => {
+	const a = makeFeed("a")
+	const b = makeFeed("b")
+	const applied: string[] = []
+	let bCalled = false
+	const gateB = Promise.withResolvers<RefreshFetchResult>()
+
+	const program = refreshFeedsBatch(
+		[a, b],
+		(feed) => {
+			if (feed.id === "a") return Promise.resolve(ok(["a-1"]))
+			bCalled = true
+			return gateB.promise
+		},
+		(feed) => {
+			applied.push(feed.id)
+		},
+		{ concurrency: 4, timeoutMs: 60_000 },
+	)
+
+	// Run the batch in flight; A's fetch resolves and applies while B's is
+	// still parked at the gate.
+	const done = Effect.runPromise(program)
+	const aApplied = await pollUntil(() => applied.includes("a"))
+	expect(aApplied).toBe(true)
+	expect(bCalled).toBe(true)
+	expect(applied).toEqual(["a"])
+	expect(applied).not.toContain("b")
+
+	gateB.resolve(ok(["b-1"]))
+	await done
+	expect(applied).toEqual(["a", "b"])
+})
+
+test("a timed-out fetch leaves that feed untouched, without stalling the batch", async () => {
+	const fast = makeFeed("fast")
+	const hung = makeFeed("hung")
+	const applied: string[] = []
+	// A promise that never settles — the fetch hangs past the timeout.
+	const never = new Promise<RefreshFetchResult>(() => {})
+
+	const program = refreshFeedsBatch(
+		[fast, hung],
+		(feed) =>
+			feed.id === "fast"
+				? Promise.resolve(ok(["f-1"]))
+				: never,
+		(feed) => {
+			applied.push(feed.id)
+		},
+		{ concurrency: 4, timeoutMs: 5_000 },
+	)
+
+	const timed = Effect.gen(function* () {
+		const fiber = yield* Effect.fork(program)
+		// Advance the TestClock past the timeout: the hung fetch's
+		// Effect.timeout fires deterministically — no real 5s wait.
+		yield* TestClock.adjust(Duration.millis(5_000))
+		yield* Fiber.join(fiber)
+	})
+	await Effect.runPromise(
+		timed.pipe(Effect.provide(TestContext.TestContext)),
+	)
+
+	// The fast feed applied; the hung one was dropped, and the batch
+	// completed anyway.
+	expect(applied).toEqual(["fast"])
+})
+
+test("a rejecting fetch leaves that feed untouched and does not fail the batch", async () => {
+	const bad = makeFeed("bad")
+	const good = makeFeed("good")
+	const applied: string[] = []
+
+	const program = refreshFeedsBatch(
+		[bad, good],
+		(feed) =>
+			feed.id === "bad"
+				? Promise.reject(new Error("feed exploded"))
+				: Promise.resolve(ok(["g-1"])),
+		(feed) => {
+			applied.push(feed.id)
+		},
+		{ concurrency: 4, timeoutMs: 60_000 },
+	)
+
+	await Effect.runPromise(program)
+	expect(applied).toEqual(["good"])
+})