PR 3/10 — Port Hacker News data layer to fetch + useFetch hook

[devanshi-gpta]

Summary

Part of the Angular -> React migration chain; based on devin-09.08.2026-devanshi/port-models-and-shared-styles.

Ports src/app/shared/services/hackernews-api.service.ts and src/app/shared/pipes/comment.pipe.ts into react-app/, dropping RxJS entirely:

• src/services/hackernews-api.ts — fetchFeed, fetchItemContent, fetchPollContent, fetchUser as plain async functions over fetch, each taking an optional AbortSignal and throwing on non-ok responses (the Angular lazyFetch Observable wrapper silently ignored HTTP errors).
• Behaviour change in the poll aggregation: the Angular version emitted the story first and mutated poll / poll_votes_count later via subscribe, so consumers saw a partially populated story. The port awaits the per-option requests in parallel, so the resolved story is already complete:

if (story.type === 'poll' && story.poll) {
    story.poll_votes_count = 0;
    const results = await Promise.all(story.poll.map((_, i) => fetchPollContent(story.id + i + 1, signal)));
    results.forEach((r, i) => { story.poll[i] = r; story.poll_votes_count += r.points; });
}

• src/hooks/useFetch.ts — useFetch<T>(fetcher, deps) returning { data, error, loading }; aborts the in-flight request on deps change/unmount and swallows AbortError. Will back the feed, item-details and user pages.
• src/utils/format-comment-count.ts — formatCommentCount(count) replacing CommentPipe ('discuss' / '1 comment' / 'N comments').

Proposed fixes

• Vitest coverage for formatCommentCount and, with a stubbed globalThis.fetch, for poll aggregation, the non-poll path, non-ok rejection and signal pass-through.
• npm run typecheck, npm run lint, npm test and npm run build pass in react-app/.
• No files under src/ (the Angular app) are touched.

Link to Devin session: https://app.devin.ai/sessions/50f5f5797eb8469d9e8e0eaab2586019
Open in Devin Desktop: https://app.devin.ai/desktop/session/50f5f5797eb8469d9e8e0eaab2586019?variant=devin
Requested by: @devanshi-gpta

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