Episode 2 — React Frontend Architecture NextJS / 2.12 — Server State and API Integration

2.12.a — `fetch` API integration in React

Learning outcomes

Fetch JSON in useEffect with correct dependencies and cleanup.
Use AbortController to cancel in-flight requests on unmount or param change.
Map HTTP results to typed success and error shapes.

Minimal `useEffect` fetch

import { useEffect, useState } from "react";

type Post = { id: string; title: string };

export function PostDetails({ id }: { id: string }) {
  const [data, setData] = useState<Post | null>(null);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    const ac = new AbortController();

    async function run() {
      setError(null);
      try {
        const res = await fetch(`/api/posts/${id}`, { signal: ac.signal });
        if (!res.ok) throw new Error(`HTTP ${res.status}`);
        const json = (await res.json()) as Post;
        setData(json);
      } catch (e) {
        if ((e as Error).name === "AbortError") return;
        setError((e as Error).message);
      }
    }

    void run();
    return () => ac.abort();
  }, [id]);

  if (error) return <p>{error}</p>;
  if (!data) return <p>Loading…</p>;
  return <h1>{data.title}</h1>;
}

Why cancellation matters

Users navigate quickly. Without abort (or an equivalent), you risk:

applying a slow response over a new route’s state
memory leaks and confusing dev-only warnings

Beyond manual `fetch`

TanStack Query implements deduplication, caching, retries, and background refetching—this chapter’s baseline teaches the HTTP + effect fundamentals those tools build on.

Appendix — Scenario bank (basic → advanced)

Flashcard rhythm: symptom → cause → fix → phrase for interviews.

API0-001 — fetch integration #1

Level: Beginner
Symptom: stale UI or spinner stuck after 13 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-002 — fetch integration #2

Level: Beginner+
Symptom: stale UI or spinner stuck after 26 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-003 — fetch integration #3

Level: Intermediate
Symptom: stale UI or spinner stuck after 39 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-004 — fetch integration #4

Level: Intermediate+
Symptom: stale UI or spinner stuck after 52 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-005 — fetch integration #5

Level: Advanced
Symptom: stale UI or spinner stuck after 65 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-006 — fetch integration #6

Level: Advanced+
Symptom: stale UI or spinner stuck after 78 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-007 — fetch integration #7

Level: Beginner
Symptom: stale UI or spinner stuck after 91 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-008 — fetch integration #8

Level: Beginner+
Symptom: stale UI or spinner stuck after 104 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-009 — fetch integration #9

Level: Intermediate
Symptom: stale UI or spinner stuck after 117 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-010 — fetch integration #10

Level: Intermediate+
Symptom: stale UI or spinner stuck after 130 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-011 — fetch integration #11

Level: Advanced
Symptom: stale UI or spinner stuck after 143 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-012 — fetch integration #12

Level: Advanced+
Symptom: stale UI or spinner stuck after 156 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-013 — fetch integration #13

Level: Beginner
Symptom: stale UI or spinner stuck after 169 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-014 — fetch integration #14

Level: Beginner+
Symptom: stale UI or spinner stuck after 182 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-015 — fetch integration #15

Level: Intermediate
Symptom: stale UI or spinner stuck after 195 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-016 — fetch integration #16

Level: Intermediate+
Symptom: stale UI or spinner stuck after 8 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-017 — fetch integration #17

Level: Advanced
Symptom: stale UI or spinner stuck after 21 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-018 — fetch integration #18

Level: Advanced+
Symptom: stale UI or spinner stuck after 34 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-019 — fetch integration #19

Level: Beginner
Symptom: stale UI or spinner stuck after 47 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-020 — fetch integration #20

Level: Beginner+
Symptom: stale UI or spinner stuck after 60 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-021 — fetch integration #21

Level: Intermediate
Symptom: stale UI or spinner stuck after 73 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-022 — fetch integration #22

Level: Intermediate+
Symptom: stale UI or spinner stuck after 86 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-023 — fetch integration #23

Level: Advanced
Symptom: stale UI or spinner stuck after 99 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-024 — fetch integration #24

Level: Advanced+
Symptom: stale UI or spinner stuck after 112 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-025 — fetch integration #25

Level: Beginner
Symptom: stale UI or spinner stuck after 125 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-026 — fetch integration #26

Level: Beginner+
Symptom: stale UI or spinner stuck after 138 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-027 — fetch integration #27

Level: Intermediate
Symptom: stale UI or spinner stuck after 151 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-028 — fetch integration #28

Level: Intermediate+
Symptom: stale UI or spinner stuck after 164 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-029 — fetch integration #29

Level: Advanced
Symptom: stale UI or spinner stuck after 177 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-030 — fetch integration #30

Level: Advanced+
Symptom: stale UI or spinner stuck after 190 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-031 — fetch integration #31

Level: Beginner
Symptom: stale UI or spinner stuck after 3 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-032 — fetch integration #32

Level: Beginner+
Symptom: stale UI or spinner stuck after 16 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-033 — fetch integration #33

Level: Intermediate
Symptom: stale UI or spinner stuck after 29 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-034 — fetch integration #34

Level: Intermediate+
Symptom: stale UI or spinner stuck after 42 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-035 — fetch integration #35

Level: Advanced
Symptom: stale UI or spinner stuck after 55 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-036 — fetch integration #36

Level: Advanced+
Symptom: stale UI or spinner stuck after 68 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-037 — fetch integration #37

Level: Beginner
Symptom: stale UI or spinner stuck after 81 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-038 — fetch integration #38

Level: Beginner+
Symptom: stale UI or spinner stuck after 94 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-039 — fetch integration #39

Level: Intermediate
Symptom: stale UI or spinner stuck after 107 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-040 — fetch integration #40

Level: Intermediate+
Symptom: stale UI or spinner stuck after 120 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-041 — fetch integration #41

Level: Advanced
Symptom: stale UI or spinner stuck after 133 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-042 — fetch integration #42

Level: Advanced+
Symptom: stale UI or spinner stuck after 146 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-043 — fetch integration #43

Level: Beginner
Symptom: stale UI or spinner stuck after 159 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-044 — fetch integration #44

Level: Beginner+
Symptom: stale UI or spinner stuck after 172 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-045 — fetch integration #45

Level: Intermediate
Symptom: stale UI or spinner stuck after 185 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-046 — fetch integration #46

Level: Intermediate+
Symptom: stale UI or spinner stuck after 198 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-047 — fetch integration #47

Level: Advanced
Symptom: stale UI or spinner stuck after 11 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-048 — fetch integration #48

Level: Advanced+
Symptom: stale UI or spinner stuck after 24 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-049 — fetch integration #49

Level: Beginner
Symptom: stale UI or spinner stuck after 37 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-050 — fetch integration #50

Level: Beginner+
Symptom: stale UI or spinner stuck after 50 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-051 — fetch integration #51

Level: Intermediate
Symptom: stale UI or spinner stuck after 63 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-052 — fetch integration #52

Level: Intermediate+
Symptom: stale UI or spinner stuck after 76 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-053 — fetch integration #53

Level: Advanced
Symptom: stale UI or spinner stuck after 89 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-054 — fetch integration #54

Level: Advanced+
Symptom: stale UI or spinner stuck after 102 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-055 — fetch integration #55

Level: Beginner
Symptom: stale UI or spinner stuck after 115 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-056 — fetch integration #56

Level: Beginner+
Symptom: stale UI or spinner stuck after 128 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-057 — fetch integration #57

Level: Intermediate
Symptom: stale UI or spinner stuck after 141 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-058 — fetch integration #58

Level: Intermediate+
Symptom: stale UI or spinner stuck after 154 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-059 — fetch integration #59

Level: Advanced
Symptom: stale UI or spinner stuck after 167 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-060 — fetch integration #60

Level: Advanced+
Symptom: stale UI or spinner stuck after 180 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-061 — fetch integration #61

Level: Beginner
Symptom: stale UI or spinner stuck after 193 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-062 — fetch integration #62

Level: Beginner+
Symptom: stale UI or spinner stuck after 6 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-063 — fetch integration #63

Level: Intermediate
Symptom: stale UI or spinner stuck after 19 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-064 — fetch integration #64

Level: Intermediate+
Symptom: stale UI or spinner stuck after 32 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-065 — fetch integration #65

Level: Advanced
Symptom: stale UI or spinner stuck after 45 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-066 — fetch integration #66

Level: Advanced+
Symptom: stale UI or spinner stuck after 58 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-067 — fetch integration #67

Level: Beginner
Symptom: stale UI or spinner stuck after 71 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-068 — fetch integration #68

Level: Beginner+
Symptom: stale UI or spinner stuck after 84 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-069 — fetch integration #69

Level: Intermediate
Symptom: stale UI or spinner stuck after 97 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-070 — fetch integration #70

Level: Intermediate+
Symptom: stale UI or spinner stuck after 110 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-071 — fetch integration #71

Level: Advanced
Symptom: stale UI or spinner stuck after 123 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-072 — fetch integration #72

Level: Advanced+
Symptom: stale UI or spinner stuck after 136 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-073 — fetch integration #73

Level: Beginner
Symptom: stale UI or spinner stuck after 149 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-074 — fetch integration #74

Level: Beginner+
Symptom: stale UI or spinner stuck after 162 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-075 — fetch integration #75

Level: Intermediate
Symptom: stale UI or spinner stuck after 175 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-076 — fetch integration #76

Level: Intermediate+
Symptom: stale UI or spinner stuck after 188 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-077 — fetch integration #77

Level: Advanced
Symptom: stale UI or spinner stuck after 1 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-078 — fetch integration #78

Level: Advanced+
Symptom: stale UI or spinner stuck after 14 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-079 — fetch integration #79

Level: Beginner
Symptom: stale UI or spinner stuck after 27 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-080 — fetch integration #80

Level: Beginner+
Symptom: stale UI or spinner stuck after 40 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-081 — fetch integration #81

Level: Intermediate
Symptom: stale UI or spinner stuck after 53 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-082 — fetch integration #82

Level: Intermediate+
Symptom: stale UI or spinner stuck after 66 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-083 — fetch integration #83

Level: Advanced
Symptom: stale UI or spinner stuck after 79 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-084 — fetch integration #84

Level: Advanced+
Symptom: stale UI or spinner stuck after 92 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-085 — fetch integration #85

Level: Beginner
Symptom: stale UI or spinner stuck after 105 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-086 — fetch integration #86

Level: Beginner+
Symptom: stale UI or spinner stuck after 118 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-087 — fetch integration #87

Level: Intermediate
Symptom: stale UI or spinner stuck after 131 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-088 — fetch integration #88

Level: Intermediate+
Symptom: stale UI or spinner stuck after 144 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-089 — fetch integration #89

Level: Advanced
Symptom: stale UI or spinner stuck after 157 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-090 — fetch integration #90

Level: Advanced+
Symptom: stale UI or spinner stuck after 170 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-091 — fetch integration #91

Level: Beginner
Symptom: stale UI or spinner stuck after 183 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-092 — fetch integration #92

Level: Beginner+
Symptom: stale UI or spinner stuck after 196 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-093 — fetch integration #93

Level: Intermediate
Symptom: stale UI or spinner stuck after 9 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-094 — fetch integration #94

Level: Intermediate+
Symptom: stale UI or spinner stuck after 22 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-095 — fetch integration #95

Level: Advanced
Symptom: stale UI or spinner stuck after 35 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-096 — fetch integration #96

Level: Advanced+
Symptom: stale UI or spinner stuck after 48 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-097 — fetch integration #97

Level: Beginner
Symptom: stale UI or spinner stuck after 61 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-098 — fetch integration #98

Level: Beginner+
Symptom: stale UI or spinner stuck after 74 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-099 — fetch integration #99

Level: Intermediate
Symptom: stale UI or spinner stuck after 87 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-100 — fetch integration #100

Level: Intermediate+
Symptom: stale UI or spinner stuck after 100 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-101 — fetch integration #101

Level: Advanced
Symptom: stale UI or spinner stuck after 113 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-102 — fetch integration #102

Level: Advanced+
Symptom: stale UI or spinner stuck after 126 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-103 — fetch integration #103

Level: Beginner
Symptom: stale UI or spinner stuck after 139 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-104 — fetch integration #104

Level: Beginner+
Symptom: stale UI or spinner stuck after 152 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-105 — fetch integration #105

Level: Intermediate
Symptom: stale UI or spinner stuck after 165 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-106 — fetch integration #106

Level: Intermediate+
Symptom: stale UI or spinner stuck after 178 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-107 — fetch integration #107

Level: Advanced
Symptom: stale UI or spinner stuck after 191 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-108 — fetch integration #108

Level: Advanced+
Symptom: stale UI or spinner stuck after 4 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-109 — fetch integration #109

Level: Beginner
Symptom: stale UI or spinner stuck after 17 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-110 — fetch integration #110

Level: Beginner+
Symptom: stale UI or spinner stuck after 30 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-111 — fetch integration #111

Level: Intermediate
Symptom: stale UI or spinner stuck after 43 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-112 — fetch integration #112

Level: Intermediate+
Symptom: stale UI or spinner stuck after 56 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-113 — fetch integration #113

Level: Advanced
Symptom: stale UI or spinner stuck after 69 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-114 — fetch integration #114

Level: Advanced+
Symptom: stale UI or spinner stuck after 82 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-115 — fetch integration #115

Level: Beginner
Symptom: stale UI or spinner stuck after 95 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-116 — fetch integration #116

Level: Beginner+
Symptom: stale UI or spinner stuck after 108 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-117 — fetch integration #117

Level: Intermediate
Symptom: stale UI or spinner stuck after 121 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-118 — fetch integration #118

Level: Intermediate+
Symptom: stale UI or spinner stuck after 134 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-119 — fetch integration #119

Level: Advanced
Symptom: stale UI or spinner stuck after 147 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-120 — fetch integration #120

Level: Advanced+
Symptom: stale UI or spinner stuck after 160 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-121 — fetch integration #121

Level: Beginner
Symptom: stale UI or spinner stuck after 173 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-122 — fetch integration #122

Level: Beginner+
Symptom: stale UI or spinner stuck after 186 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-123 — fetch integration #123

Level: Intermediate
Symptom: stale UI or spinner stuck after 199 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-124 — fetch integration #124

Level: Intermediate+
Symptom: stale UI or spinner stuck after 12 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-125 — fetch integration #125

Level: Advanced
Symptom: stale UI or spinner stuck after 25 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-126 — fetch integration #126

Level: Advanced+
Symptom: stale UI or spinner stuck after 38 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-127 — fetch integration #127

Level: Beginner
Symptom: stale UI or spinner stuck after 51 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-128 — fetch integration #128

Level: Beginner+
Symptom: stale UI or spinner stuck after 64 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-129 — fetch integration #129

Level: Intermediate
Symptom: stale UI or spinner stuck after 77 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-130 — fetch integration #130

Level: Intermediate+
Symptom: stale UI or spinner stuck after 90 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-131 — fetch integration #131

Level: Advanced
Symptom: stale UI or spinner stuck after 103 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-132 — fetch integration #132

Level: Advanced+
Symptom: stale UI or spinner stuck after 116 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-133 — fetch integration #133

Level: Beginner
Symptom: stale UI or spinner stuck after 129 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-134 — fetch integration #134

Level: Beginner+
Symptom: stale UI or spinner stuck after 142 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-135 — fetch integration #135

Level: Intermediate
Symptom: stale UI or spinner stuck after 155 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-136 — fetch integration #136

Level: Intermediate+
Symptom: stale UI or spinner stuck after 168 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-137 — fetch integration #137

Level: Advanced
Symptom: stale UI or spinner stuck after 181 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-138 — fetch integration #138

Level: Advanced+
Symptom: stale UI or spinner stuck after 194 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-139 — fetch integration #139

Level: Beginner
Symptom: stale UI or spinner stuck after 7 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-140 — fetch integration #140

Level: Beginner+
Symptom: stale UI or spinner stuck after 20 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-141 — fetch integration #141

Level: Intermediate
Symptom: stale UI or spinner stuck after 33 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-142 — fetch integration #142

Level: Intermediate+
Symptom: stale UI or spinner stuck after 46 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-143 — fetch integration #143

Level: Advanced
Symptom: stale UI or spinner stuck after 59 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-144 — fetch integration #144

Level: Advanced+
Symptom: stale UI or spinner stuck after 72 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-145 — fetch integration #145

Level: Beginner
Symptom: stale UI or spinner stuck after 85 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-146 — fetch integration #146

Level: Beginner+
Symptom: stale UI or spinner stuck after 98 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-147 — fetch integration #147

Level: Intermediate
Symptom: stale UI or spinner stuck after 111 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-148 — fetch integration #148

Level: Intermediate+
Symptom: stale UI or spinner stuck after 124 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-149 — fetch integration #149

Level: Advanced
Symptom: stale UI or spinner stuck after 137 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-150 — fetch integration #150

Level: Advanced+
Symptom: stale UI or spinner stuck after 150 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-151 — fetch integration #151

Level: Beginner
Symptom: stale UI or spinner stuck after 163 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-152 — fetch integration #152

Level: Beginner+
Symptom: stale UI or spinner stuck after 176 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-153 — fetch integration #153

Level: Intermediate
Symptom: stale UI or spinner stuck after 189 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Base URL hard-coded per environment leading to prod misconfiguration.
Primary remediation: Use env config + relative /api proxy in dev.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-154 — fetch integration #154

Level: Intermediate+
Symptom: stale UI or spinner stuck after 2 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Effect dependency array omits fetch params causing stale closure requests.
Primary remediation: Introduce TanStack Query or manual in-flight dedupe map.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-155 — fetch integration #155

Level: Advanced
Symptom: stale UI or spinner stuck after 15 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Parsing JSON without try/catch throws uncaught rejections surfaced as white screen.
Primary remediation: Set credentials intentionally; document CORS contract with backend.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-156 — fetch integration #156

Level: Advanced+
Symptom: stale UI or spinner stuck after 28 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Missing AbortController causes setState on unmounted component after fast navigation.
Primary remediation: Abort on cleanup; guard state updates with mounted flag or cancel pattern.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-157 — fetch integration #157

Level: Beginner
Symptom: stale UI or spinner stuck after 41 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: Credentials/cookies mode wrong for CORS leading to silent 401 loops.
Primary remediation: Wrap parse + validate; map HTTP status to typed error objects.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

API0-158 — fetch integration #158

Level: Beginner+
Symptom: stale UI or spinner stuck after 54 ms of navigation.
Integration smell: server errors surfaced as blank screen without recovery path.
Root cause class: No request deduplication: identical in-flight fetches hammer API.
Primary remediation: Include stable serialized params in deps or use query libraries.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Every effect fetch needs a cancellation story—navigation is a race.

<< 2.12 Overview

2.12.a — fetch API integration in React