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

2.12.b — Loading and error states (graceful UX)

Learning outcomes

Model async UI with explicit states (not a single loading boolean).
Design retry, offline, and partial failure paths.
Keep accessibility: announce errors where appropriate.

Recommended state shape (manual fetching)

type Remote<T> =
  | { status: "idle" }
  | { status: "loading" }
  | { status: "error"; message: string; retry: () => void }
  | { status: "success"; data: T };

Render each branch with purposeful UI—not a generic spinner for everything.

Error UX checklist

Human-readable message + technical request id for support
Retry button when safe (GET) vs guidance when unsafe (POST paid action)
Do not lose form input on recoverable errors

TanStack Query alignment

useQuery gives you isPending, isError, isSuccess, failureReason, refetch—prefer these over ad-hoc booleans when adopting the library.

Appendix — Scenario bank (basic → advanced)

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

API1-001 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-002 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-003 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-004 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-005 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-006 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-007 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-008 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-009 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-010 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-011 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-012 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-013 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-014 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-015 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-016 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-017 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-018 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-019 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-020 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-021 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-022 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-023 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-024 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-025 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-026 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-027 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-028 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-029 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-030 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-031 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-032 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-033 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-034 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-035 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-036 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-037 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-038 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-039 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-040 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-041 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-042 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-043 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-044 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-045 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-046 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-047 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-048 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-049 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-050 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-051 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-052 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-053 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-054 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-055 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-056 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-057 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-058 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-059 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-060 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-061 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-062 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-063 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-064 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-065 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-066 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-067 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-068 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-069 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-070 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-071 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-072 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-073 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-074 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-075 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-076 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-077 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-078 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-079 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-080 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-081 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-082 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-083 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-084 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-085 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-086 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-087 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-088 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-089 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-090 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-091 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-092 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-093 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-094 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-095 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-096 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-097 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-098 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-099 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-100 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-101 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-102 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-103 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-104 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-105 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-106 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-107 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-108 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-109 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-110 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-111 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-112 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-113 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-114 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-115 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-116 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-117 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-118 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-119 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-120 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-121 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-122 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-123 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-124 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-125 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-126 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-127 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-128 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-129 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-130 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-131 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-132 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-133 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-134 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-135 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-136 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-137 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-138 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-139 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-140 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-141 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-142 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-143 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-144 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-145 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-146 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-147 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-148 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-149 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-150 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-151 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-152 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-153 — loading & errors #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: Retry storms on 500 without exponential backoff.
Primary remediation: Backoff + jitter; respect Retry-After when present.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-154 — loading & errors #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: Errors thrown as raw strings; no retry or support correlation id.
Primary remediation: Minimum skeleton time or placeholderData patterns when appropriate.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-155 — loading & errors #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: Spinner blocks entire layout including unrelated chrome.
Primary remediation: Reserve space with aspect-ratio/skeleton components.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-156 — loading & errors #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: Boolean loading only—cannot represent empty vs error vs refreshing simultaneously.
Primary remediation: Use discriminated union or TanStack Query status union for explicit UI states.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-157 — loading & errors #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: Missing skeleton for LCP-critical content.
Primary remediation: Use partial skeletons; stream layout stability.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

API1-158 — loading & errors #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: Loading flash on fast networks (CLS / annoyance).
Primary remediation: Normalize { message, code, requestId } error model.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Loading UX is part of the API contract—design empty, loading, error, success explicitly.

<< 2.12 Overview