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

2.12.e — Mutations: updating server data properly

Learning outcomes

Use useMutation for POST/PUT/PATCH/DELETE flows.
Invalidate or patch queries after success.
Understand optimistic updates trade-offs.

Basic mutation

import { useMutation, useQueryClient } from "@tanstack/react-query";

async function renamePost(id: string, title: string) {
  const res = await fetch(`/api/posts/${id}`, {
    method: "PATCH",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ title }),
  });
  if (!res.ok) throw new Error("Save failed");
  return res.json();
}

export function RenameButton({ id }: { id: string }) {
  const qc = useQueryClient();
  const m = useMutation({
    mutationFn: (title: string) => renamePost(id, title),
    onSuccess: () => qc.invalidateQueries({ queryKey: ["post", id] }),
  });

  return (
    <button type="button" disabled={m.isPending} onClick={() => m.mutate("New title")}>
      Save
    </button>
  );
}

Invalidation vs patch

invalidateQueries: simplest; refetches soon—can be heavier.
setQueryData: instant UI if you trust the server response shape.

Optimistic updates (caution)

Great UX when latency is high and conflicts are rare—always plan rollback on error.

Appendix — Scenario bank (basic → advanced)

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

API4-001 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-002 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-003 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-004 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-005 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-006 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-007 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-008 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-009 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-010 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-011 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-012 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-013 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-014 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-015 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-016 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-017 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-018 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-019 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-020 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-021 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-022 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-023 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-024 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-025 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-026 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-027 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-028 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-029 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-030 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-031 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-032 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-033 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-034 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-035 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-036 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-037 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-038 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-039 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-040 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-041 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-042 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-043 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-044 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-045 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-046 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-047 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-048 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-049 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-050 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-051 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-052 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-053 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-054 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-055 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-056 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-057 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-058 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-059 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-060 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-061 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-062 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-063 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-064 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-065 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-066 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-067 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-068 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-069 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-070 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-071 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-072 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-073 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-074 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-075 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-076 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-077 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-078 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-079 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-080 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-081 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-082 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-083 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-084 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-085 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-086 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-087 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-088 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-089 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-090 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-091 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-092 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-093 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-094 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-095 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-096 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-097 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-098 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-099 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-100 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-101 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-102 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-103 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-104 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-105 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-106 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-107 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-108 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-109 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-110 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-111 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-112 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-113 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-114 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-115 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-116 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-117 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-118 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-119 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-120 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-121 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-122 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-123 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-124 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-125 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-126 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-127 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-128 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-129 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-130 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-131 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-132 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-133 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-134 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-135 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-136 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-137 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-138 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-139 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-140 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-141 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-142 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-143 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-144 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-145 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-146 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-147 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-148 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-149 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-150 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-151 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-152 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-153 — mutations #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: onSettled invalidates too broadly slowing UI after every keystroke-save.
Primary remediation: Invalidate narrowly; patch cache with returned entity when API returns it.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-154 — mutations #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: Double-click submit fires two POSTs without idempotency keys.
Primary remediation: Surface toast + inline error; keep mutation error in UI state.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-155 — mutations #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: Optimistic update without rollback on failure corrupts list order.
Primary remediation: Model progress via xhr/fetch reader or library support.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-156 — mutations #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: Mutation succeeds but UI stale because invalidateQueries keys mismatch.
Primary remediation: Align invalidation keys with query key factory module.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-157 — mutations #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: File upload mutation missing progress state.
Primary remediation: Use onMutate snapshot + onError restore; or pessimistic update when safer.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

API4-158 — mutations #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: Mutation error swallowed; user thinks save succeeded.
Primary remediation: Disable button + idempotency header or UUID client key per product rules.
Verify: Network tab + React Query Devtools (if used) + user retry path.
Interview one-liner: Mutations are transactions: update server, then reconcile cache or rollback explicitly.

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