2.20.b — HTTP Methods (GET → DELETE)

In one sentence: You model REST-ish behavior by exporting one async function per HTTP verb — each parses the incoming Request, performs work, and returns a Response with a deliberate status code and body.

Navigation: ← Route Handlers & Conventions · Next → Databases

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1. Supported Named Exports

Typical exports (Node / standard Web semantics):

Export	Meaning
GET	Safe reads, cacheable in principle
POST	Create resource or non-idempotent commands
PUT	Replace entire resource (idempotent when addressed to stable URI)
PATCH	Partial update
DELETE	Remove resource
HEAD, OPTIONS	Specialized — use when needed

If a client calls PATCH but you only exported PUT and POST, they get 405 (unless you add PATCH).

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2. Handler Signature (App Router)

import { NextRequest, NextResponse } from 'next/server';

type Ctx = { params: Promise<{ id: string }> }; // Next 15+: params may be async

export async function GET(request: NextRequest, context: Ctx) {
  const { id } = await context.params;
  const q = request.nextUrl.searchParams.get('q');
  return NextResponse.json({ id, q });
}

Note on params: In Next.js 15, context.params is a Promise in many route contexts. Always await context.params in new code. Older tutorials show sync params — verify your version.

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3. GET — Reads, Query Strings, Caching Hints

export async function GET(request: NextRequest) {
  const limit = Number(request.nextUrl.searchParams.get('limit') ?? '20');
  const safeLimit = Number.isFinite(limit) ? Math.min(Math.max(limit, 1), 100) : 20;
  // const rows = await listUsers({ limit: safeLimit });
  return NextResponse.json({ data: [], meta: { limit: safeLimit } });
}

GET should not mutate data that matters for correctness (analytics pixels aside). Violating this breaks caches, proxies, and user expectations.

Caching: GET Route Handlers can set Cache-Control and use Next’s fetch cache in downstream data loading — but for JSON APIs you often return no-store unless you have a deliberate CDN strategy.

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4. POST — Create, JSON Body, 201 + Location

export async function POST(request: Request) {
  let body: unknown;
  try {
    body = await request.json();
  } catch {
    return NextResponse.json({ error: { code: 'INVALID_JSON', message: 'Body must be JSON' } }, { status: 400 });
  }

  // validate with Zod, etc.
  const created = { id: 'usr_01', email: (body as { email?: string }).email };
  return NextResponse.json({ data: created }, { status: 201, headers: { Location: `/api/users/${created.id}` } });
}

Status codes (typical):

• 201 Created — resource created; Location header optional but nice.
• 400 — malformed JSON or failed validation.
• 409 — conflict (duplicate email).

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5. PUT — Full Replace

Use when the client sends a complete representation of the resource.

export async function PUT(request: Request, context: { params: Promise<{ id: string }> }) {
  const { id } = await context.params;
  const body = await request.json();
  // replaceResource(id, body) — missing fields may reset to defaults or null per your API contract
  return NextResponse.json({ data: { id, ...body } });
}

Interview nuance: Many teams treat PUT vs PATCH loosely; document your contract. Strict REST: PUT is idempotent full replacement.

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6. PATCH — Partial Update

export async function PATCH(request: Request, context: { params: Promise<{ id: string }> }) {
  const { id } = await context.params;
  const partial = await request.json();
  // mergePatch(id, partial)
  return NextResponse.json({ data: { id, name: partial.name } });
}

Return 200 with the updated body, or 204 No Content if you prefer empty success bodies (then clients must re-fetch if they need the row).

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7. DELETE — Remove

export async function DELETE(_request: Request, context: { params: Promise<{ id: string }> }) {
  const { id } = await context.params;
  // const existed = await deleteUser(id);
  const existed = true;
  if (!existed) {
    return NextResponse.json({ error: { code: 'NOT_FOUND', message: 'User not found' } }, { status: 404 });
  }
  return new Response(null, { status: 204 });
}

Common status codes: 204 success no body, 404 if missing, 403 if not allowed to delete.

---

8. Method Not Allowed Helper Pattern

When several verbs share validation, extract helpers — but each export stays thin:

async function parseJson(request: Request): Promise<{ ok: true; value: unknown } | { ok: false; response: Response }> {
  try {
    return { ok: true, value: await request.json() };
  } catch {
    return {
      ok: false,
      response: NextResponse.json({ error: { code: 'INVALID_JSON' } }, { status: 400 }),
    };
  }
}

---

9. OPTIONS / CORS (Sketch)

Browsers send preflight OPTIONS for cross-origin JSON with custom headers. If you expose a public API from another origin:

export async function OPTIONS() {
  return new NextResponse(null, {
    status: 204,
    headers: {
      'Access-Control-Allow-Origin': 'https://trusted.example',
      'Access-Control-Allow-Methods': 'GET,POST,PATCH,DELETE,OPTIONS',
      'Access-Control-Allow-Headers': 'Content-Type, Authorization',
      'Access-Control-Max-Age': '86400',
    },
  });
}

Repeat needed CORS headers on actual responses or use middleware — production setups often centralize this.

---

10. Verb Cheat Sheet (Memorize)

Verb	Body typical?	Idempotent?	Safe?
GET	No	Yes	Yes
POST	Yes	No	No
PUT	Yes	Yes*	No
PATCH	Yes	No (usually)	No
DELETE	Sometimes	Yes	No

*PUT idempotency: repeating the same full payload should leave the resource in the same state.

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Next: 2.20.c — Connecting APIs to Databases

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Part 2 — Deep Encyclopedia (HTTP methods)

How to use this section: Read sequentially or jump by drill number. Each block has a scenario, a prompt (what an interviewer might ask), a model answer, and often a code sketch.

E001 — API drill 1: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 1: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #1.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #1, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E002 — API drill 2: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 2: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #2.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #2, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E003 — API drill 3: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 3: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #3.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #3, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E004 — API drill 4: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 4: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #4.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #4, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E005 — API drill 5: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 5: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #5.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #5, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E006 — API drill 6: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 6: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #6.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #6, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E007 — API drill 7: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 7: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #7.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #7, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E008 — API drill 8: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 8: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #8.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #8, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E009 — API drill 9: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 9: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #9.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #9, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E010 — API drill 10: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 10: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #10.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #10, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E011 — API drill 11: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 11: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #11.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #11, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E012 — API drill 12: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 12: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #12.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #12, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E013 — API drill 13: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 13: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #13.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #13, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E014 — API drill 14: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 14: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #14.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #14, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E015 — API drill 15: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 15: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #15.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #15, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E016 — API drill 16: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 16: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #16.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #16, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E017 — API drill 17: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 17: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #17.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #17, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E018 — API drill 18: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 18: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #18.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #18, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E019 — API drill 19: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 19: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #19.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #19, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E020 — API drill 20: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 20: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #20.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #20, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E021 — API drill 21: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 21: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #21.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #21, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E022 — API drill 22: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 22: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #22.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #22, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E023 — API drill 23: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 23: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #23.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #23, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E024 — API drill 24: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 24: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #24.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #24, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E025 — API drill 25: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 25: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #25.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #25, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E026 — API drill 26: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 26: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #26.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #26, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E027 — API drill 27: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 27: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #27.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #27, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E028 — API drill 28: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 28: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #28.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #28, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E029 — API drill 29: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 29: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #29.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #29, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E030 — API drill 30: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 30: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #30.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #30, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E031 — API drill 31: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 31: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #31.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #31, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E032 — API drill 32: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 32: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #32.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #32, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E033 — API drill 33: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 33: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #33.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #33, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E034 — API drill 34: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 34: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #34.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #34, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E035 — API drill 35: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 35: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #35.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #35, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E036 — API drill 36: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 36: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #36.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #36, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E037 — API drill 37: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 37: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #37.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #37, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E038 — API drill 38: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 38: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #38.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #38, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E039 — API drill 39: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 39: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #39.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #39, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E040 — API drill 40: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 40: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #40.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #40, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E041 — API drill 41: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 41: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #41.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #41, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E042 — API drill 42: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 42: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #42.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #42, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E043 — API drill 43: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 43: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #43.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #43, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E044 — API drill 44: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 44: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #44.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #44, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E045 — API drill 45: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 45: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #45.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #45, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E046 — API drill 46: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 46: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #46.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #46, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E047 — API drill 47: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 47: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #47.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #47, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E048 — API drill 48: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 48: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #48.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #48, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E049 — API drill 49: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 49: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #49.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #49, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E050 — API drill 50: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 50: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #50.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #50, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E051 — API drill 51: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 51: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #51.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #51, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E052 — API drill 52: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 52: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #52.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #52, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E053 — API drill 53: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 53: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #53.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #53, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E054 — API drill 54: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 54: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #54.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #54, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E055 — API drill 55: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 55: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #55.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #55, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E056 — API drill 56: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 56: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #56.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #56, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E057 — API drill 57: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 57: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #57.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #57, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E058 — API drill 58: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 58: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #58.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #58, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E059 — API drill 59: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 59: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #59.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #59, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E060 — API drill 60: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 60: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #60.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #60, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E061 — API drill 61: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 61: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #61.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #61, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E062 — API drill 62: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 62: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #62.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #62, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E063 — API drill 63: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 63: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #63.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #63, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E064 — API drill 64: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 64: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #64.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #64, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E065 — API drill 65: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 65: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #65.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #65, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E066 — API drill 66: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 66: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #66.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #66, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E067 — API drill 67: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 67: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #67.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #67, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E068 — API drill 68: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 68: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #68.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #68, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E069 — API drill 69: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 69: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #69.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #69, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E070 — API drill 70: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 70: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #70.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #70, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E071 — API drill 71: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 71: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #71.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #71, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E072 — API drill 72: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 72: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #72.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #72, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E073 — API drill 73: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 73: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #73.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #73, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E074 — API drill 74: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 74: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #74.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #74, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E075 — API drill 75: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 75: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #75.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #75, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E076 — API drill 76: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 76: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #76.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #76, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E077 — API drill 77: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 77: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #77.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #77, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E078 — API drill 78: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 78: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #78.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #78, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E079 — API drill 79: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 79: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #79.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #79, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E080 — API drill 80: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 80: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #80.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #80, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E081 — API drill 81: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 81: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #81.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #81, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E082 — API drill 82: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 82: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #82.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #82, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E083 — API drill 83: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 83: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #83.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #83, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E084 — API drill 84: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 84: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #84.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #84, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E085 — API drill 85: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 85: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #85.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #85, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E086 — API drill 86: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 86: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #86.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #86, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E087 — API drill 87: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 87: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #87.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #87, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E088 — API drill 88: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 88: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #88.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #88, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E089 — API drill 89: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 89: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #89.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #89, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E090 — API drill 90: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 90: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #90.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #90, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E091 — API drill 91: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 91: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #91.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #91, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E092 — API drill 92: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 92: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #92.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #92, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E093 — API drill 93: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 93: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #93.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #93, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E094 — API drill 94: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 94: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #94.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #94, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E095 — API drill 95: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 95: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #95.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #95, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E096 — API drill 96: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 96: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #96.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #96, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E097 — API drill 97: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 97: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #97.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #97, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E098 — API drill 98: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 98: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #98.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #98, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E099 — API drill 99: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 99: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #99.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #99, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E100 — API drill 100: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 100: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #100.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #100, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E101 — API drill 101: Idempotency-Key header for POST /api/payments.

Scenario: Idempotency-Key header for POST /api/payments. (variation 101: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #101.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #101, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E102 — API drill 102: Content-Type negotiation JSON vs msgpack.

Scenario: Content-Type negotiation JSON vs msgpack. (variation 102: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #102.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #102, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E103 — API drill 103: Binary upload > 4.5MB on serverless

Scenario: Binary upload > 4.5MB on serverless — streaming workaround. (variation 103: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #103.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #103, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E104 — API drill 104: HMAC webhook verification constant-time compare.

Scenario: HMAC webhook verification constant-time compare. (variation 104: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #104.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #104, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E105 — API drill 105: Rate limit by API key in Redis sliding window.

Scenario: Rate limit by API key in Redis sliding window. (variation 105: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #105.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #105, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E106 — API drill 106: OpenAPI generation from Zod schemas.

Scenario: OpenAPI generation from Zod schemas. (variation 106: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #106.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #106, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E107 — API drill 107: Versioned URL /api/v2 with sunset headers.

Scenario: Versioned URL /api/v2 with sunset headers. (variation 107: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #107.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #107, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E108 — API drill 108: HEAD request to check existence without body cost.

Scenario: HEAD request to check existence without body cost. (variation 108: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #108.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #108, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E109 — API drill 109: Conditional GET with ETag round trip.

Scenario: Conditional GET with ETag round trip. (variation 109: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #109.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #109, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---

E110 — API drill 110: CORS credentialed requests with wildcard mistake.

Scenario: CORS credentialed requests with wildcard mistake. (variation 110: consider deployment on a serverless platform with regional databases.)

Prompt: Explain trade-offs and what you would measure (latency, error rate, cost) before/after a change for case #110.

Model answer: Start by naming the user-visible symptom (SEO, staleness, TTFB, consistency). List hypotheses (N+1 queries, blocking waterfall, wrong cache directive, missing revalidation). Propose one smallest experiment: add logging/timing, reduce sequential awaits, adjust revalidate window, or move work to background job. Define rollback. For #110, emphasize that measurement beats opinions: compare p50/p95 TTFB and conversion where relevant.

import { NextResponse } from 'next/server';

export async function POST(req: Request) {
  const idem = req.headers.get('idempotency-key');
  // store idem -> response mapping in Redis with TTL
  return NextResponse.json({ ok: true });
}

---