# SPEC — F-003 HTTP foundation and request context

## Problem
Every request needs identity, structured logs and predictable errors. Today the app
answers with ad-hoc console logging potential, no request correlation id, and an
error envelope without request context.

## Goal
request_id everywhere, JSON logs, one error envelope, no magic.

## Scope IN
- request_id generated or propagated on every request
- Structured JSON logging with request_id
- Single error response envelope (v2: adds stable `code` + `requestId`)
- Input validation hook on API layer (foundation helper, explicit usage)

## Scope OUT
- No tracing backend
- No metrics backend
- No production endpoints that consume validation yet (first consumer: F-005 identity)

## Acceptance criteria
1. Every response carries `request_id` (via `x-request-id` response header; error bodies also embed it).
2. Every log line for a request carries the same request_id.
3. Given an invalid request When handled Then the error envelope shape is stable.
4. Internal stack traces never leak to API responses (5xx message is generic; stack stays server-side in logs).
5. `./scripts/verify.sh` green.

## Non-functional
- JSON-only logs (no pretty printers in runtime).
- Incoming `x-request-id` must be sanitized before reuse (length/charset limits).
- No new framework magic: logging hooks and error handler are explicit code in the composition root.

## Dependencies added
- pino (JSON structured logging; Fastify ecosystem standard)
- zod (explicit input validation; no decorators/annotations magic)
Justification goes to `spec/tech.md`.