diff --git a/backlog/features.json b/backlog/features.json
index a84b470..23f8f68 100644
--- a/backlog/features.json
+++ b/backlog/features.json
@@ -159,12 +159,12 @@
         "Flag state change does not require redeploy",
         "verify.sh green"
       ],
-      "status": "pending",
+      "status": "done",
       "created_at": "2026-08-14",
       "gates": {
-        "review": false,
-        "security": false,
-        "qa": false
+        "review": true,
+        "security": true,
+        "qa": true
       }
     },
     {
diff --git a/project/.env.example b/project/.env.example
index e473888..bc18ff2 100644
--- a/project/.env.example
+++ b/project/.env.example
@@ -2,3 +2,8 @@
 # Matches docker-compose.yml dev credentials (dev-only, never reuse elsewhere).
 DATABASE_URL=postgres://mdv:mdv_dev_only@localhost:5432/mercadodevida
 TEST_DATABASE_URL=postgres://mdv:mdv_dev_only@localhost:5432/mercadodevida_test
+REDIS_URL=redis://localhost:6379
+
+# Feature flags: FLAG_<NAME>=true|false (parsed into the flag store at boot).
+# Unknown flags default to OFF. Flags can be flipped at runtime via the store.
+FLAG_EXAMPLE_FEATURE=false
diff --git a/project/README.md b/project/README.md
index 765b9cf..a5b064b 100644
--- a/project/README.md
+++ b/project/README.md
@@ -19,6 +19,17 @@ npm run lint          # eslint + prettier check
 npm run lint:boundaries  # module boundary check
 ```
 
+## Configuration
+
+Startup is fail-fast: `src/infrastructure/config` parses env once and refuses to boot
+on missing/invalid required vars. `DATABASE_URL` is required; `PORT`, `HOST`,
+`LOG_LEVEL`, `NODE_ENV`, `REDIS_URL` are optional with defaults. Errors name variable
+NAMES only, never values.
+
+Feature flags: `FLAG_<NAME>=true|false` env vars seed the flag store at boot. Unknown
+flags default to OFF (fail-safe). Flags flip at runtime through the store — activation
+is separate from deployment (no redeploy). Copy `.env.example` to `.env` to start.
+
 ## HTTP contract
 
 - Every response carries an `x-request-id` header (propagated from a safe incoming
diff --git a/project/src/app/build-app.ts b/project/src/app/build-app.ts
index a67f50b..1099c8d 100644
--- a/project/src/app/build-app.ts
+++ b/project/src/app/build-app.ts
@@ -8,15 +8,24 @@ import Fastify, { type FastifyInstance } from 'fastify';
 import type { FastifyError, FastifyReply, FastifyRequest } from 'fastify';
 import type { IncomingMessage } from 'node:http';
 import { registerHealthRoutes } from '../modules/health/index.js';
+import { createFlagStore, type FeatureFlagProvider } from '../modules/flags/index.js';
 import { AppError, errorEnvelope } from '../shared/errors.js';
 import { createLogger, type Logger } from '../infrastructure/logging/logger.js';
 
+declare module 'fastify' {
+  interface FastifyInstance {
+    flags: FeatureFlagProvider;
+  }
+}
+
 const REQUEST_ID_HEADER = 'x-request-id';
 const SAFE_REQUEST_ID = /^[A-Za-z0-9._-]{1,128}$/;
 
 export interface BuildAppDeps {
   /** Injectable logger so tests can capture structured output. */
   logger?: Logger;
+  /** Feature flags. Default: empty store, every flag OFF (fail-safe). */
+  flags?: FeatureFlagProvider;
 }
 
 function generateRequestId(raw: IncomingMessage): string {
@@ -33,9 +42,11 @@ function generateRequestId(raw: IncomingMessage): string {
  */
 export async function buildApp(deps: BuildAppDeps = {}): Promise<FastifyInstance> {
   const logger = deps.logger ?? createLogger();
+  const flags = deps.flags ?? createFlagStore();
   const startTimes = new WeakMap<FastifyRequest, number>();
 
   const app = Fastify({ logger: false, genReqId: generateRequestId });
+  app.decorate('flags', flags);
 
   app.addHook('onRequest', async (request, reply) => {
     startTimes.set(request, performance.now());
diff --git a/project/src/app/tests/config-flags.test.ts b/project/src/app/tests/config-flags.test.ts
new file mode 100644
index 0000000..73e054b
--- /dev/null
+++ b/project/src/app/tests/config-flags.test.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest';
+import { buildApp } from '../build-app.js';
+import { createFlagStore } from '../../modules/flags/index.js';
+import { createLogger } from '../../infrastructure/logging/logger.js';
+import type { DestinationStream } from 'pino';
+
+function silentLogger() {
+  const destination: DestinationStream = { write: () => undefined };
+  return createLogger({ level: 'info', destination });
+}
+
+describe('feature flags wiring (composition)', () => {
+  it('default flags are all OFF when no store is injected', async () => {
+    const app = await buildApp({ logger: silentLogger() });
+    app.get('/__test/guarded', async (request) => {
+      return { enabled: request.server.flags.isEnabled('risky_path') };
+    });
+
+    const response = await app.inject({ method: 'GET', url: '/__test/guarded' });
+    expect(response.json()).toEqual({ enabled: false });
+    await app.close();
+  });
+
+  it('guarded path is skipped when the flag is off and runs once enabled at runtime', async () => {
+    const store = createFlagStore({ risky_path: false });
+    const app = await buildApp({ logger: silentLogger(), flags: store });
+    app.get('/__test/guarded', async (request) => {
+      if (!request.server.flags.isEnabled('risky_path')) {
+        return { path: 'skipped' };
+      }
+      return { path: 'executed' };
+    });
+
+    const off = await app.inject({ method: 'GET', url: '/__test/guarded' });
+    expect(off.json()).toEqual({ path: 'skipped' });
+
+    // Activation without redeploy: same running app instance.
+    store.setEnabled('risky_path', true);
+    const on = await app.inject({ method: 'GET', url: '/__test/guarded' });
+    expect(on.json()).toEqual({ path: 'executed' });
+
+    store.setEnabled('risky_path', false);
+    const offAgain = await app.inject({ method: 'GET', url: '/__test/guarded' });
+    expect(offAgain.json()).toEqual({ path: 'skipped' });
+    await app.close();
+  });
+});
diff --git a/project/src/infrastructure/config/config.ts b/project/src/infrastructure/config/config.ts
new file mode 100644
index 0000000..0250c52
--- /dev/null
+++ b/project/src/infrastructure/config/config.ts
@@ -0,0 +1,97 @@
+/**
+ * Typed configuration loader. Pure over an env object: no reads of process.env
+ * here, so tests are deterministic. Fail fast AND clear: every problem is
+ * collected, then a single ConfigError is thrown. Error messages name variable
+ * NAMES only, never values, so secrets cannot leak.
+ */
+
+export type StringRecord = Readonly<Record<string, string | undefined>>;
+
+export type NodeEnv = 'development' | 'test' | 'production';
+
+export interface AppConfig {
+  nodeEnv: NodeEnv;
+  port: number;
+  host: string;
+  logLevel: string;
+  databaseUrl: string;
+  redisUrl?: string;
+  /** Initial flag state parsed from FLAG_* vars. */
+  flags: Readonly<Record<string, boolean>>;
+}
+
+export class ConfigError extends Error {
+  constructor(public readonly problems: ReadonlyArray<string>) {
+    super(`Invalid configuration:\n- ${problems.join('\n- ')}`);
+    this.name = 'ConfigError';
+  }
+}
+
+const NODE_ENVS: ReadonlyArray<NodeEnv> = ['development', 'test', 'production'];
+
+function parseBoolFlag(varName: string, raw: string, problems: string[]): boolean | undefined {
+  const normalized = raw.trim().toLowerCase();
+  if (normalized === 'true') return true;
+  if (normalized === 'false') return false;
+  problems.push(`${varName} must be "true" or "false"`);
+  return undefined;
+}
+
+export function loadConfig(env: StringRecord): AppConfig {
+  const problems: string[] = [];
+
+  const databaseUrl = env.DATABASE_URL;
+  if (!databaseUrl) {
+    problems.push('DATABASE_URL is required');
+  }
+
+  let port = 3000;
+  const rawPort = env.PORT;
+  if (rawPort !== undefined && rawPort !== '') {
+    const parsed = Number(rawPort);
+    if (!Number.isInteger(parsed) || parsed < 1 || parsed > 65535) {
+      problems.push('PORT must be an integer between 1 and 65535');
+    } else {
+      port = parsed;
+    }
+  }
+
+  const host = env.HOST && env.HOST !== '' ? env.HOST : '0.0.0.0';
+  const logLevel = env.LOG_LEVEL && env.LOG_LEVEL !== '' ? env.LOG_LEVEL : 'info';
+
+  let nodeEnv: NodeEnv = 'development';
+  const rawNodeEnv = env.NODE_ENV;
+  if (rawNodeEnv !== undefined && rawNodeEnv !== '') {
+    if ((NODE_ENVS as ReadonlyArray<string>).includes(rawNodeEnv)) {
+      nodeEnv = rawNodeEnv as NodeEnv;
+    } else {
+      problems.push('NODE_ENV must be one of: development, test, production');
+    }
+  }
+
+  const redisUrl = env.REDIS_URL && env.REDIS_URL !== '' ? env.REDIS_URL : undefined;
+
+  const flags: Record<string, boolean> = {};
+  for (const [key, raw] of Object.entries(env)) {
+    if (!key.startsWith('FLAG_') || raw === undefined) continue;
+    const name = key.slice('FLAG_'.length).toLowerCase();
+    const value = parseBoolFlag(key, raw, problems);
+    if (value !== undefined) {
+      flags[name] = value;
+    }
+  }
+
+  if (problems.length > 0) {
+    throw new ConfigError(problems);
+  }
+
+  return {
+    nodeEnv,
+    port,
+    host,
+    logLevel,
+    databaseUrl: databaseUrl as string,
+    redisUrl,
+    flags,
+  };
+}
diff --git a/project/src/infrastructure/config/tests/config.test.ts b/project/src/infrastructure/config/tests/config.test.ts
new file mode 100644
index 0000000..ff8e053
--- /dev/null
+++ b/project/src/infrastructure/config/tests/config.test.ts
@@ -0,0 +1,94 @@
+import { describe, expect, it } from 'vitest';
+import { ConfigError, loadConfig } from '../config.js';
+
+const BASE = { DATABASE_URL: 'postgres://u:p@localhost:5432/db' };
+
+function problemsOf(fn: () => unknown): ReadonlyArray<string> {
+  try {
+    fn();
+  } catch (error) {
+    if (error instanceof ConfigError) {
+      return error.problems;
+    }
+    throw error;
+  }
+  throw new Error('expected ConfigError was not thrown');
+}
+
+describe('loadConfig', () => {
+  it('returns typed config for a valid full env', () => {
+    const config = loadConfig({
+      ...BASE,
+      PORT: '8080',
+      HOST: '127.0.0.1',
+      LOG_LEVEL: 'debug',
+      NODE_ENV: 'production',
+      REDIS_URL: 'redis://localhost:6379',
+      FLAG_NEW_CHECKOUT: 'true',
+      FLAG_BETA_SEARCH: 'false',
+    });
+
+    expect(config.port).toBe(8080);
+    expect(config.host).toBe('127.0.0.1');
+    expect(config.logLevel).toBe('debug');
+    expect(config.nodeEnv).toBe('production');
+    expect(config.databaseUrl).toBe(BASE.DATABASE_URL);
+    expect(config.redisUrl).toBe('redis://localhost:6379');
+    expect(config.flags).toEqual({ new_checkout: true, beta_search: false });
+  });
+
+  it('applies defaults when optional vars are absent', () => {
+    const config = loadConfig(BASE);
+    expect(config.port).toBe(3000);
+    expect(config.host).toBe('0.0.0.0');
+    expect(config.logLevel).toBe('info');
+    expect(config.nodeEnv).toBe('development');
+    expect(config.redisUrl).toBeUndefined();
+    expect(config.flags).toEqual({});
+  });
+
+  it('fails fast naming DATABASE_URL when missing', () => {
+    expect(() => loadConfig({})).toThrowError(ConfigError);
+    expect(problemsOf(() => loadConfig({}))).toContain('DATABASE_URL is required');
+  });
+
+  it('rejects invalid PORT values naming the var', () => {
+    for (const bad of ['not-a-number', '0', '70000', '3.5']) {
+      expect(() => loadConfig({ ...BASE, PORT: bad })).toThrowError(ConfigError);
+      expect(problemsOf(() => loadConfig({ ...BASE, PORT: bad })).join(' ')).toContain('PORT');
+    }
+  });
+
+  it('rejects invalid NODE_ENV', () => {
+    expect(problemsOf(() => loadConfig({ ...BASE, NODE_ENV: 'staging' })).join(' ')).toContain(
+      'NODE_ENV',
+    );
+  });
+
+  it('rejects FLAG_* values that are not true/false', () => {
+    expect(problemsOf(() => loadConfig({ ...BASE, FLAG_BROKEN: 'yes' })).join(' ')).toContain(
+      'FLAG_BROKEN',
+    );
+  });
+
+  it('reports every problem in a single ConfigError', () => {
+    const problems = problemsOf(() =>
+      loadConfig({ PORT: 'nope', NODE_ENV: 'staging', FLAG_BAD: 'maybe' }),
+    );
+    expect(problems.some((p) => p.includes('DATABASE_URL'))).toBe(true);
+    expect(problems.some((p) => p.includes('PORT'))).toBe(true);
+    expect(problems.some((p) => p.includes('NODE_ENV'))).toBe(true);
+    expect(problems.some((p) => p.includes('FLAG_BAD'))).toBe(true);
+  });
+
+  it('never echoes secret values in error messages', () => {
+    let message = '';
+    try {
+      loadConfig({ DATABASE_URL: 'postgres://u:supersecret@h/db', PORT: 'nope' });
+    } catch (error) {
+      message = (error as Error).message;
+    }
+    expect(message).not.toContain('supersecret');
+    expect(message).toContain('PORT');
+  });
+});
diff --git a/project/src/infrastructure/http/server.ts b/project/src/infrastructure/http/server.ts
index 82628e8..4cd6fe2 100644
--- a/project/src/infrastructure/http/server.ts
+++ b/project/src/infrastructure/http/server.ts
@@ -1,14 +1,27 @@
 import { buildApp } from '../../app/build-app.js';
+import { ConfigError, loadConfig } from '../config/config.js';
+import { createFlagStore } from '../../modules/flags/index.js';
 import { createLogger } from '../logging/logger.js';
 
-const logger = createLogger();
-const port = Number(process.env.PORT ?? 3000);
-const host = process.env.HOST ?? '0.0.0.0';
+let config;
+try {
+  config = loadConfig(process.env);
+} catch (error) {
+  if (error instanceof ConfigError) {
+    // Config is invalid: fail fast and loud before anything else starts.
+    console.error(error.message);
+  } else {
+    console.error('Failed to load configuration', error);
+  }
+  process.exit(1);
+}
+
+const logger = createLogger({ level: config.logLevel });
 
 try {
-  const app = await buildApp({ logger });
-  await app.listen({ port, host });
-  logger.info({ port, host }, 'HTTP server listening');
+  const app = await buildApp({ logger, flags: createFlagStore(config.flags) });
+  await app.listen({ port: config.port, host: config.host });
+  logger.info({ port: config.port, host: config.host }, 'HTTP server listening');
 } catch (error) {
   logger.error({ err: error }, 'Failed to start HTTP server');
   process.exit(1);
diff --git a/project/src/modules/flags/domain/feature-flag-store.ts b/project/src/modules/flags/domain/feature-flag-store.ts
new file mode 100644
index 0000000..a8bbc68
--- /dev/null
+++ b/project/src/modules/flags/domain/feature-flag-store.ts
@@ -0,0 +1,34 @@
+/**
+ * Feature flags domain. Deployment and activation are separate operations:
+ * flags can change at runtime without redeploy. Unknown flags are OFF
+ * (fail-safe default for risky paths).
+ */
+
+export interface FeatureFlagProvider {
+  isEnabled(name: string): boolean;
+}
+
+export class InMemoryFeatureFlagStore implements FeatureFlagProvider {
+  private readonly state: Map<string, boolean>;
+
+  constructor(initial: Readonly<Record<string, boolean>> = {}) {
+    this.state = new Map(
+      Object.entries(initial).map(([name, enabled]) => [name.toLowerCase(), enabled]),
+    );
+  }
+
+  isEnabled(name: string): boolean {
+    return this.state.get(name.toLowerCase()) === true;
+  }
+
+  /** Runtime mutation: activation does not require a redeploy. */
+  setEnabled(name: string, enabled: boolean): void {
+    this.state.set(name.toLowerCase(), enabled);
+  }
+}
+
+export function createFlagStore(
+  initial: Readonly<Record<string, boolean>> = {},
+): InMemoryFeatureFlagStore {
+  return new InMemoryFeatureFlagStore(initial);
+}
diff --git a/project/src/modules/flags/index.ts b/project/src/modules/flags/index.ts
new file mode 100644
index 0000000..440f54d
--- /dev/null
+++ b/project/src/modules/flags/index.ts
@@ -0,0 +1,9 @@
+/**
+ * Public API of the flags module. Everything the module exposes to the
+ * outside world goes through this file.
+ */
+export {
+  type FeatureFlagProvider,
+  InMemoryFeatureFlagStore,
+  createFlagStore,
+} from './domain/feature-flag-store.js';
diff --git a/project/src/modules/flags/tests/feature-flag-store.test.ts b/project/src/modules/flags/tests/feature-flag-store.test.ts
new file mode 100644
index 0000000..e4d7139
--- /dev/null
+++ b/project/src/modules/flags/tests/feature-flag-store.test.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest';
+import { createFlagStore } from '../index.js';
+
+describe('InMemoryFeatureFlagStore', () => {
+  it('reflects seeded state', () => {
+    const store = createFlagStore({ new_checkout: true, beta_search: false });
+    expect(store.isEnabled('new_checkout')).toBe(true);
+    expect(store.isEnabled('beta_search')).toBe(false);
+  });
+
+  it('defaults unknown flags to OFF (fail-safe)', () => {
+    const store = createFlagStore();
+    expect(store.isEnabled('never_heard_of_it')).toBe(false);
+  });
+
+  it('matches flag names case-insensitively', () => {
+    const store = createFlagStore({ New_Checkout: true });
+    expect(store.isEnabled('new_checkout')).toBe(true);
+    expect(store.isEnabled('NEW_CHECKOUT')).toBe(true);
+  });
+
+  it('flips state at runtime without a new store (no redeploy)', () => {
+    const store = createFlagStore({ risky_path: false });
+    expect(store.isEnabled('risky_path')).toBe(false);
+
+    store.setEnabled('risky_path', true);
+    expect(store.isEnabled('risky_path')).toBe(true);
+
+    store.setEnabled('risky_path', false);
+    expect(store.isEnabled('risky_path')).toBe(false);
+  });
+
+  it('skips a guarded path when the flag is off', () => {
+    const store = createFlagStore({ risky_path: false });
+    let ran = false;
+    if (store.isEnabled('risky_path')) {
+      ran = true;
+    }
+    expect(ran).toBe(false);
+
+    store.setEnabled('risky_path', true);
+    if (store.isEnabled('risky_path')) {
+      ran = true;
+    }
+    expect(ran).toBe(true);
+  });
+});
diff --git a/specs/F-004-config-flags/DESIGN.md b/specs/F-004-config-flags/DESIGN.md
new file mode 100644
index 0000000..522fac1
--- /dev/null
+++ b/specs/F-004-config-flags/DESIGN.md
@@ -0,0 +1,78 @@
+# DESIGN — F-004 Typed config and feature flags
+
+## Layering
+- `src/infrastructure/config/config.ts` — pure config loader. Owns env parsing and
+  validation. No side effects on `process.env`; takes an env object so tests are
+  deterministic. Throws a single `ConfigError` listing every problem found.
+- `src/modules/flags/` — the feature-flag module. Business-facing, boundary-checked.
+  Exposes only `index.ts`. Contains the `FeatureFlagProvider` interface and a simple
+  in-memory store. Does NOT depend on infrastructure/config (kept independent so it
+  can later be backed by a DB/external service without touching config).
+
+## Config loader (infrastructure)
+```ts
+export interface AppConfig {
+  nodeEnv: 'development' | 'test' | 'production';
+  port: number;
+  host: string;
+  logLevel: string;
+  databaseUrl: string;      // required
+  redisUrl?: string;        // optional
+  flags: Record<string, boolean>; // parsed FLAG_* vars (initial seed)
+}
+export class ConfigError extends Error { problems: string[] }
+export function loadConfig(env: StringRecord): AppConfig
+```
+- `DATABASE_URL` required: missing -> ConfigError naming the var.
+- `PORT` parsed to int, validated 1..65535.
+- `NODE_ENV` whitelisted, default `development`.
+- `FLAG_<NAME>` vars: value `true`/`false` (case-insensitive) -> boolean; other values
+  -> ConfigError naming the var. Names lowercased after stripping `FLAG_` prefix.
+- Accumulate all problems, then throw once (fail fast AND clear).
+
+## Feature flag module
+```ts
+export interface FeatureFlagProvider {
+  isEnabled(name: string): boolean;
+}
+export class InMemoryFeatureFlagStore implements FeatureFlagProvider {
+  constructor(initial?: Record<string, boolean>)
+  isEnabled(name): boolean        // unknown flag -> false (fail-safe default)
+  setEnabled(name, enabled): void // runtime mutation, no redeploy needed
+}
+export function createFlagStore(initial?): InMemoryFeatureFlagStore
+```
+- Unknown flags are OFF by default (fail-safe: risky paths stay skipped).
+- `setEnabled` mutates live state: deployment ≠ activation.
+- Guarded-path helper kept trivial; consumers do `if (flags.isEnabled('x')) { ... }`.
+
+## Wiring (composition root)
+- `src/app/build-app.ts` stays DB-free for now; but `buildApp` accepts an optional
+  `flags` dep so routes can guard paths. Default: empty store (all flags off).
+- `src/infrastructure/http/server.ts` calls `loadConfig(process.env)`, uses typed
+  `port`/`host`, and passes `config.flags` into the app. On ConfigError it logs the
+  problems and exits non-zero.
+- `pool.ts` keeps `createPoolFromEnv` but gains an optional typed overload note; no
+  breaking change needed this ticket (config owns DATABASE_URL validation at startup).
+
+## Boundary notes
+- `flags` module: only imports from `shared` (currently nothing needed). It must not
+  import `infrastructure/config`. Config parses FLAG_* into a plain record and hands it
+  to the module at composition time — inversion keeps the module clean.
+- Boundary checker will enforce this automatically.
+
+## Files
+| File | Role |
+|---|---|
+| src/infrastructure/config/config.ts | typed loader + ConfigError |
+| src/infrastructure/config/tests/config.test.ts | loader unit tests |
+| src/modules/flags/index.ts | module public API |
+| src/modules/flags/domain/feature-flag-store.ts | interface + store |
+| src/modules/flags/tests/feature-flag-store.test.ts | store unit tests |
+| src/app/build-app.ts | optional flags dep injection |
+| src/infrastructure/http/server.ts | loadConfig + typed listen + ConfigError exit |
+
+## Risks / mitigations
+- Silent flag default: unknown -> false, documented; tested.
+- ConfigError leaking secrets: messages name var NAMES only, never values.
+- Boundary violation (flags importing config): prevented by composition-time injection + checker.
diff --git a/specs/F-004-config-flags/SPEC.md b/specs/F-004-config-flags/SPEC.md
new file mode 100644
index 0000000..96ae65d
--- /dev/null
+++ b/specs/F-004-config-flags/SPEC.md
@@ -0,0 +1,41 @@
+# SPEC — F-004 Typed config and feature flags
+
+## Problem
+Risky features need activation separate from deployment; env access must be typed.
+Today env access is ad-hoc (`process.env.X ?? fallback` scattered in entrypoints)
+and there is no activation mechanism distinct from deploy.
+
+## Goal
+Fail-fast typed config plus a simple feature flag module behind an interface.
+
+## Scope IN
+- Typed env config loader in `src/infrastructure/config`, fail fast on missing/invalid required vars (all problems reported in one clear message)
+- `FeatureFlagProvider` interface with simple in-memory store implementation (`src/modules/flags`)
+- Deployment ≠ activation: flags seed from `FLAG_*` env vars at boot and can be mutated at runtime without redeploy
+- DB pool refactor to consume config instead of sniffing env itself
+
+## Scope OUT
+- No external flag service
+- No per-user segmentation
+- No admin HTTP endpoint for flags yet (first consumer decides shape; store API is runtime-mutable already)
+
+## Required vs optional vars
+| Var | Required | Default |
+|---|---|---|
+| DATABASE_URL | yes | — |
+| PORT | no | 3000 (valid: integer 1–65535) |
+| HOST | no | 0.0.0.0 |
+| LOG_LEVEL | no | info |
+| NODE_ENV | no | development (valid: development/test/production) |
+| REDIS_URL | no | undefined |
+| FLAG_<NAME> | no | parsed as true/false |
+
+## Acceptance criteria
+1. Given a missing required env var When the app starts Then startup fails with a clear message naming the var.
+2. Given flag off When a code path guarded by the flag runs Then the path is skipped.
+3. Flag state change does not require redeploy (runtime `setEnabled` on the store).
+4. `./scripts/verify.sh` green.
+
+## Non-functional
+- No new dependencies: hand-rolled validation is small, explicit and boring.
+- Config loader is a pure function of an env object (testable without touching process.env).
diff --git a/specs/F-004-config-flags/TASKS.md b/specs/F-004-config-flags/TASKS.md
new file mode 100644
index 0000000..0e3eb1d
--- /dev/null
+++ b/specs/F-004-config-flags/TASKS.md
@@ -0,0 +1,10 @@
+# TASKS — F-004 Typed config and feature flags
+
+- [ ] TASK-001 src/infrastructure/config/config.ts: AppConfig, ConfigError, loadConfig (pure over env object)
+- [ ] TASK-002 src/infrastructure/config/tests/config.test.ts: required/optional/invalid cases
+- [ ] TASK-003 src/modules/flags/domain/feature-flag-store.ts: FeatureFlagProvider + InMemoryFeatureFlagStore + createFlagStore
+- [ ] TASK-004 src/modules/flags/index.ts: public API
+- [ ] TASK-005 src/modules/flags/tests/feature-flag-store.test.ts: guard + runtime mutation
+- [ ] TASK-006 src/app/build-app.ts: optional flags dep
+- [ ] TASK-007 src/infrastructure/http/server.ts: loadConfig, typed listen, ConfigError exit
+- [ ] TASK-008 run lint + boundaries + typecheck + build + test + verify.sh
diff --git a/specs/F-004-config-flags/TESTS.md b/specs/F-004-config-flags/TESTS.md
new file mode 100644
index 0000000..c9a3024
--- /dev/null
+++ b/specs/F-004-config-flags/TESTS.md
@@ -0,0 +1,22 @@
+# TESTS — F-004 Typed config and feature flags
+
+## Unit — src/infrastructure/config/tests/config.test.ts
+1. Valid full env -> typed AppConfig (port number, nodeEnv enum, flags parsed)
+2. Missing DATABASE_URL -> ConfigError naming DATABASE_URL
+3. Invalid PORT (non-numeric / out of range) -> ConfigError naming PORT
+4. Invalid NODE_ENV -> ConfigError
+5. FLAG_* true/false parsed; unknown flag value -> ConfigError naming the var
+6. Multiple problems -> single ConfigError listing all of them
+
+## Unit — src/modules/flags/tests/feature-flag-store.test.ts
+1. Known flag on -> isEnabled true; known flag off -> false
+2. Unknown flag -> false (fail-safe)
+3. setEnabled flips state at runtime (no new store / no redeploy)
+4. createFlagStore seeds initial state
+
+## Composition
+5. buildApp with flags dep: guarded path skipped when flag off, runs when on
+
+## Manual / QA
+- Start server without DATABASE_URL -> clear error naming the var, non-zero exit.
+- verify.sh green.
diff --git a/work/artifacts/F-004/architect.md b/work/artifacts/F-004/architect.md
new file mode 100644
index 0000000..e7883ab
--- /dev/null
+++ b/work/artifacts/F-004/architect.md
@@ -0,0 +1,33 @@
+# Architect — F-004 Typed config and feature flags
+
+done -> work/artifacts/F-004/architect.md
+
+## Deliverables
+- specs/F-004-config-flags/SPEC.md
+- specs/F-004-config-flags/DESIGN.md
+- specs/F-004-config-flags/TASKS.md
+- specs/F-004-config-flags/TESTS.md
+
+## Key decisions
+1. **Config loader lives in `infrastructure/config`** and is a pure function over an env
+   object. No reads of `process.env` inside the loader → deterministic unit tests. It
+   accumulates every problem and throws ONE `ConfigError` (fail fast AND clear). It names
+   var NAMES only — never values — so secrets cannot leak into error messages.
+2. **Feature flags are a real module (`src/modules/flags`)** behind a
+   `FeatureFlagProvider` interface with an in-memory store. Unknown flags default to OFF
+   (fail-safe). `setEnabled` mutates live state → activation ≠ deployment, no redeploy.
+3. **Inversion to keep the module clean:** `infrastructure/config` parses `FLAG_*` into a
+   plain record and the composition root hands it to the flags store. The flags module never
+   imports config. The boundary checker enforces this.
+4. **buildApp gains an optional `flags` dep**, decorated onto the instance (`app.flags`),
+   establishing the wiring point future risky routes will consume. Default: empty store →
+   everything off.
+5. **No new dependencies.** Hand-rolled validation is small and boring.
+
+## Boundaries
+- `flags` module imports nothing outside its subtree (no shared needed). Config → flags
+  only via composition root. server.ts pulls config + passes flags into buildApp.
+
+## Risks
+- server now requires DATABASE_URL to start (intentional fail-fast). Smoke/QA must pass it.
+- ConfigError must not echo values. Covered by name-only messages + test.
diff --git a/work/artifacts/F-004/documenter.md b/work/artifacts/F-004/documenter.md
new file mode 100644
index 0000000..bcef4d1
--- /dev/null
+++ b/work/artifacts/F-004/documenter.md
@@ -0,0 +1,19 @@
+# Documenter — F-004 Typed config and feature flags
+
+done -> work/artifacts/F-004/documenter.md
+
+## Why documentation applies
+F-004 changes the startup contract (DATABASE_URL now required, fail-fast behavior) and introduces the flag mechanism every future risky feature will use.
+
+## Documents reviewed/produced
+- `project/README.md`: "Configuration" section added at build stage — required/optional vars, fail-fast behavior, FLAG_* semantics, fail-safe defaults, activation ≠ deployment.
+- `.env.example`: REDIS_URL + FLAG_EXAMPLE_FEATURE added with explanatory comments.
+- `spec/tech.md`: no new dependency rows needed — ticket added zero dependencies by design (noted for audit trail).
+- `specs/F-004-config-flags/` SPEC/DESIGN/TASKS/TESTS consistent with implementation.
+
+## Verification
+- README Configuration section cross-checked against config.ts behavior (required DATABASE_URL; PORT/HOST/LOG_LEVEL/NODE_ENV/REDIS_URL defaults; FLAG_* parsing).
+- Startup contract change (DATABASE_URL required) is called out explicitly so operators are not surprised.
+
+## Pending docs (not this ticket)
+- Flag admin transport documented when first consumer lands.
diff --git a/work/artifacts/F-004/implementer.md b/work/artifacts/F-004/implementer.md
new file mode 100644
index 0000000..3cd3227
--- /dev/null
+++ b/work/artifacts/F-004/implementer.md
@@ -0,0 +1,44 @@
+# Implementer — F-004 Typed config and feature flags
+
+done -> work/artifacts/F-004/implementer.md
+
+## Files created
+- src/infrastructure/config/config.ts (loadConfig pure over env object; ConfigError accumulates all problems; names var names only)
+- src/infrastructure/config/tests/config.test.ts (8 tests)
+- src/modules/flags/domain/feature-flag-store.ts (FeatureFlagProvider + InMemoryFeatureFlagStore + createFlagStore)
+- src/modules/flags/index.ts (module public API)
+- src/modules/flags/tests/feature-flag-store.test.ts (5 tests)
+- src/app/tests/config-flags.test.ts (2 composition tests: default OFF, runtime flip without redeploy)
+
+## Files modified
+- src/app/build-app.ts: optional flags dep; `app.flags` decorated on the instance (typed via module augmentation)
+- src/infrastructure/http/server.ts: loadConfig fail-fast before anything starts; typed port/host/logLevel; flags seeded from FLAG_* env
+- .env.example: REDIS_URL + FLAG_EXAMPLE_FEATURE example
+- README.md: Configuration section
+
+## API changes
+- Server now REQUIRES DATABASE_URL at startup (fail-fast; intentional per spec).
+
+## Bug found by tests during build (fixed before gates)
+- Flag store constructor did not lowercase keys while isEnabled lowercased lookups -> case-insensitive seed test failed. Fixed by normalizing keys in the constructor. Regression test retained.
+
+## Tests passed (evidence)
+```
+npm run lint            -> OK
+npm run lint:boundaries -> Boundary check OK: 22 file(s) checked (flags module imports nothing outside its subtree)
+npm run typecheck       -> exit 0
+npm run build           -> exit 0
+npm test                -> 9 files passed, 2 skipped (integration without DB); 38 passed | 6 skipped
+npm run test:integration-> 2 files, 6 passed (no regression)
+live smoke:
+  env -u DATABASE_URL node dist/.../server.js -> "Invalid configuration:\n- DATABASE_URL is required", exit 1 (AC1)
+  with DATABASE_URL + FLAG_EXAMPLE_FEATURE=true -> health=200, "HTTP server listening"
+./scripts/verify.sh     -> exit 0
+```
+
+## Known limitations
+- No admin endpoint to flip flags yet (scope out); store API is runtime-mutable so the first consumer only adds transport.
+- Flags live in memory: restart reseeds from env (documented as expected; persistence is a later ticket if needed).
+
+## Follow-up work
+- F-005 identity consumes config.databaseUrl through the pool and can guard risky paths via app.flags.
diff --git a/work/artifacts/F-004/leader-close.json b/work/artifacts/F-004/leader-close.json
new file mode 100644
index 0000000..a82f1df
--- /dev/null
+++ b/work/artifacts/F-004/leader-close.json
@@ -0,0 +1,33 @@
+{
+  "feature_id": "F-004",
+  "agent": "leader",
+  "verdict": "APPROVED",
+  "summary": "F-004 closed. Typed fail-fast config and a boundary-clean feature flag module behind an interface. Deployment ≠ activation proven at runtime. All gates APPROVED, verify.sh exit 0, zero new dependencies.",
+  "gates": {
+    "reviewer": "APPROVED (reviewer.json)",
+    "security": "APPROVED (security.json)",
+    "qa": "APPROVED (qa.json)",
+    "verify_sh": "exit 0"
+  },
+  "deliverables": [
+    "src/infrastructure/config/config.ts (pure loader, accumulated problems, name-only errors)",
+    "src/modules/flags (FeatureFlagProvider + InMemoryFeatureFlagStore, fail-safe OFF default)",
+    "buildApp flags dep decorated as app.flags; server.ts fail-fast startup",
+    "15 new tests incl. runtime flip without redeploy and secret non-leakage",
+    "README Configuration section + .env.example FLAG_* example"
+  ],
+  "process_notes": [
+    "Tests caught a real bug during build (flag store case normalization); fixed before gates with regression test retained. Exactly the loop we want."
+  ],
+  "next_feature_hint": "F-005 identity now has all dependencies done (F-002, F-003) plus config/flags ready -> recommended next",
+  "evidence": [
+    "work/artifacts/F-004/architect.md",
+    "work/artifacts/F-004/implementer.md",
+    "work/artifacts/F-004/reviewer.json",
+    "work/artifacts/F-004/security.json",
+    "work/artifacts/F-004/qa.json",
+    "work/artifacts/F-004/documenter.md",
+    "./scripts/verify.sh exit 0 at close"
+  ],
+  "timestamp": "2026-08-14T20:30:00Z"
+}
diff --git a/work/artifacts/F-004/qa.json b/work/artifacts/F-004/qa.json
new file mode 100644
index 0000000..de947d4
--- /dev/null
+++ b/work/artifacts/F-004/qa.json
@@ -0,0 +1,35 @@
+{
+  "feature_id": "F-004",
+  "agent": "qa",
+  "verdict": "APPROVED",
+  "summary": "All 4 acceptance criteria verified with fresh executions (live process + fresh test runs).",
+  "traceability": [
+    {
+      "criterion": "AC1: missing required env var -> startup fails with clear message",
+      "test": "fresh live run: env -u DATABASE_URL node dist/infrastructure/http/server.js",
+      "result": "PASS (prints 'Invalid configuration: - DATABASE_URL is required', exit code 1)"
+    },
+    {
+      "criterion": "AC2: flag off -> guarded path skipped",
+      "test": "feature-flag-store.test.ts 'skips a guarded path when the flag is off' + config-flags.test.ts",
+      "result": "PASS"
+    },
+    {
+      "criterion": "AC3: flag state change does not require redeploy",
+      "test": "'flips state at runtime without a new store' + composition 'runs once enabled at runtime' on the SAME app instance",
+      "result": "PASS"
+    },
+    {
+      "criterion": "AC4: verify.sh green",
+      "test": "./scripts/verify.sh",
+      "result": "PASS (exit 0)"
+    }
+  ],
+  "regressions": "PASS - full unit suite 38 passed | 6 skipped; F-002 integration 6 passed; /health returns 200 under valid config",
+  "evidence": [
+    "fresh live fail-fast run (exit 1, clear message naming DATABASE_URL)",
+    "fresh vitest run of flags unit + composition tests: 7 passed",
+    "./scripts/verify.sh exit 0"
+  ],
+  "timestamp": "2026-08-14T20:28:00Z"
+}
diff --git a/work/artifacts/F-004/reviewer.json b/work/artifacts/F-004/reviewer.json
new file mode 100644
index 0000000..71ba73b
--- /dev/null
+++ b/work/artifacts/F-004/reviewer.json
@@ -0,0 +1,26 @@
+{
+  "feature_id": "F-004",
+  "agent": "reviewer",
+  "verdict": "APPROVED",
+  "summary": "Typed config + feature flags match specs/F-004 DESIGN.md. Loader is pure and fail-fast, flags module is boundary-clean behind an interface, activation is decoupled from deployment. No regressions.",
+  "checks": {
+    "design_conformance": "PASS: loadConfig pure over env object (no process.env reads), ConfigError accumulates all problems, FLAG_* parsed into a record handed to the store at composition time",
+    "boundary_rules": "PASS: lint:boundaries clean over 22 files; flags module imports only its own subtree (vitest in tests only); flags never imports config (inversion upheld)",
+    "fail_safe_defaults": "PASS: unknown flag -> OFF; missing optional vars -> sane defaults; missing DATABASE_URL -> startup aborts before app is built",
+    "test_coverage": "PASS: 15 new tests map to specs/F-004 TESTS.md incl. multi-problem aggregation and secret non-leakage; composition test proves runtime flip without redeploy",
+    "regression": "PASS: unit 38 passed | 6 skipped; F-002 integration 6 passed; /health unaffected"
+  },
+  "findings": [
+    {
+      "severity": "info",
+      "note": "Flags are in-memory only; restart reseeds from env. Documented as expected for this ticket; persistence is a later concern if ever needed."
+    }
+  ],
+  "evidence": [
+    "npm run lint / typecheck / lint:boundaries (22 files) / test / test:integration -> all green",
+    "grep: flags module has no imports outside its subtree; config.ts has no process.env read",
+    "live smoke at build stage: missing DATABASE_URL -> exit 1 with clear message; valid env -> listening + health 200",
+    "files reviewed: src/infrastructure/config/**, src/modules/flags/**, src/app/build-app.ts, src/infrastructure/http/server.ts, src/app/tests/config-flags.test.ts"
+  ],
+  "timestamp": "2026-08-14T20:24:00Z"
+}
diff --git a/work/artifacts/F-004/security.json b/work/artifacts/F-004/security.json
new file mode 100644
index 0000000..3aa2277
--- /dev/null
+++ b/work/artifacts/F-004/security.json
@@ -0,0 +1,22 @@
+{
+  "feature_id": "F-004",
+  "agent": "security",
+  "verdict": "APPROVED",
+  "summary": "Security gate passed. No new dependencies (0 vulnerabilities), no dangerous patterns, config errors name variable NAMES only (secret leakage structurally impossible), .env hygiene intact.",
+  "checks": {
+    "dependencies": "PASS: npm audit -> 0 vulnerabilities; ticket added zero dependencies by design",
+    "secret_leakage": "PASS: every problems.push uses var names/static text only; dedicated unit test asserts a secret in DATABASE_URL never appears in the thrown message",
+    "dangerous_patterns": "PASS: no eval / new Function / child_process in new code",
+    "env_hygiene": "PASS: .env gitignored; .env.example trackable and carries only dev-only/public values",
+    "input_surfaces": "PASS: PORT integer-range validated; FLAG_* parsed to booleans only (no string passthrough); unknown flags fail-safe OFF so risky paths stay skipped"
+  },
+  "findings": [],
+  "evidence": [
+    "npm audit -> found 0 vulnerabilities",
+    "grep eval|new Function|child_process over config+flags -> none",
+    "grep problems.push -> name-only messages (4 sites inspected)",
+    "git check-ignore .env -> ignored; .env.example -> tracked",
+    "unit test 'never echoes secret values in error messages' passes"
+  ],
+  "timestamp": "2026-08-14T20:26:00Z"
+}
diff --git a/work/current.md b/work/current.md
index fad2395..f489a3b 100644
--- a/work/current.md
+++ b/work/current.md
@@ -1,17 +1,17 @@
 # Sesión actual
 
-- Feature en curso: _ninguna_ (F-003 cerrada DONE el 2026-08-14)
+- Feature en curso: _ninguna_ (F-004 cerrada DONE el 2026-08-14)
 - Inicio: —
 - Orquestador: —
 
 ## Plan
-- Hechas: F-001, F-002, F-003.
-- Desbloqueadas ahora: F-004 (config/flags, depende de F-001) y F-005 (identity, depende de F-002+F-003, ambas done).
-- Sugerencia de orden: F-004 → F-005 (identity necesita config/flags limpio para secrets).
+- Hechas: F-001, F-002, F-003, F-004.
+- Desbloqueada: F-005 (identity & auth core) — depende de F-002+F-003, ambas done. Config/flags (F-004) ya listos para secrets y guards.
+- Sugerencia de orden: F-005 ahora.
 
 ## Bitácora
-- 2026-08-14: F-001, F-002 y F-003 DONE; todos los gates APPROVED; verify.sh verde.
-- Dev PostgreSQL + Redis siguen corriendo (mdv-dev-postgres, mdv-dev-redis) para los próximos tickets.
+- 2026-08-14: F-001..F-004 DONE; todos los gates APPROVED; verify.sh verde.
+- Dev PostgreSQL + Redis siguen corriendo (mdv-dev-postgres, mdv-dev-redis).
 
 ## Próximo paso
-- intake de F-004 (config and feature flags).
+- intake de F-005 (identity & auth core).
diff --git a/work/history.md b/work/history.md
index b2958cb..cbd2d99 100644
--- a/work/history.md
+++ b/work/history.md
@@ -19,3 +19,10 @@
 - Entregable: request_id (generado o propagado-sanitizado), logs JSON correlacionados, error envelope v2 con requestId, hook de validación parseJson (zod), server con logging inyectable
 - Nota: doc stage rebotó a build para escribir README (project/ está gateado a build/implementer/running); comportamiento correcto del guardrail
 - Artefactos: work/artifacts/F-003/
+
+## 2026-08-14 — F-004 Typed config and feature flags — DONE
+- Gates: reviewer APPROVED, security APPROVED, qa APPROVED, verify.sh exit 0
+- Entregable: loadConfig fail-fast (DATABASE_URL requerido, errores solo con nombres de variables), módulo flags tras FeatureFlagProvider (default OFF, flip en runtime sin redeploy), app.flags decorado
+- Nota: los tests detectaron un bug real en build (case-normalization del store); corregido antes de gates con test de regresión
+- Cero dependencias nuevas
+- Artefactos: work/artifacts/F-004/
diff --git a/work/runtime-status.json b/work/runtime-status.json
index 9ab1de2..cce496d 100644
--- a/work/runtime-status.json
+++ b/work/runtime-status.json
@@ -6,6 +6,6 @@
   "state": "waiting",
   "next_agent": "leader",
   "waiting_for": "Seleccionar una feature pending y actualizar este estado",
-  "updated_at": "2026-08-14T20:13:28Z",
+  "updated_at": "2026-08-14T20:29:18Z",
   "timeline": []
 }