## Summary
First step toward Redis-backed sessions (ADR-0010). Adds the shared `ioredis` connection that every downstream consumer (session storage, OBO token cache, …) injects via the new `REDIS_CLIENT` DI token. No session logic in this PR — that's the next one.
## What lands
- **`ioredis@^5.10.1`** as a direct dependency. Chosen by ADR-0010 for its mature Sentinel support — single-instance URL today, Sentinel-HA configuration lands with the prod infrastructure ADR.
- **[`.env.example`](apps/portal-bff/.env.example)** promotes `REDIS_URL` from its future-vars comment to an active variable, defaulting to the local Compose stack's address. The Sentinel-style keys (`REDIS_SENTINEL_HOSTS`, `REDIS_SENTINEL_NAME`, `REDIS_TLS`) stay in the future-vars comment until the prod deploy.
- **[`check-redis-config.ts`](apps/portal-bff/src/config/check-redis-config.ts)** — boot-time guard mirroring the existing four:
- Refuses to start on missing / non-`redis(s)://` / passwordless / placeholder URLs.
- Returns a typed `RedisConfig` with parsed `host` + `port` for downstream observability.
- **[`redis.token.ts`](apps/portal-bff/src/redis/redis.token.ts)** — `REDIS_CLIENT` string token + `Redis` type alias. Same shape as the existing `ENTRA_CONFIG` / `MSAL_CLIENT`.
- **[`redis.module.ts`](apps/portal-bff/src/redis/redis.module.ts)** — `RedisModule` factory provider:
- Caps `maxRetriesPerRequest: 3` so an unreachable Redis surfaces a clear command-time error rather than an infinite reconnect storm.
- Wires `connect` / `ready` / `error` / `close` / `reconnecting` events into the Pino stream under the `redis` context — easy log isolation.
- Non-global; consumers import the module to state "I depend on Redis".
- **`main.ts`** calls `assertRedisConfig()` alongside the other three validators; **`AppModule`** imports `RedisModule`.
## Decisions worth flagging
- **`maxRetriesPerRequest: 3`** rather than the ioredis default of 20. With the default, a Redis outage masquerades as request-level timeouts spread over minutes. Capping low surfaces the outage in the first command failure — the BFF can then return 503 and recover quickly when Redis comes back.
- **Single shared client.** Pub/sub use-cases (when they appear) duplicate via `redis.duplicate()` per ioredis convention. Connect/disconnect is one socket per BFF instance.
- **No explicit shutdown hook yet.** Node's process-exit handlers and ioredis's own cleanup take care of the socket on SIGTERM / Ctrl+C. If we see stuck connections in real load, we wire `OnApplicationShutdown` + `redis.quit()`.
- **Sentinel-style config stays in the future-vars comment.** ioredis supports it natively, but plumbing it on top of the URL form complicates the validator and the factory for zero v1 payoff. Lands with the prod infrastructure ADR.
## Verification
- `nx run-many -t lint test build --projects=portal-bff` — green.
- **62 / 62 specs** (was 52; +10 — `check-redis-config` covers happy path + 6 failure modes; `redis.module` covers DI resolution against an unreachable URL plus the missing-env failure).
- Boot smoke against the local Compose stack: Pino's `redis` context shows `redis.connect` → `redis.ready` on startup; killing the Redis container produces `redis.close` / `redis.reconnecting` lines.
## What this PR explicitly does NOT do
- Mount `express-session` + `connect-redis` middleware. The next PR wires the session cookie (`__Host-portal_session`), the encrypted payload, and the lookup middleware that attaches `user` to every request.
- Plug the callback into session creation. Auth still ends with a Pino log + redirect; the SPA still sees the user anonymous on the next request.
- Sentinel / TLS configuration. Future-var keys are documented in `.env.example` for when the prod deploy lands.
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Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #109
julien
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