feat(redis): add configurable MaxConnAge to bound failover error window

[lucasmonje]

What does this implement/fix? Explain your changes.

Adds a configurable MaxConnAge to the go-redis client used by every maestro Redis adapter, to bound the error window during an ElastiCache failover/switchover.

Why. During a switchover (failover, Redis→Valkey engine upgrade, scaling), AWS swaps the primary/replica role of the cluster's nodes. Pooled TCP conns stay attached to the node they originally dialed, which is now a replica, and any subsequent write returns:

READONLY You can't write against a read only replica.

go-redis does not treat READONLY as a bad-conn signal, so the offending conn is returned to the pool and reused, perpetuating the failure until it's recycled by some other means. IdleTimeout doesn't help on a hot pool (conns never sit idle long enough for the reaper). MaxConnAge is checked at every conn checkout, so it guarantees turnover regardless of traffic; after the bound elapses the next dial re-resolves DNS and lands on the new primary.

What.

• createRedisClient now reads adapters.redis.maxConnAge and sets opt.MaxConnAge when > 0. Unset/0 keeps the go-redis default (no limit), so behavior is unchanged unless configured.
• Shared knob across all six Redis adapters, mirroring the existing adapters.redis.poolSize. Env var: MAESTRO_ADAPTERS_REDIS_MAXCONNAGE (Go duration, e.g. 5m).

Operational note. Set MAESTRO_ADAPTERS_REDIS_MAXCONNAGE=5m (or shorter) on the deployment before the planned Redis→Valkey maintenance window. Safe to leave on permanently; overhead is negligible on production-sized pools and it future-proofs against unplanned failovers.

What this does not do. This bounds the post-failover error window; it does not eliminate it. A request landing on a stale conn during the swap still sees one READONLY before that conn is recycled. A retry-on-READONLY wrapper around the room-allocation Lua script would be a complementary follow-up, out of scope here.

This mirrors the matchmaker change in MR !137 (matchmaker is on go-redis v6; maestro stays on v8, where the field is still named MaxConnAge — it becomes ConnMaxLifetime in v9).

Any other comments?

• New //go:build unit test covers both the set case (5m reaches client.Options().MaxConnAge) and the unset-keeps-default case.
• Existing integration tests updated with the new GetDuration expectation.
• go build, go vet -tags=integration, goimports, license check, and the new unit tests all pass locally. Integration suite (k3d) not run locally.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.92%. Comparing base (7cb6e86) to head (49ea0d4).
⚠️ Report is 2 commits behind head on main.
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #720      +/-   ##
==========================================
- Coverage   60.93%   60.92%   -0.01%     
==========================================
  Files         144      144              
  Lines       12986    12992       +6     
==========================================
+ Hits         7913     7916       +3     
- Misses       4719     4722       +3     
  Partials      354      354              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[fbgava-wildlife]

LGTM