Add a Redis state provider, the last item on the roadmap

[ivanvyd]

The last item on the README roadmap: "A Redis state provider — the fastest option for state written on every tick."

State is written on every tick of every checker. A relational provider does a round trip to a disk-backed engine for each of those; this does one to memory. That is the whole reason to pick it.

Optimistic concurrency, in one command

SupportsOptimisticConcurrency is true, and it earns it. One hash per checker holds the state, the type it was written as, and a version — a hash rather than a plain string so the compare and the write can be a single Lua script, which Redis runs to completion without interleaving anything else:

if redis.call('HGET', KEYS[1], 'version') ~= ARGV[3] then
    return 0
end
redis.call('HSET', KEYS[1], 'value', ARGV[1], 'state_type', ARGV[2], 'version', ARGV[4])
return 1

WATCH/MULTI/EXEC would also work, but it needs its own retry loop around the optimistic failure and it holds state on the connection. A script needs neither. Creating is the same shape against EXISTS, so two writers that both find nothing cannot both create.

Tested against a real Redis, not a fake

The guarantees here are Redis's own, so a fake would only restate what the provider already believes. The tests run against redis:7-alpine in a container via Testcontainers, and skip rather than fail where there is no container runtime — the same bargain the CosmosDB combinations strike in the E2E project.

The property that matters is asserted rather than argued: twelve writers read one version, race to write it, and exactly one wins.

mutation	tests failed
conditional write ignores the version	3
create-if-absent overwrites what is there	1
the version never changes	3
the key prefix is ignored	1
a state is returned as any type asked for	1

15 Redis tests, 463 total green on both net8.0 and net10.0, zero build warnings.

Other details

• GetStatesAsync issues every read before awaiting any. StackExchange.Redis pipelines on one connection, so the dashboard listing every checker costs one round trip rather than one per checker.
• Keys are prefixed (healthie:state: by default) so the provider stays clear of whatever else is on that server.
• AddHealthieRedis() with no configuration string reuses an IConnectionMultiplexer the application already registers, rather than opening a second connection to the same server.
• A hash written before this provider versioned its writes reports as unversioned, and the caller writes it unconditionally as it did before — the same upgrade path the relational providers got.

Durability is Redis's, not this package's

Redis is in memory. Whether state survives a restart is your Redis configuration, not something this provider can promise, and the package README says so instead of implying otherwise.

The roadmap is now empty

Every item on it has shipped. What replaces it is written as what it actually is — two decisions, not two features: the Healthie.Api / dashboard authorization defaults, and restore not being hash-pinned. Both are deliberate as they stand and both are yours to make.

No release — version stays at 3.1.4.