feat: add presence-gated session leases (#7)

Closes #7

src/FinalFactory.Rendezvous.Server/State/EphemeralStateContracts.cs

@@ -53,6 +53,12 @@ internal sealed record EphemeralStoreOptions
         RequireDuration(ReplayLifetime, TimeSpan.FromSeconds(30), nameof(ReplayLifetime));
         RequireDuration(IdempotencyLifetime, TimeSpan.FromMinutes(10), nameof(IdempotencyLifetime));
         RequireDuration(GracefulDrainLifetime, TimeSpan.FromSeconds(30), nameof(GracefulDrainLifetime));
+        if (IdempotencyLifetime < LeaseLifetime || IdempotencyLifetime < JoinAttemptLifetime)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(IdempotencyLifetime),
+                "Idempotency retention must cover every idempotent resource lifetime.");
+        }
     }
 
     private static void RequirePositive(int value, string name)
@@ -74,8 +80,10 @@ internal sealed record EphemeralStoreOptions
 
 internal readonly record struct TenantScope(GameId GameId, EnvironmentId EnvironmentId);
 
-internal readonly record struct SecretFingerprint
+internal readonly struct SecretFingerprint : IEquatable<SecretFingerprint>
 {
+    private readonly string? _value;
+
     public SecretFingerprint(string value)
     {
         if (string.IsNullOrWhiteSpace(value) || value.Length > 128)
@@ -83,12 +91,33 @@ internal readonly record struct SecretFingerprint
             throw new ArgumentException("Secret fingerprints must contain 1-128 characters.", nameof(value));
         }
 
-        Value = value;
+        _value = value;
     }
 
-    public string Value { get; }
-    public bool IsValid => !string.IsNullOrWhiteSpace(Value) && Value.Length <= 128;
+    public bool IsValid => !string.IsNullOrWhiteSpace(_value) && _value.Length <= 128;
+    public bool Equals(SecretFingerprint other)
+    {
+        ReadOnlySpan<char> left = _value.AsSpan();
+        ReadOnlySpan<char> right = other._value.AsSpan();
+        if (left.Length != right.Length)
+        {
+            return false;
+        }
+
+        int difference = 0;
+        for (int index = 0; index < left.Length; index++)
+        {
+            difference |= left[index] ^ right[index];
+        }
+
+        return difference == 0;
+    }
+
+    public override bool Equals(object? obj) => obj is SecretFingerprint other && Equals(other);
+    public override int GetHashCode() => StringComparer.Ordinal.GetHashCode(_value ?? string.Empty);
     public override string ToString() => "[REDACTED]";
+    public static bool operator ==(SecretFingerprint left, SecretFingerprint right) => left.Equals(right);
+    public static bool operator !=(SecretFingerprint left, SecretFingerprint right) => !left.Equals(right);
 }
 
 internal readonly record struct ObservedEndpoint
@@ -138,6 +167,7 @@ internal sealed record ListingDefinition
     public required SecretFingerprint LeaseFingerprint { get; init; }
     public required MediationHandle HostPresenceHandle { get; init; }
     public required SecretFingerprint HostPresenceFingerprint { get; init; }
+    public required string CapabilityDerivationSalt { get; init; }
 }
 
 internal sealed record StoredListing
@@ -163,12 +193,25 @@ internal sealed record RenewLeaseCommand(
     SessionListingId ListingId,
     LeaseId LeaseId,
     SecretFingerprint LeaseFingerprint,
+    string OwnerSubject,
     long ExpectedVersion);
 
+internal sealed record UpdateListingCommand(
+    SessionListingId ListingId,
+    LeaseId LeaseId,
+    SecretFingerprint LeaseFingerprint,
+    string OwnerSubject,
+    string BuildVersion,
+    string DisplayName,
+    int CurrentPlayers,
+    int MaximumPlayers,
+    IReadOnlyDictionary<string, string> Metadata);
+
 internal sealed record DeleteListingCommand(
     SessionListingId ListingId,
     LeaseId LeaseId,
-    SecretFingerprint LeaseFingerprint);
+    SecretFingerprint LeaseFingerprint,
+    string OwnerSubject);
 
 internal sealed record BindHostPresenceCommand(
     MediationHandle Handle,
@@ -265,6 +308,7 @@ internal interface IEphemeralRendezvousStore
 
     StoreResult<StoredListing> CreateListing(CreateListingCommand command, CancellationToken cancellationToken = default);
     StoreResult<StoredListing> RenewLease(RenewLeaseCommand command, CancellationToken cancellationToken = default);
+    StoreResult<StoredListing> UpdateListing(UpdateListingCommand command, CancellationToken cancellationToken = default);
     StoreResult<bool> DeleteListing(DeleteListingCommand command, CancellationToken cancellationToken = default);
     StoreResult<StoredListing> GetListing(SessionListingId listingId, bool requireFreshPresence, CancellationToken cancellationToken = default);
     StoreResult<IReadOnlyList<StoredListing>> BrowseVisibleListings(VisibleListingQuery query, CancellationToken cancellationToken = default);