Adds GatewayConnectionState enum, GatewayRegistration record with atomic
message counters, and a full registry API on GatewayManager: RegisterGateway,
UpdateState, GetRegistration, GetAllRegistrations, UnregisterGateway,
GetConnectedGatewayCount, IncrementMessagesSent, IncrementMessagesReceived.
Covers 11 new tests in GatewayRegistrationTests.cs (all passing).
Add ReplyMapCache to ReplyMapper.cs — an LRU cache with TTL expiration
for gateway reply subject mappings, avoiding repeated string parsing on
the hot path. Includes 10 unit tests covering LRU eviction, TTL expiry,
hit/miss counters, PurgeExpired, and Count.
Adds GatewayReconnectPolicy with exponential backoff and jitter, and
reconnect attempt tracking (GetReconnectAttempts, ResetReconnectAttempts,
ReconnectGatewayAsync) to GatewayManager. 10 new tests cover delay
calculation, cap behaviour, jitter, and per-gateway counter isolation.
Adds per-account subscription tracking to GatewayConnection via
AddAccountSubscription/RemoveAccountSubscription/GetAccountSubscriptions/
AccountSubscriptionCount, with corresponding SendAccountSubscriptions and
GetAccountSubscriptions helpers on GatewayManager. Covered by 10 new unit tests.
Ports the gateway interest-only mode from Go (gateway.go:100-150, 1500-1600):
- Add GatewayInterestTracker with Optimistic/Transitioning/InterestOnly modes
- In Optimistic mode, track no-interest set; switch to InterestOnly when set
exceeds threshold (default 1000, matching Go defaultGatewayMaxRUnsubThreshold)
- In InterestOnly mode, only forward subjects with tracked RS+ interest;
use SubjectMatch.MatchLiteral for wildcard pattern support
- Integrate tracker into GatewayConnection: A+/A- messages update tracker,
SendMessageAsync skips send when ShouldForward returns false
- Expose InterestTracker property on GatewayConnection for observability
- Add 13 unit tests covering all 8 specified behaviors plus edge cases
