feat(cluster): add structured inflight proposal tracking with ops counting

Replace the simple string-keyed inflight dictionaries with account-scoped
ConcurrentDictionary<string, Dictionary<string, InflightInfo>> structures.
Adds InflightInfo record with OpsCount for duplicate proposal tracking,
TrackInflight/RemoveInflight/IsInflight methods for streams and consumers,
and ClearAllInflight(). Updates existing Propose* methods to use $G account.
Go reference: jetstream_cluster.go:1193-1278.

src/NATS.Server/JetStream/Cluster/JetStreamMetaGroup.cs

@@ -22,10 +22,12 @@ public sealed class JetStreamMetaGroup
     private readonly ConcurrentDictionary<string, StreamAssignment> _assignments =
         new(StringComparer.Ordinal);
 
-    // B8: Inflight proposal tracking -- entries that have been proposed but not yet committed.
+    // Account-scoped inflight proposal tracking -- entries proposed but not yet committed.
-    // Go reference: jetstream_cluster.go inflight tracking for proposals.
+    // Go reference: jetstream_cluster.go inflight tracking for proposals (jetstream_cluster.go:1193-1278).
-    private readonly ConcurrentDictionary<string, string> _inflightStreams = new(StringComparer.Ordinal);
+    // Outer key: account name. Inner key: stream name → InflightInfo.
-    private readonly ConcurrentDictionary<string, string> _inflightConsumers = new(StringComparer.Ordinal);
+    private readonly ConcurrentDictionary<string, Dictionary<string, InflightInfo>> _inflightStreams = new(StringComparer.Ordinal);
+    // Outer key: account name. Inner key: "stream/consumer" → InflightInfo.
+    private readonly ConcurrentDictionary<string, Dictionary<string, InflightInfo>> _inflightConsumers = new(StringComparer.Ordinal);
 
     // Running count of consumers across all stream assignments.
     private int _totalConsumerCount;
@@ -74,14 +76,152 @@ public sealed class JetStreamMetaGroup
     public int ConsumerCount => _totalConsumerCount;
 
     /// <summary>
-    /// Number of inflight stream proposals.
+    /// Total number of inflight stream proposals across all accounts.
     /// </summary>
-    public int InflightStreamCount => _inflightStreams.Count;
+    public int InflightStreamCount => _inflightStreams.Values.Sum(d => d.Count);
 
     /// <summary>
-    /// Number of inflight consumer proposals.
+    /// Total number of inflight consumer proposals across all accounts.
     /// </summary>
-    public int InflightConsumerCount => _inflightConsumers.Count;
+    public int InflightConsumerCount => _inflightConsumers.Values.Sum(d => d.Count);
+
+    // ---------------------------------------------------------------
+    // Inflight proposal tracking — public API
+    // Go reference: jetstream_cluster.go:1193-1278 inflight proposal management.
+    // ---------------------------------------------------------------
+
+    /// <summary>
+    /// Tracks a stream proposal as inflight for the given account.
+    /// Increments OpsCount on duplicate proposals for the same stream name.
+    /// Go reference: jetstream_cluster.go inflight proposal tracking.
+    /// </summary>
+    public void TrackInflightStreamProposal(string account, StreamAssignment sa)
+    {
+        var accountDict = _inflightStreams.GetOrAdd(account, _ => new Dictionary<string, InflightInfo>(StringComparer.Ordinal));
+        lock (accountDict)
+        {
+            if (accountDict.TryGetValue(sa.StreamName, out var existing))
+                accountDict[sa.StreamName] = existing with { OpsCount = existing.OpsCount + 1 };
+            else
+                accountDict[sa.StreamName] = new InflightInfo(OpsCount: 1, Deleted: false, Assignment: sa);
+        }
+    }
+
+    /// <summary>
+    /// Decrements OpsCount for a stream proposal. Removes the entry when OpsCount reaches zero.
+    /// Removes the account entry when its dictionary becomes empty.
+    /// Go reference: jetstream_cluster.go inflight proposal tracking.
+    /// </summary>
+    public void RemoveInflightStreamProposal(string account, string streamName)
+    {
+        if (!_inflightStreams.TryGetValue(account, out var accountDict))
+            return;
+
+        lock (accountDict)
+        {
+            if (!accountDict.TryGetValue(streamName, out var existing))
+                return;
+
+            if (existing.OpsCount <= 1)
+            {
+                accountDict.Remove(streamName);
+                if (accountDict.Count == 0)
+                    _inflightStreams.TryRemove(account, out _);
+            }
+            else
+            {
+                accountDict[streamName] = existing with { OpsCount = existing.OpsCount - 1 };
+            }
+        }
+    }
+
+    /// <summary>
+    /// Returns true if the given stream is currently tracked as inflight for the account.
+    /// Go reference: jetstream_cluster.go inflight check.
+    /// </summary>
+    public bool IsStreamInflight(string account, string streamName)
+    {
+        if (!_inflightStreams.TryGetValue(account, out var accountDict))
+            return false;
+
+        lock (accountDict)
+        {
+            return accountDict.TryGetValue(streamName, out var info) && info.OpsCount > 0;
+        }
+    }
+
+    /// <summary>
+    /// Tracks a consumer proposal as inflight for the given account.
+    /// Increments OpsCount on duplicate proposals for the same stream/consumer key.
+    /// Go reference: jetstream_cluster.go inflight consumer proposal tracking.
+    /// </summary>
+    public void TrackInflightConsumerProposal(string account, string streamName, string consumerName, ConsumerAssignment? ca = null)
+    {
+        var key = $"{streamName}/{consumerName}";
+        var accountDict = _inflightConsumers.GetOrAdd(account, _ => new Dictionary<string, InflightInfo>(StringComparer.Ordinal));
+        lock (accountDict)
+        {
+            if (accountDict.TryGetValue(key, out var existing))
+                accountDict[key] = existing with { OpsCount = existing.OpsCount + 1 };
+            else
+                accountDict[key] = new InflightInfo(OpsCount: 1, Deleted: false, Assignment: null);
+        }
+    }
+
+    /// <summary>
+    /// Decrements OpsCount for a consumer proposal. Removes the entry when OpsCount reaches zero.
+    /// Removes the account entry when its dictionary becomes empty.
+    /// Go reference: jetstream_cluster.go inflight consumer proposal tracking.
+    /// </summary>
+    public void RemoveInflightConsumerProposal(string account, string streamName, string consumerName)
+    {
+        var key = $"{streamName}/{consumerName}";
+        if (!_inflightConsumers.TryGetValue(account, out var accountDict))
+            return;
+
+        lock (accountDict)
+        {
+            if (!accountDict.TryGetValue(key, out var existing))
+                return;
+
+            if (existing.OpsCount <= 1)
+            {
+                accountDict.Remove(key);
+                if (accountDict.Count == 0)
+                    _inflightConsumers.TryRemove(account, out _);
+            }
+            else
+            {
+                accountDict[key] = existing with { OpsCount = existing.OpsCount - 1 };
+            }
+        }
+    }
+
+    /// <summary>
+    /// Returns true if the given consumer is currently tracked as inflight for the account.
+    /// Go reference: jetstream_cluster.go inflight check.
+    /// </summary>
+    public bool IsConsumerInflight(string account, string streamName, string consumerName)
+    {
+        var key = $"{streamName}/{consumerName}";
+        if (!_inflightConsumers.TryGetValue(account, out var accountDict))
+            return false;
+
+        lock (accountDict)
+        {
+            return accountDict.TryGetValue(key, out var info) && info.OpsCount > 0;
+        }
+    }
+
+    /// <summary>
+    /// Clears all inflight stream and consumer proposals across all accounts.
+    /// Go reference: jetstream_cluster.go — inflight cleared on shutdown/reset.
+    /// </summary>
+    public void ClearAllInflight()
+    {
+        _inflightStreams.Clear();
+        _inflightConsumers.Clear();
+    }
 
     // ---------------------------------------------------------------
     // Stream proposals
@@ -104,14 +244,16 @@ public sealed class JetStreamMetaGroup
     {
         _ = ct;
 
+        var resolvedGroup = group ?? new RaftGroup { Name = config.Name };
+
         // Track as inflight
-        _inflightStreams[config.Name] = config.Name;
+        TrackInflightStreamProposal("$G", new StreamAssignment { StreamName = config.Name, Group = resolvedGroup });
 
         // Apply the entry (idempotent via AddOrUpdate)
-        ApplyStreamCreate(config.Name, group ?? new RaftGroup { Name = config.Name });
+        ApplyStreamCreate(config.Name, resolvedGroup);
 
         // Clear inflight
-        _inflightStreams.TryRemove(config.Name, out _);
+        RemoveInflightStreamProposal("$G", config.Name);
 
         return Task.CompletedTask;
     }
@@ -131,14 +273,16 @@ public sealed class JetStreamMetaGroup
         if (_assignments.ContainsKey(config.Name))
             throw new InvalidOperationException($"Stream '{config.Name}' already exists.");
 
+        var resolvedGroup = group ?? new RaftGroup { Name = config.Name };
+
         // Track as inflight
-        _inflightStreams[config.Name] = config.Name;
+        TrackInflightStreamProposal("$G", new StreamAssignment { StreamName = config.Name, Group = resolvedGroup });
 
         // Apply the entry
-        ApplyStreamCreate(config.Name, group ?? new RaftGroup { Name = config.Name });
+        ApplyStreamCreate(config.Name, resolvedGroup);
 
         // Clear inflight
-        _inflightStreams.TryRemove(config.Name, out _);
+        RemoveInflightStreamProposal("$G", config.Name);
 
         return Task.CompletedTask;
     }
@@ -187,14 +331,13 @@ public sealed class JetStreamMetaGroup
         _ = ct;
 
         // Track as inflight
-        var inflightKey = $"{streamName}/{consumerName}";
+        TrackInflightConsumerProposal("$G", streamName, consumerName);
-        _inflightConsumers[inflightKey] = inflightKey;
 
         // Apply the entry (silently ignored if stream does not exist)
         ApplyConsumerCreate(streamName, consumerName, group);
 
         // Clear inflight
-        _inflightConsumers.TryRemove(inflightKey, out _);
+        RemoveInflightConsumerProposal("$G", streamName, consumerName);
 
         return Task.CompletedTask;
     }
@@ -219,14 +362,13 @@ public sealed class JetStreamMetaGroup
             throw new InvalidOperationException($"Stream '{streamName}' not found.");
 
         // Track as inflight
-        var inflightKey = $"{streamName}/{consumerName}";
+        TrackInflightConsumerProposal("$G", streamName, consumerName);
-        _inflightConsumers[inflightKey] = inflightKey;
 
         // Apply the entry
         ApplyConsumerCreate(streamName, consumerName, group);
 
         // Clear inflight
-        _inflightConsumers.TryRemove(inflightKey, out _);
+        RemoveInflightConsumerProposal("$G", streamName, consumerName);
 
         return Task.CompletedTask;
     }
@@ -612,3 +754,11 @@ public sealed class MetaGroupState
     /// </summary>
     public int ConsumerCount { get; init; }
 }
+
+/// <summary>
+/// Tracks an inflight stream or consumer proposal with ops counting.
+/// OpsCount increments on duplicate proposals so that each proposer must
+/// independently call Remove before the entry is cleared.
+/// Go reference: jetstream_cluster.go inflight proposal tracking.
+/// </summary>
+public record InflightInfo(int OpsCount, bool Deleted, StreamAssignment? Assignment);

tests/NATS.Server.Tests/JetStream/Cluster/JetStreamInflightTrackingTests.cs

@@ -0,0 +1,146 @@
+using NATS.Server.JetStream.Cluster;
+
+namespace NATS.Server.Tests.JetStream.Cluster;
+
+public class JetStreamInflightTrackingTests
+{
+    [Fact]
+    public void TrackInflightStreamProposal_increments_ops()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        var sa = new StreamAssignment
+        {
+            StreamName = "inflight-1",
+            Group = new RaftGroup { Name = "rg-inf", Peers = ["n1", "n2", "n3"] },
+        };
+
+        meta.TrackInflightStreamProposal("ACC", sa);
+        meta.InflightStreamCount.ShouldBe(1);
+        meta.IsStreamInflight("ACC", "inflight-1").ShouldBeTrue();
+    }
+
+    [Fact]
+    public void RemoveInflightStreamProposal_clears_when_zero()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        var sa = new StreamAssignment
+        {
+            StreamName = "inflight-2",
+            Group = new RaftGroup { Name = "rg-inf2", Peers = ["n1", "n2", "n3"] },
+        };
+
+        meta.TrackInflightStreamProposal("ACC", sa);
+        meta.RemoveInflightStreamProposal("ACC", "inflight-2");
+        meta.IsStreamInflight("ACC", "inflight-2").ShouldBeFalse();
+    }
+
+    [Fact]
+    public void Duplicate_proposal_increments_ops_count()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        var sa = new StreamAssignment
+        {
+            StreamName = "dup-stream",
+            Group = new RaftGroup { Name = "rg-dup", Peers = ["n1", "n2", "n3"] },
+        };
+
+        meta.TrackInflightStreamProposal("ACC", sa);
+        meta.TrackInflightStreamProposal("ACC", sa);
+        meta.InflightStreamCount.ShouldBe(1); // still one unique stream
+
+        // Need two removes to fully clear
+        meta.RemoveInflightStreamProposal("ACC", "dup-stream");
+        meta.IsStreamInflight("ACC", "dup-stream").ShouldBeTrue(); // ops > 0
+        meta.RemoveInflightStreamProposal("ACC", "dup-stream");
+        meta.IsStreamInflight("ACC", "dup-stream").ShouldBeFalse();
+    }
+
+    [Fact]
+    public void IsStreamInflight_returns_false_for_unknown_account()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        meta.IsStreamInflight("UNKNOWN", "no-stream").ShouldBeFalse();
+    }
+
+    [Fact]
+    public void TrackInflightConsumerProposal_tracks_by_account()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        meta.TrackInflightConsumerProposal("ACC", "stream1", "consumer1");
+
+        meta.InflightConsumerCount.ShouldBe(1);
+        meta.IsConsumerInflight("ACC", "stream1", "consumer1").ShouldBeTrue();
+    }
+
+    [Fact]
+    public void RemoveInflightConsumerProposal_clears_when_zero()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        meta.TrackInflightConsumerProposal("ACC", "stream1", "consumer1");
+        meta.RemoveInflightConsumerProposal("ACC", "stream1", "consumer1");
+
+        meta.IsConsumerInflight("ACC", "stream1", "consumer1").ShouldBeFalse();
+    }
+
+    [Fact]
+    public void ClearAllInflight_removes_everything()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        var sa = new StreamAssignment
+        {
+            StreamName = "s1",
+            Group = new RaftGroup { Name = "rg", Peers = ["n1", "n2", "n3"] },
+        };
+
+        meta.TrackInflightStreamProposal("ACC1", sa);
+        meta.TrackInflightConsumerProposal("ACC2", "s2", "c1");
+
+        meta.ClearAllInflight();
+
+        meta.InflightStreamCount.ShouldBe(0);
+        meta.InflightConsumerCount.ShouldBe(0);
+    }
+
+    [Fact]
+    public void StepDown_clears_inflight()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        var sa = new StreamAssignment
+        {
+            StreamName = "s1",
+            Group = new RaftGroup { Name = "rg", Peers = ["n1", "n2", "n3"] },
+        };
+
+        meta.TrackInflightStreamProposal("ACC", sa);
+        meta.StepDown();
+
+        meta.InflightStreamCount.ShouldBe(0);
+    }
+
+    [Fact]
+    public void Multiple_accounts_tracked_independently()
+    {
+        var meta = new JetStreamMetaGroup(3);
+        var sa1 = new StreamAssignment
+        {
+            StreamName = "s1",
+            Group = new RaftGroup { Name = "rg1", Peers = ["n1", "n2", "n3"] },
+        };
+        var sa2 = new StreamAssignment
+        {
+            StreamName = "s1", // same stream name, different account
+            Group = new RaftGroup { Name = "rg2", Peers = ["n1", "n2", "n3"] },
+        };
+
+        meta.TrackInflightStreamProposal("ACC1", sa1);
+        meta.TrackInflightStreamProposal("ACC2", sa2);
+
+        meta.InflightStreamCount.ShouldBe(2); // one per account
+        meta.IsStreamInflight("ACC1", "s1").ShouldBeTrue();
+        meta.IsStreamInflight("ACC2", "s1").ShouldBeTrue();
+
+        meta.RemoveInflightStreamProposal("ACC1", "s1");
+        meta.IsStreamInflight("ACC1", "s1").ShouldBeFalse();
+        meta.IsStreamInflight("ACC2", "s1").ShouldBeTrue(); // still tracked
+    }
+}