diff --git a/src/NATS.Server/JetStream/Storage/FileStore.cs b/src/NATS.Server/JetStream/Storage/FileStore.cs
index 373bc9d..c1170ea 100644
--- a/src/NATS.Server/JetStream/Storage/FileStore.cs
+++ b/src/NATS.Server/JetStream/Storage/FileStore.cs
@@ -25,11 +25,23 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 {
     private readonly FileStoreOptions _options;
 
-    // In-memory cache: keyed by sequence number. This is the primary data structure
-    // for reads and queries. The blocks are the on-disk persistence layer.
-    private readonly Dictionary<ulong, StoredMessage> _messages = new();
-    // _messageIndexes removed — all lookups now use _messages directly to avoid
-    // per-message StoredMessageIndex allocation on the write path.
+    // Lightweight metadata index: keyed by sequence number. Stores only the fields
+    // needed for existence checks, subject queries, and timestamp lookups.
+    // Full message payloads are materialized on demand from blocks via MaterializeMessage.
+    private readonly Dictionary<ulong, MessageMeta> _meta = new();
+
+    /// <summary>
+    /// Lightweight per-message metadata stored in the in-memory index.
+    /// Eliminates the ~200B StoredMessage allocation on the write path.
+    /// </summary>
+    private struct MessageMeta
+    {
+        public int BlockId;
+        public string Subject;
+        public int PayloadLength;
+        public int HeaderLength;
+        public long TimestampNs;
+    }
     private readonly Dictionary<string, ulong> _lastSequenceBySubject = new(StringComparer.Ordinal);
 
     // Block-based storage: the active (writable) block and sealed blocks.
@@ -147,23 +159,14 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         // Go: writeMsgRecordLocked writes directly into mb.cache.buf (a single contiguous
         // byte slice). It does NOT store a per-message object in a map.
-        // We keep _messages for LoadAsync/RemoveAsync but avoid double payload.ToArray().
+        // We store lightweight MessageMeta instead of full StoredMessage to avoid ~200B alloc.
         var persistedPayload = TransformForPersist(payload.Span);
-        var storedPayload = _noTransform ? persistedPayload : payload.ToArray();
-        TrackMessage(new StoredMessage
-        {
-            Sequence = _last,
-            Subject = subject,
-            Payload = storedPayload,
-            TimestampUtc = now,
-        });
-        _generation++;
 
         // Go: register TTL only when TTL > 0.
         if (_options.MaxAgeMs > 0)
             RegisterTtl(_last, timestamp, (long)_options.MaxAgeMs * 1_000_000L);
 
-        // Write to MsgBlock.
+        // Write to MsgBlock first so we know the block ID for the meta entry.
         EnsureActiveBlock();
         try
         {
@@ -175,6 +178,10 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             _activeBlock!.WriteAt(_last, subject, ReadOnlyMemory<byte>.Empty, persistedPayload, timestamp);
         }
 
+        // Track lightweight metadata now that we know the block ID.
+        TrackMessage(_last, subject, 0, payload.Length, timestamp, _activeBlock!.BlockId);
+        _generation++;
+
         _writeCache.TrackWrite(_activeBlock!.BlockId, persistedPayload.Length);
         _flushSignal.Writer.TryWrite(0);
 
@@ -193,16 +200,15 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
     public ValueTask<StoredMessage?> LoadAsync(ulong sequence, CancellationToken ct)
     {
-        _messages.TryGetValue(sequence, out var msg);
-        return ValueTask.FromResult(msg);
+        return ValueTask.FromResult(MaterializeMessage(sequence));
     }
 
     public ValueTask<StoredMessage?> LoadLastBySubjectAsync(string subject, CancellationToken ct)
     {
-        if (_lastSequenceBySubject.TryGetValue(subject, out var sequence)
-            && _messages.TryGetValue(sequence, out var match))
+        if (_lastSequenceBySubject.TryGetValue(subject, out var sequence))
         {
-            return ValueTask.FromResult<StoredMessage?>(match);
+            var msg = MaterializeMessage(sequence);
+            return ValueTask.FromResult(msg);
         }
 
         return ValueTask.FromResult<StoredMessage?>(null);
@@ -210,8 +216,11 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
     public ValueTask<IReadOnlyList<StoredMessage>> ListAsync(CancellationToken ct)
     {
-        var messages = _messages.Values
-            .OrderBy(m => m.Sequence)
+        var messages = _meta.Keys
+            .OrderBy(seq => seq)
+            .Select(seq => MaterializeMessage(seq))
+            .Where(m => m is not null)
+            .Cast<StoredMessage>()
             .ToArray();
         return ValueTask.FromResult<IReadOnlyList<StoredMessage>>(messages);
     }
@@ -231,7 +240,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
     public ValueTask PurgeAsync(CancellationToken ct)
     {
-        _messages.Clear();
+        _meta.Clear();
         _generation++;
         _last = 0;
         _messageCount = 0;
@@ -255,24 +264,29 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
     public ValueTask<byte[]> CreateSnapshotAsync(CancellationToken ct)
     {
-        var snapshot = _messages
-            .Values
-            .OrderBy(x => x.Sequence)
-            .Select(x => new FileRecord
+        var snapshot = _meta.Keys
+            .OrderBy(seq => seq)
+            .Select(seq =>
             {
-                Sequence = x.Sequence,
-                Subject = x.Subject,
-                HeadersBase64 = x.RawHeaders.IsEmpty ? null : Convert.ToBase64String(x.RawHeaders.Span),
-                PayloadBase64 = Convert.ToBase64String(TransformForPersist(x.Payload.Span)),
-                TimestampUtc = x.TimestampUtc,
+                var msg = MaterializeMessage(seq);
+                if (msg is null) return null;
+                return new FileRecord
+                {
+                    Sequence = msg.Sequence,
+                    Subject = msg.Subject,
+                    HeadersBase64 = msg.RawHeaders.IsEmpty ? null : Convert.ToBase64String(msg.RawHeaders.Span),
+                    PayloadBase64 = Convert.ToBase64String(TransformForPersist(msg.Payload.Span)),
+                    TimestampUtc = msg.TimestampUtc,
+                };
             })
+            .Where(r => r is not null)
             .ToArray();
         return ValueTask.FromResult(JsonSerializer.SerializeToUtf8Bytes(snapshot));
     }
 
     public ValueTask RestoreSnapshotAsync(ReadOnlyMemory<byte> snapshot, CancellationToken ct)
     {
-        _messages.Clear();
+        _meta.Clear();
         _lastSequenceBySubject.Clear();
         _last = 0;
         _messageCount = 0;
@@ -295,24 +309,30 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
                         ? ReadOnlyMemory<byte>.Empty
                         : Convert.FromBase64String(record.HeadersBase64);
                     var restoredPayload = RestorePayload(Convert.FromBase64String(record.PayloadBase64 ?? string.Empty));
-                    var message = new StoredMessage
-                    {
-                        Sequence = record.Sequence,
-                        Subject = record.Subject ?? string.Empty,
-                        RawHeaders = restoredHeaders,
-                        Payload = restoredPayload,
-                        TimestampUtc = record.TimestampUtc,
-                    };
-                    _messages[record.Sequence] = message;
+                    var persistedPayload = TransformForPersist(restoredPayload);
+                    var timestampNs = new DateTimeOffset(record.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
+                    var subject = record.Subject ?? string.Empty;
+
                     _last = Math.Max(_last, record.Sequence);
+
+                    EnsureActiveBlock();
+                    try
+                    {
+                        _activeBlock!.WriteAt(record.Sequence, subject, restoredHeaders, persistedPayload, timestampNs);
+                    }
+                    catch (InvalidOperationException)
+                    {
+                        RotateBlock();
+                        _activeBlock!.WriteAt(record.Sequence, subject, restoredHeaders, persistedPayload, timestampNs);
+                    }
+
+                    TrackMessage(record.Sequence, subject, restoredHeaders.Length, restoredPayload.Length, timestampNs, _activeBlock!.BlockId);
+
+                    if (_activeBlock!.IsSealed)
+                        RotateBlock();
                 }
             }
         }
-
-        RebuildIndexesFromMessages();
-
-        // Write all messages to fresh blocks.
-        RewriteBlocks();
         return ValueTask.CompletedTask;
     }
 
@@ -330,7 +350,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     public void TrimToMaxMessages(ulong maxMessages)
     {
         var trimmed = false;
-        while ((ulong)_messages.Count > maxMessages)
+        while ((ulong)_meta.Count > maxMessages)
         {
             var first = _firstSeq;
             if (first == 0 || !RemoveTrackedMessage(first, preserveHighWaterMark: true))
@@ -375,15 +395,6 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         var headers = hdr is { Length: > 0 } ? hdr : [];
         var payload = msg ?? [];
         var persistedPayload = TransformForPersist(payload);
-        TrackMessage(new StoredMessage
-        {
-            Sequence = _last,
-            Subject = subject,
-            RawHeaders = headers,
-            Payload = payload,
-            TimestampUtc = now,
-        });
-        _generation++;
 
         // Determine effective TTL: per-message ttl (ns) takes priority over MaxAgeMs.
         // Go: filestore.go:6830 — if msg.ttl > 0 use it, else use cfg.MaxAge.
@@ -401,6 +412,9 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             _activeBlock!.WriteAt(_last, subject, headers, persistedPayload, timestamp);
         }
 
+        TrackMessage(_last, subject, headers.Length, payload.Length, timestamp, _activeBlock!.BlockId);
+        _generation++;
+
         // Go: filestore.go:4443 (setupWriteCache) — record write in bounded cache manager.
         _writeCache.TrackWrite(_activeBlock!.BlockId, headers.Length + persistedPayload.Length);
 
@@ -419,8 +433,8 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// </summary>
     public ulong Purge()
     {
-        var count = (ulong)_messages.Count;
-        _messages.Clear();
+        var count = (ulong)_meta.Count;
+        _meta.Clear();
         _lastSequenceBySubject.Clear();
         _generation++;
         _last = 0;
@@ -457,10 +471,10 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         ulong candidateCount = 0;
         for (var current = _messageCount == 0 ? 0UL : _first; current != 0 && current <= upperBound; current++)
         {
-            if (!_messages.TryGetValue(current, out var message))
+            if (!_meta.TryGetValue(current, out var meta))
                 continue;
 
-            if (!SubjectMatchesFilter(message.Subject, subject))
+            if (!SubjectMatchesFilter(meta.Subject, subject))
                 continue;
 
             candidateCount++;
@@ -479,10 +493,10 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         ulong removed = 0;
         for (var current = _messageCount == 0 ? 0UL : _first; current != 0 && current <= upperBound && removed < targetRemoveCount; current++)
         {
-            if (!_messages.TryGetValue(current, out var message))
+            if (!_meta.TryGetValue(current, out var meta2))
                 continue;
 
-            if (!SubjectMatchesFilter(message.Subject, subject))
+            if (!SubjectMatchesFilter(meta2.Subject, subject))
                 continue;
 
             if (RemoveTrackedMessage(current, preserveHighWaterMark: true))
@@ -509,7 +523,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         if (seq == 0)
             return 0;
 
-        var toRemove = _messages.Keys.Where(k => k < seq).ToArray();
+        var toRemove = _meta.Keys.Where(k => k < seq).ToArray();
         if (toRemove.Length == 0)
             return 0;
 
@@ -521,7 +535,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         _generation++;
 
-        if (_messages.Count == 0)
+        if (_meta.Count == 0)
         {
             // Go: preserve _last (monotonically increasing), advance _first to seq.
             // Compact(seq) removes everything < seq; the new first is seq.
@@ -546,7 +560,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         if (seq == 0)
         {
             // Truncate to nothing.
-            _messages.Clear();
+            _meta.Clear();
             _lastSequenceBySubject.Clear();
             _generation++;
             _last = 0;
@@ -559,7 +573,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             return;
         }
 
-        var toRemove = _messages.Keys.Where(k => k > seq).ToArray();
+        var toRemove = _meta.Keys.Where(k => k > seq).ToArray();
         foreach (var s in toRemove)
         {
             RemoveTrackedMessage(s, preserveHighWaterMark: false);
@@ -587,12 +601,18 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     public ulong GetSeqFromTime(DateTime t)
     {
         var utc = t.Kind == DateTimeKind.Utc ? t : t.ToUniversalTime();
-        var match = _messages.Values
-            .Where(m => m.TimestampUtc >= utc)
-            .OrderBy(m => m.Sequence)
-            .FirstOrDefault();
+        var targetNs = new DateTimeOffset(utc).ToUnixTimeMilliseconds() * 1_000_000L;
+        ulong? matchSeq = null;
+        foreach (var kv in _meta)
+        {
+            if (kv.Value.TimestampNs >= targetNs)
+            {
+                if (matchSeq is null || kv.Key < matchSeq.Value)
+                    matchSeq = kv.Key;
+            }
+        }
 
-        return match?.Sequence ?? _last + 1;
+        return matchSeq ?? _last + 1;
     }
 
     /// <summary>
@@ -601,7 +621,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     ///
     /// Optimized: uses block-range binary search to skip blocks whose sequence
     /// range is entirely below <paramref name="seq"/>. For each candidate block,
-    /// messages already cached in <c>_messages</c> are filtered directly.
+    /// messages already cached in <c>_meta</c> are filtered directly.
     /// Reference: golang/nats-server/server/filestore.go:3191 (FilteredState).
     /// </summary>
     public SimpleState FilteredState(ulong seq, string subject)
@@ -614,12 +634,12 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         ulong first = 0;
         ulong last = 0;
 
-        // Collect candidates from _messages that fall in the block range.
-        // _messages is the authoritative in-memory store; blocks are on-disk backing.
-        // We iterate _messages sorted by key and filter by sequence + subject.
-        // The binary block search only tells us where to START looking; the _messages
+        // Collect candidates from _meta that fall in the block range.
+        // _meta is the authoritative in-memory index; blocks are on-disk backing.
+        // We iterate _meta sorted by key and filter by sequence + subject.
+        // The binary block search only tells us where to START looking; the _meta
         // dictionary still covers all live messages, so we filter it directly.
-        foreach (var kv in _messages)
+        foreach (var kv in _meta)
         {
             var msgSeq = kv.Key;
             if (msgSeq < seq)
@@ -705,27 +725,29 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     {
         var result = new Dictionary<string, SimpleState>(StringComparer.Ordinal);
 
-        foreach (var msg in _messages.Values)
+        foreach (var kv in _meta)
         {
-            if (!string.IsNullOrEmpty(filterSubject) && !SubjectMatchesFilter(msg.Subject, filterSubject))
+            var seq = kv.Key;
+            var meta = kv.Value;
+            if (!string.IsNullOrEmpty(filterSubject) && !SubjectMatchesFilter(meta.Subject, filterSubject))
                 continue;
 
-            if (result.TryGetValue(msg.Subject, out var existing))
+            if (result.TryGetValue(meta.Subject, out var existing))
             {
-                result[msg.Subject] = new SimpleState
+                result[meta.Subject] = new SimpleState
                 {
                     Msgs = existing.Msgs + 1,
-                    First = Math.Min(existing.First == 0 ? msg.Sequence : existing.First, msg.Sequence),
-                    Last = Math.Max(existing.Last, msg.Sequence),
+                    First = Math.Min(existing.First == 0 ? seq : existing.First, seq),
+                    Last = Math.Max(existing.Last, seq),
                 };
             }
             else
             {
-                result[msg.Subject] = new SimpleState
+                result[meta.Subject] = new SimpleState
                 {
                     Msgs = 1,
-                    First = msg.Sequence,
-                    Last = msg.Sequence,
+                    First = seq,
+                    Last = seq,
                 };
             }
         }
@@ -742,13 +764,13 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     {
         var result = new Dictionary<string, ulong>(StringComparer.Ordinal);
 
-        foreach (var msg in _messages.Values)
+        foreach (var meta in _meta.Values)
         {
-            if (!string.IsNullOrEmpty(filterSubject) && !SubjectMatchesFilter(msg.Subject, filterSubject))
+            if (!string.IsNullOrEmpty(filterSubject) && !SubjectMatchesFilter(meta.Subject, filterSubject))
                 continue;
 
-            result.TryGetValue(msg.Subject, out var count);
-            result[msg.Subject] = count + 1;
+            result.TryGetValue(meta.Subject, out var count);
+            result[meta.Subject] = count + 1;
         }
 
         return result;
@@ -764,13 +786,13 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         FastState(ref state);
 
         // Populate deleted sequences: sequences in [firstSeq, lastSeq] that are
-        // not present in _messages.
+        // not present in _meta.
         if (state.FirstSeq > 0 && state.LastSeq >= state.FirstSeq)
         {
             var deletedList = new List<ulong>();
             for (var s = state.FirstSeq; s <= state.LastSeq; s++)
             {
-                if (!_messages.ContainsKey(s))
+                if (!_meta.ContainsKey(s))
                     deletedList.Add(s);
             }
 
@@ -783,10 +805,10 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         // Populate per-subject counts.
         var subjectCounts = new Dictionary<string, ulong>(StringComparer.Ordinal);
-        foreach (var msg in _messages.Values)
+        foreach (var meta in _meta.Values)
         {
-            subjectCounts.TryGetValue(msg.Subject, out var cnt);
-            subjectCounts[msg.Subject] = cnt + 1;
+            subjectCounts.TryGetValue(meta.Subject, out var cnt);
+            subjectCounts[meta.Subject] = cnt + 1;
         }
         state.NumSubjects = subjectCounts.Count;
         state.Subjects = subjectCounts.Count > 0 ? subjectCounts : null;
@@ -820,25 +842,28 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         {
             var firstSeq = _firstSeq;
             state.FirstSeq = firstSeq;
-            state.FirstTime = _messages.TryGetValue(firstSeq, out var firstMsg) ? firstMsg.TimestampUtc : default;
+            state.FirstTime = _meta.TryGetValue(firstSeq, out var firstMeta)
+                ? DateTimeOffset.FromUnixTimeMilliseconds(firstMeta.TimestampNs / 1_000_000).UtcDateTime
+                : default;
 
             // Go parity: LastTime from the actual last stored message (not _last,
             // which may be a skip/tombstone sequence with no corresponding message).
-            if (_messages.TryGetValue(_last, out var lastMsg))
-                state.LastTime = lastMsg.TimestampUtc;
-            else if (_messages.Count > 0)
+            if (_meta.TryGetValue(_last, out var lastMeta))
+                state.LastTime = DateTimeOffset.FromUnixTimeMilliseconds(lastMeta.TimestampNs / 1_000_000).UtcDateTime;
+            else if (_meta.Count > 0)
             {
                 // _last is a skip — use the highest actual message time.
-                var actualLast = _messages.Keys.Max();
-                state.LastTime = _messages[actualLast].TimestampUtc;
+                var actualLast = _meta.Keys.Max();
+                var actualMeta = _meta[actualLast];
+                state.LastTime = DateTimeOffset.FromUnixTimeMilliseconds(actualMeta.TimestampNs / 1_000_000).UtcDateTime;
             }
 
-            // Go parity: NumDeleted = gaps between firstSeq and lastSeq not in _messages.
+            // Go parity: NumDeleted = gaps between firstSeq and lastSeq not in _meta.
             // Reference: filestore.go — FastState sets state.NumDeleted.
             if (_last >= firstSeq)
             {
                 var span = _last - firstSeq + 1;
-                var liveCount = (ulong)_messages.Count;
+                var liveCount = (ulong)_meta.Count;
                 state.NumDeleted = span > liveCount ? (int)(span - liveCount) : 0;
             }
             else
@@ -846,27 +871,60 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         }
     }
 
-    private void TrackMessage(StoredMessage message)
+    /// <summary>
+    /// Materializes a full <see cref="StoredMessage"/> from block storage using
+    /// the lightweight metadata index. Returns null if the sequence is not found
+    /// in the metadata or the block cannot be read.
+    /// </summary>
+    private StoredMessage? MaterializeMessage(ulong seq)
     {
-        _messages[message.Sequence] = message;
-        _lastSequenceBySubject[message.Subject] = message.Sequence;
+        if (!_meta.TryGetValue(seq, out var meta))
+            return null;
+        // Look up the block by ID first (O(n) scan, but blocks list is small).
+        // Fall back to sequence-range binary search if the stored blockId is stale.
+        var block = _blocks.Find(b => b.BlockId == meta.BlockId) ?? FindBlockForSequence(seq);
+        if (block is null) return null;
+        var record = block.Read(seq);
+        if (record is null) return null;
+        var payload = RestorePayload(record.Payload.Span);
+        return new StoredMessage
+        {
+            Sequence = seq,
+            Subject = meta.Subject,
+            RawHeaders = record.Headers,
+            Payload = payload,
+            TimestampUtc = DateTimeOffset.FromUnixTimeMilliseconds(meta.TimestampNs / 1_000_000).UtcDateTime,
+        };
+    }
+
+    private void TrackMessage(ulong sequence, string subject, int headerLength, int payloadLength, long timestampNs, int blockId)
+    {
+        _meta[sequence] = new MessageMeta
+        {
+            BlockId = blockId,
+            Subject = subject,
+            PayloadLength = payloadLength,
+            HeaderLength = headerLength,
+            TimestampNs = timestampNs,
+        };
+        _lastSequenceBySubject[subject] = sequence;
         _messageCount++;
-        _totalBytes += (ulong)(message.RawHeaders.Length + message.Payload.Length);
+        _totalBytes += (ulong)(headerLength + payloadLength);
 
         if (_messageCount == 1)
         {
-            _first = message.Sequence;
-            _firstSeq = message.Sequence;
+            _first = sequence;
+            _firstSeq = sequence;
         }
     }
 
     private bool RemoveTrackedMessage(ulong sequence, bool preserveHighWaterMark)
     {
-        if (!_messages.Remove(sequence, out var message))
+        if (!_meta.Remove(sequence, out var meta))
             return false;
         _messageCount--;
-        _totalBytes -= (ulong)(message.RawHeaders.Length + message.Payload.Length);
-        UpdateLastSequenceForSubject(message.Subject, sequence);
+        _totalBytes -= (ulong)(meta.HeaderLength + meta.PayloadLength);
+        UpdateLastSequenceForSubject(meta.Subject, sequence);
 
         if (_messageCount == 0)
         {
@@ -891,7 +949,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     private void AdvanceFirstSequence(ulong start)
     {
         var candidate = start;
-        while (!_messages.ContainsKey(candidate) && candidate <= _last)
+        while (!_meta.ContainsKey(candidate) && candidate <= _last)
             candidate++;
 
         if (candidate <= _last)
@@ -912,7 +970,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         for (var seq = startExclusive - 1; ; seq--)
         {
-            if (_messages.ContainsKey(seq))
+            if (_meta.ContainsKey(seq))
                 return seq;
 
             if (seq == 0)
@@ -927,7 +985,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         for (var seq = removedSequence - 1; ; seq--)
         {
-            if (_messages.TryGetValue(seq, out var candidate) && string.Equals(candidate.Subject, subject, StringComparison.Ordinal))
+            if (_meta.TryGetValue(seq, out var candidate) && string.Equals(candidate.Subject, subject, StringComparison.Ordinal))
             {
                 _lastSequenceBySubject[subject] = seq;
                 return;
@@ -948,8 +1006,21 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         _firstSeq = 0;
         _first = 0;
 
-        foreach (var message in _messages.OrderBy(kv => kv.Key).Select(kv => kv.Value))
-            TrackMessage(message);
+        // Re-derive counters from the existing _meta entries without re-inserting.
+        foreach (var kv in _meta.OrderBy(kv => kv.Key))
+        {
+            var seq = kv.Key;
+            var meta = kv.Value;
+            _lastSequenceBySubject[meta.Subject] = seq;
+            _messageCount++;
+            _totalBytes += (ulong)(meta.HeaderLength + meta.PayloadLength);
+
+            if (_messageCount == 1)
+            {
+                _first = seq;
+                _firstSeq = seq;
+            }
+        }
 
         if (_messageCount == 0 && _last > 0)
             _first = _last + 1;
@@ -991,9 +1062,9 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         // Cache miss: count matching messages and cache the result.
         ulong count = 0;
-        foreach (var msg in _messages.Values)
+        foreach (var meta in _meta.Values)
         {
-            if (SubjectMatchesFilter(msg.Subject, filter ?? string.Empty))
+            if (SubjectMatchesFilter(meta.Subject, filter ?? string.Empty))
                 count++;
         }
 
@@ -1142,13 +1213,21 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// </summary>
     private void RewriteBlocks()
     {
+        // Materialize all messages before disposing blocks (since materialization reads from blocks).
+        var messages = _meta.Keys
+            .OrderBy(seq => seq)
+            .Select(seq => MaterializeMessage(seq))
+            .Where(m => m is not null)
+            .Cast<StoredMessage>()
+            .ToList();
+
         DisposeAllBlocks();
         CleanBlockFiles();
 
-        _last = _messages.Count == 0 ? 0UL : _messages.Keys.Max();
-        RebuildIndexesFromMessages();
+        _meta.Clear();
+        _last = messages.Count == 0 ? 0UL : messages[^1].Sequence;
 
-        foreach (var message in _messages.OrderBy(kv => kv.Key).Select(kv => kv.Value))
+        foreach (var message in messages)
         {
             var persistedPayload = TransformForPersist(message.Payload.Span);
             var timestamp = new DateTimeOffset(message.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
@@ -1164,9 +1243,20 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
                 _activeBlock!.WriteAt(message.Sequence, message.Subject, message.RawHeaders, persistedPayload, timestamp);
             }
 
+            _meta[message.Sequence] = new MessageMeta
+            {
+                BlockId = _activeBlock!.BlockId,
+                Subject = message.Subject,
+                PayloadLength = message.Payload.Length,
+                HeaderLength = message.RawHeaders.Length,
+                TimestampNs = timestamp,
+            };
+
             if (_activeBlock!.IsSealed)
                 RotateBlock();
         }
+
+        RebuildIndexesFromMessages();
     }
 
     // -------------------------------------------------------------------------
@@ -1225,8 +1315,6 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             _activeBlock = lastBlock;
         }
 
-        PruneExpired(DateTime.UtcNow);
-
         // After recovery, sync _last from skip-sequence high-water marks.
         // SkipMsg/SkipMsgs write tombstone records with empty subject — these
         // intentionally advance _last without storing a live message. We must
@@ -1255,7 +1343,11 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             }
         }
 
-        // Sync _first from _messages; if empty, set to _last+1 (watermark).
+        // Prune expired messages AFTER establishing _last from blocks/skips.
+        // If all messages expire, PruneExpiredLinear resets _last to 0.
+        PruneExpired(DateTime.UtcNow);
+
+        // Sync _first from _meta; if empty, set to _last+1 (watermark).
         RebuildIndexesFromMessages();
     }
 
@@ -1278,30 +1370,27 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             if (record is null)
                 continue; // Deleted or not present.
 
-            // The payload stored in the block is the transformed (compressed/encrypted) payload.
-            // We need to reverse-transform it to get the original plaintext.
+            // Compute the original payload length for metadata tracking.
             // InvalidDataException (e.g., wrong key) propagates to the caller.
             var originalPayload = RestorePayload(record.Payload.Span);
 
-            var message = new StoredMessage
+            _meta[record.Sequence] = new MessageMeta
             {
-                Sequence = record.Sequence,
+                BlockId = block.BlockId,
                 Subject = record.Subject,
-                RawHeaders = record.Headers,
-                Payload = originalPayload,
-                TimestampUtc = DateTimeOffset.FromUnixTimeMilliseconds(record.Timestamp / 1_000_000L).UtcDateTime,
+                PayloadLength = originalPayload.Length,
+                HeaderLength = record.Headers.Length,
+                TimestampNs = record.Timestamp,
             };
 
-            _messages[message.Sequence] = message;
-            if (message.Sequence > _last)
-                _last = message.Sequence;
+            if (record.Sequence > _last)
+                _last = record.Sequence;
 
             // Go: re-register unexpired TTLs in the wheel after recovery.
             // Reference: golang/nats-server/server/filestore.go — recoverMsgs, TTL re-registration.
             if (_options.MaxAgeMs > 0)
             {
-                var msgTs = new DateTimeOffset(message.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
-                RegisterTtl(message.Sequence, msgTs, (long)_options.MaxAgeMs * 1_000_000L);
+                RegisterTtl(record.Sequence, record.Timestamp, (long)_options.MaxAgeMs * 1_000_000L);
             }
         }
     }
@@ -1366,22 +1455,40 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             return;
         }
 
-        // Add to the in-memory cache.
+        // Write all messages to fresh blocks, then populate _meta.
         foreach (var (seq, subject, payload, ts) in legacyMessages)
         {
-            _messages[seq] = new StoredMessage
-            {
-                Sequence = seq,
-                Subject = subject,
-                Payload = payload,
-                TimestampUtc = ts,
-            };
             if (seq > _last)
                 _last = seq;
+
+            var persistedPayload = TransformForPersist(payload);
+            var timestampNs = new DateTimeOffset(ts).ToUnixTimeMilliseconds() * 1_000_000L;
+
+            EnsureActiveBlock();
+            try
+            {
+                _activeBlock!.WriteAt(seq, subject, ReadOnlyMemory<byte>.Empty, persistedPayload, timestampNs);
+            }
+            catch (InvalidOperationException)
+            {
+                RotateBlock();
+                _activeBlock!.WriteAt(seq, subject, ReadOnlyMemory<byte>.Empty, persistedPayload, timestampNs);
+            }
+
+            _meta[seq] = new MessageMeta
+            {
+                BlockId = _activeBlock!.BlockId,
+                Subject = subject,
+                PayloadLength = payload.Length,
+                HeaderLength = 0,
+                TimestampNs = timestampNs,
+            };
+
+            if (_activeBlock!.IsSealed)
+                RotateBlock();
         }
 
-        // Write all messages to fresh blocks.
-        RewriteBlocks();
+        RebuildIndexesFromMessages();
 
         // Delete the legacy files.
         File.Delete(jsonlPath);
@@ -1467,9 +1574,9 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         if (_options.MaxAgeMs <= 0)
             return;
 
-        var cutoff = nowUtc.AddMilliseconds(-_options.MaxAgeMs);
-        var expired = _messages
-            .Where(kv => kv.Value.TimestampUtc < cutoff)
+        var cutoffNs = new DateTimeOffset(nowUtc.AddMilliseconds(-_options.MaxAgeMs)).ToUnixTimeMilliseconds() * 1_000_000L;
+        var expired = _meta
+            .Where(kv => kv.Value.TimestampNs < cutoffNs)
             .Select(kv => kv.Key)
             .ToArray();
 
@@ -1479,8 +1586,20 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         foreach (var sequence in expired)
         {
             RemoveTrackedMessage(sequence, preserveHighWaterMark: true);
+            DeleteInBlock(sequence);
         }
-        RewriteBlocks();
+
+        // When all messages are expired, reset sequence pointers to 0.
+        // This matches the previous RewriteBlocks behavior where an empty store
+        // resets _last to 0.
+        if (_meta.Count == 0)
+        {
+            _last = 0;
+            _first = 0;
+            _firstSeq = 0;
+        }
+
+        _generation++;
     }
 
     // Keep the old PruneExpired name as a convenience wrapper for recovery path.
@@ -1783,7 +1902,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         // When seq is 0, auto-assign next sequence.
         var skipSeq = seq == 0 ? _last + 1 : seq;
         _last = skipSeq;
-        // Do NOT add to _messages — it is a skip (tombstone).
+        // Do NOT add to _meta — it is a skip (tombstone).
         // We still need to write a record to the block so recovery
         // can reconstruct the sequence gap. Use an empty subject sentinel.
         EnsureActiveBlock();
@@ -1802,7 +1921,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
 
         // After a skip, if there are no real messages, the next real first
         // would be skipSeq+1. Track this so FastState reports correctly.
-        if (_messages.Count == 0)
+        if (_meta.Count == 0)
             _first = skipSeq + 1;
 
         return skipSeq;
@@ -1837,46 +1956,45 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// Loads a message by exact sequence number into the optional reusable container
     /// <paramref name="sm"/>. Throws <see cref="KeyNotFoundException"/> if not found.
     ///
-    /// Fast path: O(1) hash lookup in <c>_messages</c> (all live messages are cached).
+    /// Fast path: O(1) hash lookup in <c>_meta</c> (all live messages are cached).
     /// Fallback: binary-search <c>_blocks</c> by sequence range (O(log n) blocks) to
     /// locate the containing block, then read from disk. This covers cases where a
-    /// future memory-pressure eviction removes entries from <c>_messages</c>.
+    /// future memory-pressure eviction removes entries from <c>_meta</c>.
     /// Reference: golang/nats-server/server/filestore.go:8308 (LoadMsg).
     /// </summary>
     public StoreMsg LoadMsg(ulong seq, StoreMsg? sm)
     {
-        // Fast path: O(1) in-memory lookup.
-        if (_messages.TryGetValue(seq, out var stored))
+        var stored = MaterializeMessage(seq);
+        if (stored is null)
         {
+            // Fallback: binary-search blocks by sequence range (O(log n)).
+            // Handles cases where _meta does not contain the sequence.
+            var block = FindBlockForSequence(seq);
+            if (block is null)
+                throw new KeyNotFoundException($"Message sequence {seq} not found.");
+
+            var record = block.Read(seq);
+            if (record is null)
+                throw new KeyNotFoundException($"Message sequence {seq} not found.");
+
             sm ??= new StoreMsg();
             sm.Clear();
-            sm.Subject = stored.Subject;
-            sm.Header = stored.RawHeaders.Length > 0 ? stored.RawHeaders.ToArray() : null;
-            sm.Data = stored.Payload.Length > 0 ? stored.Payload.ToArray() : null;
-            sm.Sequence = stored.Sequence;
-            sm.Timestamp = new DateTimeOffset(stored.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
+            sm.Subject = record.Subject;
+            sm.Header = record.Headers.Length > 0 ? record.Headers.ToArray() : null;
+            var originalPayload = RestorePayload(record.Payload.Span);
+            sm.Data = originalPayload.Length > 0 ? originalPayload : null;
+            sm.Sequence = record.Sequence;
+            sm.Timestamp = record.Timestamp;
             return sm;
         }
 
-        // Fallback: binary-search blocks by sequence range (O(log n)).
-        // Handles cases where _messages does not contain the sequence, e.g. future
-        // memory-pressure eviction. FindBlockForSequence avoids an O(n) block scan.
-        var block = FindBlockForSequence(seq);
-        if (block is null)
-            throw new KeyNotFoundException($"Message sequence {seq} not found.");
-
-        var record = block.Read(seq);
-        if (record is null)
-            throw new KeyNotFoundException($"Message sequence {seq} not found.");
-
         sm ??= new StoreMsg();
         sm.Clear();
-        sm.Subject = record.Subject;
-        sm.Header = record.Headers.Length > 0 ? record.Headers.ToArray() : null;
-        var originalPayload = RestorePayload(record.Payload.Span);
-        sm.Data = originalPayload.Length > 0 ? originalPayload : null;
-        sm.Sequence = record.Sequence;
-        sm.Timestamp = record.Timestamp;
+        sm.Subject = stored.Subject;
+        sm.Header = stored.RawHeaders.Length > 0 ? stored.RawHeaders.ToArray() : null;
+        sm.Data = stored.Payload.Length > 0 ? stored.Payload.ToArray() : null;
+        sm.Sequence = stored.Sequence;
+        sm.Timestamp = new DateTimeOffset(stored.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
         return sm;
     }
 
@@ -1917,14 +2035,21 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// </summary>
     public StoreMsg LoadLastMsg(string subject, StoreMsg? sm)
     {
-        var match = _messages.Values
-            .Where(m => string.IsNullOrEmpty(subject)
-                        || SubjectMatchesFilter(m.Subject, subject))
-            .MaxBy(m => m.Sequence);
+        ulong? bestSeq = null;
+        foreach (var kv in _meta)
+        {
+            if (!string.IsNullOrEmpty(subject) && !SubjectMatchesFilter(kv.Value.Subject, subject))
+                continue;
+            if (bestSeq is null || kv.Key > bestSeq.Value)
+                bestSeq = kv.Key;
+        }
 
-        if (match is null)
+        if (bestSeq is null)
             throw new KeyNotFoundException($"No message found for subject '{subject}'.");
 
+        var match = MaterializeMessage(bestSeq.Value)
+            ?? throw new KeyNotFoundException($"No message found for subject '{subject}'.");
+
         sm ??= new StoreMsg();
         sm.Clear();
         sm.Subject = match.Subject;
@@ -1943,26 +2068,31 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// </summary>
     public (StoreMsg Msg, ulong Skip) LoadNextMsg(string filter, bool wc, ulong start, StoreMsg? sm)
     {
-        var match = _messages
-            .Where(kv => kv.Key >= start)
-            .Where(kv => string.IsNullOrEmpty(filter) || SubjectMatchesFilter(kv.Value.Subject, filter))
-            .OrderBy(kv => kv.Key)
-            .Cast<KeyValuePair<ulong, StoredMessage>?>()
-            .FirstOrDefault();
+        ulong? bestSeq = null;
+        foreach (var kv in _meta)
+        {
+            if (kv.Key < start) continue;
+            if (!string.IsNullOrEmpty(filter) && !SubjectMatchesFilter(kv.Value.Subject, filter))
+                continue;
+            if (bestSeq is null || kv.Key < bestSeq.Value)
+                bestSeq = kv.Key;
+        }
 
-        if (match is null)
+        if (bestSeq is null)
             throw new KeyNotFoundException($"No message found at or after seq {start} matching filter '{filter}'.");
 
-        var found = match.Value;
-        var skip = found.Key > start ? found.Key - start : 0UL;
+        var found = MaterializeMessage(bestSeq.Value)
+            ?? throw new KeyNotFoundException($"No message found at or after seq {start} matching filter '{filter}'.");
+
+        var skip = bestSeq.Value > start ? bestSeq.Value - start : 0UL;
 
         sm ??= new StoreMsg();
         sm.Clear();
-        sm.Subject = found.Value.Subject;
-        sm.Header = found.Value.RawHeaders.Length > 0 ? found.Value.RawHeaders.ToArray() : null;
-        sm.Data = found.Value.Payload.Length > 0 ? found.Value.Payload.ToArray() : null;
-        sm.Sequence = found.Key;
-        sm.Timestamp = new DateTimeOffset(found.Value.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
+        sm.Subject = found.Subject;
+        sm.Header = found.RawHeaders.Length > 0 ? found.RawHeaders.ToArray() : null;
+        sm.Data = found.Payload.Length > 0 ? found.Payload.ToArray() : null;
+        sm.Sequence = found.Sequence;
+        sm.Timestamp = new DateTimeOffset(found.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
         return (sm, skip);
     }
 
@@ -1974,7 +2104,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     public ulong[] AllLastSeqs()
     {
         var lastPerSubject = new Dictionary<string, ulong>(StringComparer.Ordinal);
-        foreach (var kv in _messages)
+        foreach (var kv in _meta)
         {
             var subj = kv.Value.Subject;
             if (!lastPerSubject.TryGetValue(subj, out var existing) || kv.Key > existing)
@@ -1996,7 +2126,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     {
         var lastPerSubject = new Dictionary<string, ulong>(StringComparer.Ordinal);
 
-        foreach (var kv in _messages)
+        foreach (var kv in _meta)
         {
             var seq = kv.Key;
             if (maxSeq > 0 && seq > maxSeq)
@@ -2027,9 +2157,9 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// </summary>
     public string SubjectForSeq(ulong seq)
     {
-        if (!_messages.TryGetValue(seq, out var stored))
+        if (!_meta.TryGetValue(seq, out var meta))
             throw new KeyNotFoundException($"Message sequence {seq} not found.");
-        return stored.Subject;
+        return meta.Subject;
     }
 
     /// <summary>
@@ -2041,7 +2171,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
     /// </summary>
     public (ulong Total, ulong ValidThrough) NumPending(ulong sseq, string filter, bool lastPerSubject)
     {
-        var candidates = _messages
+        var candidates = _meta
             .Where(kv => kv.Key >= sseq)
             .Where(kv => string.IsNullOrEmpty(filter) || SubjectMatchesFilter(kv.Value.Subject, filter))
             .ToList();
@@ -2087,22 +2217,6 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         var headers = hdr is { Length: > 0 } ? hdr : [];
         var payload = msg ?? [];
         var persistedPayload = TransformForPersist(payload);
-        // Recover UTC DateTime from caller-supplied Unix nanosecond timestamp.
-        var storedUtc = DateTimeOffset.FromUnixTimeMilliseconds(ts / 1_000_000L).UtcDateTime;
-
-        var stored = new StoredMessage
-        {
-            Sequence = seq,
-            Subject = subject,
-            RawHeaders = headers,
-            Payload = payload,
-            TimestampUtc = storedUtc,
-        };
-        TrackMessage(stored);
-        _generation++;
-
-        // Go: update _last to the high-water mark — do not decrement.
-        _last = Math.Max(_last, seq);
 
         // Register TTL using the caller-supplied timestamp and TTL.
         var effectiveTtlNs = ttl > 0 ? ttl : (_options.MaxAgeMs > 0 ? (long)_options.MaxAgeMs * 1_000_000L : 0L);
@@ -2119,6 +2233,12 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
             _activeBlock!.WriteAt(seq, subject, headers, persistedPayload, ts);
         }
 
+        TrackMessage(seq, subject, headers.Length, payload.Length, ts, _activeBlock!.BlockId);
+        _generation++;
+
+        // Go: update _last to the high-water mark — do not decrement.
+        _last = Math.Max(_last, seq);
+
         // Go: filestore.go:4443 (setupWriteCache) — record write in bounded cache manager.
         _writeCache.TrackWrite(_activeBlock!.BlockId, headers.Length + persistedPayload.Length);
 
@@ -2137,20 +2257,24 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         if (start == 0)
             throw new KeyNotFoundException("No message found before seq 0.");
 
-        var first = _messages.Count > 0 ? _messages.Keys.Min() : 1UL;
+        var first = _meta.Count > 0 ? _meta.Keys.Min() : 1UL;
 
         for (var seq = start - 1; seq >= first && seq <= _last; seq--)
         {
-            if (_messages.TryGetValue(seq, out var stored))
+            if (_meta.ContainsKey(seq))
             {
-                sm ??= new StoreMsg();
-                sm.Clear();
-                sm.Subject = stored.Subject;
-                sm.Header = stored.RawHeaders.Length > 0 ? stored.RawHeaders.ToArray() : null;
-                sm.Data = stored.Payload.Length > 0 ? stored.Payload.ToArray() : null;
-                sm.Sequence = stored.Sequence;
-                sm.Timestamp = new DateTimeOffset(stored.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
-                return sm;
+                var stored = MaterializeMessage(seq);
+                if (stored is not null)
+                {
+                    sm ??= new StoreMsg();
+                    sm.Clear();
+                    sm.Subject = stored.Subject;
+                    sm.Header = stored.RawHeaders.Length > 0 ? stored.RawHeaders.ToArray() : null;
+                    sm.Data = stored.Payload.Length > 0 ? stored.Payload.ToArray() : null;
+                    sm.Sequence = stored.Sequence;
+                    sm.Timestamp = new DateTimeOffset(stored.TimestampUtc).ToUnixTimeMilliseconds() * 1_000_000L;
+                    return sm;
+                }
             }
 
             // Prevent underflow on ulong subtraction.
@@ -2215,7 +2339,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         // Enforce per-subject limits immediately after config change.
         if (_options.MaxMsgsPerSubject > 0)
         {
-            var subjects = _messages.Values.Select(m => m.Subject).Distinct(StringComparer.Ordinal).ToList();
+            var subjects = _meta.Values.Select(m => m.Subject).Distinct(StringComparer.Ordinal).ToList();
             foreach (var subject in subjects)
                 EnforceMaxMsgsPerSubject(subject);
         }
@@ -2232,7 +2356,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         if (limit <= 0)
             return;
 
-        var subjectMsgs = _messages
+        var subjectMsgs = _meta
             .Where(kv => string.Equals(kv.Value.Subject, subject, StringComparison.Ordinal))
             .OrderBy(kv => kv.Key)
             .ToList();
@@ -2240,16 +2364,16 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable, IDisposable
         while (subjectMsgs.Count > limit)
         {
             var oldest = subjectMsgs[0];
-            _totalBytes -= (ulong)oldest.Value.Payload.Length;
+            _totalBytes -= (ulong)(oldest.Value.HeaderLength + oldest.Value.PayloadLength);
             _messageCount--;
-            _messages.Remove(oldest.Key);
+            _meta.Remove(oldest.Key);
             DeleteInBlock(oldest.Key);
             subjectMsgs.RemoveAt(0);
             _generation++;
         }
 
-        if (_messages.Count > 0)
-            _firstSeq = _messages.Keys.Min();
+        if (_meta.Count > 0)
+            _firstSeq = _meta.Keys.Min();
     }
 
     /// <summary>
diff --git a/src/NATS.Server/JetStream/Storage/MsgBlock.cs b/src/NATS.Server/JetStream/Storage/MsgBlock.cs
index 06361c0..ef30d7d 100644
--- a/src/NATS.Server/JetStream/Storage/MsgBlock.cs
+++ b/src/NATS.Server/JetStream/Storage/MsgBlock.cs
@@ -315,6 +315,10 @@ public sealed class MsgBlock : IDisposable
 
             _index[sequence] = (offset, written);
 
+            // If this sequence was previously soft-deleted, clear the deletion marker
+            // so that subsequent Read calls return the new record rather than null.
+            _deleted.Remove(sequence);
+
             // Go: cache populated lazily on read, not eagerly on write.
             // Reads that miss _cache flush pending buf to disk and decode from there.