refactor(imap): remove connection pool, revert to per-call Imap, add batch flags fetch

- ImapConnectionPool removed (over-engineered; IMAP server allows multiple concurrent connections)
- LimilabsImapEmailService reverted to stateless per-call new Imap() pattern (same as original)
- GetFlagsByUIDAsync(List<long>) replaces per-message GetFlagsByUID — one round-trip for all flags
- markAsSeen wired through: GetMessageByUIDAsync (true) vs PeekMessageByUIDAsync (false)
- DependencyInjection: pool registration removed, service registered directly as before

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -27,6 +27,7 @@ public static class DependencyInjection
         services.AddSingleton<IEmailService, LimilabsEmailService>();
 
         // Email Service - IMAP inbound (Limilabs Mail.dll)
+        // Fresh connection per call — stateless and thread-safe.
         services.AddSingleton<IImapEmailService, LimilabsImapEmailService>();
         
         // PDF Processing Service (using DevExpress.Pdf)

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/LimilabsImapEmailService.cs

@@ -12,7 +12,7 @@ namespace DigitalData.MessagingService.Infrastructure.Services;
 
 /// <summary>
 /// IMAP email service using Limilabs Mail.dll.
-/// Opens a fresh connection per call — stateless and thread-safe.
+/// Opens a fresh connection per call — stateless and thread-safe.
 /// </summary>
 public class LimilabsImapEmailService(
     IEncryptionService encryptionService,
@@ -27,6 +27,7 @@ public class LimilabsImapEmailService(
     public async Task<IEnumerable<ReceivedEmailContext>> FetchEmailsAsync(
         EmailAccountDto account,
         MailSearchFilter filter,
+        bool markAsSeen = true,
         CancellationToken cancellationToken = default)
     {
         using var imap = new Imap();
@@ -55,12 +56,9 @@ public class LimilabsImapEmailService(
             if (filter.Uid is UidFilter uidF)
             {
                 if (uidF.Absolute is long exactUid)
-                {
                     criterions.Add(Expression.UID(new Limilabs.Client.IMAP.Range(exactUid, exactUid)));
-                }
                 else
                 {
-                    // Open-ended ranges: fall back to 1 / null when one side is omitted
                     long lo = uidF.Min ?? 1L;
                     long? hi = uidF.Max;
                     criterions.Add(Expression.UID(new Limilabs.Client.IMAP.Range(lo, hi)));
@@ -77,17 +75,26 @@ public class LimilabsImapEmailService(
                     criterions.Add(Expression.SentBefore(before.Date.AddDays(1)));
             }
 
-            // Get UIDs to fetch
             var searchExpression = criterions.Count > 0 ? Expression.And([.. criterions]) : Expression.All();
             List<long> uids = [.. await imap.SearchAsync(searchExpression, cancellationToken)];
 
-            // Apply requested sort order
             if (filter.SortOrder == MailSortOrder.NewestFirst)
                 uids.Reverse();
 
             if (filter.MaxCount > 0 && uids.Count > filter.MaxCount)
                 uids = [.. uids.Take(filter.MaxCount)];
 
+            if (uids.Count == 0)
+                return [];
+
+            // Fetch flags for all UIDs in one round-trip
+            var allFlags = await imap.GetFlagsByUIDAsync(uids, cancellationToken);
+            var flagsById = allFlags
+                .Where(f => f.UID.HasValue)
+                .ToDictionary(f => f.UID!.Value, f => f.Flags);
+
+            // markAsSeen=true  → BODY[]      (server sets \Seen automatically)
+            // markAsSeen=false → BODY.PEEK[] (\Seen untouched, non-destructive read)
             var results = new List<ReceivedEmailContext>(uids.Count);
 
             foreach (var uid in uids)
@@ -96,15 +103,18 @@ public class LimilabsImapEmailService(
 
                 try
                 {
-                    var eml   = await imap.PeekMessageByUIDAsync(uid, cancellationToken);
+                    var eml = markAsSeen
-                    var mail  = new MailBuilder().CreateFromEml(eml);
+                        ? await imap.GetMessageByUIDAsync(uid, cancellationToken)
-                    var flags = await imap.GetFlagsByUIDAsync(uid, cancellationToken);
+                        : await imap.PeekMessageByUIDAsync(uid, cancellationToken);
-
+                    var mail = new MailBuilder().CreateFromEml(eml);
+                    flagsById.TryGetValue(uid, out var flags);
                     results.Add(MapToContext(uid, mail, flags, filter.WithAttachments));
                 }
                 catch (Exception ex)
                 {
-                    logger.LogWarning(ex, "Failed to fetch IMAP message UID={Uid} from folder {Folder}. Skipping.", uid, filter.Folder);
+                    logger.LogWarning(ex,
+                        "Failed to fetch IMAP message UID={Uid} from folder {Folder}. Skipping.",
+                        uid, filter.Folder);
                 }
             }
 
@@ -205,6 +215,7 @@ public class LimilabsImapEmailService(
         long uid,
         string folder = "INBOX",
         bool withAttachments = false,
+        bool markAsSeen = true,
         CancellationToken cancellationToken = default)
     {
         using var imap = new Imap();
@@ -213,7 +224,9 @@ public class LimilabsImapEmailService(
             await ConnectAndAuthenticateAsync(imap, account);
             await SelectFolderAsync(imap, folder);
 
-            var eml   = await imap.PeekMessageByUIDAsync(uid, cancellationToken);
+            var eml = markAsSeen
+                ? await imap.GetMessageByUIDAsync(uid, cancellationToken)
+                : await imap.PeekMessageByUIDAsync(uid, cancellationToken);
             var mail  = new MailBuilder().CreateFromEml(eml);
             var flags = await imap.GetFlagsByUIDAsync(uid, cancellationToken);
 
@@ -285,7 +298,7 @@ public class LimilabsImapEmailService(
             await imap.SelectAsync(folder);
     }
 
-    private static ReceivedEmailContext MapToContext(long uid, IMail mail, List<Flag> flags, bool withAttachments = false)
+    private static ReceivedEmailContext MapToContext(long uid, IMail mail, List<Flag>? flags, bool withAttachments = false)
     {
         var attachments = new List<EmailAttachmentContext>();