fix(categories): correct all 7 smart-folder bugs at source (PHASE 2) (#38)

src/InboxIntel.Infrastructure/Sync/SyncService.cs

@@ -228,9 +228,34 @@ public class SyncService : ISyncService
         await _db.SaveChangesAsync(ct);
     }
 
-    /// <summary>Resolves domain/sender/thread, then inserts the email and attachment metadata.</summary>
+    // Per-sync-run cache of the user's GmailLabelId -> local Label.Id, so email/label linkage
+    // costs no extra query per message. Populated lazily; labels are synced before messages.
+    private Dictionary<string, Guid>? _labelCache;
+    private Guid _labelCacheUserId;
+
+    private async Task<Dictionary<string, Guid>> GetLabelMapAsync(Guid userId, CancellationToken ct)
+    {
+        if (_labelCache is null || _labelCacheUserId != userId)
+        {
+            _labelCache = await _db.Labels
+                .Where(l => l.UserId == userId)
+                .ToDictionaryAsync(l => l.GmailLabelId, l => l.Id, ct);
+            _labelCacheUserId = userId;
+        }
+        return _labelCache;
+    }
+
+    /// <summary>Resolves domain/sender/thread, then upserts the email, its labels, and
+    /// attachment metadata. Idempotent: re-syncing a message replaces the prior row (and its
+    /// labels) rather than duplicating it.</summary>
     private async Task UpsertMessageAsync(Guid userId, GmailMessageDetail d, CancellationToken ct)
     {
+        // True upsert: drop any existing copy first so labels/flags re-populate cleanly and
+        // an incrementally-changed message can't be duplicated. EmailLabels/Attachments cascade.
+        var prior = await _db.Emails.FirstOrDefaultAsync(
+            e => e.UserId == userId && e.GmailMessageId == d.GmailMessageId, ct);
+        if (prior is not null) _db.Emails.Remove(prior);
+
         var sender = await ResolveSenderAsync(userId, d.FromAddress, d.FromDisplayName, ct);
         var thread = await ResolveThreadAsync(userId, d.GmailThreadId, d.Subject, d.Snippet, d.SentAtUtc, ct);
 
@@ -256,6 +281,7 @@ public class SyncService : ISyncService
             IsInInbox = d.LabelIds.Contains("INBOX"),
             IsStarred = d.LabelIds.Contains("STARRED"),
             IsImportant = d.LabelIds.Contains("IMPORTANT"),
+            IsTrashed = d.LabelIds.Contains("TRASH"),
             HasAttachments = d.HasAttachments,
             HasListUnsubscribe = d.HasListUnsubscribe,
             ListUnsubscribeRaw = Trunc(d.ListUnsubscribeRaw, 2048),
@@ -264,6 +290,14 @@ public class SyncService : ISyncService
         };
         _db.Emails.Add(email);
 
+        // Link the email to its Gmail labels (system + user) so label-based folders — Sent,
+        // Spam, and "Unlabelled" (no user label) — resolve correctly. Previously no EmailLabel
+        // rows were ever created, so every label folder was empty and every email looked unlabelled.
+        var labelMap = await GetLabelMapAsync(userId, ct);
+        foreach (var gmailLabelId in d.LabelIds.Distinct())
+            if (labelMap.TryGetValue(gmailLabelId, out var localLabelId))
+                _db.Set<EmailLabel>().Add(new EmailLabel { EmailId = email.Id, LabelId = localLabelId });
+
         foreach (var (fileName, mime, size, attId) in d.Attachments)
         {
             _db.Attachments.Add(new Attachment