fix(categories): correct all seven smart-folder bugs at the source (PHASE 2)

Root causes + fixes:
- Archive leaked Sent mail: filter was just 'not in inbox'. Added ExcludeGmailLabels;
  Archive now excludes SENT/DRAFT/SPAM/TRASH/CHAT by label.
- Read Later / Pinned / Unlabelled returned EVERYTHING (no folder case -> default all).
  Pinned = IsImportant; Read Later = new local IsReadLater marker (+toggle endpoints);
  Unlabelled = HasUserLabels=false.
- Trash & Spam always empty: IncludeSpamTrash=false + sync never set IsTrashed nor created
  EmailLabel rows. Now fetches spam/trash, sets IsTrashed from the TRASH label, and links
  every message to its Gmail labels (also fixes Sent/Spam/category-by-label/Unlabelled).
- Old Mail: now strictly older than 6 months (was 1 year).

Guardrail: sync upsert is now idempotent (drops prior copy before reinsert) so re-sync
can't duplicate a message or leave stale labels. 4 new filter tests; 65 backend + frontend
green; migration is a single non-destructive column add.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/InboxIntel.IntegrationTests/CategoryFilterTests.cs

@@ -0,0 +1,115 @@
+using FluentAssertions;
+using InboxIntel.Application.Abstractions;
+using InboxIntel.Application.DTOs;
+using InboxIntel.Domain.Entities;
+using InboxIntel.Infrastructure.Persistence;
+using InboxIntel.Infrastructure.Search;
+using Microsoft.EntityFrameworkCore;
+using Xunit;
+
+namespace InboxIntel.IntegrationTests;
+
+/// <summary>
+/// PHASE 2 (smart-category correctness): each reported folder bug — Archive leaking Sent,
+/// Read Later / Pinned / Unlabelled returning everything, Old Mail duration — is fixed at the
+/// filter source. These prove the SearchService filters that back the corrected folder mappings.
+/// </summary>
+public class CategoryFilterTests
+{
+    private sealed class FakeCurrentUser : ICurrentUser
+    {
+        public Guid UserId { get; set; }
+        public bool IsAuthenticated => UserId != Guid.Empty;
+    }
+
+    private static AppDbContext Db(string name, Guid uid) =>
+        new(new DbContextOptionsBuilder<AppDbContext>().UseInMemoryDatabase(name).Options,
+            new FakeCurrentUser { UserId = uid });
+
+    // A small fixture: an inbox email, a sent email (SENT label), one important, one read-later,
+    // and one filed under a user label.
+    private static async Task<Guid> SeedAsync(string name)
+    {
+        var uid = Guid.NewGuid();
+        using var db = Db(name, Guid.Empty);
+        var sender = new Sender { UserId = uid, Address = "s@x.x" };
+        db.Senders.Add(sender);
+        var sentLabel = new Label { UserId = uid, GmailLabelId = "SENT", Name = "Sent", Type = "system" };
+        var userLabel = new Label { UserId = uid, GmailLabelId = "Label_1", Name = "Projects", Type = "user" };
+        db.Labels.AddRange(sentLabel, userLabel);
+
+        Email E(string id, Action<Email> cfg)
+        {
+            var e = new Email { UserId = uid, GmailMessageId = id, Subject = id, Sender = sender, SentAtUtc = DateTimeOffset.UtcNow };
+            cfg(e);
+            db.Emails.Add(e);
+            return e;
+        }
+        var inbox = E("inbox", e => e.IsInInbox = true);
+        var sent = E("sent", e => e.IsInInbox = false);       // archived-looking, but it's Sent
+        var important = E("important", e => e.IsImportant = true);
+        var later = E("later", e => e.IsReadLater = true);
+        var filed = E("filed", e => e.IsInInbox = false);
+        await db.SaveChangesAsync();
+
+        db.Set<EmailLabel>().AddRange(
+            new EmailLabel { EmailId = sent.Id, LabelId = sentLabel.Id },
+            new EmailLabel { EmailId = filed.Id, LabelId = userLabel.Id });
+        await db.SaveChangesAsync();
+        return uid;
+    }
+
+    private static async Task<List<string>> RunAsync(string name, Guid uid, SearchRequestDto req)
+    {
+        using var db = Db(name, uid);
+        var res = await new SearchService(db).SearchAsync(uid, req);
+        return res.Items.Select(i => i.GmailMessageId).OrderBy(x => x).ToList();
+    }
+
+    private static SearchRequestDto Base() => new(null, null, null, null, null, null, null, false, 1, 50);
+
+    [Fact]
+    public async Task Archive_excludes_sent_mail()
+    {
+        var name = nameof(Archive_excludes_sent_mail);
+        var uid = await SeedAsync(name);
+        // Archive: not-in-inbox, not-trashed, excluding SENT — must NOT contain "sent".
+        var items = await RunAsync(name, uid, Base() with
+        {
+            IsInInbox = false,
+            IsTrashed = false,
+            ExcludeGmailLabels = new[] { "SENT", "SPAM", "DRAFT" }
+        });
+        items.Should().NotContain("sent");
+        items.Should().Contain("filed"); // a genuinely archived, user-filed mail stays
+    }
+
+    [Fact]
+    public async Task Pinned_returns_only_important_not_everything()
+    {
+        var name = nameof(Pinned_returns_only_important_not_everything);
+        var uid = await SeedAsync(name);
+        var items = await RunAsync(name, uid, Base() with { IsImportant = true });
+        items.Should().Equal("important");
+    }
+
+    [Fact]
+    public async Task ReadLater_returns_only_flagged_not_everything()
+    {
+        var name = nameof(ReadLater_returns_only_flagged_not_everything);
+        var uid = await SeedAsync(name);
+        var items = await RunAsync(name, uid, Base() with { IsReadLater = true });
+        items.Should().Equal("later");
+    }
+
+    [Fact]
+    public async Task Unlabelled_excludes_user_labelled_mail()
+    {
+        var name = nameof(Unlabelled_excludes_user_labelled_mail);
+        var uid = await SeedAsync(name);
+        // "filed" has a user label → must be absent; everything else (no user label) present.
+        var items = await RunAsync(name, uid, Base() with { HasUserLabels = false });
+        items.Should().NotContain("filed");
+        items.Should().Contain("inbox");
+    }
+}