perf(search): keyset pagination + fix the format-gate line-ending flip-flop

RECOMMENDATIONS #8: additive AfterSentAtUtc+AfterId cursor — browse windows fetch
via a (SentAtUtc, Id) keyset filter, O(pageSize) at any depth, COUNT skipped
(TotalCount=-1). Adds the Id tie-break to browse ordering (fixes latent
duplicate/skip on equal timestamps). Verified: InMemory continuation test + a
live-Postgres throwaway proving the Guid cursor comparison translates (removed).

Also root-causes the recurring pre-commit/CI format failures: dotnet-format on
Windows defaulted to CRLF while .gitattributes stores LF — the two fought forever.
Adds .editorconfig (end_of_line=lf etc.) so every tool agrees, and normalises the
straggler files. This bug bit three separate commits before being diagnosed.

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

.editorconfig

@@ -0,0 +1,13 @@
+# Root editor/formatter config. end_of_line=lf makes dotnet-format agree with
+# .gitattributes (eol=lf) — without this, format-on-Windows wants CRLF while git
+# stores LF, and the pre-commit/CI format gates flip-flop forever.
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+
+[*.cs]
+indent_style = space
+indent_size = 4

src/InboxIntel.Application/DTOs/SearchDtos.cs

@@ -23,4 +23,9 @@ public record SearchRequestDto(
     bool? IsTrashed = null,
     string? GmailLabel = null,   // e.g. "SENT", "DRAFT", "SPAM"
     string? Category = null,     // EmailCategory name, e.g. "Finance"
-    long? MinSizeBytes = null);
+    long? MinSizeBytes = null,
+    // Keyset cursor for the date-ordered browse path (RECOMMENDATIONS #8): pass the last
+    // row's SentAtUtc+Id to fetch the next window without OFFSET (O(pageSize), not O(page)).
+    // When set, TotalCount is not recomputed (-1). Additive; offset paging still works.
+    DateTimeOffset? AfterSentAtUtc = null,
+    Guid? AfterId = null);

src/InboxIntel.Infrastructure/Migrations/20260630140733_InitialCreate.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Microsoft.EntityFrameworkCore.Migrations;
 using NpgsqlTypes;
 

src/InboxIntel.Infrastructure/Migrations/20260630200946_AddUserDigestFields.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable

src/InboxIntel.Infrastructure/Migrations/20260630201607_AddUnsubscribeConfidence.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
 

src/InboxIntel.Infrastructure/Migrations/20260701192100_WeightSearchVectorSubjectBody.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 using NpgsqlTypes;
 
 #nullable disable

src/InboxIntel.Infrastructure/Migrations/20260701203001_EnablePgTrgm.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
 

src/InboxIntel.Infrastructure/Migrations/20260701235112_TrigramIndexesSenderDomain.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
 

src/InboxIntel.Infrastructure/Migrations/20260702002304_AddEmbeddingColumn.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 using Pgvector;
 
 #nullable disable

src/InboxIntel.Infrastructure/Search/SearchService.cs

@@ -114,9 +114,23 @@ public class SearchService : ISearchService
             ranked = matched.OrderByDescending(e => e.SearchVector!.RankCoverDensity(EF.Functions.WebSearchToTsQuery("english", term)))
                             .ThenByDescending(e => e.SentAtUtc);
         else
-            ranked = matched.OrderByDescending(e => e.SentAtUtc);
+            ranked = matched.OrderByDescending(e => e.SentAtUtc).ThenByDescending(e => e.Id);
 
-        var paged = ranked.Skip((r.Page - 1) * r.PageSize).Take(r.PageSize);
+        // Keyset (cursor) pagination for the browse path: O(pageSize) regardless of depth,
+        // vs OFFSET's O(page*pageSize). The (SentAtUtc, Id) pair with the Id tie-break above
+        // makes the ordering total, so windows never duplicate or skip rows.
+        IQueryable<Email> paged;
+        if (!hasFreeTextQuery && r is { AfterSentAtUtc: { } afterAt, AfterId: { } afterId })
+        {
+            paged = ranked
+                .Where(e => e.SentAtUtc < afterAt || (e.SentAtUtc == afterAt && e.Id.CompareTo(afterId) < 0))
+                .Take(r.PageSize);
+            total = -1; // not recomputed on cursor windows (that's the point)
+        }
+        else
+        {
+            paged = ranked.Skip((r.Page - 1) * r.PageSize).Take(r.PageSize);
+        }
 
         // "Why this matched" ts_headline only for EXACT free-text hits (fuzzy/browse get no
         // highlight — a fuzzy hit has no literal match to headline). Unconditional projections

tests/InboxIntel.IntegrationTests/KeysetPaginationTests.cs

@@ -0,0 +1,57 @@
+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>
+/// RECOMMENDATIONS #8: keyset (cursor) pagination for the browse path — the window after a
+/// (SentAtUtc, Id) cursor returns the next rows with no duplicates/skips and no OFFSET scan.
+/// </summary>
+public class KeysetPaginationTests
+{
+    private sealed class FakeCurrentUser : ICurrentUser
+    {
+        public Guid UserId { get; set; }
+        public bool IsAuthenticated => UserId != Guid.Empty;
+    }
+
+    [Fact]
+    public async Task Cursor_window_continues_exactly_after_the_previous_page()
+    {
+        var user = Guid.NewGuid();
+        var opts = new DbContextOptionsBuilder<AppDbContext>()
+            .UseInMemoryDatabase(nameof(Cursor_window_continues_exactly_after_the_previous_page)).Options;
+
+        var baseline = DateTimeOffset.UtcNow;
+        using (var seed = new AppDbContext(opts, new FakeCurrentUser()))
+        {
+            var sender = new Sender { UserId = user, Address = "s@x.x" };
+            seed.Senders.Add(sender);
+            for (var i = 0; i < 5; i++)
+                seed.Emails.Add(new Email { UserId = user, GmailMessageId = $"m{i}", Sender = sender, SentAtUtc = baseline.AddMinutes(-i) });
+            await seed.SaveChangesAsync();
+        }
+
+        using var ctx = new AppDbContext(opts, new FakeCurrentUser { UserId = user });
+        var svc = new SearchService(ctx);
+
+        // First window via offset (page 1, size 2): m0, m1 (newest first).
+        var page1 = await svc.SearchAsync(user, new SearchRequestDto(null, null, null, null, null, null, null, false, 1, 2));
+        page1.Items.Select(i => i.GmailMessageId).Should().Equal("m0", "m1");
+
+        // Next window via cursor from the last row of page 1.
+        var last = page1.Items[^1];
+        var page2 = await svc.SearchAsync(user, new SearchRequestDto(
+            null, null, null, null, null, null, null, false, 1, 2,
+            AfterSentAtUtc: last.SentAtUtc, AfterId: last.Id));
+
+        page2.Items.Select(i => i.GmailMessageId).Should().Equal("m2", "m3"); // no dupes, no skips
+        page2.TotalCount.Should().Be(-1, "cursor windows skip the COUNT — that's the perf win");
+    }
+}