test(series): pin the SSR pagination contract under tied timestamps

New integration test mirroring a prod bulk import: a dedicated test
library with 30 series whose items share ONE identical created_at
(single-transaction NOW()), the exact data shape that made prod
pagination look broken.

Pins, via the real SSR /series route:
- page 1 renders exactly 24 deterministic series (01-24) with chip
  "Page 1 of 2", no Previous, and a Next href carrying library_id and
  page (templ escapes & as & inside attributes)
- page 2 renders the remaining 6, disjoint from page 1, chip
  "Page 2 of 2", no Next, Previous href correct
- missing page param defaults to page 1; page=0/-3/two clamp to page 1

Guards both the SQL tiebreaker and the /series handler contract;
would fail on any return of the stomp or an unstable sort.

cmd/server/tests/series_pagination_test.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"regexp"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestSeriesPagination pins the SSR series-page pagination contract
+// (2026-10-19 paginator fix). The /series page renders its grid and
+// paginator entirely server-side (templates/series.templ); page state
+// lives in the ?page= query param. The fixture mirrors a prod bulk
+// import: 30 series whose items share ONE identical created_at (a single
+// transaction's NOW()), which historically left the ORDER BY tied — the
+// tiebreaker (library_id, series) makes pages deterministic.
+func TestSeriesPagination(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skipping integration test in short mode")
+	}
+	setup := setupTestServer(t)
+
+	libID := createTestLibraryWithFolder(t, setup.Server, setup.Token, "Test Pagination Library", false)
+
+	ctx := context.Background()
+	const totalSeries = 30
+	for i := 1; i <= totalSeries; i++ {
+		_, err := setup.DBPool.Exec(ctx,
+			`INSERT INTO media_items (library_id, title, file_path, series, created_at, imported_at, updated_at)
+			 VALUES ($1, $2, $3, $4, '2026-01-01 00:00:00+00', '2026-01-01 00:00:00+00', '2026-01-01 00:00:00+00')`,
+			libID, fmt.Sprintf("Pagination Probe Book %02d", i),
+			fmt.Sprintf("/tmp/test-pagination/book-%02d.epub", i),
+			fmt.Sprintf("Pagination Probe Series %02d", i),
+		)
+		require.NoError(t, err)
+	}
+	t.Cleanup(func() {
+		_, _ = setup.DBPool.Exec(ctx, "DELETE FROM libraries WHERE id = $1", libID)
+	})
+
+	// templ separates dynamic text segments with HTML comments; strip them
+	// so plain regexes work on names and the page chip.
+	stripComments := func(html string) string {
+		return regexp.MustCompile(`<!--.*?-->`).ReplaceAllString(html, "")
+	}
+	seriesNames := func(html string) map[string]bool {
+		names := map[string]bool{}
+		for _, m := range regexp.MustCompile(`<h3[^>]*>([^<]+)</h3>`).FindAllStringSubmatch(stripComments(html), -1) {
+			names[strings.TrimSpace(m[1])] = true
+		}
+		return names
+	}
+	pageChip := func(html string) string {
+		m := regexp.MustCompile(`Page\s+(\d+)\s+of\s+(\d+)`).FindStringSubmatch(stripComments(html))
+		if m == nil {
+			return ""
+		}
+		return fmt.Sprintf("Page %s of %s", m[1], m[2])
+	}
+
+	perPage := 24 // internal/router/frontend.go perSeriesPage
+
+	t.Run("page1 defaults and next link", func(t *testing.T) {
+		code, body := ssrGet(t, setup.Server.URL+"/series?library_id="+libID, setup.Token)
+		require.Equal(t, 200, code)
+
+		assert.Equal(t, fmt.Sprintf("Page 1 of 2"), pageChip(body))
+		names := seriesNames(body)
+		assert.Len(t, names, perPage, "page 1 renders exactly 24 cards")
+		assert.Contains(t, names, "Pagination Probe Series 01", "deterministic order: page 1 starts at the first series")
+		assert.Contains(t, names, fmt.Sprintf("Pagination Probe Series %02d", perPage), "page 1 ends at the 24th series")
+		assert.NotContains(t, names, fmt.Sprintf("Pagination Probe Series %02d", perPage+1), "page 1 must not leak page-2 rows")
+
+		assert.NotContains(t, body, "Previous", "no Previous link on page 1")
+		// templ HTML-escapes & as &amp; inside attribute values.
+		assert.Contains(t, body, fmt.Sprintf(`href="/series?library_id=%s&amp;page=2"`, libID), "Next link carries library_id and page")
+	})
+
+	t.Run("page2 is disjoint and terminal", func(t *testing.T) {
+		code, body := ssrGet(t, setup.Server.URL+"/series?library_id="+libID+"&page=2", setup.Token)
+		require.Equal(t, 200, code)
+
+		assert.Equal(t, "Page 2 of 2", pageChip(body))
+		names := seriesNames(body)
+		assert.Len(t, names, totalSeries-perPage, "page 2 renders the remainder")
+
+		code1, body1 := ssrGet(t, setup.Server.URL+"/series?library_id="+libID+"&page=1", setup.Token)
+		require.Equal(t, 200, code1)
+		page1 := seriesNames(body1)
+
+		for name := range names {
+			assert.NotContains(t, page1, name, "pages must be disjoint even with fully tied created_at")
+		}
+		assert.NotContains(t, body, "Next", "no Next link on the last page")
+		assert.Contains(t, body, fmt.Sprintf(`href="/series?library_id=%s&amp;page=1"`, libID), "Previous link carries library_id and page")
+	})
+
+	t.Run("missing page param defaults to page 1", func(t *testing.T) {
+		code, body := ssrGet(t, setup.Server.URL+"/series?library_id="+libID, setup.Token)
+		require.Equal(t, 200, code)
+		assert.Equal(t, "Page 1 of 2", pageChip(body))
+	})
+
+	t.Run("invalid page param falls back to page 1", func(t *testing.T) {
+		for _, bad := range []string{"0", "-3", "two"} {
+			code, body := ssrGet(t, setup.Server.URL+"/series?library_id="+libID+"&page="+bad, setup.Token)
+			require.Equal(t, 200, code, "page=%s", bad)
+			assert.Equal(t, "Page 1 of 2", pageChip(body), "page=%s must clamp to page 1", bad)
+		}
+	})
+}