feat(backend)!: split Series from Bookmark, keeping the wire format flat

Series becomes a shared row keyed (site, series_id) owning title, cover,
canonical URL, kind, latest chapter and last-checked time (ADR-0003).
A bookmark keeps only progress, favourite, lifecycle bucket, updated_at.

Store.Upsert decomposes one flat body across both tables in one
transaction: client title/series_url/cover apply only when the series row
is new, then only the poll may change them (security boundary — the row
is shared and the values are scraped page content). Reads join series
back in, so GET/PUT emit and accept exactly the flat field set they did
before (ADR-0004), asserted by TestFlatWireFieldSet.

The poller walks Series instead of Bookmarks: one fetch per shared
series per due cycle, due queue ordered reader_count DESC then
latest_checked_at ASC, orphaned series never due and never deleted, row
still stamped before the fetch. Batch/stagger/interval unchanged.

Migration 0002 backfills series from existing bookmarks; verified by
TestMigration0002BackfillsExistingBookmarks.

REDEPLOY.md

@@ -59,7 +59,7 @@ network can reach it — so every command below goes in through the container:
 
 ```bash
 $COMPOSE exec -T postgres psql -U bookmarks -d bookmarks -c '\dt'
-# -> bookmarks, schema_migrations
+# -> bookmarks, schema_migrations, series
 ```
 
 Inside the container that connects over the local socket as the `bookmarks`
@@ -100,6 +100,7 @@ docker run --rm -v "$BACKUP_DIR":/backup postgres:17-alpine \
   pg_restore --list "/backup/bookmarks-$STAMP.dump" | grep 'TABLE DATA'
 # -> 1234; 0 0 TABLE DATA public bookmarks bookmarks
 # -> 1235; 0 0 TABLE DATA public schema_migrations bookmarks
+# -> 1236; 0 0 TABLE DATA public series series
 
 # 2. Sanity-check the live row count you just captured.
 $COMPOSE exec -T postgres psql -U bookmarks -d bookmarks \

backend/AGENTS.md

@@ -21,7 +21,15 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   container per test binary (`TestMain` -> `pgtest.Main`) and hands each test
   its own database (`pgtest.URL(t)`). A package whose tests touch the store
   must have that `TestMain`.
-- **Single-user store.** One `bookmarks` table keyed `<site>:<series_id>` (`asura`|`demonic`|`comix`|`kagane`|`novelfull`|`lightnovelworld`), with a `kind` column (`manga`|`novel`) splitting the two libraries. Sync **last-write-wins**. Schema and endpoint list in plan.
+- **Single-user store, two tables.** `series` keyed `(site, series_id)`
+  (`asura`|`demonic`|`comix`|`kagane`|`novelfull`|`lightnovelworld`) owns the
+  shared facts — title, cover, canonical URL, `kind` (`manga`|`novel`),
+  Latest Chapter, `latest_checked_at` — and `bookmarks` holds only what
+  differs between readers: progress, favourite, lifecycle bucket,
+  `updated_at`. Sync **last-write-wins**; the wire format stays flat
+  (ADR-0004). `Store.Upsert` decomposes one flat body across both tables and
+  enforces the ownership rule: client `title`/`series_url`/`cover` are
+  written only when the series row is new (ADR-0003).
 - **Endpoints:** `GET /bookmarks`, `PUT /bookmarks/{key}` (upsert; see `updated_at` rule below), `DELETE /bookmarks/{key}`, `GET /healthz` (no auth).
 - **Web UI:** same binary serve password-gated browser UI on second
   hostname — `GET /` (list, or login page when no session),
@@ -53,22 +61,25 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   network access, so `latest_chapter` stay fresh when user not
   browsing. Second, parallel signal — userscript keep own
   `maybeCaptureLatestOnSeriesPage`/`backgroundRefreshLatest` logic unchanged.
-  Two independent clocks: per-bookmark cooldown (`latest_checked_at` column,
+  Two independent clocks: per-series cooldown (`series.latest_checked_at`,
   enforced by `Store.DueForLatestCheck`'s WHERE clause) and wake interval.
-  Row stamped *before* fetch so broken series wait out full
+  The poller walks **Series, not Bookmarks** — a series referenced by several
-  cooldown instead of retrying every tick, and writes go through
+  bookmarks is fetched once per cycle, and the due queue orders
-  `Store.Get` + `Store.Upsert` so new chapter never reorders list.
+  `reader_count DESC, latest_checked_at ASC` (ADR-0003). Series row stamped
+  *before* fetch so broken series wait out full cooldown instead of retrying
+  every tick; found chapter written straight to the series row via
+  `Store.SetLatestChapter`, so a bookmark's `updated_at` — and the list
+  order — is never touched.
   Fetches use `bogdanfinn/tls-client` with Chrome profile as defence in depth
   against fingerprint-based blocking; any failure log and skip. kagane and
   novelfull sit behind Cloudflare JavaScript challenges the TLS client can't
   clear, so they are browser-only: fetched over CDP via `BROWSER_WS_URL`, and
   simply not polled when that's unset. See
   `docs/superpowers/specs/2026-07-26-server-latest-chapter-polling-design.md`.
-  Poller's `Store.Get` + `Store.Upsert` not wrapped in transaction, so
+  The poller's series write is a single-column UPDATE
-  userscript `PUT` that commits between the two can get overwritten by
+  (`Store.SetLatestChapter`), not a read-modify-write of the whole bookmark:
-  poller's stale re-read — reverting that read progress and, since stored
+  it cannot revert read progress or move `updated_at`, so the old
-  value now differs, moving `updated_at` and reordering list. Known,
+  stale-re-read race is gone with the Get+Upsert flow.
-  accepted limitation for single-user deployment, not bug to fix.
 - **`updated_at` drives list order, so moves only on real reading progress:** server apply its timestamp when row new or `last_chapter_num` changes, else keep stored value — favouriting series or recording newly published chapter must not reorder list. `PUT` therefore returns row **as stored**, clients must adopt that response rather than own payload. See `plans/2026-07-25-bookmark-list-favorites-design.md` §4.
 - **Lifecycle buckets:** `status` on each bookmark is `reading` | `archived` |
   `finished`, orthogonal to `favorite`. Archived and finished appear only in

backend/api_test.go

@@ -50,26 +50,35 @@ func auth(req *http.Request) *http.Request {
 
 func floatPtr(f float64) *float64 { return &f }
 
-// seedForCheck inserts a bookmark and forces its latest_checked_at.
+// seedForCheck inserts a bookmark (and with it its series) and forces the
+// series' latest_checked_at.
 func seedForCheck(t *testing.T, s *store.Store, key, seriesURL string, checkedAt int64) {
 	t.Helper()
+	site, seriesID, ok := strings.Cut(key, ":")
+	if !ok {
+		t.Fatalf("key %q: no ':' separator", key)
+	}
 	if _, err := s.Upsert(store.Bookmark{
 		Key:       key,
-		Site:      "asura",
+		Site:      site,
-		SeriesID:  key,
+		SeriesID:  seriesID,
 		SeriesURL: seriesURL,
 		UpdatedAt: 1000,
 	}); err != nil {
 		t.Fatalf("seed %q: %v", key, err)
 	}
-	if err := s.MarkLatestChecked(key, checkedAt); err != nil {
+	if err := s.MarkLatestChecked(site, seriesID, checkedAt); err != nil {
 		t.Fatalf("seed mark %q: %v", key, err)
 	}
 }
 
 func readLatestCheckedAt(t *testing.T, s *store.Store, key string) int64 {
 	t.Helper()
-	ts, err := s.LatestCheckedAt(key)
+	site, seriesID, ok := strings.Cut(key, ":")
+	if !ok {
+		t.Fatalf("key %q: no ':' separator", key)
+	}
+	ts, err := s.LatestCheckedAt(site, seriesID)
 	if err != nil {
 		t.Fatalf("LatestCheckedAt %q: %v", key, err)
 	}
@@ -229,6 +238,125 @@ func TestBookmarkRoundTrip(t *testing.T) {
 	}
 }
 
+// The wire contract (ADR-0004): GET and PUT speak exactly the flat field set
+// they always did, with the series-owned fields as siblings of the bookmark
+// fields, not nested. Asserted as a key set, not by inspection.
+func TestFlatWireFieldSet(t *testing.T) {
+	srv := newTestServer(t)
+	key := "comix:some-title"
+	in := store.Bookmark{
+		Key:              key,
+		Site:             "comix",
+		SeriesID:         "some-title",
+		Title:            "Some Title",
+		SeriesURL:        "https://comix.to/title/some-title",
+		Cover:            "https://comix.to/covers/some-title.jpg",
+		LastChapter:      "Chapter 7",
+		LastChapterNum:   7,
+		LastChapterURL:   "https://comix.to/title/some-title/ch/7",
+		Favorite:         true,
+		LatestChapter:    "Chapter 8",
+		LatestChapterNum: floatPtr(8),
+		Status:           store.StatusArchived,
+		Kind:             store.KindManga,
+	}
+	body, _ := json.Marshal(in)
+
+	wantKeys := map[string]bool{
+		"key": true, "site": true, "series_id": true, "title": true,
+		"series_url": true, "cover": true, "last_chapter": true,
+		"last_chapter_num": true, "last_chapter_url": true, "favorite": true,
+		"latest_chapter": true, "latest_chapter_num": true, "updated_at": true,
+		"status": true, "kind": true,
+	}
+	checkFlat := func(t *testing.T, payload []byte) map[string]json.RawMessage {
+		t.Helper()
+		var obj map[string]json.RawMessage
+		if err := json.Unmarshal(payload, &obj); err != nil {
+			t.Fatalf("decode: %v", err)
+		}
+		if len(obj) != len(wantKeys) {
+			t.Fatalf("field count = %d, want %d (%s)", len(obj), len(wantKeys), payload)
+		}
+		for k := range obj {
+			if !wantKeys[k] {
+				t.Fatalf("unexpected field %q", k)
+			}
+		}
+		return obj
+	}
+
+	// PUT
+	rr := httptest.NewRecorder()
+	srv.ServeHTTP(rr, auth(httptest.NewRequest(http.MethodPut, "/bookmarks/"+key, bytes.NewReader(body))))
+	if rr.Code != http.StatusOK {
+		t.Fatalf("PUT status = %d, want 200", rr.Code)
+	}
+	checkFlat(t, rr.Body.Bytes())
+
+	// Every field round-trips with its value, and updated_at is server-stamped.
+	var stored store.Bookmark
+	if err := json.Unmarshal(rr.Body.Bytes(), &stored); err != nil {
+		t.Fatalf("decode PUT response: %v", err)
+	}
+	latestNum := floatPtr(8)
+	want := store.Bookmark{
+		Key: key, Site: "comix", SeriesID: "some-title",
+		Title: in.Title, SeriesURL: in.SeriesURL, Cover: in.Cover,
+		LastChapter: in.LastChapter, LastChapterNum: in.LastChapterNum,
+		LastChapterURL: in.LastChapterURL, Favorite: true,
+		LatestChapter: in.LatestChapter, LatestChapterNum: latestNum,
+		Status: store.StatusArchived, Kind: store.KindManga,
+	}
+	if stored.Title != want.Title || stored.SeriesURL != want.SeriesURL || stored.Cover != want.Cover ||
+		stored.LastChapter != want.LastChapter || stored.LastChapterNum != want.LastChapterNum ||
+		stored.LastChapterURL != want.LastChapterURL || stored.Favorite != want.Favorite ||
+		stored.LatestChapter != want.LatestChapter ||
+		stored.LatestChapterNum == nil || *stored.LatestChapterNum != *want.LatestChapterNum ||
+		stored.Status != want.Status || stored.Kind != want.Kind {
+		t.Fatalf("PUT response = %+v, want %+v", stored, want)
+	}
+	if stored.UpdatedAt == 0 {
+		t.Fatal("updated_at not server-stamped")
+	}
+
+	// GET reports the same flat shape.
+	list := getBookmarks(t, srv)
+	if len(list) != 1 {
+		t.Fatalf("list = %d items, want 1", len(list))
+	}
+	body2, _ := json.Marshal(list[0])
+	checkFlat(t, body2)
+}
+
+// A PUT naming an existing series must ignore client-supplied title, cover and
+// URL — the security boundary from ADR-0003, where a hostile site's scraped
+// values could otherwise land on a shared row — while progress still lands.
+func TestPutExistingSeriesIgnoresClientTitleCoverURL(t *testing.T) {
+	srv := newTestServer(t)
+	key := "asura:solo"
+
+	first := putBookmark(t, srv, key, store.Bookmark{
+		Title:          "Solo Leveling",
+		SeriesURL:      "https://asurascans.com/comics/solo",
+		Cover:          "https://asurascans.com/covers/solo.jpg",
+		LastChapterNum: 10,
+	})
+
+	second := putBookmark(t, srv, key, store.Bookmark{
+		Title:          "Scraped Rename",
+		SeriesURL:      "https://evil.example/solo",
+		Cover:          "https://evil.example/solo.jpg",
+		LastChapterNum: 11,
+	})
+	if second.Title != first.Title || second.SeriesURL != first.SeriesURL || second.Cover != first.Cover {
+		t.Fatalf("stored = %+v, want original title/url/cover kept", second)
+	}
+	if second.LastChapterNum != 11 {
+		t.Fatalf("LastChapterNum = %v, want 11 — progress must still land", second.LastChapterNum)
+	}
+}
+
 // putBookmark PUTs b at key and returns the bookmark the server echoes back,
 // which is the row as actually stored (not the request payload).
 func putBookmark(t *testing.T, srv http.Handler, key string, b store.Bookmark) store.Bookmark {

backend/internal/latest/poller.go

@@ -23,9 +23,9 @@ type Fetcher interface {
 // Two clocks, deliberately independent:
 //
 //   - Interval is how often this goroutine wakes up and looks.
-//   - Cooldown is how long one bookmark rests since its own last check.
+//   - Cooldown is how long one series rests since its own last check.
 //
-// Only the cooldown is per bookmark, and it is enforced by the WHERE clause in
+// Only the cooldown is per series, and it is enforced by the WHERE clause in
 // DueForLatestCheck rather than by any timer. Shortening Interval therefore
 // cannot shorten anyone's cooldown; it only makes the poller wake up and find
 // nothing due more often.
@@ -78,7 +78,7 @@ func (p *Poller) Run(ctx context.Context) {
 	}
 }
 
-// runOnce processes one batch of due bookmarks.
+// runOnce processes one batch of due series.
 func (p *Poller) runOnce(ctx context.Context) {
 	cutoff := p.Now().Add(-p.Cooldown).UnixMilli()
 	due, err := p.Store.DueForLatestCheck(cutoff, p.Batch)
@@ -88,7 +88,7 @@ func (p *Poller) runOnce(ctx context.Context) {
 	}
 
 	checked := 0
-	for i, b := range due {
+	for i, sr := range due {
 		if ctx.Err() != nil {
 			break
 		}
@@ -107,7 +107,7 @@ func (p *Poller) runOnce(ctx context.Context) {
 		if stopped {
 			break
 		}
-		p.checkOne(ctx, b)
+		p.checkOne(ctx, sr)
 		checked++
 	}
 	// due vs checked is how you tell which constraint is binding: ticks that
@@ -119,10 +119,10 @@ func (p *Poller) runOnce(ctx context.Context) {
 // checkOne re-checks one series. Every failure path here is "log and move on":
 // the poller is a best-effort enhancement, and no single bad series may stall a
 // batch or take down the process.
-func (p *Poller) checkOne(ctx context.Context, b store.Bookmark) {
+func (p *Poller) checkOne(ctx context.Context, sr store.Series) {
 	defer func() {
 		if r := recover(); r != nil {
-			log.Printf("latest poll %q: recovered from panic: %v", b.Key, r)
+			log.Printf("latest poll %q: recovered from panic: %v", sr.Key(), r)
 		}
 	}()
 
@@ -130,8 +130,8 @@ func (p *Poller) checkOne(ctx context.Context, b store.Bookmark) {
 	// mid-request still consumes the cooldown. Otherwise a renamed or deleted
 	// series would be retried on every single tick forever. The userscript
 	// stamps in the same order and for the same reason (L471-473).
-	if err := p.Store.MarkLatestChecked(b.Key, p.Now().UnixMilli()); err != nil {
+	if err := p.Store.MarkLatestChecked(sr.Site, sr.SeriesID, p.Now().UnixMilli()); err != nil {
-		log.Printf("latest poll %q: mark checked: %v", b.Key, err)
+		log.Printf("latest poll %q: mark checked: %v", sr.Key(), err)
 		return
 	}
 
@@ -142,69 +142,52 @@ func (p *Poller) checkOne(ctx context.Context, b store.Bookmark) {
 	// link-local/internal addresses or non-https schemes. The cooldown above
 	// is already consumed, so a row that never passes this check is retried at
 	// cooldown pace rather than hot-looping.
-	if !fetchableSeriesURL(b.Site, b.SeriesURL) {
+	if !fetchableSeriesURL(sr.Site, sr.SeriesURL) {
-		log.Printf("latest poll %q: not fetchable: site=%q url=%q", b.Key, b.Site, b.SeriesURL)
+		log.Printf("latest poll %q: not fetchable: site=%q url=%q", sr.Key(), sr.Site, sr.SeriesURL)
 		return
 	}
 
-	f := p.fetcherFor(b.Site)
+	f := p.fetcherFor(sr.Site)
 	if f == nil {
-		log.Printf("latest poll %q: no fetcher for site %q", b.Key, b.Site)
+		log.Printf("latest poll %q: no fetcher for site %q", sr.Key(), sr.Site)
 		return
 	}
 
-	body, status, err := f.Get(ctx, b.SeriesURL)
+	body, status, err := f.Get(ctx, sr.SeriesURL)
 	if err != nil {
-		log.Printf("latest poll %q: fetch %s: %v", b.Key, b.SeriesURL, err)
+		log.Printf("latest poll %q: fetch %s: %v", sr.Key(), sr.SeriesURL, err)
 		return
 	}
 	if status != 200 {
-		log.Printf("latest poll %q: fetch %s: status %d", b.Key, b.SeriesURL, status)
+		log.Printf("latest poll %q: fetch %s: status %d", sr.Key(), sr.SeriesURL, status)
 		return
 	}
 
-	latest, ok := latestChapterFrom(b.Site, b.SeriesURL, body)
+	latest, ok := latestChapterFrom(sr.Site, sr.SeriesURL, body)
 	if !ok {
 		// Most likely a challenge page or a layout change. Either way the row is
 		// already stamped, so this waits out a cooldown instead of hot-looping.
-		log.Printf("latest poll %q: no chapter links in %d bytes", b.Key, len(body))
+		log.Printf("latest poll %q: no chapter links in %d bytes", sr.Key(), len(body))
 		return
 	}
 
-	// Re-read: the row may have been updated or deleted while the fetch was in
-	// flight, and writing b back wholesale would undo that.
-	//
-	// ponytail: non-transactional read-modify-write, wrap Get+Upsert in a tx if
-	// this ever runs for more than one user. A client PUT that commits between
-	// these two statements is lost to the stale re-read — reverting read
-	// progress or a status change, and moving updated_at because the stored
-	// value now differs. Accepted for a single-user deployment: the window is
-	// milliseconds and the loser is one poll cycle.
-	cur, found, err := p.Store.Get(b.Key)
-	if err != nil {
-		log.Printf("latest poll %q: reread: %v", b.Key, err)
-		return
-	}
-	if !found {
-		return
-	}
 	// Equality, not >, mirroring the userscript (L427): a site that retracts a
-	// chapter should correct the stored number downward.
+	// chapter should correct the stored number downward. The comparison is
-	if cur.LatestChapterNum != nil && *cur.LatestChapterNum == latest.Num {
+	// against the due-query snapshot; a concurrent write in between only costs
+	// one redundant UPDATE of the same absolute value, never a wrong one.
+	if sr.LatestChapterNum != nil && *sr.LatestChapterNum == latest.Num {
 		return
 	}
 
-	num := latest.Num
+	// Series-level write: the row is shared, so one update refreshes every
-	cur.LatestChapter = latest.Label
+	// bookmark joining to it, and the bookmark's updated_at is never touched —
-	cur.LatestChapterNum = &num
+	// a newly published chapter is not reading progress and must not reorder
-	// A candidate only. last_chapter_num is untouched, so the CASE in Upsert
+	// the list.
-	// keeps the stored updated_at and the bookmark list does not reorder.
+	if err := p.Store.SetLatestChapter(sr.Site, sr.SeriesID, latest.Label, latest.Num); err != nil {
-	cur.UpdatedAt = p.Now().UnixMilli()
+		log.Printf("latest poll %q: set latest chapter: %v", sr.Key(), err)
-	if _, err := p.Store.Upsert(cur); err != nil {
-		log.Printf("latest poll %q: upsert: %v", b.Key, err)
 		return
 	}
-	log.Printf("latest poll %q: latest is now %s", b.Key, latest.Label)
+	log.Printf("latest poll %q: latest is now %s", sr.Key(), latest.Label)
 }
 
 // fetchableSeriesURL reports whether site is a site latestChapterFrom knows how

backend/internal/latest/poller_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"os"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -25,26 +26,35 @@ func newTestStore(t *testing.T) *store.Store {
 	return s
 }
 
-// seedForCheck inserts a bookmark and forces its latest_checked_at.
+// seedForCheck inserts a bookmark (and with it its series) and forces the
+// series' latest_checked_at.
 func seedForCheck(t *testing.T, s *store.Store, key, seriesURL string, checkedAt int64) {
 	t.Helper()
+	site, seriesID, ok := strings.Cut(key, ":")
+	if !ok {
+		t.Fatalf("key %q: no ':' separator", key)
+	}
 	if _, err := s.Upsert(store.Bookmark{
 		Key:       key,
-		Site:      "asura",
+		Site:      site,
-		SeriesID:  key,
+		SeriesID:  seriesID,
 		SeriesURL: seriesURL,
 		UpdatedAt: 1000,
 	}); err != nil {
 		t.Fatalf("seed %q: %v", key, err)
 	}
-	if err := s.MarkLatestChecked(key, checkedAt); err != nil {
+	if err := s.MarkLatestChecked(site, seriesID, checkedAt); err != nil {
 		t.Fatalf("seed mark %q: %v", key, err)
 	}
 }
 
 func readLatestCheckedAt(t *testing.T, s *store.Store, key string) int64 {
 	t.Helper()
-	ts, err := s.LatestCheckedAt(key)
+	site, seriesID, ok := strings.Cut(key, ":")
+	if !ok {
+		t.Fatalf("key %q: no ':' separator", key)
+	}
+	ts, err := s.LatestCheckedAt(site, seriesID)
 	if err != nil {
 		t.Fatalf("LatestCheckedAt %q: %v", key, err)
 	}
@@ -217,6 +227,41 @@ func TestRunOnceRespectsBatchLimit(t *testing.T) {
 	}
 }
 
+// The point of the split (ADR-0003): a series referenced by several bookmarks
+// is fetched once per due cycle, not once per bookmark. Today the bookmark key
+// is <site>:<series_id>, so the second bookmark only exists once keys stop
+// being derived from the series identity (issue #22).
+func TestRunOnceFetchesSharedSeriesOnce(t *testing.T) {
+	s := newTestStore(t)
+	// The slug must match the fixture's own anchors: asura's parser scopes
+	// chapter links to the stored slug.
+	const slug = "chronicles-of-the-demon-faction-f886a8af"
+	const url = "https://asurascans.com/comics/" + slug
+	seedForCheck(t, s, "asura:"+slug, url, 0)
+	if _, err := s.Upsert(store.Bookmark{
+		Key: "asura:" + slug + ":2", Site: "asura", SeriesID: slug, UpdatedAt: 2000,
+	}); err != nil {
+		t.Fatalf("seed second reader: %v", err)
+	}
+
+	f := &fakeFetcher{body: asuraSeriesFixture, status: 200}
+	newTestPoller(t, s, f, time.UnixMilli(5_000_000)).runOnce(context.Background())
+
+	if got := f.callCount(); got != 1 {
+		t.Fatalf("fetched shared series %d times, want 1", got)
+	}
+	// Both bookmarks join to the same updated series row.
+	for _, key := range []string{"asura:" + slug, "asura:" + slug + ":2"} {
+		b, ok, err := s.Get(key)
+		if err != nil || !ok {
+			t.Fatalf("Get %s: %v ok=%v", key, err, ok)
+		}
+		if b.LatestChapterNum == nil || *b.LatestChapterNum != 181 {
+			t.Fatalf("%s LatestChapterNum = %v, want 181", key, b.LatestChapterNum)
+		}
+	}
+}
+
 // One unreachable series must not abandon the rest of the batch.
 func TestRunOnceOneBadSeriesDoesNotStallBatch(t *testing.T) {
 	s := newTestStore(t)
@@ -330,8 +375,8 @@ func TestCheckOneValidatesSeriesURLBeforeFetching(t *testing.T) {
 
 			now := time.UnixMilli(4_000_000)
 			f := &fakeFetcher{body: asuraSeriesFixture, status: 200}
-			newTestPoller(t, s, f, now).checkOne(context.Background(), store.Bookmark{
+			newTestPoller(t, s, f, now).checkOne(context.Background(), store.Series{
-				Key: key, Site: tt.site, SeriesURL: tt.seriesURL,
+				Site: tt.site, SeriesID: "x", SeriesURL: tt.seriesURL,
 			})
 
 			if got := f.callCount(); got != tt.wantCalls {

backend/internal/store/migrations/0002_series.sql

@@ -0,0 +1,45 @@
+-- One row per distinct work, shared by every bookmark that tracks it
+-- (ADR-0003). Keyed (site, series_id), the pair a bookmark key decomposes
+-- into. title/series_url/cover are written once, at creation, and never
+-- again: client-supplied values are ignored once the row exists and the
+-- poller is the only party that may change them. kind and the latest-chapter
+-- fields are last-write-wins like the bookmark's own fields.
+CREATE TABLE series (
+  site               text NOT NULL,
+  series_id          text NOT NULL,
+  title              text NOT NULL DEFAULT '',
+  series_url         text NOT NULL DEFAULT '',
+  cover              text NOT NULL DEFAULT '',
+  kind               text NOT NULL DEFAULT 'manga',
+  latest_chapter     text NOT NULL DEFAULT '',
+  latest_chapter_num double precision,
+  -- When the server last polled this series, unix ms; 0 means never, and sorts
+  -- first so a new bookmark is picked up on the next tick with no special case.
+  latest_checked_at  bigint NOT NULL DEFAULT 0,
+  PRIMARY KEY (site, series_id)
+);
+
+-- Backfill from today's rows. The bookmark key's uniqueness makes
+-- (site, series_id) unique in practice; DISTINCT is belt and braces.
+INSERT INTO series (site, series_id, title, series_url, cover, kind,
+                    latest_chapter, latest_chapter_num, latest_checked_at)
+SELECT DISTINCT site, series_id, title, series_url, cover, kind,
+                latest_chapter, latest_chapter_num, latest_checked_at
+FROM bookmarks;
+
+-- The bookmark keeps only what differs between readers (ADR-0003): progress,
+-- favourite, lifecycle bucket. The dropped columns now live on series.
+ALTER TABLE bookmarks
+  DROP COLUMN title,
+  DROP COLUMN series_url,
+  DROP COLUMN cover,
+  DROP COLUMN kind,
+  DROP COLUMN latest_chapter,
+  DROP COLUMN latest_chapter_num,
+  DROP COLUMN latest_checked_at;
+
+-- A bookmark may not point at a series that does not exist. No cascade: a
+-- series outlives its last bookmark, and deleting one is not a store operation.
+ALTER TABLE bookmarks
+  ADD CONSTRAINT bookmarks_series_fk
+  FOREIGN KEY (site, series_id) REFERENCES series (site, series_id);

backend/internal/store/store.go

@@ -19,6 +19,11 @@ import (
 //
 // LastChapter* is the user's read progress; LatestChapter* is the newest
 // chapter the site has published, captured opportunistically by the userscript.
+//
+// Title, SeriesURL, Cover, Kind and LatestChapter* live on the shared Series
+// row (ADR-0003) and are joined in on read; Bookmark carries only what differs
+// between readers: progress, favourite, lifecycle bucket, updated_at. The wire
+// format stays flat regardless — see ADR-0004.
 type Bookmark struct {
 	Key              string   `json:"key"`
 	Site             string   `json:"site"`
@@ -42,6 +47,35 @@ type Bookmark struct {
 	Kind string `json:"kind"`
 }
 
+// Series is one distinct work, shared by every bookmark that tracks it. It is
+// keyed (site, series_id) — the pair a bookmark key decomposes into — and
+// exists once no matter how many bookmarks point at it (ADR-0003).
+//
+// Title, SeriesURL and Cover are written once, at creation: a PUT naming an
+// existing Series has them ignored, and only the backend's own Poll may change
+// them. Kind and the latest-chapter fields are last-write-wins like the
+// bookmark's own fields. Never serialized: the wire format is the flat
+// Bookmark (ADR-0004).
+type Series struct {
+	Site             string
+	SeriesID         string
+	Title            string
+	SeriesURL        string
+	Cover            string
+	Kind             string
+	LatestChapter    string
+	LatestChapterNum *float64 // nil until first captured
+	LatestCheckedAt  int64    // unix ms; see MarkLatestChecked
+
+	// readerCount is the number of bookmarks referencing this series, filled
+	// only by the due-queue query that orders on it.
+	readerCount int
+}
+
+// Key returns the canonical identity in bookmark-key form ("<site>:<series_id>"),
+// used by the poller's logs and by tests asserting on the due queue.
+func (s Series) Key() string { return s.Site + ":" + s.SeriesID }
+
 // HasNewChapter reports whether the site has published past the read point.
 // A nil LatestChapterNum means nothing has been captured yet, which is not the
 // same as "nothing new".
@@ -122,10 +156,18 @@ const (
 var migrations embed.FS
 
 // bookmarkColumns is the only value ever concatenated into query text. It is a
-// compile-time constant; every request value is bound as a parameter.
+// compile-time constant; every request value is bound as a parameter. The
-const bookmarkColumns = `key, site, series_id, title, series_url, cover,
+// series-owned fields are joined in from the series table, in scanBookmark
-	last_chapter, last_chapter_num, last_chapter_url,
+// order, so the flat Bookmark reads back whole despite the split (ADR-0004).
-	favorite, latest_chapter, latest_chapter_num, updated_at, status, kind`
+const bookmarkColumns = `b.key, b.site, b.series_id, s.title, s.series_url, s.cover,
+	b.last_chapter, b.last_chapter_num, b.last_chapter_url,
+	b.favorite, s.latest_chapter, s.latest_chapter_num, b.updated_at, b.status, s.kind`
+
+// seriesColumns is the series row in scanSeries order, used by the poller's
+// due query. latest_checked_at lives only on series — see MarkLatestChecked
+// for why it stays off every client-visible write.
+const seriesColumns = `s.site, s.series_id, s.title, s.series_url, s.cover,
+	s.kind, s.latest_chapter, s.latest_chapter_num, s.latest_checked_at`
 
 // Store is the Postgres-backed bookmark store.
 type Store struct {
@@ -237,14 +279,37 @@ func scanBookmark(scan func(...any) error) (Bookmark, error) {
 	return b, nil
 }
 
+// scanSeries reads one row in seriesColumns order, plus the due query's
+// reader_count column. latest_chapter_num is NULL until the first capture,
+// same as on the bookmark read path.
+func scanSeries(scan func(...any) error) (Series, error) {
+	var (
+		sr               Series
+		latestChapterNum sql.NullFloat64
+	)
+	if err := scan(
+		&sr.Site, &sr.SeriesID, &sr.Title, &sr.SeriesURL, &sr.Cover,
+		&sr.Kind, &sr.LatestChapter, &latestChapterNum, &sr.LatestCheckedAt,
+		&sr.readerCount,
+	); err != nil {
+		return Series{}, err
+	}
+	if latestChapterNum.Valid {
+		sr.LatestChapterNum = &latestChapterNum.Float64
+	}
+	return sr, nil
+}
+
 // Close releases the underlying database handle.
 func (s *Store) Close() error { return s.db.Close() }
 
-// List returns every bookmark, newest activity first.
+// List returns every bookmark, newest activity first. Series-owned fields are
+// joined in, so each Bookmark reads back whole and flat (ADR-0004).
 func (s *Store) List() ([]Bookmark, error) {
 	rows, err := s.db.Query(`SELECT ` + bookmarkColumns + `
-		FROM bookmarks
+		FROM bookmarks b
-		ORDER BY updated_at DESC`)
+		JOIN series s ON s.site = b.site AND s.series_id = b.series_id
+		ORDER BY b.updated_at DESC`)
 	if err != nil {
 		return nil, fmt.Errorf("query bookmarks: %w", err)
 	}
@@ -266,7 +331,9 @@ func (s *Store) List() ([]Bookmark, error) {
 // the fields they do not touch.
 func (s *Store) Get(key string) (Bookmark, bool, error) {
 	b, err := scanBookmark(s.db.QueryRow(
-		`SELECT `+bookmarkColumns+` FROM bookmarks WHERE key = $1`, key).Scan)
+		`SELECT `+bookmarkColumns+` FROM bookmarks b
+		JOIN series s ON s.site = b.site AND s.series_id = b.series_id
+		WHERE b.key = $1`, key).Scan)
 	if errors.Is(err, sql.ErrNoRows) {
 		return Bookmark{}, false, nil
 	}
@@ -277,7 +344,15 @@ func (s *Store) Get(key string) (Bookmark, bool, error) {
 }
 
 // Upsert inserts or replaces a bookmark by key (last-write-wins) and returns
-// the row as actually stored.
+// the row as actually stored — one flat object with the series-owned fields
+// joined in, exactly as GET reports it (ADR-0004).
+//
+// The flat body is decomposed across two tables in one transaction. The series
+// row is written first (the bookmarks FK requires it to exist), then the
+// bookmark row. On the series side, title/series_url/cover are applied only
+// when the row is brand new: once a series exists, client-supplied values are
+// ignored, because the row is shared and the values are scraped page content —
+// see ADR-0003. Kind and the latest-chapter fields are last-write-wins.
 //
 // b.UpdatedAt is only a candidate: it is applied when the row is new or when
 // last_chapter_num changes, and otherwise the stored value is kept. Clients
@@ -296,53 +371,65 @@ func (s *Store) Upsert(b Bookmark) (Bookmark, error) {
 		latestNum = *b.LatestChapterNum
 	}
 
-	// IS DISTINCT FROM is Postgres's null-safe comparison, and it is what
+	// The kind column resolves on the VALUES side, not in the conflict clause:
-	// implements the ordering rule. Within DO UPDATE, a bare column is the
+	// excluded.* is the row *after* these expressions are evaluated, so a
-	// stored row and excluded.* is the incoming one; a brand-new key never
+	// default applied there would look identical to a real 'manga' and would
-	// reaches this clause, so it keeps the fresh timestamp from VALUES.
+	// overwrite a novel series on every PUT from a client that knows nothing
-	//
+	// about the column. Resolved once here, an empty incoming kind means "keep
-	// The status and kind columns resolve on the VALUES side, not in the
+	// what is stored", and only a brand-new row falls through to the literal
-	// conflict clause: excluded.* is the row *after* these expressions are
+	// default. The subquery runs inside this transaction, so it sees the row
-	// evaluated, so a default applied there would look identical to a real
+	// this statement is about to conflict with. Same pattern as the status
-	// 'reading' / 'manga' and would overwrite an archived or novel row on
+	// COALESCE on the bookmark insert below.
-	// every PUT from a client that knows nothing about the column. Resolved
-	// once here, an empty incoming status or kind means "keep what is
-	// stored", and only a brand-new row falls through to the literal
-	// default. The subquery runs inside this transaction, so it sees the
-	// row this statement is about to conflict with.
 	//
 	// The ::text casts are load-bearing: inside COALESCE/NULLIF there is no
 	// target column to infer the parameter type from, and Postgres rejects the
 	// statement rather than guessing.
 	if _, err := tx.Exec(`
-		INSERT INTO bookmarks (`+bookmarkColumns+`)
+		INSERT INTO series (site, series_id, title, series_url, cover, kind,
-		VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13,
+		                    latest_chapter, latest_chapter_num)
-		        COALESCE(NULLIF($14::text, ''), (SELECT status FROM bookmarks WHERE key = $1), 'reading'),
+		VALUES ($1, $2, $3, $4, $5,
-		        COALESCE(NULLIF($15::text, ''), (SELECT kind FROM bookmarks WHERE key = $1), 'manga'))
+		        COALESCE(NULLIF($6::text, ''), (SELECT kind FROM series WHERE site = $1 AND series_id = $2), 'manga'),
+		        $7, $8)
+		ON CONFLICT (site, series_id) DO UPDATE SET
+		  kind=excluded.kind,
+		  latest_chapter=excluded.latest_chapter,
+		  latest_chapter_num=excluded.latest_chapter_num`,
+		b.Site, b.SeriesID, b.Title, b.SeriesURL, b.Cover, b.Kind,
+		b.LatestChapter, latestNum); err != nil {
+		return Bookmark{}, fmt.Errorf("upsert series for %q: %w", b.Key, err)
+	}
+
+	// IS DISTINCT FROM is Postgres's null-safe comparison, and it is what
+	// implements the ordering rule. Within DO UPDATE, a bare column is the
+	// stored row and excluded.* is the incoming one; a brand-new key never
+	// reaches this clause, so it keeps the fresh timestamp from VALUES.
+	if _, err := tx.Exec(`
+		INSERT INTO bookmarks (key, site, series_id, last_chapter, last_chapter_num,
+		                       last_chapter_url, favorite, status, updated_at)
+		VALUES ($1, $2, $3, $4, $5, $6, $7,
+		        COALESCE(NULLIF($8::text, ''), (SELECT status FROM bookmarks WHERE key = $1), 'reading'),
+		        $9)
 		ON CONFLICT (key) DO UPDATE SET
-		  site=excluded.site, series_id=excluded.series_id, title=excluded.title,
+		  site=excluded.site, series_id=excluded.series_id,
-		  series_url=excluded.series_url, cover=excluded.cover,
 		  last_chapter=excluded.last_chapter, last_chapter_num=excluded.last_chapter_num,
 		  last_chapter_url=excluded.last_chapter_url,
 		  favorite=excluded.favorite,
-		  latest_chapter=excluded.latest_chapter,
-		  latest_chapter_num=excluded.latest_chapter_num,
 		  status=excluded.status,
-		  kind=excluded.kind,
 		  updated_at=CASE
 		    WHEN bookmarks.last_chapter_num IS DISTINCT FROM excluded.last_chapter_num
 		    THEN excluded.updated_at
 		    ELSE bookmarks.updated_at
 		  END`,
-		b.Key, b.Site, b.SeriesID, b.Title, b.SeriesURL, b.Cover,
+		b.Key, b.Site, b.SeriesID,
 		b.LastChapter, b.LastChapterNum, b.LastChapterURL,
-		b.Favorite, b.LatestChapter, latestNum, b.UpdatedAt,
+		b.Favorite, b.Status, b.UpdatedAt); err != nil {
-		b.Status, b.Kind); err != nil {
 		return Bookmark{}, fmt.Errorf("upsert %q: %w", b.Key, err)
 	}
 
 	stored, err := scanBookmark(tx.QueryRow(
-		`SELECT `+bookmarkColumns+` FROM bookmarks WHERE key = $1`, b.Key).Scan)
+		`SELECT `+bookmarkColumns+` FROM bookmarks b
+		JOIN series s ON s.site = b.site AND s.series_id = b.series_id
+		WHERE b.key = $1`, b.Key).Scan)
 	if err != nil {
 		return Bookmark{}, fmt.Errorf("read back %q: %w", b.Key, err)
 	}
@@ -360,71 +447,94 @@ func (s *Store) Delete(key string) error {
 	return nil
 }
 
-// DueForLatestCheck returns bookmarks whose server-side latest-chapter check has
+// DueForLatestCheck returns series whose server-side latest-chapter check has
-// aged past cutoffMs, least-recently-checked first, at most limit of them.
+// aged past cutoffMs, ordered by how many bookmarks reference them (descending)
+// then least-recently-checked first, at most limit of them.
 //
-// Oldest-first is what keeps the poller fair when the backlog outgrows its
+// The reader_count ordering is the point of the split (ADR-0003): a series
+// shared by several readers is fetched once per due cycle, and the popular
+// ones stay freshest while the long tail absorbs any shortfall. Within one
+// reader count, oldest-first keeps the poll fair when the backlog outgrows its
 // throughput: the most neglected series is always next, so a large collection
 // refreshes uniformly slower rather than leaving a tail that never refreshes at
 // all. The userscript sorts its own queue the same way (L453).
 //
-// Bookmarks with no series_url are skipped — there is nothing to fetch, which
+// Series with no series_url are skipped — there is nothing to fetch, which is
-// is the same filter the userscript applies at L452.
+// the same filter the userscript applies at L452. Series whose only bookmarks
-//
+// are finished are skipped too: nothing more is coming, so fetching them only
-// Finished series are excluded: nothing more is coming, so fetching them only
+// burns requests. Archived bookmarks still count — knowing what a shelved
-// burns requests. Archived ones are deliberately still polled — knowing what a
+// series is up to is the whole reason for archiving instead of deleting.
-// shelved series is up to is the whole reason for archiving instead of deleting.
+// A series with no bookmarks at all never appears: the join excludes it.
-func (s *Store) DueForLatestCheck(cutoffMs int64, limit int) ([]Bookmark, error) {
+func (s *Store) DueForLatestCheck(cutoffMs int64, limit int) ([]Series, error) {
-	rows, err := s.db.Query(`SELECT `+bookmarkColumns+`
+	rows, err := s.db.Query(`SELECT `+seriesColumns+`, COUNT(b.key) AS reader_count
-		FROM bookmarks
+		FROM series s
-		WHERE series_url <> ''
+		JOIN bookmarks b ON b.site = s.site AND b.series_id = s.series_id
-		  AND status IS DISTINCT FROM 'finished'
+		WHERE s.series_url <> ''
-		  AND latest_checked_at <= $1
+		  AND s.latest_checked_at <= $1
-		ORDER BY latest_checked_at ASC
+		GROUP BY s.site, s.series_id, s.title, s.series_url, s.cover,
+		         s.kind, s.latest_chapter, s.latest_chapter_num, s.latest_checked_at
+		HAVING COUNT(b.key) FILTER (WHERE b.status <> 'finished') > 0
+		ORDER BY reader_count DESC, s.latest_checked_at ASC
 		LIMIT $2`, cutoffMs, limit)
 	if err != nil {
-		return nil, fmt.Errorf("query due bookmarks: %w", err)
+		return nil, fmt.Errorf("query due series: %w", err)
 	}
 	defer rows.Close()
 
-	out := []Bookmark{}
+	out := []Series{}
 	for rows.Next() {
-		b, err := scanBookmark(rows.Scan)
+		sr, err := scanSeries(rows.Scan)
 		if err != nil {
-			return nil, fmt.Errorf("scan due bookmark: %w", err)
+			return nil, fmt.Errorf("scan due series: %w", err)
 		}
-		out = append(out, b)
+		out = append(out, sr)
 	}
 	return out, rows.Err()
 }
 
-// MarkLatestChecked records that the server looked at key at ts, whatever the
+// MarkLatestChecked records that the server looked at a series at ts, whatever
-// look turned up. Marking a missing key is not an error: the row may have been
+// the look turned up. Marking a missing series is not an error: the row may
-// deleted while a fetch was in flight.
+// have been orphaned while a fetch was in flight.
 //
 // This is the one write that does not go through Upsert, and the column is kept
-// out of bookmarkColumns on purpose. PUT /bookmarks/{key} decodes a whole
+// out of the client-visible read path on purpose. PUT /bookmarks/{key} decodes
-// Bookmark from the client and Upsert writes every column it knows about, so a
+// a whole Bookmark from the client and Upsert writes every series column it
-// userscript PUT — which has no idea this field exists — would write a zero and
+// knows about, so a userscript PUT — which has no idea this field exists —
-// reset the cooldown, making the poller re-fetch that series every tick for as
+// would write a zero and reset the cooldown, making the poller re-fetch that
-// long as the user kept reading it.
+// series every tick for as long as the user kept reading it.
-func (s *Store) MarkLatestChecked(key string, ts int64) error {
+func (s *Store) MarkLatestChecked(site, seriesID string, ts int64) error {
 	if _, err := s.db.Exec(
-		`UPDATE bookmarks SET latest_checked_at = $1 WHERE key = $2`, ts, key); err != nil {
+		`UPDATE series SET latest_checked_at = $1 WHERE site = $2 AND series_id = $3`,
-		return fmt.Errorf("mark checked %q: %w", key, err)
+		ts, site, seriesID); err != nil {
+		return fmt.Errorf("mark checked %s:%s: %w", site, seriesID, err)
 	}
 	return nil
 }
 
 // LatestCheckedAt reads the column MarkLatestChecked writes. It exists for
 // tests outside this package (the poller's own tests assert on cooldown
-// bookkeeping) — see MarkLatestChecked for why the field itself stays off
+// bookkeeping) — see MarkLatestChecked for why the field stays off the
-// Bookmark.
+// client-visible row.
-func (s *Store) LatestCheckedAt(key string) (int64, error) {
+func (s *Store) LatestCheckedAt(site, seriesID string) (int64, error) {
 	var ts int64
 	if err := s.db.QueryRow(
-		`SELECT latest_checked_at FROM bookmarks WHERE key = $1`, key).Scan(&ts); err != nil {
+		`SELECT latest_checked_at FROM series WHERE site = $1 AND series_id = $2`,
-		return 0, fmt.Errorf("latest checked at %q: %w", key, err)
+		site, seriesID).Scan(&ts); err != nil {
+		return 0, fmt.Errorf("latest checked at %s:%s: %w", site, seriesID, err)
 	}
 	return ts, nil
 }
+
+// SetLatestChapter records the newest chapter the poll found on a series page.
+// The poller walks Series rather than Bookmarks, so this is a series-level
+// write: the row is shared, and updating it once refreshes every bookmark that
+// joins to it. Touching a missing series is not an error.
+func (s *Store) SetLatestChapter(site, seriesID, label string, num float64) error {
+	if _, err := s.db.Exec(
+		`UPDATE series SET latest_chapter = $3, latest_chapter_num = $4
+		 WHERE site = $1 AND series_id = $2`,
+		site, seriesID, label, num); err != nil {
+		return fmt.Errorf("set latest chapter %s:%s: %w", site, seriesID, err)
+	}
+	return nil
+}

backend/internal/store/store_test.go

@@ -1,7 +1,9 @@
 package store
 
 import (
+	"database/sql"
 	"os"
+	"strings"
 	"testing"
 	"time"
 
@@ -124,30 +126,41 @@ func TestBookmarkContinueURL(t *testing.T) {
 }
 
 // readLatestCheckedAt reads the column directly. It is deliberately absent from
-// Bookmark (see Store.Upsert), so tests cannot assert on it any other way.
+// Series (see Store.MarkLatestChecked), so tests cannot assert on it any other
+// way. The key splits the same way the API handler derives site/series_id.
 func readLatestCheckedAt(t *testing.T, s *Store, key string) int64 {
 	t.Helper()
+	site, seriesID, ok := strings.Cut(key, ":")
+	if !ok {
+		t.Fatalf("key %q: no ':' separator", key)
+	}
 	var ts int64
 	if err := s.db.QueryRow(
-		`SELECT latest_checked_at FROM bookmarks WHERE key = $1`, key).Scan(&ts); err != nil {
+		`SELECT latest_checked_at FROM series WHERE site = $1 AND series_id = $2`,
+		site, seriesID).Scan(&ts); err != nil {
 		t.Fatalf("read latest_checked_at %q: %v", key, err)
 	}
 	return ts
 }
 
-// seedForCheck inserts a bookmark and forces its latest_checked_at.
+// seedForCheck inserts a bookmark (and with it its series) and forces the
+// series' latest_checked_at.
 func seedForCheck(t *testing.T, s *Store, key, seriesURL string, checkedAt int64) {
 	t.Helper()
+	site, seriesID, ok := strings.Cut(key, ":")
+	if !ok {
+		t.Fatalf("key %q: no ':' separator", key)
+	}
 	if _, err := s.Upsert(Bookmark{
 		Key:       key,
-		Site:      "asura",
+		Site:      site,
-		SeriesID:  key,
+		SeriesID:  seriesID,
 		SeriesURL: seriesURL,
 		UpdatedAt: 1000,
 	}); err != nil {
 		t.Fatalf("seed %q: %v", key, err)
 	}
-	if err := s.MarkLatestChecked(key, checkedAt); err != nil {
+	if err := s.MarkLatestChecked(site, seriesID, checkedAt); err != nil {
 		t.Fatalf("seed mark %q: %v", key, err)
 	}
 }
@@ -198,8 +211,8 @@ func TestDueForLatestCheckOldestFirstAndLimited(t *testing.T) {
 	if len(due) != 2 {
 		t.Fatalf("got %d rows, want 2 (limit)", len(due))
 	}
-	if due[0].Key != "asura:a" || due[1].Key != "asura:b" {
+	if due[0].Key() != "asura:a" || due[1].Key() != "asura:b" {
-		t.Fatalf("got %q,%q; want asura:a,asura:b (oldest first)", due[0].Key, due[1].Key)
+		t.Fatalf("got %q,%q; want asura:a,asura:b (oldest first)", due[0].Key(), due[1].Key())
 	}
 }
 
@@ -207,20 +220,21 @@ func TestMarkLatestChecked(t *testing.T) {
 	s := newTestStore(t)
 	seedForCheck(t, s, "asura:x", "https://asurascans.com/comics/x", 0)
 
-	if err := s.MarkLatestChecked("asura:x", 4242); err != nil {
+	if err := s.MarkLatestChecked("asura", "x", 4242); err != nil {
 		t.Fatalf("MarkLatestChecked: %v", err)
 	}
 	if got := readLatestCheckedAt(t, s, "asura:x"); got != 4242 {
 		t.Fatalf("latest_checked_at = %d, want 4242", got)
 	}
-	// A missing key is not an error: the row may have been deleted mid-fetch.
+	// A missing series is not an error: its bookmarks may have been deleted
-	if err := s.MarkLatestChecked("asura:gone", 1); err != nil {
+	// mid-fetch.
-		t.Fatalf("MarkLatestChecked on missing key: %v", err)
+	if err := s.MarkLatestChecked("asura", "gone", 1); err != nil {
+		t.Fatalf("MarkLatestChecked on missing series: %v", err)
 	}
 }
 
 // Upsert must not touch latest_checked_at. If the column ever migrates into
-// bookmarkColumns, this fails and the cooldown is silently dead.
+// the client-visible write path, this fails and the cooldown is silently dead.
 func TestUpsertPreservesLatestCheckedAt(t *testing.T) {
 	s := newTestStore(t)
 	seedForCheck(t, s, "asura:x", "https://asurascans.com/comics/x", 999)
@@ -362,7 +376,7 @@ func TestDueForLatestCheckSkipsFinishedKeepsArchived(t *testing.T) {
 		{"asura:finished", StatusFinished},
 	} {
 		if _, err := store.Upsert(Bookmark{
-			Key: tc.key, Site: "asura", SeriesID: tc.key,
+			Key: tc.key, Site: "asura", SeriesID: strings.TrimPrefix(tc.key, "asura:"),
 			SeriesURL: "https://asurascans.com/comics/" + tc.key,
 			Status:    tc.status, UpdatedAt: time.Now().UnixMilli(),
 		}); err != nil {
@@ -375,8 +389,8 @@ func TestDueForLatestCheckSkipsFinishedKeepsArchived(t *testing.T) {
 		t.Fatalf("DueForLatestCheck: %v", err)
 	}
 	got := map[string]bool{}
-	for _, b := range due {
+	for _, sr := range due {
-		got[b.Key] = true
+		got[sr.Key()] = true
 	}
 	if !got["asura:reading"] || !got["asura:archived"] {
 		t.Fatalf("due = %v, want reading and archived present", got)
@@ -476,3 +490,264 @@ func TestUpsertEmptyKindKeepsStoredValue(t *testing.T) {
 		t.Fatalf("LastChapterNum = %v, want 11 — progress in the same request must still land", got.LastChapterNum)
 	}
 }
+
+// The 0002 backfill must survive a database that already ran 0001 with real
+// rows: one series row per distinct (site, series_id) carrying the moved
+// columns, and the bookmark keeping the rest. That is the upgrade path for
+// every deployed database, so it is exercised rather than trusted.
+func TestMigration0002BackfillsExistingBookmarks(t *testing.T) {
+	url := pgtest.URL(t)
+	db, err := sql.Open("pgx", url)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	t.Cleanup(func() { db.Close() })
+
+	// Run only 0001, as a database created before this change would have.
+	// migrate() normally creates the version table first; do the same here.
+	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
+		version    bigint PRIMARY KEY,
+		applied_at timestamptz NOT NULL DEFAULT now())`); err != nil {
+		t.Fatalf("create version table: %v", err)
+	}
+	body, err := migrations.ReadFile("migrations/0001_bookmarks.sql")
+	if err != nil {
+		t.Fatalf("read 0001: %v", err)
+	}
+	if err := applyMigration(db, 1, string(body)); err != nil {
+		t.Fatalf("apply 0001: %v", err)
+	}
+	if _, err := db.Exec(`
+		INSERT INTO bookmarks (key, site, series_id, title, series_url, cover,
+			last_chapter, last_chapter_num, last_chapter_url, favorite, latest_chapter,
+			latest_chapter_num, latest_checked_at, status, kind, updated_at)
+		VALUES ('asura:solo', 'asura', 'solo', 'Solo Leveling',
+			'https://asurascans.com/comics/solo', 'https://asurascans.com/covers/solo.jpg',
+			'Chapter 10', 10, 'https://asurascans.com/comics/solo/ch/10', true,
+			'Chapter 11', 11, 123456, 'reading', 'manga', 1000)`); err != nil {
+		t.Fatalf("seed legacy row: %v", err)
+	}
+
+	// Bring it current: 0002 must backfill the series row, not lose data.
+	if err := migrate(db); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+	var (
+		title   string
+		checked int64
+		fav     bool
+		lastNum float64
+	)
+	if err := db.QueryRow(`SELECT title, latest_checked_at FROM series
+		WHERE site = 'asura' AND series_id = 'solo'`).Scan(&title, &checked); err != nil {
+		t.Fatalf("series row missing after migration: %v", err)
+	}
+	if title != "Solo Leveling" || checked != 123456 {
+		t.Fatalf("series = (%q, %d), want backfilled title and latest_checked_at", title, checked)
+	}
+	if err := db.QueryRow(`SELECT favorite, last_chapter_num FROM bookmarks
+		WHERE key = 'asura:solo'`).Scan(&fav, &lastNum); err != nil {
+		t.Fatalf("bookmark row missing after migration: %v", err)
+	}
+	if !fav || lastNum != 10 {
+		t.Fatalf("bookmark = (%v, %v), want favorite and progress kept", fav, lastNum)
+	}
+
+	// The migrated database opens as a normal store.
+	st, err := Open(url)
+	if err != nil {
+		t.Fatalf("Open after migrate: %v", err)
+	}
+	defer st.Close()
+}
+
+// readSeries reads the series row directly, for asserting on what Upsert
+// actually stored rather than what the joined Bookmark reports.
+func readSeries(t *testing.T, s *Store, site, seriesID string) Series {
+	t.Helper()
+	sr, err := scanSeries(s.db.QueryRow(
+		`SELECT `+seriesColumns+`, 0 AS reader_count FROM series s
+		 WHERE s.site = $1 AND s.series_id = $2`, site, seriesID).Scan)
+	if err != nil {
+		t.Fatalf("read series %s:%s: %v", site, seriesID, err)
+	}
+	return sr
+}
+
+// The first PUT for a series creates its row from the client's title, cover
+// and URL — there is no other source for them (ADR-0003).
+func TestUpsertCreatesSeriesFromClient(t *testing.T) {
+	store := newTestStore(t)
+	if _, err := store.Upsert(Bookmark{
+		Key: "asura:solo", Site: "asura", SeriesID: "solo",
+		Title: "Solo Leveling", SeriesURL: "https://asurascans.com/comics/solo",
+		Cover: "https://asurascans.com/covers/solo.jpg", Kind: KindManga,
+		UpdatedAt: 1000,
+	}); err != nil {
+		t.Fatalf("Upsert: %v", err)
+	}
+
+	sr := readSeries(t, store, "asura", "solo")
+	if sr.Title != "Solo Leveling" || sr.SeriesURL != "https://asurascans.com/comics/solo" ||
+		sr.Cover != "https://asurascans.com/covers/solo.jpg" {
+		t.Fatalf("series = %+v, want client title/url/cover stored", sr)
+	}
+}
+
+// A PUT naming an existing series must not overwrite its title, cover or URL:
+// the row is shared, and those values are scraped page content (ADR-0003).
+func TestUpsertExistingSeriesIgnoresClientTitleCoverURL(t *testing.T) {
+	store := newTestStore(t)
+	base := Bookmark{
+		Key: "asura:solo", Site: "asura", SeriesID: "solo",
+		Title: "Solo Leveling", SeriesURL: "https://asurascans.com/comics/solo",
+		Cover: "https://asurascans.com/covers/solo.jpg", LastChapterNum: 10,
+		UpdatedAt: 1000,
+	}
+	if _, err := store.Upsert(base); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+
+	// Same series, hostile/compromised values, real progress advance.
+	base.Title = "Scraped Rename"
+	base.SeriesURL = "https://evil.example/solo"
+	base.Cover = "https://evil.example/solo.jpg"
+	base.LastChapterNum = 11
+	got, err := store.Upsert(base)
+	if err != nil {
+		t.Fatalf("Upsert: %v", err)
+	}
+	if got.Title != "Solo Leveling" || got.SeriesURL != "https://asurascans.com/comics/solo" ||
+		got.Cover != "https://asurascans.com/covers/solo.jpg" {
+		t.Fatalf("stored = %+v, want original title/url/cover kept", got)
+	}
+	if got.LastChapterNum != 11 {
+		t.Fatalf("LastChapterNum = %v, want 11 — progress in the same request must still land", got.LastChapterNum)
+	}
+}
+
+// Kind and latest-chapter are last-write-wins even on an existing series: the
+// poller and the userscript both report the latest chapter, and kind is only
+// known to whichever client created the row.
+func TestUpsertExistingSeriesAcceptsKindAndLatest(t *testing.T) {
+	store := newTestStore(t)
+	base := Bookmark{
+		Key: "asura:solo", Site: "asura", SeriesID: "solo", Kind: KindManga,
+		UpdatedAt: 1000,
+	}
+	if _, err := store.Upsert(base); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+
+	num := 12.0
+	base.Kind = KindNovel
+	base.LatestChapter = "Chapter 12"
+	base.LatestChapterNum = &num
+	got, err := store.Upsert(base)
+	if err != nil {
+		t.Fatalf("Upsert: %v", err)
+	}
+	if got.Kind != KindNovel || got.LatestChapter != "Chapter 12" ||
+		got.LatestChapterNum == nil || *got.LatestChapterNum != 12 {
+		t.Fatalf("stored = %+v, want kind and latest chapter updated", got)
+	}
+}
+
+// Deleting the last bookmark must leave the series row behind, so a later
+// re-bookmark shows title and cover immediately instead of waiting for a poll.
+func TestDeleteKeepsSeriesRow(t *testing.T) {
+	store := newTestStore(t)
+	if _, err := store.Upsert(Bookmark{
+		Key: "asura:solo", Site: "asura", SeriesID: "solo",
+		Title: "Solo Leveling", Cover: "https://asurascans.com/covers/solo.jpg",
+		UpdatedAt: 1000,
+	}); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+	if err := store.Delete("asura:solo"); err != nil {
+		t.Fatalf("Delete: %v", err)
+	}
+
+	sr := readSeries(t, store, "asura", "solo")
+	if sr.Title != "Solo Leveling" {
+		t.Fatalf("series = %+v, want it kept after the last bookmark is deleted", sr)
+	}
+
+	// Re-bookmark with nothing but progress: the stored title/cover come back.
+	stored, err := store.Upsert(Bookmark{
+		Key: "asura:solo", Site: "asura", SeriesID: "solo",
+		LastChapterNum: 5, UpdatedAt: 2000,
+	})
+	if err != nil {
+		t.Fatalf("re-upsert: %v", err)
+	}
+	if stored.Title != "Solo Leveling" || stored.Cover != "https://asurascans.com/covers/solo.jpg" {
+		t.Fatalf("re-bookmark = %+v, want title/cover from the surviving series row", stored)
+	}
+}
+
+// seedSecondReader inserts an extra bookmark on an existing series. Today the
+// bookmark key is <site>:<series_id>, so two bookmarks can share a series only
+// once keys stop being derived from the series identity (issue #22); the due
+// queue's reader-count ordering must already be right for that world.
+func seedSecondReader(t *testing.T, s *Store, key, site, seriesID string, updatedAt int64) {
+	t.Helper()
+	if _, err := s.Upsert(Bookmark{
+		Key: key, Site: site, SeriesID: seriesID, UpdatedAt: updatedAt,
+	}); err != nil {
+		t.Fatalf("seed second reader %q: %v", key, err)
+	}
+}
+
+// The whole point of the split: a shared series is due once, ordered ahead of
+// single-reader series by how many bookmarks reference it.
+func TestDueForLatestCheckOrdersByReaderCountThenAge(t *testing.T) {
+	s := newTestStore(t)
+	// "pop" has two bookmarks but was checked most recently; "solo" has one and
+	// was checked long ago. Reader count must win over age.
+	seedForCheck(t, s, "asura:pop", "https://asurascans.com/comics/pop", 900)
+	seedSecondReader(t, s, "asura:pop:2", "asura", "pop", 1001)
+	seedForCheck(t, s, "asura:solo", "https://asurascans.com/comics/solo", 100)
+
+	due, err := s.DueForLatestCheck(1000, 10)
+	if err != nil {
+		t.Fatalf("DueForLatestCheck: %v", err)
+	}
+	if len(due) != 2 {
+		t.Fatalf("due = %d rows, want 2", len(due))
+	}
+	if due[0].Key() != "asura:pop" || due[1].Key() != "asura:solo" {
+		t.Fatalf("due order = %q, %q; want asura:pop (2 readers), asura:solo (1)",
+			due[0].Key(), due[1].Key())
+	}
+}
+
+// A series with no bookmarks must never appear in the due queue, and nothing
+// in the store ever deletes it (see TestDeleteKeepsSeriesRow).
+func TestDueForLatestCheckExcludesOrphanSeries(t *testing.T) {
+	s := newTestStore(t)
+	seedForCheck(t, s, "asura:kept", "https://asurascans.com/comics/kept", 0)
+	if _, err := s.db.Exec(`
+		INSERT INTO series (site, series_id, title, series_url, cover, kind,
+		                    latest_chapter, latest_chapter_num, latest_checked_at)
+		VALUES ('asura', 'orphan', 'Orphan', 'https://asurascans.com/comics/orphan',
+		        '', 'manga', '', NULL, 0)`); err != nil {
+		t.Fatalf("seed orphan series: %v", err)
+	}
+
+	due, err := s.DueForLatestCheck(1000, 10)
+	if err != nil {
+		t.Fatalf("DueForLatestCheck: %v", err)
+	}
+	if len(due) != 1 || due[0].Key() != "asura:kept" {
+		t.Fatalf("due = %+v, want only the bookmarked series", due)
+	}
+	var n int
+	if err := s.db.QueryRow(
+		`SELECT count(*) FROM series WHERE site = 'asura' AND series_id = 'orphan'`).Scan(&n); err != nil {
+		t.Fatalf("count orphan series: %v", err)
+	}
+	if n != 1 {
+		t.Fatalf("orphan series count = %d, want 1 (never deleted)", n)
+	}
+}