Persist kagane covers in Postgres

backend/internal/store/migrations/0007_covers.sql

@@ -0,0 +1,8 @@
+-- Kagane cover bytes belong in their own table so image blobs never enter the
+-- series queries that drive the latest-chapter poller.
+CREATE TABLE covers (
+  image_id    text PRIMARY KEY,
+  body        bytea NOT NULL,
+  content_type text NOT NULL,
+  fetched_at  timestamptz NOT NULL DEFAULT now()
+);

backend/internal/store/store.go

@@ -529,6 +529,37 @@ func scanSeries(scan func(...any) error) (Series, error) {
 // Close releases the underlying database handle.
 func (s *Store) Close() error { return s.db.Close() }
 
+// GetKaganeCover returns one persisted cover. Missing covers are reported with
+// ok=false rather than as an error so the web handler can fetch them once.
+func (s *Store) GetKaganeCover(imageID string) ([]byte, string, bool, error) {
+	var (
+		body        []byte
+		contentType string
+	)
+	err := s.db.QueryRow(
+		`SELECT body, content_type FROM covers WHERE image_id = $1`, imageID,
+	).Scan(&body, &contentType)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, "", false, nil
+	}
+	if err != nil {
+		return nil, "", false, fmt.Errorf("get kagane cover %q: %w", imageID, err)
+	}
+	return body, contentType, true, nil
+}
+
+// PutKaganeCover persists one fetched cover. Image ids are immutable, so a
+// later fetch cannot replace the bytes already made durable.
+func (s *Store) PutKaganeCover(imageID string, body []byte, contentType string) error {
+	if _, err := s.db.Exec(`
+		INSERT INTO covers (image_id, body, content_type)
+		VALUES ($1, $2, $3)
+		ON CONFLICT (image_id) DO NOTHING`, imageID, body, contentType); err != nil {
+		return fmt.Errorf("put kagane cover %q: %w", imageID, err)
+	}
+	return nil
+}
+
 // List returns every bookmark of one reader, newest activity first.
 // Series-owned fields are joined in, so each Bookmark reads back whole and
 // flat (ADR-0004).

backend/internal/store/store_test.go

@@ -1231,3 +1231,30 @@ func TestTwoReadersShareOneSeriesWithIndependentProgress(t *testing.T) {
 		t.Fatalf("due after one Reader left = %+v, want the series still polled", due)
 	}
 }
+func TestKaganeCoverPersistsAcrossReopen(t *testing.T) {
+	url := pgtest.URL(t)
+	first, err := Open(url, testOwner)
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	body := []byte("stored-cover")
+	if err := first.PutKaganeCover("019fe11a-84c3-7fc3-a84b-88787374b617", body, "image/webp"); err != nil {
+		t.Fatalf("PutKaganeCover: %v", err)
+	}
+	if err := first.Close(); err != nil {
+		t.Fatalf("close first store: %v", err)
+	}
+
+	second, err := Open(url, testOwner)
+	if err != nil {
+		t.Fatalf("reopen: %v", err)
+	}
+	defer second.Close()
+	got, contentType, ok, err := second.GetKaganeCover("019fe11a-84c3-7fc3-a84b-88787374b617")
+	if err != nil {
+		t.Fatalf("GetKaganeCover: %v", err)
+	}
+	if !ok || !bytes.Equal(got, body) || contentType != "image/webp" {
+		t.Fatalf("stored cover = (%q, %q, %v), want (%q, image/webp, true)", got, contentType, ok, body)
+	}
+}

backend/internal/web/cover.go

@@ -5,7 +5,6 @@ import (
 	"log"
 	"net/http"
 	"regexp"
-	"sync"
 	"time"
 )
 
@@ -39,40 +38,6 @@ var coverTypes = map[string]bool{
 // holding a connection open.
 const coverTimeout = 20 * time.Second
 
-// coverCacheMax caps the in-memory cover cache. Covers are immutable per image
-// id and a library holds tens of series, so this is a ceiling that is never
-// reached in practice; reaching it clears the map rather than evicting by age.
-//
-// ponytail: flush-on-full, not LRU. Swap it for an LRU if a library ever grows
-// past this and the flush starts costing refetches.
-const coverCacheMax = 500
-
-type cachedCover struct {
-	body        []byte
-	contentType string
-}
-
-type coverCache struct {
-	mu sync.Mutex
-	m  map[string]cachedCover
-}
-
-func (c *coverCache) get(id string) (cachedCover, bool) {
-	c.mu.Lock()
-	defer c.mu.Unlock()
-	v, ok := c.m[id]
-	return v, ok
-}
-
-func (c *coverCache) put(id string, v cachedCover) {
-	c.mu.Lock()
-	defer c.mu.Unlock()
-	if c.m == nil || len(c.m) >= coverCacheMax {
-		c.m = make(map[string]cachedCover, coverCacheMax)
-	}
-	c.m[id] = v
-}
-
 // kaganeCover serves a kagane cover from the backend's own origin.
 //
 // kagane answers image requests with a Cloudflare challenge and
@@ -81,23 +46,22 @@ func (c *coverCache) put(id string, v cachedCover) {
 // (verified 2026-08-08). Fetching it through the headless browser that already
 // clears the challenge, and re-serving it here, is what puts the bytes on an
 // origin the page may load from.
-//
-// ponytail: covers are fetched on first view, one browser navigation at a time
-// behind the fetcher's mutex, so a first load of a large kagane library
-// trickles in over a few seconds. The cache makes it a one-off. Prefetching
-// during the poll cycle is the upgrade if that ever grates.
 func (h *Handler) kaganeCover(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
 	if !coverIDRe.MatchString(id) {
 		http.NotFound(w, r)
 		return
 	}
-	if h.covers == nil {
-		http.NotFound(w, r)
+	if body, contentType, ok, err := h.store.GetKaganeCover(id); err != nil {
+		log.Printf("read kagane cover %s: %v", id, err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	} else if ok {
+		writeCover(w, body, contentType)
 		return
 	}
-	if v, ok := h.coverCache.get(id); ok {
-		writeCover(w, v)
+	if h.covers == nil {
+		http.NotFound(w, r)
 		return
 	}
 
@@ -114,16 +78,18 @@ func (h *Handler) kaganeCover(w http.ResponseWriter, r *http.Request) {
 		http.NotFound(w, r)
 		return
 	}
-
-	v := cachedCover{body: body, contentType: contentType}
-	h.coverCache.put(id, v)
-	writeCover(w, v)
+	if err := h.store.PutKaganeCover(id, body, contentType); err != nil {
+		log.Printf("persist kagane cover %s: %v", id, err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return
+	}
+	writeCover(w, body, contentType)
 }
 
 // writeCover sends the bytes with a long cache life: an image id names one
 // immutable rendering, so a client that has it never needs to ask again.
-func writeCover(w http.ResponseWriter, v cachedCover) {
-	w.Header().Set("Content-Type", v.contentType)
+func writeCover(w http.ResponseWriter, body []byte, contentType string) {
+	w.Header().Set("Content-Type", contentType)
 	w.Header().Set("Cache-Control", "private, max-age=604800, immutable")
-	w.Write(v.body)
+	w.Write(body)
 }

backend/internal/web/web.go

@@ -52,8 +52,7 @@ type Handler struct {
 	httpClient *http.Client
 	// covers proxies kagane cover images, which no browser can load directly.
 	// Nil disables the endpoint — see CoverFetcher.
-	covers     CoverFetcher
-	coverCache coverCache
+	covers CoverFetcher
 }
 
 // listView is what every list-rendering template receives.