fix(api): lazy cover self-heal + tmp-file skip

backend/internal/api/content_test.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
@@ -47,6 +48,29 @@ func TestCoverCBZAndPlaceholder(t *testing.T) {
 	}
 }
 
+// 不经 scanner 直接入库(模拟缓存丢失/卷漂移)→ GET cover 就地抽图自愈并落盘(tmp+rename)
+func TestCoverSelfHeal(t *testing.T) {
+	st, _, h, booksDir := setupAPI(t)
+	atok := adminToken(t, h)
+	lib, root := newLibrary(t, st, h, atok, booksDir, "comics")
+	p := filepath.Join(root, "heal.cbz")
+	writeCBZ(t, p, 2)
+	fi, err := os.Stat(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	id, err := st.InsertBook(context.Background(), lib.ID, "heal.cbz", "heal", "cbz", fi.Size(), fi.ModTime().Unix(), 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 1; i <= 2; i++ { // 第二次走已缓存目录,均应 200 image/*
+		w := do(h, "GET", "/api/books/"+itoa(id)+"/cover", atok, nil)
+		if w.Code != 200 || !strings.Contains(w.Header().Get("Content-Type"), "image/") {
+			t.Fatalf("self-heal cover pass %d: %d %q", i, w.Code, w.Header().Get("Content-Type"))
+		}
+	}
+}
+
 func TestPages(t *testing.T) {
 	h, cbzID, txtID := serveFixture(t)
 	tok := adminToken(t, h)