fix(api): classify DB errors in library paths

backend/internal/api/books.go

@@ -42,9 +42,13 @@ func (a *api) bookFromParam(c *gin.Context) (store.Book, bool) {
 func (a *api) getLibRow(c *gin.Context, id int64) (store.Library, bool) {
 	l, e := a.st.GetLibrary(c, id)
 	if e != nil {
+		if errors.Is(e, pgx.ErrNoRows) {
 			err(c, http.StatusNotFound, "not_found", "no such library")
 			return store.Library{}, false
 		}
+		dbErr(c, e)
+		return store.Library{}, false
+	}
 	return l, true
 }
 
@@ -102,8 +106,16 @@ func (a *api) getBook(c *gin.Context) {
 	if !ok {
 		return
 	}
-	p, _ := a.st.GetProgress(c, uid(c), b.LibraryID, b.Path) // ErrNoRows → 零值 percent
-	lib, _ := a.st.GetLibrary(c, b.LibraryID)
+	p, e := a.st.GetProgress(c, uid(c), b.LibraryID, b.Path) // ErrNoRows → 零值 percent
+	if e != nil && !errors.Is(e, pgx.ErrNoRows) {
+		dbErr(c, e)
+		return
+	}
+	lib, e := a.st.GetLibrary(c, b.LibraryID)
+	if e != nil && !errors.Is(e, pgx.ErrNoRows) { // 库被并发删则留空 library 名,书仍可见
+		dbErr(c, e)
+		return
+	}
 	c.JSON(http.StatusOK, bookJSON(b, p.Percent, lib.Name))
 }
 

backend/internal/api/libraries.go

@@ -2,6 +2,7 @@ package api
 
 import (
 	"context"
+	"errors"
 	"io"
 	"net/http"
 	"os"
@@ -11,6 +12,7 @@ import (
 	"time"
 
 	"github.com/gin-gonic/gin"
+	"github.com/jackc/pgx/v5"
 
 	"booklib/internal/bookfile"
 	"booklib/internal/store"
@@ -60,7 +62,7 @@ func (a *api) createLibrary(c *gin.Context) {
 			err(c, http.StatusConflict, "exists", "root_path taken")
 			return
 		}
-		err(c, http.StatusBadRequest, "bad_request", "invalid input")
+		dbErr(c, e)
 		return
 	}
 	c.JSON(http.StatusCreated, gin.H{"id": id, "name": req.Name, "root_path": filepath.Clean(req.RootPath)})
@@ -74,9 +76,13 @@ func (a *api) getLibrary(c *gin.Context) (store.Library, bool) {
 	}
 	lib, e := a.st.GetLibrary(c, id)
 	if e != nil {
+		if errors.Is(e, pgx.ErrNoRows) {
 			err(c, http.StatusNotFound, "not_found", "no such library")
 			return store.Library{}, false
 		}
+		dbErr(c, e)
+		return store.Library{}, false
+	}
 	return lib, true
 }