feat(ports): define consumer-side interfaces, sentinel errors, IsUniqueViolation

backend/internal/ports/errors.go

@@ -0,0 +1,24 @@
+package ports
+
+import (
+	"errors"
+
+	"booklib/internal/store"
+)
+
+// Re-export sentinel errors so handlers can use errors.Is via ports.
+var (
+	ErrLastAdmin       = store.ErrLastAdmin
+	ErrUniqueViolation = store.ErrUniqueViolation
+)
+
+// IsUniqueViolation consolidates the pg 23505 check into a single predicate.
+func IsUniqueViolation(err error) bool { return store.IsUniqueViolation(err) }
+
+// Upload sentinel errors.
+var (
+	ErrTooLarge     = errors.New("file too large")
+	ErrIncomplete   = errors.New("upload incomplete")
+	ErrSizeMismatch = errors.New("size mismatch")
+	ErrNotFound     = errors.New("not found")
+)