feat: first commit

backend/internal/domain/errors.go

@@ -0,0 +1,18 @@
+package domain
+
+import "errors"
+
+// Sentinel errors crossing the port boundary. Adapters translate infra errors
+// into these; HTTP layer maps these to status codes.
+var (
+	ErrNotFound     = errors.New("not found")
+	ErrCodeTaken    = errors.New("code already taken")
+	ErrReserved     = errors.New("code is reserved")
+	ErrInvalidURL   = errors.New("invalid destination url")
+	ErrInvalidAlias = errors.New("invalid custom alias")
+	ErrInvalidPin   = errors.New("pin must be exactly 6 digits")
+	ErrUnauthorized = errors.New("authentication required")
+	ErrForbidden    = errors.New("not allowed")
+	ErrPinRequired  = errors.New("pin required")
+	ErrPinInvalid   = errors.New("incorrect pin")
+)