feat: add precise diagnostics and optional client copy logging controls

contract/policy.go

@@ -3,9 +3,11 @@ package contract
 import (
 	"context"
 	"errors"
-	"fmt"
 	"io"
+	"strings"
 	"unicode/utf8"
+
+	"git.yuntuo.hk/k2safe/go-omni/internal/configdiag"
 )
 
 // RequestPolicy describes protocol strictness, independently of business
@@ -35,7 +37,7 @@ func (p RequestPolicy) Validate() error {
 			ok = ok || value == item.value
 		}
 		if !ok {
-			return fmt.Errorf("request policy: invalid %s", item.name)
+			return configdiag.New(item.name, "must be one of "+strings.Join(item.allowed, ", "))
 		}
 	}
 	return nil