编辑器执行 code 的三种校验失败拆成独立变体

- EditorExecuteError 的 CodeInvalid 拆成 CodeEmpty / CodeContainsNul / CodeTooLong{got_bytes,max_bytes}，每个 case 一个变体
- editor_execute/error.rs 新增 EDITOR_CODE_MAX_BYTES 常量，direct_tool_bridge 的校验改用该常量并分别返回对应变体
- 模型能从文案看出具体违反了哪条规则，不再只看到一句话笼统覆盖三种失败

apps/ai-game-creator-shell/src-tauri/src/agent/direct_tool_bridge.rs

@@ -14,7 +14,9 @@ use crate::agent::tool::edit_image::error::EditImageError;
     target_arch = "x86_64",
     any(feature = "unity-editor-execute", feature = "godot-editor-execute")
 ))]
-use crate::agent::tool::editor_execute::error::{EditorExecuteError, EditorKind};
+use crate::agent::tool::editor_execute::error::{
+    EditorExecuteError, EditorKind, EDITOR_CODE_MAX_BYTES,
+};
 use crate::agent::tool::environment_check::error::EnvironmentCheckError;
 use crate::agent::tool::error::{
     bounded_echo, DirectExecutionGateRejection, DirectTurnGateRejection, ProjectManifestRejection,
@@ -3663,8 +3665,17 @@ pub(in crate::agent) fn editor_execute_code_input(
         .get("code")
         .and_then(Value::as_str)
         .ok_or(EditorExecuteError::CodeNotText { editor })?;
-    if code.trim().is_empty() || code.len() > 131072 || code.contains('\0') {
-        return Err(EditorExecuteError::CodeInvalid);
+    if code.trim().is_empty() {
+        return Err(EditorExecuteError::CodeEmpty);
+    }
+    if code.len() > EDITOR_CODE_MAX_BYTES {
+        return Err(EditorExecuteError::CodeTooLong {
+            got_bytes: code.len(),
+            max_bytes: EDITOR_CODE_MAX_BYTES,
+        });
+    }
+    if code.contains('\0') {
+        return Err(EditorExecuteError::CodeContainsNul);
     }
     Ok(code.to_string())
 }

apps/ai-game-creator-shell/src-tauri/src/agent/tool/editor_execute/error.rs

@@ -5,6 +5,9 @@
 use crate::agent::tool::error::{ProjectPermissionRejection, ToolArgumentsRejection, ToolFailure};
 use serde_json::Value;
 
+/// `code` 的长度上限（字节）：编辑器适配器按 UTF-8 字节数收代码。
+pub(crate) const EDITOR_CODE_MAX_BYTES: usize = 131_072;
+
 /// 两个编辑器执行工具之间的差异：插件身份、给用户看的编辑器名、代码语言名。
 ///
 /// 差异做成枚举，错误变体只带 `EditorKind`，不在文案里手写编辑器名。
@@ -48,7 +51,15 @@ pub(crate) enum EditorExecuteError {
     CodeNotText {
         editor: EditorKind,
     },
-    CodeInvalid,
+    /// `code` 只有空白。
+    CodeEmpty,
+    /// `code` 含 NUL：适配器与传输层都不接受。
+    CodeContainsNul,
+    /// `code` 超过 [`EDITOR_CODE_MAX_BYTES`]。
+    CodeTooLong {
+        got_bytes: usize,
+        max_bytes: usize,
+    },
     /// 编辑器适配器拒绝了这次执行，或回执不可用。
     EditorRejected {
         cause: String,
@@ -87,7 +98,12 @@ impl ToolFailure for EditorExecuteError {
             Self::CodeNotText { editor } => {
                 format!("code 必须是 {}。", editor.language())
             }
-            Self::CodeInvalid => "code 不能为空、包含 NUL 或超过 128 KiB。".to_string(),
+            Self::CodeEmpty => "code 不能为空。".to_string(),
+            Self::CodeContainsNul => "code 不能包含 NUL。".to_string(),
+            Self::CodeTooLong {
+                got_bytes,
+                max_bytes,
+            } => format!("code 有 {got_bytes} 字节，超过上限 {max_bytes} 字节。"),
             Self::EditorRejected { cause } => cause.to_string(),
             Self::ExecutionNotCompleted { editor, report } => {
                 format!("{} 执行未完成：{report}", editor.label())