分页 offset 上限收成必填参数与单一常量，三个列表工具口径一致

- arguments::page 的 max_offset 由 Option<usize> 改成 usize：调用点必须显式给出上限，不能靠漏传 Option 变成无上限
- 新增 TOOL_PAGE_MAX_OFFSET = 500（与 agc_list_project_files / agc_list_account_assets 的 inputSchema offset.maximum 一致），三个列表工具统一传它；agc_list_registered_assets 原来传 None（无上限），现在同样收敛到 500
- agc_list_registered_assets 的 inputSchema offset 同步补 maximum: 500，保持 schema 与校验一致（这是一个公开入参范围的收窄）
- 只改 offset 边界来源；limit 默认值与上限、分页语义不变

验证：cargo test --bin genarrative-ai-game-creator-shell -- agent:: 952 passed / 0 failed

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

@@ -1,6 +1,8 @@
 use super::*;
 use crate::agent::tool::apply_patch::error::ApplyPatchError;
-use crate::agent::tool::arguments::{optional_text, page, required_text, ToolPage, ToolTextField};
+use crate::agent::tool::arguments::{
+    optional_text, page, required_text, ToolPage, ToolTextField, TOOL_PAGE_MAX_OFFSET,
+};
 use crate::agent::tool::browser_playtest::error::BrowserPlaytestError;
 #[cfg(all(windows, feature = "cocos-editor-execute"))]
 use crate::agent::tool::cocos_execute::error::CocosExecuteError;
@@ -1191,7 +1193,7 @@ pub(in crate::agent) fn list_registered_assets_input(
         arguments,
         50,
         DIRECT_TOOL_BRIDGE_MAX_RESOURCE_PAGE_SIZE,
-        None,
+        TOOL_PAGE_MAX_OFFSET,
     )?;
     Ok(ListRegisteredAssetsInput {
         kind,
@@ -1537,7 +1539,7 @@ pub(in crate::agent) fn list_project_files_input(
         arguments,
         100,
         DIRECT_TOOL_BRIDGE_MAX_RESOURCE_PAGE_SIZE,
-        Some(500),
+        TOOL_PAGE_MAX_OFFSET,
     )?;
     Ok(ListProjectFilesInput {
         path,
@@ -1955,7 +1957,7 @@ pub(in crate::agent) fn list_account_assets_input(
         arguments,
         100,
         DIRECT_TOOL_BRIDGE_MAX_RESOURCE_PAGE_SIZE,
-        Some(500),
+        TOOL_PAGE_MAX_OFFSET,
     )?;
     Ok(ListAccountAssetsInput {
         folder_id,

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

@@ -405,7 +405,7 @@ fn direct_tools_mcp_specs_for_plugins(
                             "default": false,
                             "description": prompt_text!("directTools.agc_list_registered_assets.parameters.includeSequenceFrames")
                         },
-                        "offset": { "type": "integer", "minimum": 0, "default": 0 },
+                        "offset": { "type": "integer", "minimum": 0, "maximum": 500, "default": 0 },
                         "limit": { "type": "integer", "minimum": 1, "maximum": 100, "default": 50 }
                     },
                     "additionalProperties": false

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

@@ -53,12 +53,18 @@ pub(crate) struct ToolPage {
     pub limit: usize,
 }
 
+/// 三个列表工具共用的 `offset` 上限：每个调用点都必须显式传值，避免某一路悄悄不设上限。
+///
+/// 取值与 `agc_list_project_files` / `agc_list_account_assets` 的 inputSchema
+/// `offset.maximum` 一致；`agc_list_registered_assets` 的 schema 同步为同一个值。
+pub(crate) const TOOL_PAGE_MAX_OFFSET: usize = 500;
+
 /// 解析 `offset`/`limit`。分页规则在三个列表工具之间一致，只有默认值与上限不同。
 pub(crate) fn page(
     arguments: &Value,
     default_limit: usize,
     max_limit: usize,
-    max_offset: Option<usize>,
+    max_offset: usize,
 ) -> Result<ToolPage, ToolPageRejection> {
     let offset = arguments
         .get("offset")
@@ -73,8 +79,11 @@ pub(crate) fn page(
         })
         .transpose()?
         .unwrap_or(0);
-    if let Some(max) = max_offset.filter(|max| offset > *max) {
-        return Err(ToolPageRejection::OffsetTooLarge { got: offset, max });
+    if offset > max_offset {
+        return Err(ToolPageRejection::OffsetTooLarge {
+            got: offset,
+            max: max_offset,
+        });
     }
     let limit = arguments
         .get("limit")