给 Skill 引用补上每条消息的数量上限

- apps/ai-game-creator-shell/src-tauri/src/agent/direct_codex_user_item/validation.rs 新增 MAX_DIRECT_CODEX_SKILL_REFERENCES=32 与 skill_count 计数，超出即拒绝
- 附件与素材引用已有上限，Skill 引用是唯一没有上限的非文本 part：每条都会触发一次 root/<name>/SKILL.md 文件探测并往 turn/start.input 里加一项，畸形超长 userItem 可以放大文件探测与模型输入
- 补上 inline_skill_reference_count_is_bounded_independently；cargo test direct_codex_user_item::validation：7 passed

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

@@ -10,6 +10,9 @@ use crate::agent::{
 use std::path::Path;
 
 pub(crate) const MAX_DIRECT_CODEX_REFERENCES: usize = 32;
+// Skill 引用也是非文本 part，但没有走 reference_count：它每一条都会触发一次
+// `root/<name>/SKILL.md` 文件探测并往 turn input 里加一项，所以单独设上限。
+pub(crate) const MAX_DIRECT_CODEX_SKILL_REFERENCES: usize = 32;
 
 pub(crate) fn validate_direct_codex_user_item(
     root: &Path,
@@ -30,6 +33,7 @@ pub(crate) fn validate_direct_codex_user_item(
     let manifest = read_manifest_for_project(root)?;
     let mut reference_count = 0usize;
     let mut attachment_count = 0usize;
+    let mut skill_count = 0usize;
     for part in &message.content {
         match part {
             DirectCodexUserContentPart::InputText { .. } => {}
@@ -38,6 +42,12 @@ pub(crate) fn validate_direct_codex_user_item(
                 validate_resource_id_and_manifest(&manifest, resource_id)?;
             }
             DirectCodexUserContentPart::AgcSkillReference { name } => {
+                skill_count = skill_count.saturating_add(1);
+                if skill_count > MAX_DIRECT_CODEX_SKILL_REFERENCES {
+                    return Err(format!(
+                        "一次最多引用 {MAX_DIRECT_CODEX_SKILL_REFERENCES} 个 Skill"
+                    ));
+                }
                 let name = name.trim();
                 if name.is_empty()
                     || name.chars().count() > 120
@@ -150,7 +160,10 @@ fn validate_runtime_region_reference(
 
 #[cfg(test)]
 mod tests {
-    use super::{content_has_meaningful_input, validate_direct_codex_user_item};
+    use super::{
+        content_has_meaningful_input, validate_direct_codex_user_item,
+        MAX_DIRECT_CODEX_SKILL_REFERENCES,
+    };
     use crate::agent::direct_codex_user_item::model::DirectCodexUserContentPart;
     use serde_json::json;
 
@@ -246,6 +259,26 @@ mod tests {
         assert!(error.contains("缺少项目路径"), "{error}");
     }
 
+    #[test]
+    fn inline_skill_reference_count_is_bounded_independently() {
+        let root = tempfile::tempdir().expect("temp project");
+        crate::init_local_game_project_at(root.path(), "validation-test", "校验测试")
+            .expect("init project");
+        let content = (0..=MAX_DIRECT_CODEX_SKILL_REFERENCES)
+            .map(|index| json!({ "type": "agc_skill_reference", "name": format!("skill-{index}") }))
+            .collect::<Vec<_>>();
+        let item = serde_json::from_value(json!({
+            "type": "message",
+            "role": "user",
+            "content": content,
+            "id": "turn-1:user"
+        }))
+        .expect("deserialize user item");
+        let error = validate_direct_codex_user_item(root.path(), &item)
+            .expect_err("too many skill references must be rejected");
+        assert!(error.contains("最多引用"), "{error}");
+    }
+
     #[test]
     fn attachment_name_and_media_type_are_bounded_and_well_formed() {
         let root = tempfile::tempdir().expect("temp project");