打通多模态 UI 工作流与 Agent Runtime 路由

- 接入 Codex app-server 原生图片输入与隔离暂存

- 统一 UI 识别、合并、绑定到 Agent Runtime Provider

- 增加页面自动发现、UI 资源桥接与阶段持久化

- 同步画布编辑器投影、测试与技术文档

server-rs/crates/platform-llm/src/lib.rs

@@ -1295,7 +1295,12 @@ impl LlmRunRequest {
         self
     }
 
-    fn validate(&self) -> Result<(), LlmError> {
+    /// Validate a request before handing it to any transport adapter.
+    ///
+    /// Runtime adapters such as Codex app-server do not use `LlmClient::run`
+    /// and therefore must still enforce the exact same message/tool contract
+    /// before opening an upstream request.
+    pub fn validate_for_transport(&self) -> Result<(), LlmError> {
         if self.messages.is_empty() {
             return Err(LlmError::InvalidRequest(
                 "LLM messages 不能为空".to_string(),
@@ -1327,15 +1332,16 @@ impl LlmRunRequest {
                 ));
             }
 
-            if self.api_kind == LlmApiKind::OpenAiResponses
-                && message.role == LlmMessageRole::Assistant
-                && message
-                    .content_parts
-                    .iter()
-                    .any(|part| matches!(part, LlmMessageContentPart::InputImage { .. }))
+            if matches!(
+                message.role,
+                LlmMessageRole::System | LlmMessageRole::Assistant
+            ) && message
+                .content_parts
+                .iter()
+                .any(|part| matches!(part, LlmMessageContentPart::InputImage { .. }))
             {
                 return Err(LlmError::InvalidRequest(
-                    "OpenAI Responses assistant 消息不支持 input_image".to_string(),
+                    "system/assistant 消息不支持 input_image；图片必须放在 user 消息".to_string(),
                 ));
             }
         }
@@ -1408,6 +1414,10 @@ impl LlmRunRequest {
         Ok(())
     }
 
+    fn validate(&self) -> Result<(), LlmError> {
+        self.validate_for_transport()
+    }
+
     fn resolved_model<'a>(&'a self, fallback_model: &'a str) -> &'a str {
         self.model
             .as_deref()