feat: 更新工具描述，添加重要的目标配置说明以优化任务执行逻辑

src/providers/openai.rs

@@ -128,12 +128,24 @@ impl OpenAIProvider {
         let normalized = self.normalize_tool_arguments(arguments);
 
         if self.uses_json_tool_arguments() {
+            // Model expects JSON object format
             normalized
         } else {
+            // Standard OpenAI format: arguments as JSON string
+            // But ensure we serialize valid JSON, not null
             match normalized {
-                Value::String(raw) => Value::String(raw),
+                Value::String(raw) => {
+                    // If the string is already valid JSON, keep it as-is
+                    // Otherwise, ensure it's a proper JSON string
+                    if serde_json::from_str::<Value>(raw).is_ok() {
+                        Value::String(raw)
+                    } else {
+                        // Invalid JSON string - wrap it as a proper JSON string
+                        serde_json::to_string(&raw).unwrap_or_else(|_| "null".to_string())
+                    }
+                }
                 value => Value::String(
-                    serde_json::to_string(&value).unwrap_or_else(|_| "null".to_string()),
+                    serde_json::to_string(&value).unwrap_or_else(|_| "{}".to_string()),
                 ),
             }
         }

src/tools/scheduler_manage.rs

@@ -31,7 +31,16 @@ impl Tool for SchedulerManageTool {
     }
 
     fn description(&self) -> &str {
-        "Manage repository-backed scheduled jobs. Supports actions: list, get, put, delete, pause, resume. Jobs are persisted by the configured scheduler job repository and executed by the scheduler runtime. When creating agent_task or silent_agent_task jobs, keep prompt/system_prompt focused on the work to perform; do not restate execution times unless the task logic truly depends on them, because the trigger already controls timing. For cron schedules, standard cron syntax is supported: use 1-5 for Monday-Friday, 0 or 7 for Sunday."
+        "Manage repository-backed scheduled jobs. Supports actions: list, get, put, delete, pause, resume. Jobs are persisted by the configured scheduler job repository and executed by the scheduler runtime. \
+        \
+        When creating agent_task or silent_agent_task jobs, keep prompt/system_prompt focused on the work to perform; do not restate execution times unless the task logic truly depends on them, because the trigger already controls timing. For cron schedules, standard cron syntax is supported: use 1-5 for Monday-Friday, 0 or 7 for Sunday. \
+        \
+        IMPORTANT - Target Configuration: \
+        For agent_task and silent_agent_task, the target.channel and target.chat_id determine where notifications are sent. \
+        - If target is omitted or fields are empty, they are automatically filled from the current conversation context. \
+        - To send to the current conversation: omit target or set target fields to null/empty. \
+        - To send to a specific target: explicitly provide channel (e.g., 'feishu', 'wechat', 'cli') and chat_id (e.g., 'oc_xxx'). \
+        - Do NOT use placeholder values like 'current' or 'default' - these will be treated as literal values and cause message delivery failures."
     }
 
     fn parameters_schema(&self) -> serde_json::Value {