diff --git a/src/gateway/execution.rs b/src/gateway/execution.rs
index 4964a46..b812470 100644
--- a/src/gateway/execution.rs
+++ b/src/gateway/execution.rs
@@ -6,7 +6,7 @@ use crate::agent::{AgentError, AgentProcessResult, EmittedMessageHandler, Persis
 use crate::bus::message::ToolMessageState;
 use crate::bus::{ChatMessage, MediaItem, OutboundMessage, SYSTEM_CONTEXT_SCHEDULED_PROMPT};
 use crate::config::LLMProviderConfig;
-use crate::storage::ConversationRepository;
+use crate::storage::{persistent_session_id, ConversationRepository};
 use tokio::sync::Mutex;
 
 use super::compaction::schedule_background_history_compaction;
@@ -252,7 +252,7 @@ impl AgentExecutionService {
 
         // 构建系统提示词上下文
         let system_prompt_context = SystemPromptContext {
-            session_id: Some(format!("{}:{}", request.channel_name, request.chat_id)),
+            session_id: Some(persistent_session_id(request.channel_name, request.chat_id)),
             chat_id: request.chat_id.to_string(),
             user_message_count,
         };
@@ -356,7 +356,7 @@ impl AgentExecutionService {
 
         // 构建系统提示词上下文
         let system_prompt_context = SystemPromptContext {
-            session_id: Some(format!("{}:{}", request.channel_name, request.chat_id)),
+            session_id: Some(persistent_session_id(request.channel_name, request.chat_id)),
             chat_id: request.chat_id.to_string(),
             user_message_count,
         };
diff --git a/src/storage/mod.rs b/src/storage/mod.rs
index dc2f198..6a5d0f2 100644
--- a/src/storage/mod.rs
+++ b/src/storage/mod.rs
@@ -1601,6 +1601,13 @@ impl SessionStore {
 }
 
 pub fn persistent_session_id(channel_name: &str, chat_id: &str) -> String {
+    // 幂等：循环去除已存在的 "{channel_name}:" 前缀，防止前缀累积
+    let prefix = format!("{}:", channel_name);
+    let mut chat_id = chat_id;
+    while chat_id.starts_with(&prefix) {
+        chat_id = &chat_id[prefix.len()..];
+    }
+
     if channel_name == "cli" || channel_name == "websocket" {
         chat_id.to_string()
     } else {
@@ -2288,8 +2295,12 @@ mod tests {
     #[test]
     fn test_persistent_session_id_for_cli_and_channel() {
         assert_eq!(persistent_session_id("cli", "abc"), "abc");
-        assert_eq!(persistent_session_id("websocket", "websocket:abc"), "websocket:abc");
+        // 幂等：已带前缀的 chat_id 会被清理，不会累积前缀
+        assert_eq!(persistent_session_id("websocket", "websocket:abc"), "abc");
+        assert_eq!(persistent_session_id("websocket", "websocket:websocket:abc"), "abc");
         assert_eq!(persistent_session_id(TEST_CHANNEL, "abc"), "test-channel:abc");
+        // 其他通道也幂等
+        assert_eq!(persistent_session_id(TEST_CHANNEL, "test-channel:abc"), "test-channel:abc");
     }
 
     #[test]