diff --git a/src/storage/mod.rs b/src/storage/mod.rs
index a62cd34..ead4bbe 100644
--- a/src/storage/mod.rs
+++ b/src/storage/mod.rs
@@ -3,7 +3,7 @@ use std::path::{Path, PathBuf};
 
 use r2d2::Pool;
 use r2d2_sqlite::SqliteConnectionManager;
-use rusqlite::{Connection, OptionalExtension, params};
+use rusqlite::{Connection, OptionalExtension, TransactionBehavior, params};
 
 use crate::bus::ChatMessage;
 
@@ -62,7 +62,7 @@ impl SessionStore {
     /// The connection is used for schema initialization only; the pool
     /// manages subsequent connections using the same file path.
     fn from_connection(conn: Connection, db_uri: &str) -> Result<Self, StorageError> {
-        conn.busy_timeout(std::time::Duration::from_secs(5))?;
+        conn.busy_timeout(std::time::Duration::from_secs(30))?;
         conn.execute_batch(
             "
             PRAGMA journal_mode = WAL;
@@ -230,7 +230,7 @@ impl SessionStore {
 
         let manager = SqliteConnectionManager::file(db_uri)
             .with_init(|c| {
-                c.busy_timeout(std::time::Duration::from_secs(5))?;
+                c.busy_timeout(std::time::Duration::from_secs(30))?;
                 Ok(())
             });
         let pool = Pool::builder()
@@ -575,8 +575,8 @@ impl SessionStore {
         topic_id: Option<&str>,
         message: &ChatMessage,
     ) -> Result<(), StorageError> {
-        let conn = self.pool.get()?;
-        let tx = conn.unchecked_transaction()?;
+        let mut conn = self.pool.get()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
 
         let seq: i64 = tx.query_row(
             "SELECT COALESCE(MAX(seq), 0) + 1 FROM messages WHERE session_id = ?1",
@@ -651,8 +651,8 @@ impl SessionStore {
             return Ok(());
         }
 
-        let conn = self.pool.get()?;
-        let tx = conn.unchecked_transaction()?;
+        let mut conn = self.pool.get()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
 
         let mut seq: i64 = tx.query_row(
             "SELECT COALESCE(MAX(seq), 0) + 1 FROM messages WHERE session_id = ?1",
@@ -736,8 +736,8 @@ impl SessionStore {
         summary_message: &ChatMessage,
         preserved_messages: &[ChatMessage],
     ) -> Result<bool, StorageError> {
-        let conn = self.pool.get()?;
-        let tx = conn.unchecked_transaction()?;
+        let mut conn = self.pool.get()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
 
         let current_max_seq: i64 = tx.query_row(
             "SELECT COALESCE(MAX(seq), 0) FROM messages WHERE session_id = ?1",
@@ -833,8 +833,8 @@ impl SessionStore {
         session_id: &str,
         messages: &[ChatMessage],
     ) -> Result<(), StorageError> {
-        let conn = self.pool.get()?;
-        let tx = conn.unchecked_transaction()?;
+        let mut conn = self.pool.get()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
         let now = current_timestamp();
 
         // Delete all existing messages for this session
@@ -892,8 +892,8 @@ impl SessionStore {
         topic_id: &str,
         messages: &[ChatMessage],
     ) -> Result<(), StorageError> {
-        let conn = self.pool.get()?;
-        let tx = conn.unchecked_transaction()?;
+        let mut conn = self.pool.get()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
         let now = current_timestamp();
 
         // Delete only messages belonging to this topic — other topics'
@@ -1023,8 +1023,8 @@ impl SessionStore {
 
     pub fn put_memory(&self, input: &MemoryUpsert) -> Result<MemoryRecord, StorageError> {
         let now = current_timestamp();
-        let conn = self.pool.get()?;
-        let tx = conn.unchecked_transaction()?;
+        let mut conn = self.pool.get()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
 
         let existing: Option<(String, i64)> = tx
             .query_row(
@@ -1611,10 +1611,11 @@ impl SessionStore {
         items: &[TodoRecord],
     ) -> Result<Vec<TodoRecord>, StorageError> {
         let mut conn = self.pool.get()?;
-        // 用 transaction()（非 unchecked_transaction）保证严格事务语义：
+        // 用 BEGIN IMMEDIATE 事务保证严格语义：写锁在事务开始时获取，
+        // 避免并发写事务在提交时死锁导致 "database is locked"。
         // 用户数据替换需保证原子性——中途失败必须回滚，避免 DELETE 后 INSERT
         // 异常导致 todos 列表丢失且无法恢复。
-        let tx = conn.transaction()?;
+        let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
         let now = current_timestamp();
 
         // Delete existing todos for this scope_key