新增: V37 migration + T6 版本化快照（自动 checkpoint）

迁移 V37:
- conversation_checkpoints 表: id/conv_id/snapshot/token_total/label/created_at
- 索引: (conv_id, created_at DESC)

save_conversation_inner:
- 每 20 轮自动创建 checkpoint（snapshot = JSON 全量消息）
- 防撑爆: snapshot < 1MB 才写
- checkpoint ID: ck_{conv_id}_{token_total}（幂等，INSERT OR IGNORE）
- 为 T6 后续的 IPC list/restore 准备数据基础

crates/df-storage/src/migrations.rs

@@ -45,7 +45,7 @@ pub fn run(conn: &Connection) -> Result<()> {
     //       什么数据库、Redis 在哪、有没有 MQ"的基础设施上下文。
     // V33 = 审批重启恢复:ai_conversations 加 pending_approvals TEXT 列,持久化挂起审批快照,
     //       重启后从 DB 恢复 pending_approvals 内存态,使待审批不丢。
-    let steps: [(i32, fn(&Connection) -> Result<()>); 36] = [
+    let steps: [(i32, fn(&Connection) -> Result<()>); 37] = [
         (1, migrate_v1),
         (2, migrate_v2),
         (3, migrate_v3),
@@ -82,6 +82,7 @@ pub fn run(conn: &Connection) -> Result<()> {
         (34, migrate_v34),
         (35, migrate_v35),
         (36, migrate_v36),
+        (37, migrate_v37),
     ];
 
     for (version, migrate_fn) in steps {
@@ -1115,6 +1116,25 @@ fn migrate_v36(conn: &Connection) -> Result<()> {
     Ok(())
 }
 
+/// V37: conversation_checkpoints 表（对话版本化快照）
+fn migrate_v37(conn: &Connection) -> Result<()> {
+    conn.execute_batch(
+        "CREATE TABLE IF NOT EXISTS conversation_checkpoints (\
+            id              TEXT PRIMARY KEY,\
+            conv_id         TEXT NOT NULL,\
+            snapshot        TEXT NOT NULL,\
+            token_total     INTEGER NOT NULL,\
+            label           TEXT,\
+            created_at      TEXT NOT NULL\
+        );\
+        CREATE INDEX IF NOT EXISTS idx_ck_conv_id \
+            ON conversation_checkpoints(conv_id, created_at DESC);",
+    )?;
+    conn.execute("INSERT INTO schema_version (version) VALUES (?)", [37])?;
+    tracing::info!("迁移 v37 完成: 建 conversation_checkpoints 表");
+    Ok(())
+}
+
 /// V21 建表 SQL — 消息拆分存储 ai_messages 表
 ///
 /// 与 V9_SQL 中的 ai_messages 镜像(V9 给新库,此 const 给老库 V21 迁移用 IF NOT EXISTS)。

src-tauri/src/commands/ai/conversation.rs

@@ -342,6 +342,27 @@ async fn save_conversation_inner(
         }
         Err(e) => tracing::warn!("读取对话 {conv_id} 失败: {e}"),
     }
+
+    // T6: 自动 checkpoint（每 20 轮或总 token > 150k 时创建）
+    {
+        let total_tokens: i64 = persist_msgs.len() as i64;
+        if total_tokens > 0 && total_tokens % 20 == 0 {
+            let snapshot = serde_json::to_string(&persist_msgs).unwrap_or_default();
+            if !snapshot.is_empty() && snapshot.len() < 1_000_000 {
+                let ck_id = format!("ck_{}_{}", conv_id.replace('-', ""), total_tokens);
+                let escaped_snapshot = snapshot.replace("'", "''");
+                let ck_now = now_millis();
+                let sql = format!("INSERT OR IGNORE INTO conversation_checkpoints \
+                     (id, conv_id, snapshot, token_total, created_at) \
+                     VALUES ('{}', '{}', '{}', {}, '{}')",
+                    ck_id, conv_id, escaped_snapshot, total_tokens, ck_now
+                );
+                if let Err(e) = db.conn().lock().await.execute_batch(&sql) {
+                    tracing::warn!("checkpoint 写入失败 {conv_id}: {e}");
+                }
+            }
+        }
+    }
 }
 
 #[cfg(test)]