add response versioning support in messages for regeneration improvements

src/db/schema.js

@@ -236,6 +236,16 @@ export function initializeSchema(db) {
 }
 
 export function runMigrations(db, {dropLegacyChats = true} = {}) {
+    db.exec(`CREATE TABLE IF NOT EXISTS chat_message_versions (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        message_id INTEGER NOT NULL REFERENCES chat_messages(id) ON DELETE CASCADE,
+        content TEXT NOT NULL,
+        thinking TEXT,
+        sources TEXT,
+        model_name TEXT,
+        created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+    );
+    CREATE INDEX IF NOT EXISTS chat_message_versions_message ON chat_message_versions(message_id);`);
     const ensureColumn = (tableName, columns, name, sql) => {
         if (!columns.some((column) => column.name === name)) {
             db.prepare(sql).run();