Fix startup crash when a widget's old-named table already coexists with its new widget_<id>_ name

migrate()'s PoE2/Stocks/Bookmarks table renames assumed the old-named
table's mere existence meant the widget_<id>_-named table didn't exist
yet, and failed with "already another table or index with this name"
on any DB where both were already present (e.g. an interrupted prior
migration, or an earlier widget-system build that created the new
name directly via plugin.migrate()'s CREATE TABLE IF NOT EXISTS).
renameTableIfSafe() now checks the destination name first and drops
the redundant old-named leftover instead of colliding with it — the
widget_<id>_-named table is always the one actually read from/written
to, so it's authoritative whenever both are present.

backend/src/storage/db/index.ts

@@ -18,6 +18,25 @@ db.exec('PRAGMA journal_mode = WAL;');
 db.exec('PRAGMA foreign_keys = ON;');
 
 export function migrate() {
+	const tableExists = (name: string) =>
+		!!db.prepare(`SELECT name FROM sqlite_master WHERE type='table' AND name=?`).get(name);
+
+	// Renames oldName to newName, but only if newName isn't already taken — a DB that's
+	// been through an interrupted migration, or an earlier build of the widget system
+	// that created the widget_<id>_-named table directly (e.g. via plugin.migrate()'s
+	// CREATE TABLE IF NOT EXISTS running before this rename ever got a chance to), can
+	// end up with both names present. In that case the widget_<id>_-named table is the
+	// one actually in use (every read/write goes through it), so the old-named leftover
+	// is just dropped rather than failing outright on the name collision.
+	const renameTableIfSafe = (oldName: string, newName: string) => {
+		if (!tableExists(oldName)) return;
+		if (tableExists(newName)) {
+			db.exec(`DROP TABLE "${oldName}";`);
+			return;
+		}
+		db.exec(`ALTER TABLE "${oldName}" RENAME TO "${newName}";`);
+	};
+
 	// Admin auth moved from username/password + sessions to a per-launch API key (see
 	// api/apiKey.ts, api/auth.ts) — these tables, and any stored password hash or live
 	// session in them, have no further purpose and are dropped rather than left as
@@ -38,25 +57,19 @@ export function migrate() {
 	// a plain rename (metadata-only in SQLite, no row copy) rather than grandfathering
 	// the old names in via an exceptions list, since it's cheap and PoE2 is meant to be
 	// the reference implementation of the convention it establishes.
-	const hasOldPoe2Table = db.prepare(`SELECT name FROM sqlite_master WHERE type='table' AND name='poe2_watchlist'`).get();
-	if (hasOldPoe2Table) {
-		db.exec('ALTER TABLE poe2_watchlist RENAME TO widget_poe2_watchlist;');
-		db.exec('ALTER TABLE poe2_rate_history RENAME TO widget_poe2_rate_history;');
-		db.exec('DROP INDEX IF EXISTS idx_poe2_rate_history_watchlist;');
-	}
+	renameTableIfSafe('poe2_watchlist', 'widget_poe2_watchlist');
+	renameTableIfSafe('poe2_rate_history', 'widget_poe2_rate_history');
+	db.exec('DROP INDEX IF EXISTS idx_poe2_rate_history_watchlist;');
 
 	// Stocks and Bookmarks moved into the pluggable-widget system too (backend/src/widgets/
 	// stocks/, widgets/bookmarks/) — same plain-rename treatment as PoE2 above, now owned by
 	// each widget's own plugin.migrate() instead of this file's CREATE TABLE block.
-	const hasOldStockTickersTable = db.prepare(`SELECT name FROM sqlite_master WHERE type='table' AND name='stock_tickers'`).get();
-	if (hasOldStockTickersTable) {
-		db.exec('ALTER TABLE stock_tickers RENAME TO widget_stocks_tickers;');
-	}
+	renameTableIfSafe('stock_tickers', 'widget_stocks_tickers');
 	// "bookmarks" is generic enough to collide with something else entirely — check for the
 	// old bookmarks shape specifically (its distinctive is_private column) before renaming.
 	const oldBookmarksCols = db.prepare(`PRAGMA table_info(bookmarks)`).all() as { name: string }[];
 	if (oldBookmarksCols.some((c) => c.name === 'is_private')) {
-		db.exec('ALTER TABLE bookmarks RENAME TO widget_bookmarks_items;');
+		renameTableIfSafe('bookmarks', 'widget_bookmarks_items');
 	}
 
 	db.exec(`