db+game: schema_version on saves with ordered idempotent backfill (v2 bodies, v3 crew) — no more DB wipes

lib/db/client.ts

@@ -24,7 +24,8 @@ CREATE TABLE IF NOT EXISTS saves (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   seed TEXT NOT NULL,
   turn INTEGER NOT NULL DEFAULT 0,
-  created_at TEXT NOT NULL
+  created_at TEXT NOT NULL,
+  schema_version INTEGER -- which save-schema version this row was backfilled up to (NULL = v1)
 );
 
 CREATE TABLE IF NOT EXISTS solar_systems (
@@ -98,6 +99,14 @@ async function open(file: string): Promise<GameDb> {
   const raw = bytes ? new SQL.Database(new Uint8Array(bytes)) : new SQL.Database();
   raw.exec(DDL); // no-op for tables that already exist in an older file
 
+  // Idempotent evolution for files created by older code: CREATE TABLE IF NOT EXISTS above cannot
+  // add columns, so check and add any that are missing. This is what makes DB wipes unnecessary —
+  // old saves open fine and get backfilled by ensureSave (see lib/game/save.ts).
+  const saveCols = raw.exec('PRAGMA table_info(saves)')[0]?.values.map((v) => v[1]) ?? [];
+  if (!saveCols.includes('schema_version')) {
+    raw.exec('ALTER TABLE saves ADD COLUMN schema_version INTEGER');
+  }
+
   const instance: GameDb = { db: drizzle(raw, { schema }), raw, file };
 
   // First run: stamp when this DB was created and land the file on disk so the ./db volume