初始提交：DSH 多租户平台（dshs）

src/db/prepared.ts

@@ -0,0 +1,29 @@
+/**
+ * Prepared-statement cache. better-sqlite3 does not cache `db.prepare`, so
+ * re-preparing the same SQL on every call re-parses it. This memoizes prepared
+ * statements per connection (WeakMap), which matters for hot paths such as
+ * authentication and the reverse proxy.
+ * @module dshs/db/prepared
+ */
+
+import type Database from 'better-sqlite3'
+import type { Database as Db } from './connection.js'
+
+type Statement = Database.Statement<unknown[], unknown>
+
+const caches = new WeakMap<Db, Map<string, Statement>>()
+
+/** Prepare (and cache) a statement for a connection. */
+export function prepare(db: Db, sql: string): Statement {
+  let cache = caches.get(db)
+  if (cache === undefined) {
+    cache = new Map()
+    caches.set(db, cache)
+  }
+  let statement = cache.get(sql)
+  if (statement === undefined) {
+    statement = db.prepare(sql)
+    cache.set(sql, statement)
+  }
+  return statement
+}