Remove shared prepared statement cache (Refs #76)

src/lib/server/db/index.ts

@@ -645,21 +645,15 @@ export function db(): Database.Database {
         throw err;
     }
 
-    // Cache only runtime queries, after migrations have finished. Statements
-    // belong to this connection, so reopening the DB starts with an empty cache.
-    // Callers share statement options (e.g. raw()); use consistent options for
-    // identical SQL and pass values to run/get/all rather than binding permanently.
-    const statements = new Map<string, Database.Statement>();
+    // Instrument runtime queries after migrations. Each prepare must return a
+    // fresh statement: modes, permanent bindings, and active iterators are mutable
+    // state owned by the caller, even when another caller uses identical SQL.
     const slowMs = Number(process.env.EC_SLOW_SQL_MS ?? 0);
-    const prepare = handle.prepare.bind(handle);
-    handle.prepare = ((sql: string) => {
-        let statement = statements.get(sql);
-        if (!statement) {
-            statement = timeStatement(prepare(sql), sql, slowMs);
-            statements.set(sql, statement);
-        }
-        return statement;
-    }) as typeof handle.prepare;
+    if (Number.isFinite(slowMs) && slowMs > 0) {
+        const prepare = handle.prepare.bind(handle);
+        handle.prepare = ((sql: string) =>
+            timeStatement(prepare(sql), sql, slowMs)) as typeof handle.prepare;
+    }
 
     _db = handle;
     optimizeTimer = setInterval(() => {