Add opt-in slow SQL and database diagnostics

tests/unit/slow-statements.test.ts

@@ -0,0 +1,32 @@
+import Database from 'better-sqlite3';
+import { afterEach, expect, it, vi } from 'vitest';
+import { timeStatement } from '../../src/lib/server/db/slow-statements.js';
+
+afterEach(() => vi.restoreAllMocks());
+
+it('preserves results and errors, logs slow query shapes without values', () => {
+    const db = new Database(':memory:');
+    const log = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    vi.spyOn(performance, 'now').mockReturnValueOnce(0).mockReturnValueOnce(21)
+        .mockReturnValueOnce(30).mockReturnValueOnce(31).mockReturnValueOnce(40).mockReturnValueOnce(62);
+    try {
+        const query = timeStatement(db.prepare("SELECT ? AS value, 'private''literal' AS literal"), "SELECT ? AS value, 'private''literal' AS literal", 20);
+        expect(query.get('secret')).toEqual({ value: 'secret', literal: "private'literal" });
+        expect(query.all('other')).toHaveLength(1);
+        expect(() => query.get()).toThrow();
+        expect(log).toHaveBeenCalledTimes(2);
+        expect(log.mock.calls[0]).toEqual(['[sql]', { ms: 21, method: 'get', sql: 'SELECT ? AS value, ? AS literal' }]);
+        expect(JSON.stringify(log.mock.calls)).not.toMatch(/secret|private|other/);
+    } finally { db.close(); }
+});
+
+it('does not wrap statements when disabled or invalid', () => {
+    const db = new Database(':memory:');
+    try {
+        const statement = db.prepare('SELECT 1');
+        const get = statement.get;
+        for (const threshold of [0, -1, NaN, Infinity]) {
+            expect(timeStatement(statement, 'SELECT 1', threshold).get).toBe(get);
+        }
+    } finally { db.close(); }
+});