feat: add driver interface, database resolution

test/unit/db/driver.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from 'vitest'
+import type { ConnectionConfig } from '../../../src/config/types.js'
+import { MissingDatabaseError, resolveDatabase } from '../../../src/db/driver.js'
+
+const config: ConnectionConfig = {
+    name: 'c',
+    type: 'postgres',
+    host: 'h',
+    user: 'u',
+    readonly: false
+}
+
+describe('resolveDatabase', () => {
+    it('prefers the explicit parameter', () => {
+        expect(resolveDatabase({ ...config, database: 'default-db' }, 'explicit')).toBe('explicit')
+    })
+
+    it('falls back to the connection default', () => {
+        expect(resolveDatabase({ ...config, database: 'default-db' }, undefined)).toBe('default-db')
+    })
+
+    it('throws when neither is set', () => {
+        expect(() => resolveDatabase(config, undefined)).toThrow(MissingDatabaseError)
+    })
+})