test: add property-based tests for export and dedup invariants (issue #44 phase 2)

tests/helpers/memdb.ts

@@ -0,0 +1,17 @@
+// Test helper: fresh in-memory database with the full Recall schema.
+//
+// Property-based suites create a database per generated case (dozens per
+// test), so the file-backed setupTestDb harness is too heavy — this builds
+// the same tables/indexes in memory in ~1ms. FTS virtual tables and triggers
+// are omitted: the export/dedup logic under property test never touches them.
+import { Database } from 'bun:sqlite';
+import { CREATE_TABLES, CREATE_INDEXES, CREATE_VECTOR_TABLES } from '../../src/db/schema';
+
+export function createMemoryDb(): Database {
+  const db = new Database(':memory:');
+  db.exec('PRAGMA foreign_keys = ON'); // matches production getDb()
+  db.exec(CREATE_TABLES);
+  db.exec(CREATE_INDEXES);
+  db.exec(CREATE_VECTOR_TABLES);
+  return db;
+}