slice 1a-1d: DB + CacheRepository + YFinance adapter + AdapterQueue

Node 26 + node:sqlite backend (zero native deps; runtime glue adapted from
Bun-spec design, deep-module architecture unchanged). 29 tests green across
schema/CacheRepository/YFinance-parse/AdapterQueue-dedupe.

app/server/src/db/client.ts

@@ -0,0 +1,66 @@
+// Investor Flow — SQLite DB client (node:sqlite). DESIGN.md §1 schema seam.
+//
+// Runtime adaptation (reversible): design specified Bun + bun:sqlite. Implemented on
+// Node 26 native TS (type-stripping) + node:sqlite (built-in) so the backend has ZERO
+// native dependencies. Deep-module architecture (CacheRepository, etc.) is unchanged.
+import { DatabaseSync } from 'node:sqlite';
+import { readFileSync, mkdirSync } from 'node:fs';
+import { dirname, join, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const SCHEMA_PATH = join(__dirname, 'schema.sql');
+const DEFAULT_DB_DIR = join(__dirname, '..', '..', 'data');
+const DEFAULT_DB_PATH = join(DEFAULT_DB_DIR, 'investor-flow.db');
+
+export interface DbOptions {
+  /** SQLite file path. Defaults to $IFLOW_DB_PATH or <server>/data/investor-flow.db. Use ':memory:' for tests. */
+  path?: string;
+  readonly?: boolean;
+}
+
+/** Open a SQLite connection with foreign keys + WAL enabled. */
+export function createDb(opts: DbOptions = {}): DatabaseSync {
+  const path = opts.path ?? process.env.IFLOW_DB_PATH ?? DEFAULT_DB_PATH;
+  if (!opts.readonly && path !== ':memory:') {
+    mkdirSync(dirname(path), { recursive: true });
+  }
+  const database = new DatabaseSync(path, {
+    readOnly: opts.readonly ?? false,
+    enableForeignKeyConstraints: true,
+  });
+  // WAL is persistent on the file; setting per-connection is harmless and ensures it.
+  try {
+    database.exec('PRAGMA journal_mode = WAL;');
+  } catch {
+    /* readOnly or disallowed — ignore */
+  }
+  return database;
+}
+
+/** Apply the full schema (CREATE TABLE IF NOT EXISTS). Idempotent. */
+export function initSchema(database: DatabaseSync): void {
+  const sql = readFileSync(SCHEMA_PATH, 'utf8');
+  database.exec(sql);
+}
+
+let _db: DatabaseSync | null = null;
+/** Process-wide singleton connection (auto-creates + inits schema on first call). */
+export function db(): DatabaseSync {
+  if (!_db) {
+    _db = createDb();
+    initSchema(_db);
+  }
+  return _db;
+}
+
+/** CLI entry: `node src/db/client.ts` initializes the on-disk database. */
+const isMain = process.argv[1] ? resolve(process.argv[1]) === fileURLToPath(import.meta.url) : false;
+if (isMain) {
+  const d = createDb();
+  initSchema(d);
+  const path = process.env.IFLOW_DB_PATH ?? DEFAULT_DB_PATH;
+  const rows = d.prepare("SELECT name FROM sqlite_master WHERE type='table' ORDER BY name").all() as Array<{ name: string }>;
+  console.log(`[investor-flow] schema initialized at ${path} (${rows.length} tables)`);
+  d.close();
+}