feat(db): seed reserved guest principal idempotently

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/data/database.test.ts

@@ -1,5 +1,9 @@
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 import { describe, it, expect, beforeEach, afterEach } from "vitest";
 import { createDatabase, type BotDatabase, type BotInstance, type PlayHistoryEntry } from "./database.js";
+import { createUserStore, GUEST_USER_ID } from "./users.js";
 
 describe("database", () => {
   let botDb: BotDatabase;
@@ -148,3 +152,28 @@ describe("database", () => {
     expect(botDb.getCustomAvatarPath("bot-1")).toBeNull();
   });
 });
+
+describe("guest principal migration", () => {
+  it("creates exactly one reserved guest row, idempotently", () => {
+    const dir = mkdtempSync(join(tmpdir(), "tsmb-db-"));
+    const p = join(dir, "t.db");
+    const a = createDatabase(p); a.db.close();
+    const b = createDatabase(p); // run again — must not duplicate
+    const row = b.db.prepare("SELECT id, role FROM users WHERE id = ?").get(GUEST_USER_ID) as { id: string; role: string } | undefined;
+    expect(row?.role).toBe("guest");
+    const n = (b.db.prepare("SELECT COUNT(*) AS n FROM users WHERE role='guest'").get() as { n: number }).n;
+    expect(n).toBe(1);
+    b.db.close();
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  it("guest row does not break first-run detection (countUsers excludes it)", () => {
+    const dir = mkdtempSync(join(tmpdir(), "tsmb-db2-"));
+    const p = join(dir, "t.db");
+    const d = createDatabase(p);
+    const users = createUserStore(d.db);
+    expect(users.countUsers()).toBe(0); // guest excluded → still needs setup
+    d.db.close();
+    rmSync(dir, { recursive: true, force: true });
+  });
+});