fix(demo): flag a seeded world an app emulator no longer holds - #21

Motivation

The readiness strip reported Ready from health checks alone. Plaid and Xero keep their data in memory, so after a restart they answer health but have lost the access token and invoices the demo saved at seeding. The page showed three green Ready badges, and the first click failed at Connect with INVALID_ACCESS_TOKEN. This happens whenever an app emulator restarts between a rehearsal and a live demo.

Changes

• world.Verify checks that each app emulator still holds what seeding saved: the connected Stripe account, the Plaid access token (/item/get) and the Xero invoice count. Only a definite 4xx counts as stale. A timeout, refused connection or 5xx is not called stale, because the health check already reports those.
• GET /api/status gains stale and no longer reports ready while any vendor is stale.
• The UI shows an Out of date badge on the vendor, names it in the readiness card and beside the disabled Apply button, and says to press Reset.
• The troubleshooting guide gets a row for it.
• The Plaid sandbox credentials move to constants so the seeder and the check send the same ones.

Tests

make vet                      # clean
make test                     # ok, every module
make check-kits check-samples # ok
cd web && pnpm install --frozen-lockfile
cd web/demos/acme-commerce-lenders
pnpm type-check               # clean
pnpm exec biome check .       # clean
pnpm exec vitest run          # 9 files, 46 tests passed

New tests: world/verify_test.go (holds, missing Plaid token, missing Stripe account, short Xero invoices, and no report for a 500 or a refused connection), TestAStaleWorldIsNotReadyUntilItIsReset in internal/api, and a DemoPage test for the Out of date state.

Against real app emulators (WonderTwin twin-stripe, twin-plaid, twin-xero on throwaway ports): after Reset the status is ready: true. After restarting twin-plaid it is ready: false, stale: [plaid] with the Plaid INVALID_ACCESS_TOKEN answer in the reason. After Reset again it is ready: true.

Related

Part of making the demo easy to run on a laptop. Next: doctor, a one-command start, and pinned emulator versions.