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8ad68b278f
The freshness rule rests on the app popping one entry back to the ledger, not on anything the frame carries, so the assumption and the measurements behind it belong next to it.
Folio
A minimal Kotlin Multiplatform personal-ledger app: login with demo credentials, create accounts, add credits and debits. Shared UI across Android, iOS, and web (wasmJs via Compose for Web). Doubles as the example sanderling runs its property-based specs against.
Stack
- Kotlin Multiplatform + Compose Multiplatform (shared UI)
- SQLDelight for the data layer (unified across platforms)
- kotlinx.coroutines for state flows
- kotlinx.serialization for
@Serializableroute types
Prerequisites
just- JDK 17
- Android SDK (auto-discovered under
$ANDROID_HOME,~/Library/Android/sdk, or the Homebrew cask) - Xcode 16+ and
xcodegen(brew install xcodegen) for iOS
Android
just install # build + install on a booted emulator / device
just uninstall
just clean
iOS
just ios # default device: iPhone 17 Pro
IOS_DEVICE="iPhone 15" just ios # pick a different simulator
just ios regenerates app/iosApp/iosApp.xcodeproj from app/iosApp/project.yml,
builds the KMP framework (Shared.framework from :app:shared), links it
into the SwiftUI host, installs, and launches.
Web
just web # webpack dev server with COOP/COEP headers
just web-build # produce a webpack distributable bundle
just web runs :app:webApp:wasmJsBrowserDevelopmentRun --continuous, so
edits to shared code reload in the browser.
Demo credentials
email: [email protected]
password: ledger123
Run a sanderling test (Android)
just test
If no device is connected, sanderling boots the single AVD it finds. With multiple AVDs, pick one:
AVD=Pixel_7 just test
Persistent settings can live in .env alongside the justfile:
AVD=Pixel_7
DURATION=5m
Traces land in ./sanderling/runs/<timestamp>/.
Run with the LLM action generator
The same sanderling/spec.ts runs under either generator: --generator seeded
(the default weighted fuzzer) or --generator llm, where a vision model picks
from the SAME weighted candidate set (reading the screenshot plus a numbered,
weight-annotated list of concrete actions) and returns one number. The spec's
generator = llm({ model, instructions }) export configures it.
export OPENROUTER_API_KEY=sk-or-... # or OPENAI_API_KEY=sk-... for OpenAI direct
just test-llm # or: sanderling test --generator llm --spec sanderling/spec.ts --bundle-id app.folio
OpenRouter wins when both keys are set. With a plain OpenAI key, drop the vendor
prefix from the model id in spec.ts (gpt-5.4-nano, not
openai/gpt-5.4-nano). The model must support image input and strict
json_schema structured outputs. Each step is one multimodal call, so keep the
duration / step budget modest. The trace records the model's reasoning, the
chosen number, and source: "llm" on each action, so the replay UI shows why
each pick was made.
Run a sanderling test (iOS)
just test-ios # default simulator: iPhone 17 Pro
IOS_DEVICE="iPhone 15" just test-ios # pick a different simulator
just test-ios boots the simulator if needed, runs just ios to install
and launch the app, then invokes sanderling test --platform ios. Same
DURATION, SEED, and OUTPUT env vars as the Android target.
How it connects to sanderling
- Each screen sets a stable Compose
testTag(HomeScreen,AccountCard,LedgerRow,TxnAmount, ...). The Sanderling SDK resolvestestTagtoresource-idon Android andaccessibilityIdentifieron iOS. - Identity for list items is the visible text content (account name; txn note + amount). No synthetic IDs encoded in semantics.
contentDescriptionis reserved for real accessibility labels, never as a data carrier.sanderling/spec.tsimports@sanderling/spec, reads state vias.ax.*, asserts properties, and weights the actions the fuzzer picks from.just testinvokessanderling testagainst the installed APK.