> **Sync rule:** `AGENTS.md` (read by other coding agents) carries the same content as this file, differing only in this header block. Any edit here must be mirrored there in the same commit.
Operate as an **expert in cryptocurrencies and cryptography**: reason with the domain's rigor about UTXO consensus, HD key derivation (BIP32/39/SLIP-132), signature schemes and scripts (P2PKH/P2SH/P2WPKH, PSBT), address encoding (base58/bech32), Merkle/SPV proofs, and at-rest encryption. When a choice touches cryptographic correctness or fund safety, judge it through that lens and flag known risks and pitfalls (nonce reuse, missing validation, exposed keys/seed, wrong fee/coin-selection, unverified server responses). Explain trade-offs with technical precision; never take for granted what hasn't been verified.
On **every requested change**, before implementing, judge whether it makes sense and say so plainly: if a request is useful and consistent with the project, proceed; if it is useless, redundant, already covered elsewhere, or risks degrading the code, **say so** with a short rationale and propose the better alternative (or doing nothing). No automatic agreement — an honest opinion is worth more than blind execution.
SPV wallet (Sparrow-style) for the **Palladium (PLM)** cryptocurrency, a Bitcoin-derived UTXO chain. Targets desktop (Windows/Linux) and Android, from the same source. Lightning is excluded from the first release.
**Non-negotiable dependency rule:**`App`/`Cli` depend only on `Core`; the UI goes through the wallet domain, never directly through network or cryptography. `Core` knows nothing about the UI.
- Tests (headless, the primary verification layer): `dotnet test` — single: `dotnet test --filter "FullyQualifiedName~TestName"`; property-based tests (CsCheck, `PropertyTests.cs`) run in the same command and take ~30 s; coverage: `dotnet test tests/PalladiumWallet.Tests --collect:"XPlat Code Coverage"` (coverlet, Cobertura XML). The test tree mirrors `src/Core` (`Chain/ Crypto/ Net/ Spv/ Storage/ Wallet/`) — put new tests in the folder matching the code under test. Network/SPV code (`ElectrumClient`, `WalletSynchronizer`, `TransactionInspector`, TOFU pinning) is tested against the in-process fake ElectrumX server in `tests/PalladiumWallet.Tests/Net/FakeElectrumServer.cs` (loopback TCP + optional TLS, per-method handlers, call counters): extend that, don't mock the client — it isn't an interface, by design.
- **Release binaries (all 3 targets): `./docker/build.sh [windows|linux|android|all]`** — reproducible builds in Docker (toolchain pinned in `docker/Dockerfile.*`, no SDK needed on host), artifacts in `dist/`, version taken from the App csproj. See `docker/README.md`. Gotchas already encoded there: single-file desktop publishes need `-p:IncludeNativeLibrariesForSelfExtract=true` (without it Avalonia's native libs — Skia/HarfBuzz/ANGLE — stay outside the exe, which then silently fails to start); the android workload dictates the SDK API level (error XA5207 → bump `ANDROID_SDK_PLATFORM` in `Dockerfile.android`). Android release builds need a persistent signing keystore, generated once with `docker/keystore/generate-keystore.sh` (never committed — see `docker/keystore/README.md`): without it every build gets a different random signature and users must uninstall the old app to receive an update instead of updating in place.
- **Shared `MainView` + heads:** the whole UI is a single `MainView` (UserControl), so it works both as a desktop window's content and as Android's single-view root. Top-level APIs (file/folder picker, clipboard) are reached via `TopLevel.GetTopLevel(this)` since a UserControl doesn't expose them. `MainWindowViewModel.IsDesktop` (from `OperatingSystem.IsAndroid()`) hides filesystem-only features (open-from-file; the data-location wizard step auto-skips on Android because the head sets `AppPaths.OverrideDataRoot`).
- **Single ViewModel** `MainWindowViewModel` (CommunityToolkit.Mvvm: `[ObservableProperty]`, `[RelayCommand]`); `Core` is driven directly from here. It is split into **partial classes by feature** (`MainWindowViewModel.Send.cs`, `.Receive.cs`, `.Sync.cs`, `.Settings.cs`, `.Wizard.cs`, `.Contacts.cs`, `.Update.cs`, …): new feature logic goes in the matching partial (or a new one), not in the main file.
- **In-app overlays, not OS windows:** details (address, transaction), settings, and help are full-screen `Border`s gated by an `IsXxxOpen` flag, not separate `Window`s — instant open/close, mobile-friendly, and popups/top-levels are slow on WSLg. Pattern: bool property + Open/Close commands + backdrop handler and Esc key in `MainView`'s code-behind; overlay close buttons bind via `$parent[UserControl]` (not `$parent[Window]`, absent on mobile). Heavy network work runs off the UI thread (`Task.Run`) so the overlay never freezes.
- **Localization:** `Localization/Loc.cs`, key→6 languages dictionary (it/en/es/fr/pt/de); in XAML `{Binding Loc[key]}`, in C# `Loc.Tr("key")`. On language change the `Loc` instance is replaced.
- **App version:** single source = `<Version>` in `src/App/PalladiumWallet.App.csproj`; read at runtime (`MainWindowViewModel.AppVersion`) and shown in the title. On startup `Core/Net/UpdateChecker.cs` compares it against the latest GitHub release and `MainWindowViewModel.Update.cs` prompts the user if newer.
- **Storage paths:** `Core/Storage/AppPaths` resolves data locations; `AppPaths.OverrideDataRoot` (top priority) is the per-platform seam — the Android head sets it to the app sandbox (`Context.FilesDir`), desktop leaves it null.
- **Cross-implementation tests:** compare addresses, txids, and PSBTs against a reference wallet (golden vectors). A different address or txid is a blocking bug.
- **Security:** seed and private keys never in plaintext on disk/logs/network; every server response validated with Merkle + checkpoints; watch-only truly read-only. `SECURITY.md` is the published threat model (SPV trust boundaries, encryption parameters, key handling): any change to crypto, SPV validation, or key/seed handling must keep it accurate in the same commit.
- **Releases:** bump the version with `./update-version.sh` (interactive) — it updates `<Version>` in the App csproj (the single source), mirrors `ApplicationDisplayVersion` in the Android head, increments `ApplicationVersion` (Android versionCode, which **must strictly increase** every release or users can't update in place), and stubs a `CHANGELOG.md` entry. Fill in that entry before/with the tag — it's the technical record of what shipped, not optional bookkeeping — then commit and tag manually.
