docs: sync AGENTS.md with CLAUDE.md and fix stale references

AGENTS.md had drifted from CLAUDE.md (ASCII dashes instead of em-dashes,
missing recent updates); both now carry identical content except for the
header, with an explicit rule to keep them in sync on future edits. Also
documents update-version.sh as the release workflow, the per-feature
partial-class split of MainWindowViewModel, UpdateChecker, and fixes a
reference to a nonexistent Core/Spv/MerkleVerifier.cs (the real file is
MerkleProof.cs) in SECURITY.md.

CLAUDE.md

@@ -2,6 +2,8 @@
 
 This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
 
+> **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.
+
 ## Role
 
 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.
@@ -44,7 +46,7 @@ by `MainWindow` on desktop and as the single-view root on Android.
 `export PATH="$HOME/.dotnet10:$PATH" DOTNET_ROOT="$HOME/.dotnet10"`.
 
 - Build: `dotnet build`
-- 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). 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.
+- 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.
 - GUI hot reload: `dotnet watch --project src/App.Desktop` (on WSL2/WSLg the window shows on the Windows desktop, no graphics dependencies to install)
 - CLI: `dotnet run --project src/Cli -- <command>` (no args → usage)
 - **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.
@@ -74,14 +76,14 @@ Note: a plain `dotnet build` at the solution level needs the Android SDK path fo
 ## GUI conventions (`src/App`)
 
 - **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.
+- **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.
+- **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.
 
 ## Working rules
 
 - **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.
-- **Releases:** whenever a new version tag is created (bumping `<Version>` in `src/App/PalladiumWallet.App.csproj`), update `CHANGELOG.md` with an entry for that version before/with the tag — it's the technical record of what shipped, not optional bookkeeping.
+- **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.