feat(android): sign release builds with the persistent keystore

build_android now requires the keystore generated by the previous commit,
prompts for its passwords at build time, and signs the APK with it instead
of an ephemeral debug key auto-generated per container run — that was the
actual cause of every release needing a manual uninstall to update. Also
derives versionCode from <Version> instead of leaving it fixed at 1, so
version ordering stays monotonic across releases.

Docs (docker/README.md, CLAUDE.md) updated to match the new signing flow.

CLAUDE.md

@@ -47,7 +47,7 @@ by `MainWindow` on desktop and as the single-view root on Android.
 - 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
 - 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`).
+- **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.
 - Manual Windows publish: `dotnet publish src/App.Desktop -r win-x64 -p:PublishSingleFile=true -p:IncludeNativeLibrariesForSelfExtract=true --self-contained`
 - Manual Linux publish: same with `-r linux-x64` (single-file binary; AppImage via PupNet Deploy is a future step, no pupnet.conf yet)
 

docker/README.md

@@ -46,6 +46,16 @@ automatically on first use — a few minutes for desktop, 10–20 minutes for
 Android (large downloads). Subsequent builds reuse the cached images and take
 well under a minute (desktop) / a few minutes (Android).
 
+**Android release signing:** before the first `android` build, generate the
+persistent signing keystore once — see [`keystore/README.md`](keystore/README.md):
+
+```bash
+./docker/keystore/generate-keystore.sh
+```
+
+Without it, `build_android` refuses to run — every APK must be signed with
+the same key so future releases can update a previous install in place.
+
 ---
 
 ## Quick start
@@ -64,7 +74,7 @@ Running without arguments shows an interactive menu — pick a single target or
 Targets:
   windows   Win x64 single-file executable (native libs embedded)
   linux     Linux x64 single-file binary (runs as-is, nothing to install)
-  android   Android APK (debug-signed)
+  android   Android APK (release-signed, prompts for keystore passwords)
   all       All three targets
 
 Options:
@@ -109,16 +119,16 @@ effectively all of them); no .NET or other packages to install. If you
 transfer it through a channel that strips permissions (e.g. a web download),
 restore the execute bit with `chmod +x`.
 
-**Android** — a debug-signed APK for sideloading: transfer it to the phone
+**Android** — a release-signed APK for sideloading: transfer it to the phone
 and open it (enable "install from unknown sources" if prompted), or install
 via `adb install dist/android/PalladiumWallet-*.apk`. Supports Android 6.0+
 (API 23), arm64 phones and x86_64 emulators.
 
-> **Signature caveat:** debug-signed APKs built on different machines carry
+> **Signature:** every APK is signed with the persistent keystore in
-> different keys. If a previous build is already installed, Android refuses
+> `docker/keystore/` (see [Prerequisites](#prerequisites)), so installing a
-> the update (`INSTALL_FAILED_UPDATE_INCOMPATIBLE`) — uninstall the old app
+> newer build over an existing one updates it in place — no uninstall, no
-> first. **Uninstalling deletes the app's data: back up the wallet seed
+> data loss. This only holds as long as every release keeps using that same
-> before doing this.** Release signing with a stable key is not set up yet.
+> keystore file; see `docker/keystore/README.md` for the backup story.
 
 ---
 
@@ -166,8 +176,14 @@ docker volume rm plm-nuget-cache
   android workload moved to a newer API level. Bump
   `ANDROID_SDK_PLATFORM` (and `ANDROID_SDK_BUILD_TOOLS`) in
   `Dockerfile.android` to the level the error names, then `--rebuild`.
-- **APK won't install over an existing app** — signature mismatch between
+- **APK won't install over an existing app
-  debug keys; see the signature caveat above.
+  (`INSTALL_FAILED_UPDATE_INCOMPATIBLE`)** — the new build wasn't signed with
+  the same keystore as the installed one. Make sure `docker/keystore/release.keystore`
+  hasn't changed since the installed build; if it's genuinely a different key,
+  the user must uninstall the old app first (this deletes app data — back up
+  the wallet seed before doing this).
+- **`build_android` refuses to run, asks to generate a keystore** — run
+  `./docker/keystore/generate-keystore.sh` once (see `docker/keystore/README.md`).
 - **Everything is broken / start from scratch** —
   `docker system prune -a && docker volume rm plm-nuget-cache`, then rerun
   the script (images and packages are re-downloaded).

docker/build.sh

@@ -29,7 +29,7 @@ $(bold "Usage:") $(basename "$0") [TARGET] [OPTIONS]
 $(bold "Targets:")
   windows   Win x64 single-file executable  →  dist/windows/
   linux     Linux x64 single-file binary    →  dist/linux/
-  android   Android APK (debug-signed)      →  dist/android/
+  android   Android APK (release-signed)    →  dist/android/
   all       All three targets
 
 $(bold "Options:")
@@ -112,6 +112,10 @@ ensure_android_image() {
 # $1 = image name, $2 = inline bash commands to execute inside the container.
 # Source is copied to /tmp/build inside the container so bin/obj never pollute
 # the repo. Output is written to /output (→ host DIST_DIR sub-folder).
+# Optional extra `docker run` args (e.g. keystore mount, signing passwords via
+# -e) can be set by the caller in the EXTRA_DOCKER_ARGS array beforehand.
+EXTRA_DOCKER_ARGS=()
+
 run_build() {
     local image="$1"
     local commands="$2"
@@ -123,6 +127,7 @@ run_build() {
         --volume "${PROJECT_ROOT}:/src:ro" \
         --volume "${out_dir}:/output" \
         --volume "${NUGET_VOLUME}:/root/.nuget/packages" \
+        "${EXTRA_DOCKER_ARGS[@]}" \
         "$image" \
         bash -euo pipefail -c "
             cp -r /src/. /tmp/build
@@ -169,16 +174,45 @@ build_linux() {
 
 build_android() {
     ensure_android_image
+
+    local keystore="${SCRIPT_DIR}/keystore/release.keystore"
+    [[ -f "$keystore" ]] || die "No release keystore found at docker/keystore/release.keystore. Run ./docker/keystore/generate-keystore.sh once first (see docker/keystore/README.md)."
+
     info "Building Android APK …"
+    read -r -s -p "Keystore password: " ANDROID_KS_PASS
+    echo
+    read -r -s -p "Key password (press Enter to reuse the keystore password): " ANDROID_KEY_PASS
+    echo
+    ANDROID_KEY_PASS="${ANDROID_KEY_PASS:-$ANDROID_KS_PASS}"
+
+    # versionCode derived from <Version> (MAJOR.MINOR.PATCH, pre-release suffix
+    # stripped) so it always increases with releases — required for some
+    # installers to accept an in-place update even when the signature matches.
+    local semver="${VERSION%%-*}"
+    IFS='.' read -r VMAJOR VMINOR VPATCH <<< "$semver"
+    local VERSION_CODE=$(( ${VMAJOR:-0} * 10000 + ${VMINOR:-0} * 100 + ${VPATCH:-0} ))
+    info "versionCode: ${VERSION_CODE}"
+
+    EXTRA_DOCKER_ARGS=(
+        --volume "${keystore}:/keystore/release.keystore:ro"
+        --env "ANDROID_KS_PASS=${ANDROID_KS_PASS}"
+        --env "ANDROID_KEY_PASS=${ANDROID_KEY_PASS}"
+    )
     run_build "$IMAGE_ANDROID" \
         "JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 \
          dotnet build src/App.Android \
             -c Release \
             -t:SignAndroidPackage \
-            -p:AndroidSdkDirectory=\${ANDROID_HOME}
+            -p:AndroidSdkDirectory=\${ANDROID_HOME} \
+            -p:ApplicationVersion=${VERSION_CODE} \
+            -p:AndroidSigningKeyStore=/keystore/release.keystore \
+            -p:AndroidSigningKeyAlias=palladiumwallet \
+            -p:AndroidSigningStorePass=\${ANDROID_KS_PASS} \
+            -p:AndroidSigningKeyPass=\${ANDROID_KEY_PASS}
          cp src/App.Android/bin/Release/net10.0-android/*-Signed.apk \
             \"/output/PalladiumWallet-${VERSION}.apk\"" \
         "${DIST_DIR}/android"
+    EXTRA_DOCKER_ARGS=()
     ok "Android → dist/android/PalladiumWallet-${VERSION}.apk"
 }