Harden reconnection, fix resource leaks, improve security and UX

.github/workflows/build-apk.yml

@@ -0,0 +1,52 @@
+name: Build APK
+
+on:
+  push:
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: Build obfuscated release APK
+    runs-on: ubuntu-latest
+    timeout-minutes: 45
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Java
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: '17'
+
+      - name: Set up Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          flutter-version: '3.41.1'
+          channel: stable
+          cache: true
+
+      - name: Install dependencies
+        run: flutter pub get
+
+      # --obfuscate scrambles Dart symbol names in the AOT snapshot;
+      # --split-debug-info writes the symbol maps needed to de-obfuscate
+      # crash stack traces (flutter symbolize). Without those maps a release
+      # crash is unreadable, so they are uploaded as a separate artifact.
+      - name: Build obfuscated release APK
+        run: flutter build apk --release --obfuscate --split-debug-info=build/symbols
+
+      - name: Upload APK artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: seeonce-release-apk
+          path: build/app/outputs/flutter-apk/app-release.apk
+          if-no-files-found: error
+
+      - name: Upload de-obfuscation symbols
+        uses: actions/upload-artifact@v4
+        with:
+          name: obfuscation-symbols
+          path: build/symbols
+          if-no-files-found: error

CLAUDE.md

@@ -60,6 +60,8 @@ Senders compress → encrypt → chunk → send: `image_sender` (+ `image_compre
 
 Handshake/wire changes require both devices to run a matching build and may force re-pairing. Existing on-wire choices that are load-bearing: RSA-OAEP uses SHA-256 (not the SHA-1 default), reconnect key-hash IDs are the full 256-bit hash, and reconnect includes an `auth_challenge`/`auth_response` step. Changing any of these is a breaking protocol change.
 
+The reconnect auth handshake is **v2** (`_authProtocolVersion` in `local_reconnect_service.dart`). v2 signs `nonce || channelBinding` rather than the bare nonce, where `channelBinding` is a SHA-256 over the two DTLS certificate fingerprints (sorted) pulled from the local/remote SDP. This binds the proof-of-key-possession to the specific DTLS connection, so a LAN relay/MITM — which must terminate DTLS with its own certificate on each leg — is detected (the fingerprints, and therefore the binding, won't match). v2 peers refuse to authenticate with v1 peers, so upgrading one side forces a re-pair. Bump the version on any further change to the signed material.
+
 ## Reference
 
 `IMPLEMENTATION_PLAN.md` (repo root) and the "Security notes" section of `README.md` contain deeper rationale for the trust model, platform differences, and ephemerality guarantees.

android/.gitignore

@@ -1,4 +1,5 @@
 gradle-wrapper.jar
+/build/
 /.gradle
 /captures/
 /gradlew