Enhance README with reproducible build instructions, emphasizing the use of FVM for Flutter version management and specifying JDK 17 requirements.

README.md

@@ -7,8 +7,6 @@ The open app store powered by your social network
 ## Build from source
 
 ```bash
-# Using FVM (recommended for reproducible builds)
-# Note: do NOT use "stable" in FVM. This repo pins Flutter via .fvmrc.
 fvm install
 fvm flutter pub get
 fvm flutter build apk --split-per-abi --debug
@@ -21,6 +19,30 @@ flutter pub get
 flutter build apk --split-per-abi --debug
 ```
 
+## Reproducible builds
+
+This repo pins:
+
+- **Flutter** via `.fvmrc` (do not use `stable` in FVM)
+- **Dart/Flutter dependencies** via `pubspec.lock`
+- **Android toolchain** via Gradle/AGP, and expects **JDK 17**
+
+Build "proof" (prints versions + builds):
+
+```bash
+# Use JDK 17 (set JAVA_HOME in your environment/CI if needed)
+# Examples:
+# export JAVA_HOME=$(/usr/libexec/java_home -v 17)            # macOS
+# export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64         # Ubuntu/Debian
+java -version
+
+fvm install
+fvm flutter --version
+fvm flutter pub get --enforce-lockfile
+
+fvm flutter build apk --split-per-abi --release
+```
+
 APK will be available at `build/app/outputs/flutter-apk`.
 
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