docs: add build script design document

Captures the design for an interactive bash build script that
handles release signing, keystore management, and APK output.

Made-with: Cursor

docs/plans/2026-03-11-build-script-design.md

@@ -0,0 +1,97 @@
+# Build Script Design
+
+## Problem
+
+Building the app requires Android Studio or memorizing Gradle commands. Sharing signed APKs with friends requires keystore setup and signing configuration. This is friction that a simple interactive script can eliminate.
+
+## Solution
+
+A single `build.sh` bash script at the project root that provides an interactive terminal menu for building, signing, and outputting APKs.
+
+## Design
+
+### Main Menu
+
+```
+╔══════════════════════════════════╗
+║     Radio 247 Build Tool         ║
+╚══════════════════════════════════╝
+
+What would you like to do?
+
+  1) Build Release APK  (signed, shareable)
+  2) Build Debug APK    (quick, for testing)
+  3) Manage Keystore    (create or check signing key)
+  4) Clean              (remove build artifacts)
+  5) Exit
+```
+
+### Build Flow — Release
+
+1. Check for keystore at `keystore/radio247-release.jks` — if missing, redirect to keystore creation
+2. Prompt for keystore password (hidden input)
+3. Run `./gradlew assembleRelease` with signing injected via CLI properties
+4. Copy signed APK to `dist/` with descriptive filename
+5. Print path and file size
+
+### Build Flow — Debug
+
+1. Run `./gradlew assembleDebug`
+2. Copy APK to `dist/`
+3. Print path
+
+### Keystore Management
+
+- Stored at `keystore/radio247-release.jks` (gitignored)
+- Created via `keytool` (ships with JDK)
+- Prompts: name, optional organization, password (with confirmation)
+- Key alias: `radio247`
+- Validity: 10,000 days
+
+### Signing Method
+
+Signing config is injected via Gradle command-line properties rather than modifying `build.gradle.kts`:
+
+```bash
+./gradlew assembleRelease \
+  -Pandroid.injected.signing.store.file=keystore/radio247-release.jks \
+  -Pandroid.injected.signing.store.password=<password> \
+  -Pandroid.injected.signing.key.alias=radio247 \
+  -Pandroid.injected.signing.key.password=<password>
+```
+
+This keeps secrets out of version control and build files clean.
+
+### Output
+
+- Directory: `dist/` at project root (auto-created, gitignored)
+- Naming: `radio247-v{versionName}-{buildType}.apk`
+- Example: `radio247-v1.0-release.apk`
+- Same version+type overwrites previous file
+
+### Pre-flight Checks
+
+- `java` or `JAVA_HOME` available
+- `./gradlew` exists and is executable
+- Keystore exists (for release builds)
+
+### Error Handling
+
+- Build failures show last ~20 lines of Gradle output with colored error banner
+- Non-zero exit codes propagated
+- Password never written to disk or logged
+
+### Gitignore Additions
+
+- `dist/`
+- `keystore/`
+
+## Decisions
+
+| Aspect | Choice | Rationale |
+|--------|--------|-----------|
+| Language | Bash | Zero dependencies, macOS ships with it |
+| Interface | `select` menu | Built-in, no external tools needed |
+| Signing | CLI properties | Keeps build.gradle.kts clean, secrets out of git |
+| Keystore location | `keystore/` dir | Separate from source, easy to gitignore |
+| Output location | `dist/` | User preference, clear separation from build artifacts |