Add spec.md: goal, limits and rules for working on the project

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

spec.md

@@ -0,0 +1,56 @@
+# Calendar Lite (Android) — spec
+
+The short contract for working on this app. `README.md` is the user guide (and keeps the old TLS-bridge
+setup); this file says what the app is for, what limits it lives within, and what must not break.
+
+## Goal
+
+A native Nextcloud (CalDAV) calendar for the Samsung Galaxy Mini that works at home and away, offline,
+with reminders.
+
+## Target and hard limits
+
+- Samsung Galaxy Mini GT-S5570, Android 2.3.5 (API 9/10, `minSdkVersion` 8), 240×320 ldpi.
+- Native Java, no libraries beyond the bundled TLS stack. No calendar-provider integration (2.3 has no
+  public API for it).
+- Galician by default (weeks start Monday, month/day names built in), English in Settings.
+
+## Current scope (1.6)
+
+- Month view (6-week grid, colour marks, swipe, long-press to create) and Agenda view; choice remembered.
+- SQLite cache of the last 35 days and the next 60 ("Days ahead"); months outside it fetched on demand.
+- Create, edit and delete events (title, all-day, start/end, location, notes, alarm). Repeating events are
+  shown (server expansion, client fallback) and can be deleted, but are edited only in Nextcloud.
+- Pick visible calendars and the default one for new events.
+- Background sync every 1–24 h; notifications N minutes before timed events.
+- Bundled TLS 1.2 to the normal `https://` address; pinned certificates for self-signed servers or the old
+  TLS 1.0 bridge (still supported).
+
+## Out of scope
+
+- Editing repeating events, tasks/VTODO, contacts, feeding the stock Samsung calendar.
+
+## Must not break
+
+- Package `org.gingercal` and `gingercal.keystore` (password `android`): updates install over GingerCal.
+- Signing with `apksigner` v1 only; never `jarsigner` (that was the first build's bug).
+- `src/` stays platform-neutral (CalDAV core runs on a desktop JVM for tests); Android code lives in
+  `android/`.
+- `android/org/gingercal/net/` is a copy of `tlskit`, copied by hand (its `install.sh` doesn't handle this
+  path): change it in `../tlskit` first.
+- `bridge/` stays working for anyone still on a bridge address.
+
+## Code map
+
+`src/` discovery, PROPFIND/REPORT, iCalendar, sync, pinning · `android/` activities, `SyncService`, alarms,
+`Db` (SQLite), `NetHttp` · `stubs/` compile-only API 10 signatures · `bridge/` nginx legacy-TLS endpoint ·
+`tools/` dex/API checkers, zipalign, d8 workaround.
+
+## Build, test, release
+
+- `./build.sh` (finds d8, apksigner and apktool in `~/android-toolchain/calendar-tools`, and a JDK). Its own
+  route: javac → d8 → baksmali/smali → aapt v1 → apksigner v1 → zipalign → `apksigner verify` for API 8–10.
+- Tests on the desktop JVM: `CoreTest` (needs Radicale on :5232, user `xose`/`secret`), `RedirectTest`,
+  `I18nTest`, `NetTest`. `tools/check_i18n.py` and `tools/check_api.py` run in the build.
+- Release: raise `versionCode`/`versionName`, build, add `changes` in `../tenda-lite/repo/apps.json`, commit
+  and push, `../tenda-lite/repo/publish.sh`.