Add repo-root AGENTS.md: agent onboarding facts

AGENTS.md

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+# AGENTS.md — repo-specific guidance for agents
+
+> The agent instruction floor lives at [.opencode/AGENTS.md](.opencode/floor.md)
+> (loaded by the platform). This file adds only repo-specific facts the floor
+> does not carry.
+
+## Repo in one line
+
+A Godot 3.3 game (Godot game template by crystal-bit) re-teaching the Cherokee
+animal names — created as a port of the retired libGDX app of the same name.
+
+## The two codebases in one tree
+
+- `core/src/com/cherokeelessons/**` is the **legacy libGDX Java** game
+  (~10k lines, screens/controllers/views). It is **reference material for the
+  port, not active code** — no gradle module or CI builds it; do not "fix" it,
+  do not read `core/bin/`.
+- The active product is everything else: `project.godot` + `scenes/`,
+  `autoload/game.gd`, `classes/`, `addons/`, `assets/`.
+
+## Build / run / test reality
+
+- Godot **3.3** (`config_version=4`, scene format 2), **GLES2 driver**
+  configured with fallback — do not "modernize" syntax to Godot 4 or GLES3.
+- Main scene: `res://scenes/main/main.tscn`. Autoload: `Game`
+  (`autoload/game.gd`) — scene changes go through `Game.change_scene()`, using
+  the template's `pre_start()`/`start()` convention.
+- **There is no runnable test suite or build command in a bare checkout.** The
+  only CI is CodeQL. Verification means: opening the scene in the Godot editor
+  (3.3) or structural checks (grep/git). If a Godot binary is absent, say so —
+  don't fake a run.
+- The root `gradlew` / `build.gradle` / `settings.gradle` are **Rider IDE
+  workspace stubs, not a build** (they only provide the `idea` module; the
+  wrapper is unused — Godot's Android preset uses prebuilt templates,
+  `use_custom_build=false`). Never invoke them to build.
+
+## Challenge-data pipeline (the one generated-code flow)
+
+- `classes/ChallengeData.gd` is **generated output** — header says so. Never
+  hand-edit it.
+- Generator: `Assets.Source/challenges/create_challenge_data.py` (Python,
+  `requirements.txt` = `pillow` + `pydub`; audio steps additionally need
+  ffmpeg). Re-running it **rmtree's `assets/challenges/audio` and
+  `assets/challenges/images`** and regenerates them — run it only when you
+  intend a full regeneration.
+- Data keys are **Cherokee syllabary strings** (UTF-8). Preserve encoding;
+  fixtures live in `Assets.Source/challenges/animals-game-mco.txt`.
+- Git convention: `.import` metadata files are committed alongside assets;
+  `rejected-challenges/` holds unused TTS takes and is dead weight, not data.
+
+## Audio architecture
+
+- SFX/music run through `addons/smart_audio_stream/` (`SmartAudioStream`
+  accepts any `AudioStream`), the `EffectAudio`/`WrongAudio` scenes, and per
+  bus layout (`default_bus_layout.tres`); SFX sources are `.wav`
+  (`assets/audio-effects/`), spoken challenge audio is `.mp3`
+  (`assets/challenges/audio/`, TTS takes named `en-<id>-<f|m>-<word>.mp3`).
+  Menu navigation plays through the scene-local `fx` player
+  (`scenes/menu/menu.tscn`). `project.godot` sets `audio/output_latency=10`
+  — deliberate; keep it.
+
+## Text content
+
+- User-facing strings live in `text/` (changelog/credits/instructions, English
+  + Cherokee) and inline in scenes; game copy is bilingual — when editing UI,
+  keep the Cherokee half intact.
+
+## Git repo facts
+
+- Trunk: `master` (hook-protected; branch before any edit). Platform issues:
+  GitHub `CherokeeLanguage/Animals`; local mirror lives in the `.issues/`
+  worktree on the orphan `issues-data` branch — never stage `/.issues/` or
+  `/.mono/`.
+- Committed tooling noise to ignore: `espeak-ng/`, `adb-*.sh`, `notes/`,
+  `Artwork.Source/` (source artwork, incl. GDX-era tools). `readme.md` is the
+  template's readme; `README.md` still describes the libGDX app — both are
+  stale; trust the code, and `changelog.md` too is the template's.