Prepare for open-source release under GPL-3.0-or-later; docs & test maintenance

- Add GPL-3.0 LICENSE and SPDX headers (GPL-3.0-or-later) to every source file
  (58 Kotlin, the C++ file, and the sample-pack HTML tool).
- README: state the GPL-3.0-or-later license (+ badge); fix stale "256 beats"
  -> "256 bars"; fix build instructions (the Gradle wrapper is committed);
  mention master recording and the sample-pack tool.
- DEVELOPER_HANDOVER: resync with the codebase — corrected the wrapper note,
  architecture diagram, full file map, the add-instrument/effect guide, Oboe
  (now default with fallback, not an opt-in toggle), moved SF2/XI to implemented,
  and added recently shipped features with an honest remaining/optional list.
- Fix a pre-existing broken unit test: SngFormatTest called the old
  SngFormat.import(text); the API is importInto(project, text). Tests compile
  and pass again.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

LICENSE

@@ -0,0 +1,674 @@
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+  Later license versions may give you additional or different
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+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -8,13 +8,14 @@ gamepad, and MIDI** (USB or Bluetooth).
   <img alt="platform" src="https://img.shields.io/badge/platform-Android%208%2B-0b0d0e">
   <img alt="language" src="https://img.shields.io/badge/kotlin-2.0-7cfc9a">
   <img alt="ui" src="https://img.shields.io/badge/UI-Jetpack%20Compose-f2c14e">
+  <img alt="license" src="https://img.shields.io/badge/license-GPL--3.0--or--later-e05a4b">
 </p>
 
 ## Features at a glance
 
 - **Tracker tab** — 4-track pattern grid (note / velocity-hex / MIDI-channel per
   track), beat & bar coloring, tap-to-focus + drag-to-edit with haptics and
-  scale-aware note entry; plus an 8-lane arrangement piano-roll (up to 256 beats)
+  scale-aware note entry; plus an 8-lane arrangement piano-roll (up to 256 bars)
   with A/B loop regions.
 - **Mix tab** — 4 channels, each with an instrument + 4 FX slots, MIDI channel,
   volume, mute/solo.
@@ -23,16 +24,21 @@ gamepad, and MIDI** (USB or Bluetooth).
   bitcrusher). Every device has an auto-generated editor and text presets.
 - **Setup tab** — `.sng` project save/load, color themes (with import/export),
   gamepad bindings, and searchable/collapsible MIDI bindings.
+- **Master recording** — render the master bus (with FX tail) to a WAV file.
 - **Background playback** with a media notification (Play/Pause/Stop).
 - **Two-thread design** — Compose UI on the main thread, a sample-accurate sound
   engine on its own high-priority thread.
 
+There is also a standalone `tools/samplepack-builder.html` — an offline page for
+assembling Sampler preset bundles (drop audio onto 16 note-labelled pads, then
+download an importable `.zip`).
+
 ## Build & run
 
-Open the project in **Android Studio** (2024.1+), let it create the Gradle
+Open the project in **Android Studio** (2024.1+) and Run on an **API 26+**
-wrapper if prompted, and Run on an **API 26+** device or emulator.
+device or emulator.
 
-CLI (after the wrapper exists — `gradle wrapper --gradle-version 8.9`):
+From the CLI (the Gradle wrapper is committed, so a fresh clone needs no setup):
 ```
 ./gradlew assembleDebug
 ```
@@ -57,4 +63,9 @@ compatibility shim is a listed TODO in the handover doc.
 
 ## License
 
-TBD by the project owner.
+Sizzletracker is free software: you can redistribute it and/or modify it under
+the terms of the **GNU General Public License v3.0 or later**
+(`GPL-3.0-or-later`). See the [`LICENSE`](LICENSE) file for the full text; every
+source file carries an SPDX `GPL-3.0-or-later` header.
+
+Copyright © 2026 Reactorcoremeltdown

app/src/main/cpp/native_audio.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // Native Oboe (AAudio) output backend for Sizzletracker.
 //
 // Opens a low-latency mono float Oboe output stream. On each real-time data

app/src/main/java/com/reactorcoremeltdown/sizzletracker/MainActivity.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker
 
 import android.Manifest

app/src/main/java/com/reactorcoremeltdown/sizzletracker/SizzleApp.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker
 
 import android.app.Application

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/AmbienceReverb.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import com.reactorcoremeltdown.sizzletracker.model.AmbiencePresets

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/AudioEngine.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import android.media.AudioAttributes

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/Effects.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import com.reactorcoremeltdown.sizzletracker.model.DelayDivisions

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/MasterRecorder.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import java.io.File

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/NativeAudioBridge.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/SampleRecorder.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import android.annotation.SuppressLint

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/SampleStore.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import java.nio.ByteBuffer

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/SampleVoice.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import kotlin.math.exp

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/SoundFontLoader.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 import java.nio.ByteBuffer

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/SynthVoice.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/audio/Transport.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.audio
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/BindingStore.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 import android.content.Context

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/GamepadInput.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 import android.view.InputDevice

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/InputAction.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/InputActions.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/InputRouter.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 import kotlinx.coroutines.flow.MutableSharedFlow

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/KeyboardInput.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 import android.view.KeyEvent

app/src/main/java/com/reactorcoremeltdown/sizzletracker/input/MidiInput.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.input
 
 import android.content.Context

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/PresetIo.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.model.ToolboxSlot

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/PresetLibrary.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.audio.SampleStore

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/ProjectIo.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.model.Cell

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/ProjectStore.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.model.Project

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/SettingsStore.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import android.content.Context

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/SngFormat.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.model.Arrangement

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/SongLibrary.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import java.io.File

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/ThemeIo.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import androidx.compose.ui.graphics.Color

app/src/main/java/com/reactorcoremeltdown/sizzletracker/io/ThemeLibrary.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.ui.theme.RetroPalette

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/AmbiencePresets.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/Arrangement.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/Mixer.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/Music.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/Pattern.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/Project.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/model/Toolbox.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.model
 
 /**

app/src/main/java/com/reactorcoremeltdown/sizzletracker/playback/EnginePlayer.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.playback
 
 import android.os.Looper

app/src/main/java/com/reactorcoremeltdown/sizzletracker/playback/PlaybackService.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.playback
 
 import android.content.Context

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/App.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui
 
 import androidx.activity.compose.BackHandler

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/AppViewModel.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui
 
 import androidx.compose.runtime.getValue

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/Responsive.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui
 
 import android.content.res.Configuration

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/StackedKeyboard.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui
 
 import androidx.compose.foundation.background

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/components/GlyphCache.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.components
 
 import androidx.compose.ui.text.TextLayoutResult

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/components/Piano.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.components
 
 import androidx.compose.foundation.background

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/components/Widgets.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.components
 
 import androidx.compose.foundation.background

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/mixer/MixerScreen.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.mixer
 
 import androidx.activity.compose.rememberLauncherForActivityResult

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/settings/SettingsScreen.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.settings
 
 import android.content.Context

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/theme/Theme.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.theme
 
 import android.app.Activity

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/toolbox/DelayEditor.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.toolbox
 
 import androidx.compose.foundation.Canvas

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/toolbox/LfoEditor.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.toolbox
 
 import androidx.compose.foundation.layout.Arrangement

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/toolbox/ParamControl.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.toolbox
 
 import androidx.compose.foundation.layout.Column

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/toolbox/SamplerEditor.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.toolbox
 
 import androidx.activity.compose.rememberLauncherForActivityResult

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/toolbox/SoundFontEditor.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.toolbox
 
 import androidx.activity.compose.rememberLauncherForActivityResult

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/toolbox/ToolboxScreen.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.toolbox
 
 import android.content.Intent

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/tracker/ArrangementRoll.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.tracker
 
 import androidx.compose.foundation.Canvas

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/tracker/PatternGrid.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.tracker
 
 import androidx.compose.foundation.Canvas

app/src/main/java/com/reactorcoremeltdown/sizzletracker/ui/tracker/TrackerScreen.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.ui.tracker
 
 import androidx.compose.foundation.background

app/src/test/java/com/reactorcoremeltdown/sizzletracker/io/SngFormatTest.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Reactorcoremeltdown
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package com.reactorcoremeltdown.sizzletracker.io
 
 import com.reactorcoremeltdown.sizzletracker.model.Arrangement
@@ -28,7 +31,7 @@ class SngFormatTest {
 
     @Test
     fun parsesReferenceExample() {
-        val p = SngFormat.import(reference)
+        val p = SngFormat.importInto(Project(), reference)
 
         assertEquals(120f, p.tempoBpm, 0.001f)
         assertEquals(TimeSignature.FOUR_FOUR, p.timeSignature)
@@ -64,7 +67,7 @@ class SngFormatTest {
         p.arrangement.set(0, 0, 0)
         p.arrangement.set(0, 1, 0)
 
-        val restored = SngFormat.import(SngFormat.export(p))
+        val restored = SngFormat.importInto(Project(), SngFormat.export(p))
 
         assertEquals(140f, restored.tempoBpm, 0.001f)
         assertEquals(TimeSignature.FIVE_FOUR, restored.timeSignature)

docs/DEVELOPER_HANDOVER.md

@@ -30,15 +30,14 @@ Requirements: **Android Studio** (Koala / 2024.1 or newer) which bundles a
 JDK 17 and the Android SDK.
 
 1. Open the project root in Android Studio. It will detect the Gradle build.
-2. If prompted, let it **create the Gradle wrapper** (or run
+2. Let it download the SDK for `compileSdk 34`.
-   `gradle wrapper --gradle-version 8.9` from a shell that has Gradle).
+3. Pick a device/emulator running **Android 8.0 (API 26)** or newer and press
-3. Let it download the SDK for `compileSdk 34`.
-4. Pick a device/emulator running **Android 8.0 (API 26)** or newer and press
    **Run**.
 
-> The command line here (`./gradlew assembleDebug`) needs the wrapper JAR, which
+> The Gradle wrapper (`gradle/wrapper/gradle-wrapper.jar`) **is committed**
-> is generated by step 2. The wrapper JAR is intentionally not committed as a
+> (Gradle's recommended practice), so `./gradlew assembleDebug` works on a fresh
-> binary; generating it is a one-time step.
+> clone with no extra setup. A `staging` build type (`./gradlew assembleStaging`)
+> gives release-like performance while still using the debug signing key.
 
 Key versions live in **one file**: `gradle/libs.versions.toml` (the "version
 catalog"). Change a number there and the whole project follows.
@@ -58,7 +57,7 @@ catalog"). Change a number there and the whole project follows.
                                                           Project  (the song)
                                                               ▲
                                      reads on audio thread    │
-                                          AudioEngine ─────────┘  ──▶ AudioTrack ──▶ speakers
+                                          AudioEngine ─────────┘  ──▶ Oboe / AudioTrack ──▶ speakers
                                           (own thread)
 ```
 
@@ -92,14 +91,17 @@ com.reactorcoremeltdown.sizzletracker
 ├── model/                  Pure data, no Android imports (unit-test friendly)
 │   ├── Music.kt            Pitch, TimeSignature, Scale (incl. scale-step logic)
 │   ├── Pattern.kt          Cell, CellColumn, Pattern (4 tracks x N lines)
-│   ├── Arrangement.kt      Arrangement (8 lanes x 256 beats), LoopRegion A/B
+│   ├── Arrangement.kt      Arrangement (8 lanes; canvas denominated in bars, up to 256), LoopRegion A/B
-│   ├── Mixer.kt            Mixer, MixerChannel (4 channels)
+│   ├── Mixer.kt            Mixer, MixerChannel (4 channels; volume/mute/solo/limiter)
-│   ├── Toolbox.kt          ToolboxType (all instruments+effects), ParamSpec, ToolboxSlot
+│   ├── Toolbox.kt          ToolboxType (all instruments+effects), ParamSpec, ToolboxSlot, SamplerPads
+│   ├── AmbiencePresets.kt  Factory reverb spaces seeded into the preset library
 │   └── Project.kt          The whole song
 │
 ├── input/                  The unified input layer
 │   ├── InputAction.kt      The neutral action vocabulary
-│   ├── InputRouter.kt      Flow-based message bus
+│   ├── InputActions.kt     Bindable-action catalogue (for the rebind/learn UI)
+│   ├── InputRouter.kt      Flow-based message bus (+ learn mode)
+│   ├── BindingStore.kt     Persists gamepad/MIDI bindings
 │   ├── KeyboardInput.kt    KeyEvent  -> InputAction (+ a 2-octave typing piano)
 │   ├── GamepadInput.kt     KeyEvent/MotionEvent -> InputAction (rebindable)
 │   └── MidiInput.kt        MIDI bytes -> InputAction (USB & Bluetooth via MidiManager)
@@ -107,23 +109,43 @@ com.reactorcoremeltdown.sizzletracker
 ├── audio/                  The real-time sound engine (own thread)
 │   ├── Transport.kt        TransportState snapshot published to the UI
 │   ├── SynthVoice.kt       One NES-style voice: pulse/triangle/noise + ADSR
-│   └── AudioEngine.kt      AudioTrack + sample-accurate sequencer + voice mixing
+│   ├── SampleVoice.kt      Pitched + sliced playback of a decoded sample
+│   ├── SampleStore.kt      Process-wide decoded-PCM cache + WAV encode/decode
+│   ├── SampleRecorder.kt   Ad-hoc mic/USB capture into a sample
+│   ├── SoundFontLoader.kt  Extract PCM from an .sf2 / .xi into the SampleStore
+│   ├── Effects.kt          Insert DSP: TapeDelay, Filter, Bitcrusher, GraphicEq (+ AudioEffect API)
+│   ├── AmbienceReverb.kt   FDN reverb processor
+│   ├── MasterRecorder.kt   Renders the master bus (with FX tail) to a WAV
+│   ├── NativeAudioBridge.kt  JNI bridge to the Oboe callback (calls fillBlock)
+│   └── AudioEngine.kt      Oboe/AudioTrack + sample-accurate sequencer + voice/FX mixing
+│
+├── cpp/native_audio.cpp    Low-latency Oboe stream; RT callback pulls audio via JNI
 │
 ├── io/                     Human-readable text persistence
 │   ├── PresetIo.kt         Instrument/effect preset  <->  KEY=VALUE text
-│   └── ProjectIo.kt        Whole song  <->  .sng text
+│   ├── PresetLibrary.kt    On-disk preset library (+ .zip sample bundles)
+│   ├── ProjectIo.kt        Whole song  <->  internal .sng text (full fidelity)
+│   ├── ProjectStore.kt     Autosave / load of the current project
+│   ├── SongLibrary.kt      Named project save/load browser backing
+│   ├── SngFormat.kt        Desktop-compatible .sng interchange read/write
+│   ├── SettingsStore.kt    App settings (theme, recording dir, keyboard) via DataStore
+│   ├── ThemeIo.kt          RetroPalette  <->  .szt text
+│   └── ThemeLibrary.kt     On-disk theme library (import/export/delete)
 │
 ├── playback/
-│   └── PlaybackService.kt  Foreground service: background playback + media notification
+│   ├── EnginePlayer.kt     SimpleBasePlayer wrapping the engine for MediaSession
+│   └── PlaybackService.kt  MediaSessionService: background playback + media notification
 │
 └── ui/
     ├── AppViewModel.kt     Screen state + THE single InputAction handler
     ├── App.kt              Tab shell
+    ├── Responsive.kt       Portrait/landscape layout helpers (nav rail, two-column)
+    ├── StackedKeyboard.kt  On-screen audition / punch-in piano
     ├── theme/Theme.kt      RetroPalette + monospace typography + SizzleTheme
-    ├── components/Widgets.kt  RetroButton, RetroDropdown, SectionLabel, PixelGlyph
+    ├── components/         Widgets (RetroButton/Dropdown…), GlyphCache, Piano
     ├── tracker/            TrackerScreen, PatternGrid, ArrangementRoll
     ├── mixer/MixerScreen.kt
-    ├── toolbox/            ToolboxScreen, ParamControl
+    ├── toolbox/            ToolboxScreen, ParamControl, Sampler/SoundFont/Delay/Lfo editors
     └── settings/SettingsScreen.kt
 ```
 
@@ -185,10 +207,18 @@ are both **generated** from that list. See §6 to add a new device.
 
 ### Add a new instrument or effect
 1. Add an entry to `ToolboxType` (`model/Toolbox.kt`) with its `ParamSpec` list.
-2. Teach `AudioEngine` how to render/process it (today only `NES_SYNTH` is
+2. Teach the engine how to sound it:
-   rendered; see `synthParamsForTrack`). Add a branch there.
+   - **Instrument**: handle its type where the engine picks a voice per channel
-That's it — the Toolbox picker, parameter editor, and preset save/load all work
+     (see how `NES_SYNTH`, `SAMPLER`, and `SOUNDFONT` are dispatched in
-automatically.
+     `AudioEngine`).
+   - **Signal effect**: add a processor in `audio/Effects.kt` implementing
+     `AudioEffect` and register it in `AudioEffect.create(...)`; the per-channel
+     insert chain picks it up automatically.
+   - **MIDI effect** (arp/transpose/LFO-style): hook into the sequencer instead
+     of the signal path (see `advanceArps` / `applyLfos` in `AudioEngine`).
+The Toolbox picker, parameter editor, and preset save/load all work automatically
+from the `ParamSpec` list. A device with many parameters can ship a bespoke
+editor (see `ui/toolbox/DelayEditor.kt`, `SamplerEditor.kt`).
 
 ### Add a new input gesture/control
 1. Add a case to `InputAction`.
@@ -249,8 +279,9 @@ Line-oriented, sectioned (`[PATTERN ...]`, `[ARRANGEMENT ...]`, `[MIXER]`,
 ## 9. Current status — implemented vs. TODO
 
 This is an honest map so you know where the edges are. The **architecture and
-all four tabs are in place and interactive**; several deep features are scaffolded
+all four tabs are in place and interactive**, and the feature set below is
-with a clear seam to finish them.
+implemented and working; the short "Remaining / optional" list at the end is
+polish and interchange niceties, not functional gaps.
 
 ### Implemented and working
 - Full 4-tab UI, retro monospace theme (+ theme switching), tab navigation.
@@ -307,12 +338,13 @@ with a clear seam to finish them.
   (`version`/`bpm`/`sig`, `block`…`endblock` with `roll`/`track`/steps) — covered
   by passing JVM unit tests in `app/src/test`.
 - Background playback foreground service with Play/Pause/Stop notification.
-- **Oboe / AAudio native output** ✓ (opt-in): `src/main/cpp/native_audio.cpp`
+- **Oboe / AAudio native output** ✓ (default): `src/main/cpp/native_audio.cpp`
   opens a low-latency Oboe stream whose real-time callback pulls audio via JNI
   (`audio/NativeAudioBridge.kt`) from the SAME `AudioEngine.fillBlock` the
   AudioTrack loop uses — so both backends produce identical sound, only the
-  delivery path differs. Toggle it in Settings → Audio Devices ("Low-latency
+  delivery path differs. Oboe is the default engine; it falls back to the
-  engine (Oboe)"); it falls back to AudioTrack if the native lib is absent.
+  AudioTrack loop only if it fails to initialise (or the native lib is absent),
+  surfacing a popup with the reason (there is no user toggle).
   Built via **NDK r27** (`ndkVersion` in `app/build.gradle.kts`) + CMake + the
   `com.google.oboe:oboe:1.10.0` prefab AAR. All packaged `.so` files are **16 KB
   page-aligned** (Android 15 / Google Play requirement): NDK r27 aligns ELF load
@@ -320,17 +352,34 @@ with a clear seam to finish them.
   lib is aligned, our `CMakeLists.txt` also passes `-Wl,-z,max-page-size=16384`,
   and AGP stores each `.so` at a 16 KB-aligned offset in the APK. (Verify with
   `llvm-readelf -l <lib>.so` → LOAD `Align 0x4000`.)
+- **SF2 / XI loader instrument** ✓: `audio/SoundFontLoader.kt` extracts PCM from
+  an `.sf2` / `.xi` into the `SampleStore`, played back through the same
+  `SampleVoice` path as the Sampler; edited via `ui/toolbox/SoundFontEditor.kt`
+  (root note, volume, ADSR).
+- **Master recording** ✓: `audio/MasterRecorder.kt` renders the stereo master bus
+  (plus a configurable FX tail) to a WAV in a user-chosen folder (SAF).
+- **Stereo output & recording** ✓: `fillBlock` renders interleaved stereo and the
+  recorder captures two channels (voices/inserts are mono, so both channels carry
+  the same sum).
+- **Responsive landscape layout** ✓ (`ui/Responsive.kt`): nav rail, side-by-side
+  screens, two-column mixer/editors, wider on-screen keyboards for tablets/handhelds.
+- **Arrangement niceties** ✓: 256-bar canvas with viewport-culled drawing,
+  per-lane mutes, and centre-follow scrolling.
+- **Per-bus soft-clip limiter** ✓, sampler QoL (fire-on-tap, clear, normalize),
+  theme import/export, and preset `.zip` bundle import/export.
+- **Sample-pack builder** ✓: `tools/samplepack-builder.html`, a standalone offline
+  page that assembles importable Sampler `.zip` bundles.
 
-### Scaffolded — remaining
+### Remaining / optional
-1. **SF2 / XI loader instrument.** The Sampler (WAV) is done; the SoundFont/XI
-   loader still falls back to the synth. Parse `.sf2`/`.xi`, feed the extracted
-   PCM through the existing `SampleStore`/`SampleVoice` path. (This was not in the
-   original milestone list; noted for completeness.)
 
-All spec milestones are implemented. Next steps are polish/hardening: routing the
+- **Byte-exact desktop `.sng` compatibility.** `io/SngFormat.kt` reads/writes the
-Oboe backend through the chosen output device (Oboe `setDeviceId`), a full C++
+  reference line format and round-trips musically; a field-for-field byte match
-port of the synth/mixer to remove JVM/GC from the native audio callback, and the
+  with the CLI project layout is the remaining interchange nicety.
-SF2/XI loader above.
+- **Full C++ audio port.** The DSP currently runs in Kotlin behind the Oboe
+  callback (via JNI). Porting the hot path to C++ would remove JVM/GC from the
+  real-time thread — a performance hardening step, not a functional gap.
+- **Route the Oboe backend through the chosen output device** (Oboe
+  `setDeviceId`), matching the AudioTrack path's device selection.
 
 ---
 

tools/samplepack-builder.html

@@ -1,4 +1,6 @@
 <!doctype html>
+<!-- SPDX-FileCopyrightText: 2026 Reactorcoremeltdown -->
+<!-- SPDX-License-Identifier: GPL-3.0-or-later -->
 <html lang="en">
 <head>
 <meta charset="utf-8">