ADR 0001: Gate A bootstrap target

Status: accepted for the first implementation slice
Date: 2026-08-10

Context

SonicMatter needs executable evidence before selecting a native DSP language or attempting the hybrid B0 renderer. Editing an existing game would couple the first experiment to unrelated project state and make the open-source example harder to reproduce.

Decision

• Use Godot 4.6.1 as the exact development and validation version for Gate A.
• Start with a self-contained 3D acceptance scene under examples/gate_a_3d/.
• Support Windows first; this slice makes no cross-platform support claim.
• Use GDScript and engine-native AudioStreamPlayer3D playback for Gate A.
• Keep one shared emitter with a hard eight-voice ceiling.
• Drive impacts from RigidBody3D.body_entered; configure contact monitoring explicitly and treat velocity-derived intensity as estimated, not measured impulse.
• Use project-authored, runtime-generated PCM fixtures. They test routing, determinism, variation, and voice policy; they are not quality Foley.
• Defer native DSP, resonators, scrape lifecycle, footsteps, WAV baking, and active-game integration to later decisions and gates.

Consequences

The first code can validate sample-first contracts with no compiler, model, cloud service, downloaded audio, or third-party asset license. It cannot prove the B0 research hypothesis or claim production sound quality.

Godot's documented positional player and rigid-body contact APIs are the current integration boundary:

• https://docs.godotengine.org/en/4.6/classes/class_audiostreamplayer3d.html
• https://docs.godotengine.org/en/4.6/classes/class_rigidbody3d.html

Revisit conditions

Revisit this ADR if the acceptance scene cannot reproduce routing decisions, cannot keep the voice ceiling bounded, or cannot run in an exported Godot 4.6.x build without a local compiler.