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docs/decisions/0001-modular-engine-first.md

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+# Decision 0001: Modular engine first
+
+**Status:** Accepted
+
+## Context
+
+The project aims to preserve energyXT's combination of a simple workflow and a
+flexible modular routing model.
+
+## Decision
+
+Use one unified processing graph for sources, instruments, effects, mixers,
+and outputs. The sequencer is a timeline/event source integrated with that
+graph. The default GUI is simple and sequencer-oriented, while a graph editor
+exposes routing when needed.
+
+## Consequences
+
+- Graph validation, scheduling, buffer allocation, and safe graph replacement
+  are foundational requirements.
+- Initial audio graph rejects cycles.
+- Graph execution plans are prepared off the audio thread.
+- The UI must not create a separate routing model disconnected from the engine.