Initial commit.

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.

docs/decisions/0002-c-core-fltk-gui.md

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+# Decision 0002: C core with FLTK/C++ GUI
+
+**Status:** Accepted
+
+## Context
+
+The project prioritizes a readable, small C implementation while using FLTK
+for a lightweight desktop GUI.
+
+## Decision
+
+Keep the engine, DSP, project model, graph, and public core API in C (C99
+baseline). Use C++ only for FLTK windows and widgets. Communicate through
+documented C headers with `extern "C"` guards.
+
+## Consequences
+
+- No C++ classes, STL containers, exceptions, or FLTK types cross the C API.
+- GUI code cannot mutate engine internals directly.
+- Keep C++ simple and limited to the presentation layer.

docs/decisions/0003-realtime-thread-rules.md

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+# Decision 0003: Real-time thread rules
+
+**Status:** Accepted
+
+## Context
+
+Audio glitches and unsafe graph changes can undermine the whole application.
+
+## Decision
+
+The audio callback performs bounded processing using preallocated resources.
+It performs no allocation/free, blocking locks, file I/O, logging, GUI calls,
+plugin loading, or waits. Graphs are prepared outside the callback and active
+graph resources are retired only after safe reclamation.
+
+## Consequences
+
+Thread ownership and publication mechanisms must be documented and tested.
+Any exception to these rules requires explicit evidence and review.