# Contrapunk Audio Chain Cutover

> Wire or review feature-flagged audio-chain cutovers in Contrapunk, especially replacing the legacy built-in Synth with ElixirSynthBlock behind elixir-synth. Use when touching src-tauri/src/audio_clock.rs, src/chain/*, built-in synth routing, Chain AudioBlock setup, or A-Cut work. Use when this capability is needed.

- Skill: `tomevault-io/contrapunk-audio-chain-cutover` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/contrapunk-audio-chain-cutover`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/contrapunk-audio-chain-cutover/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/contrapunk-audio-chain-cutover

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# Contrapunk Audio Chain Cutover

## Pattern

When replacing a built-in audio component, keep the chain contract stable and switch only the block instantiation behind a Cargo feature. The router should continue sending the same `SynthEvent`/MIDI events unless a dedicated event bridge is explicitly part of the task.

## Default Approach

1. Preserve public commands and UI behavior first.
2. Add a small constructor/helper that selects the first `AudioBlock`:
   - `#[cfg(feature = "elixir-synth")]` → `ElixirSynthBlock`
   - `#[cfg(not(feature = "elixir-synth"))]` → legacy `Synth`
3. Keep `BlockDescriptor` type IDs honest:
   - legacy: `builtin.synth`
   - Elixir: `builtin.elixir-synth`
4. Do not import root `src/fx` into `elixir-core`; share only neutral primitives through `contrapunk-dsp`.
5. Validate both feature configurations:
   - `cargo check -p contrapunk`
   - `cargo check -p contrapunk --features elixir-synth`
   - relevant Tauri/chain tests when touched

## A-Cut Gotchas

- `src-tauri/src/audio_clock.rs` owns the cpal chain startup; this is where the first synth block is instantiated.
- `src/chain/elixir_block.rs` already adapts `elixir_core::Engine` to the `AudioBlock` trait behind `elixir-synth`.
- `src-tauri/src/commands/engine.rs` still emits `SynthEvent` to the built-in synth channel; if Elixir is selected through the chain, ensure events still reach the chain or add a bridge explicitly.
- Keep non-F32 cpal paths safe; they currently output silence and tick transport only.
- Avoid adding locks or allocation to the cpal callback.

## Success Criteria

- Both feature-on and feature-off builds compile.
- Feature-off behavior remains legacy-compatible.
- Feature-on chain reports/uses `builtin.elixir-synth` and renders notes through Elixir.
- No new audio-thread allocation or blocking beyond existing chain behavior.

---
> Source: [contrapunk-audio/contrapunk](https://github.com/contrapunk-audio/contrapunk) — distributed by [TomeVault](https://tomevault.io).
<!-- tomevault:4.0:skill_md:2026-06-24 -->