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Zustand Slices (react_ui/src/data/slices/)

Each Zustand store is defined as a slice — a function that returns state + actions for one domain. Slices are composed into full stores in store.ts.

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Files

SliceStore IDPersisted ToPurpose
transport.tssongbird-transportdaw.session.jsonBPM, key signature, scale, loop state, playback position. Session-only (not in undo/redo).
mixer.tssongbird-mixerdaw.state.jsonTrack list, volumes, pans, mutes, solos, sends, plugins, notes, sections. Git-tracked — changes trigger commits.
chat.tssongbird-chatdaw.session.jsonAI chat messages, threads, right panel visibility, active model. Session-only.
lyria.tssongbird-lyriadaw.session.jsonAI music generation config per track (temperature, density, brightness, prompts). Session-only.
index.ts——Barrel exports.

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Slice Pattern

Each slice follows this pattern: 
export const TransportStateID = 'songbird-transport';

export interface TransportState {
  bpm: number;
  // ... state fields
  setBpm: (bpm: number) => void;
  // ... actions
}

export const useTransportSlice: StateCreator<TransportState> = (set, get) => ({
  bpm: 120,
  setBpm: (bpm) => set({ bpm }),
});
Slices are composed in store.ts: 
export const useTransportStore = create<TransportState>()(
  persist((...a) => ({ ...useTransportSlice(...a) }), { name: TransportStateID, ... })
);

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Design Principles

  • One slice per domain — Don’t mix mixer state with transport state. Each slice owns one file and one StateCreator.
  • Actions inside the slice — State actions (setters, computed updates) live in the slice, not in components.
  • Integer rounding for mixer — setVolume() and setPan() round to integers. This is critical for echo prevention — float precision diffs would cause infinite commit loops.
  • Partial merge for C++ updates — When C++ pushes state via events, use setState((prev) => ({ ...prev, ...partial })) to avoid overwriting fields the C++ side doesn’t know about.
  • partialize for persistence — Use the partialize option to exclude transient fields (like initialized) from persistence. Only persist what should survive a reload.