feat(05-01): extend activeSessionSlice and sessionUISlice for JamTrack

activeSessionSlice extensions:
- Add availableMixdowns array to store mixdown objects
- Add activeMixdown for currently selected mixdown
- Add mixdownCache for package metadata
- Add 4 reducers: setAvailableMixdowns, setActiveMixdown, cacheMixdownPackage, clearMixdowns
- Add 3 selectors for mixdown state

sessionUISlice extensions:
- Add openJamTrack to track currently open JamTrack ID
- Add jamTrackUI for user preferences (lastUsedMixdownId, volume)
- Add 3 reducers: setOpenJamTrack, updateJamTrackUI, clearOpenJamTrack
- Add 2 selectors for JamTrack UI state

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/store/features/activeSessionSlice.js

@@ -63,6 +63,11 @@ const initialState = {
   // Backing track data (for currently active backing track)
   backingTrackData: null,
 
+  // Mixdown management (Phase 5)
+  availableMixdowns: [], // Array of mixdown objects: { id, type: 'master'|'custom-mix'|'stem', name, jamTrackId, packageId }
+  activeMixdown: null, // Currently selected mixdown object
+  mixdownCache: {}, // Map of packageId -> { metadata, sampleRate, fileType, encryptType }
+
   // Recording state
   recordingState: {
     isRecording: false,
@@ -204,6 +209,25 @@ export const activeSessionSlice = createSlice({
       state.recordingState.recordedTracks = [];
     },
 
+    // Phase 5: Mixdown management
+    setAvailableMixdowns: (state, action) => {
+      state.availableMixdowns = action.payload;
+    },
+
+    setActiveMixdown: (state, action) => {
+      state.activeMixdown = action.payload;
+    },
+
+    cacheMixdownPackage: (state, action) => {
+      state.mixdownCache[action.payload.packageId] = action.payload.metadata;
+    },
+
+    clearMixdowns: (state) => {
+      state.availableMixdowns = [];
+      state.activeMixdown = null;
+      state.mixdownCache = {};
+    },
+
     // Phase 4: Update session data (for partial updates)
     updateSessionData: (state, action) => {
       if (state.sessionData) {
@@ -287,6 +311,10 @@ export const {
   stopRecording,
   addRecordedTrack,
   clearRecordedTracks,
+  setAvailableMixdowns,
+  setActiveMixdown,
+  cacheMixdownPackage,
+  clearMixdowns,
   updateSessionData,
   clearSession
 } = activeSessionSlice.actions;
@@ -316,3 +344,6 @@ export const selectIsRecording = (state) => state.activeSession.recordingState.i
 export const selectRecordedTracks = (state) => state.activeSession.recordingState.recordedTracks;
 export const selectActiveSessionLoading = (state) => state.activeSession.loading;
 export const selectActiveSessionError = (state) => state.activeSession.error;
+export const selectAvailableMixdowns = (state) => state.activeSession.availableMixdowns;
+export const selectActiveMixdown = (state) => state.activeSession.activeMixdown;
+export const selectMixdownCache = (state) => state.activeSession.mixdownCache;

jam-ui/src/store/features/sessionUISlice.js

@@ -45,6 +45,13 @@ const initialState = {
       min: null,
       max: null
     }
+  },
+
+  // JamTrack UI state (Phase 5)
+  openJamTrack: null, // Currently open JamTrack ID or null
+  jamTrackUI: {
+    lastUsedMixdownId: null, // User's last selected mixdown for this session
+    volume: 100 // Last used volume (0-100)
   }
 };
 
@@ -155,6 +162,19 @@ export const sessionUISlice = createSlice({
       state.mixerUI.currentMixerRange = action.payload;
     },
 
+    // Phase 5: JamTrack UI reducers
+    setOpenJamTrack: (state, action) => {
+      state.openJamTrack = action.payload;
+    },
+
+    updateJamTrackUI: (state, action) => {
+      state.jamTrackUI = { ...state.jamTrackUI, ...action.payload };
+    },
+
+    clearOpenJamTrack: (state) => {
+      state.openJamTrack = null;
+    },
+
     // Reset UI state (useful when leaving session)
     resetUI: (state) => {
       return { ...initialState };
@@ -189,6 +209,10 @@ export const {
   setMixMode,
   toggleMixMode,
   setCurrentMixerRange,
+  // Phase 5: JamTrack UI actions
+  setOpenJamTrack,
+  updateJamTrackUI,
+  clearOpenJamTrack,
   resetUI
 } = sessionUISlice.actions;
 
@@ -220,3 +244,7 @@ export const selectMediaUI = (state) => state.sessionUI.mediaUI;
 export const selectMixMode = (state) => state.sessionUI.mixerUI.mixMode;
 export const selectCurrentMixerRange = (state) => state.sessionUI.mixerUI.currentMixerRange;
 export const selectMixerUI = (state) => state.sessionUI.mixerUI;
+
+// Phase 5: JamTrack UI selectors
+export const selectOpenJamTrack = (state) => state.sessionUI.openJamTrack;
+export const selectJamTrackUI = (state) => state.sessionUI.jamTrackUI;