diff --git a/.planning/ROADMAP.md b/.planning/ROADMAP.md
index 4db3c8d21..286803e46 100644
--- a/.planning/ROADMAP.md
+++ b/.planning/ROADMAP.md
@@ -70,10 +70,14 @@ Plans:
 **Goal**: Build JamTrack player with file opening, mixdown selection, and playback controls
 **Depends on**: Phase 4
 **Research**: Unlikely (following patterns established in Phase 4)
-**Plans**: TBD
+**Plans**: 5 plans
 
 Plans:
-- [ ] TBD during phase planning
+- [x] 05-01: Redux infrastructure & bug fixes
+- [ ] 05-02: Async thunks & component core
+- [ ] 05-03: Playback controls & polling
+- [ ] 05-04: Mixdown selection & download UI
+- [ ] 05-05: Error handling & final UAT
 
 ### Phase 6: Metronome Research & Design
 **Goal**: Understand legacy metronome implementation and design React migration strategy
@@ -105,6 +109,6 @@ Phases execute in numeric order: 1 → 2 → 3 → 4 → 5 → 6 → 7
 | 2. Backing Track Seek Controls | 1/1 | Complete | 2026-01-14 |
 | 3. Backing Track Finalization | 3/3 | Complete | 2026-01-14 |
 | 4. JamTrack Research & Design | 2/2 | Complete | 2026-01-14 |
-| 5. JamTrack Implementation | 0/TBD | Not started | - |
+| 5. JamTrack Implementation | 1/5 | In progress | - |
 | 6. Metronome Research & Design | 0/TBD | Not started | - |
 | 7. Metronome Implementation | 0/TBD | Not started | - |
diff --git a/.planning/STATE.md b/.planning/STATE.md
index e454ee4ea..23a7a0940 100644
--- a/.planning/STATE.md
+++ b/.planning/STATE.md
@@ -5,21 +5,21 @@
 See: .planning/PROJECT.md (updated 2026-01-13)
 
 **Core value:** Modernize media opening features (Backing Track, JamTrack, Metronome) from legacy jQuery/Rails to React patterns in jam-ui
-**Current focus:** Phase 4 — JamTrack Research & Design
+**Current focus:** Phase 5 — JamTrack Implementation
 
 ## Current Position
 
-Phase: 4 of 7 (JamTrack Research & Design) - COMPLETE
-Plan: 2 of 2 in current phase
-Status: Complete
-Last activity: 2026-01-14 — Completed Phase 4 (JamTrack Research & Design)
+Phase: 5 of 7 (JamTrack Implementation) - IN PROGRESS
+Plan: 1 of 5 in current phase
+Status: Complete (Plan 1)
+Last activity: 2026-01-14 — Completed Phase 5 Plan 1 (Redux Infrastructure & Bug Fixes)
 
-Progress: ██████████ 100%
+Progress: ████████░░ 20%
 
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 8
+- Total plans completed: 9
 - Average duration: TBD
 - Total execution time: TBD
 
@@ -31,10 +31,11 @@ Progress: ██████████ 100%
 | 2 | 1 | 120 min | 120 min |
 | 3 | 3 | TBD | TBD |
 | 4 | 2 | 41 min | 20.5 min |
+| 5 | 1/5 | TBD | TBD |
 
 **Recent Trend:**
-- Last 5 plans: TBD, TBD, 21 min, 20 min
-- Trend: Phase 4 complete (documentation-focused, 41 min total), ready for Phase 5
+- Last 5 plans: TBD, 21 min, 20 min, Plan 05-01 (Redux infrastructure)
+- Trend: Phase 5 started (implementation), Plan 1 complete
 
 ## Accumulated Context
 
@@ -88,6 +89,16 @@ Recent decisions affecting current work:
 - HIGH risks identified: Download/sync state machine complexity, native client race conditions
 - Component architecture: 10 sub-components (PlaybackControls, SeekSlider, TimeDisplay, MixdownPicker, DownloadProgress, ErrorDisplay, SyncStatus, VolumeControl, LoadingSpinner, EmptyState)
 
+**From Phase 5 Plan 1 (05-jamtrack-implementation):**
+- **CRITICAL BUG FIXED**: loadJamTrack now uses fqId format for JamTrackPlay call, unblocking all JamTrack functionality
+- fqId construction moved outside conditional block to ensure consistent availability for all jamClient calls
+- State organization: Separated concerns with jamTrackState (playback), downloadState (sync machine), mixdown state (availableMixdowns)
+- jamTrackState structure: 7 fields tracking real-time playback (isPlaying, isPaused, currentPositionMs, durationMs, selectedMixdownId, playbackMode, lastUpdate)
+- downloadState structure: 8 fields tracking 6-state machine (jamTrackId, mixdownId, fqId, state, progress, currentStep, totalSteps, error)
+- Mixdown management: availableMixdowns array, activeMixdown object, mixdownCache map for efficient package lookups
+- UI preferences: openJamTrack tracks currently open player, jamTrackUI stores user preferences (lastUsedMixdownId, volume)
+- Redux foundation complete: 10 new reducers and 8 new selectors across 3 slices ready for Phase 5 Plans 2-5
+
 ### Deferred Issues
 
 **From Phase 3 Plan 3 UAT:**
@@ -114,7 +125,7 @@ None yet.
 ## Session Continuity
 
 Last session: 2026-01-14
-Stopped at: Completed Phase 4 Plan 2 (Design React Architecture)
+Stopped at: Completed Phase 5 Plan 1 (Redux Infrastructure & Bug Fixes)
 Resume file: None
 
-**Next:** Phase 5 (JamTrack Implementation) - Ready for planning with `/gsd:plan-phase 5`
+**Next:** Phase 5 Plan 2 (Async Thunks & Component Core) - Execute with `/gsd:execute-plan .planning/phases/05-jamtrack-implementation/05-02-PLAN.md`
diff --git a/.planning/phases/05-jamtrack-implementation/05-01-SUMMARY.md b/.planning/phases/05-jamtrack-implementation/05-01-SUMMARY.md
new file mode 100644
index 000000000..320bd8499
--- /dev/null
+++ b/.planning/phases/05-jamtrack-implementation/05-01-SUMMARY.md
@@ -0,0 +1,60 @@
+# Phase 5 Plan 1: Redux Infrastructure & Bug Fixes Summary
+
+**Fixed critical fqId bug and established Redux foundation for JamTrack player**
+
+## Accomplishments
+
+- **CRITICAL BUG FIX**: Fixed loadJamTrack to use `fqId` format instead of `jamTrack.id`, unblocking all JamTrack functionality
+- Extended mediaSlice with comprehensive jamTrackState (7 fields) and downloadState (8 fields, 6-state machine)
+- Extended activeSessionSlice with mixdown management (availableMixdowns, activeMixdown, mixdownCache)
+- Extended sessionUISlice with JamTrack UI preferences (openJamTrack, jamTrackUI)
+- Added 10 new reducers across 3 slices for complete state management
+- Added 8 new selectors for accessing JamTrack state
+
+## Files Created/Modified
+
+- `jam-ui/src/store/features/mediaSlice.js` - Critical bug fix + state extensions (commit: bb74c5046)
+- `jam-ui/src/store/features/activeSessionSlice.js` - Mixdown state management (commit: 52ee8f3ea)
+- `jam-ui/src/store/features/sessionUISlice.js` - JamTrack UI preferences (commit: 52ee8f3ea)
+
+## Decisions Made
+
+- **fqId construction**: Moved outside conditional block to ensure consistent availability for all jamClient calls
+- **State organization**: Separated jamTrackState (playback), downloadState (sync machine), and mixdown state (availableMixdowns) for clear separation of concerns
+- **Download state machine**: Implemented 6-state machine (idle → checking → downloading → keying → synchronized → error) following Phase 4 design
+- **Mixdown types**: Support for master, custom-mix, and stem types with full metadata caching
+- **UI preferences**: Separated user preferences (lastUsedMixdownId, volume) from session state for better state management
+
+## Technical Details
+
+### mediaSlice Changes
+- **Bug fix**: Line 29 now uses `fqId` instead of `jamTrack.id` for JamTrackPlay call
+- **jamTrackState**: 7 fields tracking real-time playback (isPlaying, isPaused, currentPositionMs, durationMs, selectedMixdownId, playbackMode, lastUpdate)
+- **downloadState**: 8 fields tracking sync machine (jamTrackId, mixdownId, fqId, state, progress, currentStep, totalSteps, error)
+- **New reducers**: setJamTrackState, setDownloadState, clearDownloadState
+- **Updated reducers**: clearJamTrackState and clearAllMedia now properly reset to structured state
+- **Updated extraReducers**: loadJamTrack now updates downloadState instead of simple boolean flag
+
+### activeSessionSlice Changes
+- **availableMixdowns**: Array for storing all mixdowns (master, custom-mix, stem)
+- **activeMixdown**: Currently selected mixdown object
+- **mixdownCache**: Map of packageId to metadata for efficient lookups
+- **New reducers**: setAvailableMixdowns, setActiveMixdown, cacheMixdownPackage, clearMixdowns
+- **clearSession**: Automatically resets mixdown state when user leaves session
+
+### sessionUISlice Changes
+- **openJamTrack**: Tracks currently open JamTrack ID (null when closed)
+- **jamTrackUI**: User preferences object (lastUsedMixdownId, volume)
+- **New reducers**: setOpenJamTrack, updateJamTrackUI, clearOpenJamTrack
+- **resetUI**: Automatically resets JamTrack UI state when UI is reset
+
+## Issues Encountered
+
+None - implementation followed Phase 4 design specifications precisely.
+
+## Next Step
+
+Ready for Plan 2: Async Thunks & Component Core
+- Implement 6 async thunks (enhanced loadJamTrack, downloadJamTrack, checkJamTrackSync, loadJMEP, seekJamTrack, closeJamTrack)
+- Create JKSessionJamTrackPlayer component skeleton
+- Wire up Redux connections and jamClient integration