docs(quick-15): complete audio glitch fix plan

- Add 15-SUMMARY.md with implementation details
- Update STATE.md with quick task 15 completion

.planning/STATE.md

@@ -63,17 +63,18 @@ Decisions from v1.0 are archived in PROJECT.md Key Decisions table. Key patterns
 | 012 | Add favorite icon to album dropdown track rows | 2026-03-05 | 12a0bbc |
 | 013 | Fix all golangci-lint issues (zero issues) | 2026-03-05 | e1a95e6 |
 | 014 | Fix queue/player desync after track load failure | 2026-03-05 | 2820de2 |
+| 015 | Fix audio glitches with BufferedStreamer read-ahead | 2026-03-05 | 8a0b16a |
 
 ## Session Continuity
 
 ### Last Session
 
 **Date:** 2026-03-05
-**What happened:** Quick task 14 — fixed queue/player desync after track load failure. Added roll-back-on-failure semantics to all queue index advancement paths (Next, Previous, OnPlaybackFinished, PlayIndex, playFromStart). `playCurrentTrack` and `playOrLoadCurrentTrack` now return bool.
-**Where we stopped:** Quick task 14 complete. All 28 queue tests pass, go vet clean.
+**What happened:** Quick task 15 — fixed audio glitches and skips by adding a BufferedStreamer with goroutine read-ahead between decoder/resampler and speaker output. Ring buffer provides 2s of audio runway. Speaker buffer increased from 100ms to 200ms. 5 unit tests, all 12 player tests pass.
+**Where we stopped:** Quick task 15 complete. All player tests pass, go build/vet clean.
 **Next action:** Continue with next task
 
 ---
 *State initialized: 2026-02-27*
-Last activity: 2026-03-05 - Fix queue/player desync after track load failure
+Last activity: 2026-03-05 - Fix audio glitches with BufferedStreamer read-ahead
 *Last updated: 2026-03-05*

.planning/quick/15-fix-audio-glitches-and-skips-in-decoding/15-SUMMARY.md

@@ -0,0 +1,76 @@
+---
+phase: 15-fix-audio-glitches
+plan: 01
+subsystem: player
+tags: [audio, buffering, performance, glitch-fix]
+dependency_graph:
+  requires: []
+  provides: [BufferedStreamer, read-ahead-buffering]
+  affects: [player-pipeline, speaker-init]
+tech_stack:
+  added: []
+  patterns: [ring-buffer, goroutine-read-ahead, channel-signaling]
+key_files:
+  created:
+    - backend/player/buffered_streamer.go
+    - backend/player/buffered_streamer_test.go
+  modified:
+    - backend/player/player.go
+decisions:
+  - "2-second ring buffer (88200 samples at 44100 Hz) provides sufficient runway for I/O stalls and GC pauses"
+  - "Source reads happen outside mutex lock to avoid blocking speaker callback"
+  - "Empty buffer returns silence rather than blocking or signaling end-of-stream"
+  - "Speaker buffer doubled from 100ms to 200ms as secondary underrun protection"
+metrics:
+  duration: "10m 38s"
+  completed: "2026-03-05"
+  tasks: 2
+  files_changed: 3
+---
+
+# Quick Task 15: Fix Audio Glitches and Skips in Decoding Summary
+
+Ring-buffer `BufferedStreamer` with goroutine read-ahead between decoder/resampler and speaker output, plus 200ms speaker buffer — eliminates glitches from disk I/O stalls, GC pauses, and CPU scheduling delays.
+
+## Tasks Completed
+
+| # | Task | Commit | Key Changes |
+|---|------|--------|-------------|
+| 1 | Create BufferedStreamer with goroutine read-ahead | 85b23ac | New `BufferedStreamer` type with ring buffer, read-ahead goroutine, silence-on-empty, Close() cleanup; 5 unit tests |
+| 2 | Insert BufferedStreamer into player pipeline and increase speaker buffer | 8a0b16a | Chain: decode→resample→**BufferedStreamer**→ctrl→volume→speaker; speaker buffer 100ms→200ms; Close on unload/track-change |
+
+## Implementation Details
+
+### BufferedStreamer Design
+
+- **Ring buffer**: Pre-allocated `[][2]float64` of configurable size (default 88200 samples ≈ 2 seconds at 44100 Hz)
+- **Read-ahead goroutine**: Reads from source in 512-sample chunks outside the mutex, copies into ring under lock
+- **Thread safety**: Mutex protects ring metadata only; source I/O never holds the lock, so the speaker goroutine is never blocked by disk
+- **Empty buffer handling**: Returns silence (`len(samples), true`) when buffer temporarily empty — brief silence is far better than a glitch or premature track end
+- **Shutdown**: `Close()` signals goroutine via channel; safe to call multiple times; called on track change and unload
+
+### Player Pipeline Changes
+
+- `buffered *BufferedStreamer` field added to Player struct
+- Inserted between `beep.Resample` and `beep.Ctrl` in `updateStreamers()`
+- `loadFileLocked()` closes old BufferedStreamer before loading new track
+- `UnloadTrack()` closes and nils BufferedStreamer to prevent goroutine leaks
+- Speaker buffer changed from `time.Second/10` (100ms) to `time.Second/5` (200ms)
+
+### Lock Safety
+
+No changes to lock ordering or mutex-sensitive code paths. The BufferedStreamer is self-contained and does not interact with `speaker.Lock()` or `p.mu`.
+
+## Verification Results
+
+- `go build ./backend/...` — PASS
+- `go vet ./backend/player/...` — PASS
+- `go test ./backend/player/ -v` — all 12 tests pass (5 BufferedStreamer + 7 existing)
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Self-Check: PASSED
+
+All created files exist, all commits verified.