docs: record §3.4 PlayAlbum queue seam closure (P11 W1 follow-up)

CutDetail Play affordances now consume IQueueService.PlayRelease; annotate
PLAN.md §11 landed note and add COMPLETED.md entry.

COMPLETED.md

@@ -8,6 +8,16 @@ Newest entries at the top. Group by phase/wave header (mirroring `PLAN.md` / `CM
 
 ## Phase 11 — Public Site Enhancements
 
+### §3.4 PlayAlbum queue seam — wired (follow-up to 11.A + 11.F)
+
+**Landed:** 2026-06-16 on dev.
+
+- **What:** The §3.4 integration seam between 11.A (`/cuts/{id}`) and 11.F (`IQueueService`) is now closed. `CutDetail.razor` consumes the cascaded `IQueueService`: header Play calls `Queue.PlayRelease(ViewModel.Tracks, 0)` (loads the full album as an ordered queue starting at track 0); per-row play calls `Queue.PlayRelease(ViewModel.Tracks, index)` (album continues from the chosen track). The currently-playing row still toggles play/pause via `IPlayerService.TogglePlayPause`. Null-safe fallback to `PlayerService.SelectTrackStreaming` is retained for prerender/non-interactive contexts where the queue cascade is absent. Consumption-only — no changes to `IQueueService`, `QueueService`, the player, or `AudioPlayerProvider`.
+- **Why:** 11.A shipped with a documented one-line seam in `PlayAlbum()` noting the future swap to `IQueueService.PlayRelease`. 11.F landed the queue. This follow-up closes the seam so the Cut detail page actually plays the full album as an ordered queue rather than single-track only.
+- **Shape:** `CutDetail.razor` (`DeepDrftPublic.Client/Pages/`) adds `[CascadingParameter] public IQueueService? Queue { get; set; }` and rewrites `PlayAlbum()` and `PlayTrack()` to branch on `Queue is not null` before falling back to direct `SelectTrackStreaming`.
+
+---
+
 ### 11.A — `/cuts/{id}` album-detail page
 
 **Landed:** 2026-06-16 on dev.