docs: log WaveformSeeker W1-T2 completion in COMPLETED.md

COMPLETED.md

@@ -8,7 +8,7 @@ Newest entries at the top. Group by phase/wave header (mirroring `PLAN.md` / `CM
 
 ## WaveformSeeker Wave 1 — Loudness profile + layout refactor
 
-**Status:** W1-T1 (backend loudness computation) and W1-T3 (player layout refactor) landed on 2026-06-05.
+**Status:** W1-T1 (backend loudness computation), W1-T2 (HTTP transport), and W1-T3 (player layout refactor) landed on 2026-06-05.
 
 ### W1-T1 — Backend waveform loudness profiling
 
@@ -37,6 +37,33 @@ Implemented Phase 1 of the WaveformSeeker feature (`product-notes/spectrum-seeke
 - No external audio-processing dependency pulled in for RMS — reuses existing PCM parser from `AudioProcessor`.
 - Cost: one linear pass over PCM buffer at upload (few hundred ms for typical WAV); never on playback path.
 
+### W1-T2 — Waveform profile HTTP transport
+
+**Landed 2026-06-05.**
+
+Implemented Phase 2 of the WaveformSeeker feature: HTTP transport layer for waveform profile data from backend to client, enabling client-side display of loudness profiles in future seeking UI.
+
+**API endpoint (`DeepDrftAPI`):**
+- New `GET api/track/{trackId}/waveform` endpoint — unauthenticated, returns `WaveformProfileDto` (base64-encoded quantized bytes + `BucketCount`) on success, 404 if track or profile not found.
+- Leverages existing `WaveformProfileService` to load profile from vault on demand.
+- No authentication required — mirrors `GET api/track/{id}` streaming policy (public audio access).
+
+**Proxy forward (`DeepDrftPublic`):**
+- Thin buffered forward in `TrackProxyController` — proxies request from client to `DeepDrftAPI` waveform endpoint with same path parameters.
+- Preserves error semantics: 404 from API passes through to client; network errors surface as HTTP errors.
+
+**HTTP client (`DeepDrftPublic.Client`):**
+- New `TrackMediaClient.GetWaveformProfileAsync(trackId, cancellationToken)` method on the content HTTP client.
+- 404 response maps to `Result.Failure` (fail-result signal for WaveformSeeker to render flat fallback).
+- Network/timeout errors map to separate `Result.Failure` with distinct code.
+- Callsite can discriminate via result error code whether to retry (transient) or render fallback (not found).
+
+**Architecture notes:**
+- Transport layer is independent of loudness algorithm (W1-T1) — client receives opaque quantized bytes; future algorithm changes on backend do not affect wire format, as long as `BucketCount` is included.
+- HTTP caching via ETag/Last-Modified is deferred to Phase 2 optimization work.
+- Profile loading from vault is on-demand (not pre-cached in memory) — load cost amortizes across all requests to the same track.
+- 404 handling unambiguous: client renders flat fallback, distinguishing "track has no profile" from "track not found" via error code.
+
 ### W1-T3 — Player layout refactor (SpectrumVisualizer relocation + VolumeZone rename)
 
 **Landed 2026-06-05.**