feat(acoustid): pre-parse upload guard + settings UI to enable it

- /api/enrichment/identify is now async: a pre-parse Content-Length check +
  request.form(max_part_size=…) reject an oversized body BEFORE Starlette spools
  the multipart to temp disk (mirrors the song-upload endpoint), and the blocking
  fpcalc subprocess + AcoustID HTTP run off the event loop via run_in_executor.
- The v3 Metadata-matching settings card gains an 'Identify by audio' opt-in
  toggle (acoustid_enabled, default OFF) + an AcoustID key input
  (acoustid_api_key), wired in match-review.js — so the advertised feature is
  reachable from the UI instead of only via a manual settings POST. Reuses
  existing classes only; committed tailwind.min.css stays fresh.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server.py

@@ -7616,41 +7616,58 @@ def api_enrichment_search(artist: str = "", title: str = "", limit: int = 8,
 
 
 @app.post("/api/enrichment/identify")
-def api_enrichment_identify(file: UploadFile = File(...)):
+async def api_enrichment_identify(request: Request):
     """Identify a song by AUDIO FINGERPRINT (AcoustID) rather than text — the
     reliable way to get the EXACT recording/version (the studio take, not a live
     bootleg or an extended cut). Upload the master audio; returns candidates in
     the same shape as /search, so the review UI and the editor's Match popup can
     render fingerprint hits identically. 412 `needs_setup` when the user hasn't
     opted in / has no key (the UI nudges them to Settings); 503 when it's set up
-    but the fpcalc Chromaprint binary is missing or the network is off. Sync
-    route: the fpcalc subprocess + HTTP run in FastAPI's threadpool."""
+    but the fpcalc Chromaprint binary is missing or the network is off. Async so
+    the multipart is size-capped BEFORE spooling; the blocking fpcalc subprocess
+    + AcoustID HTTP run in the threadpool via run_in_executor."""
     gate = _acoustid_gate()
     if gate is not None:
         return gate
+    # Pre-parse Content-Length guard — reject an oversized body before Starlette
+    # spools the multipart to temp disk (mirrors the song-upload endpoint). The
+    # per-part cap below is the authoritative limit; this is the fast up-front no.
+    cl = request.headers.get("content-length")
+    if cl is not None:
+        try:
+            cl_int = int(cl)
+        except ValueError:
+            return JSONResponse({"error": "Invalid Content-Length header"}, status_code=400)
+        if cl_int > _ACOUSTID_MAX_UPLOAD_BYTES + _MULTIPART_OVERHEAD_SLACK:
+            return JSONResponse({"error": "audio upload too large (256 MB max)"}, status_code=413)
+    try:
+        form = await request.form(max_part_size=_ACOUSTID_MAX_UPLOAD_BYTES)
+    except Exception:
+        return JSONResponse({"error": "audio upload too large (256 MB max)"}, status_code=413)
+    file = form.get("file")
+    if not isinstance(file, UploadFile):
+        raise HTTPException(status_code=400, detail="missing file upload")
     import tempfile
     ext = (Path(file.filename or "").suffix or ".bin").lower()
     tmpdir = tempfile.mkdtemp(prefix="feedback_acoustid_")
     tmp = os.path.join(tmpdir, "audio" + ext)
     try:
-        # Stream the upload to disk with a cap instead of reading it all into
-        # memory — an oversized upload must not balloon RAM (fpcalc reads from
-        # the temp file anyway). Generous ceiling for an uncompressed master.
         total = 0
         with open(tmp, "wb") as fh:
             while True:
-                chunk = file.file.read(1024 * 1024)
+                chunk = await file.read(1024 * 1024)
                 if not chunk:
                     break
                 total += len(chunk)
                 if total > _ACOUSTID_MAX_UPLOAD_BYTES:
-                    raise HTTPException(
-                        status_code=413,
-                        detail="audio upload too large (256 MB max)")
+                    return JSONResponse(
+                        {"error": "audio upload too large (256 MB max)"}, status_code=413)
                 fh.write(chunk)
         if total == 0:
             raise HTTPException(status_code=400, detail="empty upload")
-        cands = _identify_by_fingerprint(tmp)
+        # fpcalc subprocess + AcoustID HTTP are blocking — off the event loop.
+        cands = await asyncio.get_event_loop().run_in_executor(
+            None, _identify_by_fingerprint, tmp)
     except EnrichTransportError as e:
         return JSONResponse({"error": "acoustid unavailable", "detail": str(e)},
                             status_code=503)

static/v3/index.html

@@ -771,6 +771,13 @@
                             </div>
                             <div class="text-[11px] text-gray-600 mt-1">What a confident match may fill in on its own — matches you confirm in the review queue always apply in full.</div>
                         </div>
+                        <!-- Audio fingerprint (AcoustID) — opt-in, default OFF. Wired by match-review.js. -->
+                        <div class="fb-srow-wide mb-1">
+                            <div class="text-[10px] uppercase tracking-wide text-gray-500 mb-1">Audio fingerprint (AcoustID)</div>
+                            <label class="flex items-center gap-2 text-xs text-gray-400 mb-1"><input type="checkbox" id="acoustid-enabled" class="rounded border-gray-600 bg-dark-700 text-accent"> Identify by audio — reads the recording itself for the exact version (studio vs live/extended)</label>
+                            <input type="text" id="acoustid-api-key" placeholder="AcoustID application key" class="w-full bg-dark-700 border border-gray-800 rounded-xl px-2 py-1.5 text-xs text-gray-300 outline-none">
+                            <div class="text-[11px] text-gray-600 mt-1">Opt-in. Get a free key at acoustid.org/new-application; the fpcalc (Chromaprint) binary must be on the server's PATH.</div>
+                        </div>
                         <div class="grid grid-cols-2 gap-2 mb-1 text-xs text-gray-400 fb-srow-wide">
                             <label class="flex items-center gap-2">Review queue order
                                 <select id="enrich-review-order" class="bg-dark-700 border border-gray-800 rounded-xl px-2 py-1.5 text-xs text-gray-300 outline-none">

static/v3/match-review.js

@@ -531,7 +531,10 @@
         // opt-IN per the dev-chat thread.
         const optInToggles = [
             ['artist-external-links', 'artist_external_links'],
+            // Audio fingerprinting is opt-in (needs a key + fpcalc), default OFF.
+            ['acoustid-enabled', 'acoustid_enabled'],
         ].map(([id, key]) => [document.getElementById(id), key]).filter(([el]) => el);
+        const acoustidKeyEl = document.getElementById('acoustid-api-key');
         if (!toggles.length && !optInToggles.length && !sel && !btn) return;
         (async () => {
             try {
@@ -540,6 +543,7 @@
                     const cfg = await r.json();
                     for (const [el, key] of toggles) el.checked = cfg[key] !== false;
                     for (const [el, key] of optInToggles) el.checked = cfg[key] === true;
+                    if (acoustidKeyEl) acoustidKeyEl.value = cfg.acoustid_api_key || '';
                     if (sel) {
                         const t = Number(cfg.enrich_auto_threshold);
                         const want = Number.isFinite(t) ? t : 0.9;
@@ -564,6 +568,7 @@
         }
         sel?.addEventListener('change', () => save('enrich_auto_threshold', Number(sel.value)));
         order?.addEventListener('change', () => save('enrich_review_order', order.value));
+        acoustidKeyEl?.addEventListener('change', () => save('acoustid_api_key', acoustidKeyEl.value.trim()));
         btn?.addEventListener('click', async () => {
             await post('/api/enrichment/kick');
             const line = document.getElementById('enrich-status');