fix(analysis): dedupe concurrent seed_from_bytes for the same track_id

Six independent paths reach analysis_cache::seed_from_bytes for the same
track_id during a cache-miss play under LUFS:

- track_download_task legacy stream capture-complete
- ranged_download_task HTTP buffer full
- audio_preload bytes-ready
- psysonic-local file-read complete
- spawn_analysis_seed_from_in_memory_bytes (gapless reuse / preloaded /
  stream cache)
- analysis_enqueue_seed_from_url (frontend backfill triggered by
  refresh:miss while a playback path is mid-seed)

Whenever a track is streamed for the first time with loudness on, two of
these fire in parallel and Symphonia + EBU R128 decode the same buffer
twice — ~30 s of duplicate CPU per track, plus a redundant SQLite write
of an identical row. Reproduced on multiple cache-miss tracks (KjP… ranged
+ backfill, mPdz… preloaded bytes + backfill).

Coordinate at the funnel:

- New SeedFromBytesOutcome::SkippedConcurrent variant.
- SEEDS_IN_FLIGHT static (Mutex<HashSet<String>>) tracks track_ids whose
  analysis is currently running. First caller into seed_from_bytes
  wins the slot via HashSet::insert; later callers return SkippedConcurrent
  immediately and let the winner publish the analysis:waveform-updated
  event.
- SeedInFlightGuard (RAII) releases the slot on every exit path including
  panics, so a crashing analysis cannot leak the marker.
- enqueue_analysis_seed in lib.rs distinguishes the SkippedConcurrent log
  from the genuine "seed result" log so the frontend backfill case
  (when it arrives second) doesn't read like a backfill failure.

Existing call-site match arms in audio.rs already use Ok(_) => {} for
non-Upserted outcomes — no changes needed there. enqueue_analysis_seed in
lib.rs already gates the waveform-updated emit on outcome == Upserted, so
the new variant is silent there too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src-tauri/src/analysis_cache.rs

@@ -1,6 +1,7 @@
+use std::collections::HashSet;
 use std::path::PathBuf;
 use std::io::Cursor;
-use std::sync::Mutex;
+use std::sync::{Mutex, OnceLock};
 use std::time::{Instant, SystemTime, UNIX_EPOCH};
 
 use ebur128::{EbuR128, Mode as Ebur128Mode};
@@ -324,6 +325,39 @@ pub enum SeedFromBytesOutcome {
     SkippedWaveformCacheHit,
     /// `AnalysisCache` was not registered on the app handle.
     SkippedNoAnalysisCache,
+    /// Another seed for the same `track_id` is already running on a different
+    /// thread; this caller bails out so the winner's result is used.
+    SkippedConcurrent,
+}
+
+/// Track-ids whose `seed_from_bytes` is currently running. There are six
+/// independent producers (legacy stream capture, ranged stream completion,
+/// audio_preload, psysonic-local file read, in-memory play paths, and the
+/// frontend-triggered `analysis_enqueue_seed_from_url` backfill) that can
+/// fire for the same id concurrently when LUFS is on. Without this guard
+/// the same MP3 gets fully decoded by Symphonia + EBU R128 twice — ~30 s
+/// of wasted CPU per cache-miss track. First caller wins; the rest return
+/// `SkippedConcurrent` immediately.
+static SEEDS_IN_FLIGHT: OnceLock<Mutex<HashSet<String>>> = OnceLock::new();
+
+fn seeds_in_flight() -> &'static Mutex<HashSet<String>> {
+    SEEDS_IN_FLIGHT.get_or_init(|| Mutex::new(HashSet::new()))
+}
+
+/// RAII helper: removes the in-flight marker on drop. Survives panics and
+/// any early `?`-returns inside `seed_from_bytes`.
+struct SeedInFlightGuard {
+    track_id: String,
+}
+
+impl Drop for SeedInFlightGuard {
+    fn drop(&mut self) {
+        if let Some(set) = SEEDS_IN_FLIGHT.get() {
+            if let Ok(mut g) = set.lock() {
+                g.remove(&self.track_id);
+            }
+        }
+    }
 }
 
 pub fn seed_from_bytes(
@@ -331,6 +365,23 @@ pub fn seed_from_bytes(
     track_id: &str,
     bytes: &[u8],
 ) -> Result<SeedFromBytesOutcome, String> {
+    // Reserve the slot for this track_id. Atomic under the mutex: insert()
+    // returns false if the id was already present.
+    let track_key = track_id.to_string();
+    let claimed = {
+        let mut guard = seeds_in_flight().lock().map_err(|_| "seeds-in-flight lock poisoned".to_string())?;
+        guard.insert(track_key.clone())
+    };
+    if !claimed {
+        crate::app_deprintln!(
+            "[analysis] full-track analysis skip track_id={} reason=concurrent_seed_in_flight bytes={}",
+            track_id,
+            bytes.len()
+        );
+        return Ok(SeedFromBytesOutcome::SkippedConcurrent);
+    }
+    let _flight_guard = SeedInFlightGuard { track_id: track_key };
+
     let started = Instant::now();
     let Some(cache) = app.try_state::<AnalysisCache>() else {
         crate::app_deprintln!(