perf: round 10 — auth alloc purge, parent-herd batching, query-shape pack, NC 304s

Benchmark-gated (benches/ROUND10.md; every change carries a BEFORE/AFTER
harness with equivalence/safety gates — two designs were rejected or
rewritten by their own benches before adoption):

- Auth hot path: TokenClaims/CurrentUser display fields to Arc<str>, role
  to inline SmolStr end-to-end (Bearer, cookie, Basic-auth cache) — 4→1
  allocs per authenticated request, 3→0 per warm DAV request; JWT
  Encoding/Decoding/Validation built once.
- Cold shared-album herd: leader-inline parent batching in PgAclEngine
  (+ cascade try_get_with single-flight) — 100→2 parent queries per
  100-thumb cold herd, herd wall 1.9x, sequential + warm paths unchanged,
  all ROUND8/9 safety gates plus new herd-equivalence gates.
- Query-shape pack: share download double-fetch 2→1 (2.18x), contact-group
  COUNT(*) 14.9x, save_faces UNNEST 3.9x, playlist reorder UNNEST 63.7x
  (now atomic), search files∥folders join! 1.45x, move drive-lookup join!
  2.14x, trash partial (drive_id, trashed_at) indexes, CalDAV event-gate
  narrow read, favorites/recents binary-decode port, dead count_files
  removed.
- NC surface: preview + avatar honour If-None-Match (e2e: 5 KB and 197 KB
  → 0 bytes per revalidation), avatar WebP→PNG transcode memoised,
  PROPFIND/trashbin integer+date emits on stack formatters, folder-header
  enrichment join!, chunk-PUT retry stat folded into create_new open.
- common::fmt integer rendering rewritten on the std 2-digit LUT after the
  round's own bench caught the div-loop losing to to_string (16.1 ns vs
  22.5; speeds every prior-round call site).
- Micro-pack: WebDAV scope probe borrow-only, ShareService base_url
  snapshot, cookie_secure OnceLock, Arc'd AES-GCM cipher, stack request-id,
  tantivy analyzer clone dropped.
- SPA: search stale-guard + AbortController (10→1 completed round-trips,
  stale-clobber gone), getFolder in-flight dedup, gridColumns matchMedia
  hoist (10k→0 style reads).

Backend: cargo fmt + clippy -D warnings clean, 524 tests green.
Frontend: npm run check clean, 301 vitest green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DdM7V7M3QPW7HEHg3gLov

src/infrastructure/repositories/pg/face_pg_repository.rs

@@ -115,29 +115,70 @@ impl FaceRepository for FacePgRepository {
         if faces.is_empty() {
             return Ok(());
         }
-        let mut tx = self.pool.begin().await.map_err(|e| db_err("begin", e))?;
+        // One multi-row INSERT over parallel UNNEST arrays instead of one
+        // round-trip per face — a group photo yields many faces per indexed
+        // image. The `bbox` float4[] can't ride an array-of-arrays through
+        // unnest (PG flattens), so its 4 components travel as 4 parallel
+        // arrays and are reassembled server-side. A single statement is
+        // atomic on its own; the per-row transaction wrapper is gone.
+        let n = faces.len();
+        let mut ids = Vec::with_capacity(n);
+        let mut file_ids = Vec::with_capacity(n);
+        let mut user_ids = Vec::with_capacity(n);
+        let mut person_ids: Vec<Option<Uuid>> = Vec::with_capacity(n);
+        let (mut bx, mut by, mut bw, mut bh) = (
+            Vec::with_capacity(n),
+            Vec::with_capacity(n),
+            Vec::with_capacity(n),
+            Vec::with_capacity(n),
+        );
+        let mut det_scores = Vec::with_capacity(n);
+        let mut qualities: Vec<Option<f32>> = Vec::with_capacity(n);
+        let mut embeddings = Vec::with_capacity(n);
+        let mut blob_hashes: Vec<Option<&str>> = Vec::with_capacity(n);
         for f in faces {
-            sqlx::query(
-                r#"
-                INSERT INTO faces.faces
-                    (id, file_id, user_id, person_id, bbox, det_score, quality, embedding, blob_hash)
-                VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
-                "#,
-            )
-            .bind(f.id)
-            .bind(f.file_id)
-            .bind(f.user_id)
-            .bind(f.person_id)
-            .bind(f.bbox.to_array())
-            .bind(f.det_score)
-            .bind(f.quality)
-            .bind(embedding_to_bytes(&f.embedding))
-            .bind(f.blob_hash.as_deref())
-            .execute(&mut *tx)
-            .await
-            .map_err(|e| db_err("save_faces", e))?;
+            ids.push(f.id);
+            file_ids.push(f.file_id);
+            user_ids.push(f.user_id);
+            person_ids.push(f.person_id);
+            bx.push(f.bbox.x);
+            by.push(f.bbox.y);
+            bw.push(f.bbox.w);
+            bh.push(f.bbox.h);
+            det_scores.push(f.det_score);
+            qualities.push(f.quality);
+            embeddings.push(embedding_to_bytes(&f.embedding));
+            blob_hashes.push(f.blob_hash.as_deref());
         }
-        tx.commit().await.map_err(|e| db_err("commit", e))?;
+        sqlx::query(
+            r#"
+            INSERT INTO faces.faces
+                (id, file_id, user_id, person_id, bbox, det_score, quality, embedding, blob_hash)
+            SELECT t.id, t.file_id, t.user_id, t.person_id,
+                   ARRAY[t.bx, t.by, t.bw, t.bh]::real[],
+                   t.det_score, t.quality, t.embedding, t.blob_hash
+              FROM unnest($1::uuid[], $2::uuid[], $3::uuid[], $4::uuid[],
+                          $5::real[], $6::real[], $7::real[], $8::real[],
+                          $9::real[], $10::real[], $11::bytea[], $12::text[])
+                   AS t(id, file_id, user_id, person_id,
+                        bx, by, bw, bh, det_score, quality, embedding, blob_hash)
+            "#,
+        )
+        .bind(&ids)
+        .bind(&file_ids)
+        .bind(&user_ids)
+        .bind(&person_ids)
+        .bind(&bx)
+        .bind(&by)
+        .bind(&bw)
+        .bind(&bh)
+        .bind(&det_scores)
+        .bind(&qualities)
+        .bind(&embeddings)
+        .bind(&blob_hashes)
+        .execute(self.pool.as_ref())
+        .await
+        .map_err(|e| db_err("save_faces", e))?;
         Ok(())
     }