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/services/encrypted_blob_backend.rs

@@ -56,7 +56,10 @@ const PLAINTEXT_EMIT_SIZE: usize = 64 * 1024;
 /// `BlobStorageBackend` decorator that encrypts blobs at rest.
 pub struct EncryptedBlobBackend {
     inner: Arc<dyn BlobStorageBackend>,
-    cipher: Aes256Gcm,
+    /// `Arc` so the per-op `clone()` handed to `offload_crypto` closures is
+    /// an atomic bump instead of copying the ~240-byte expanded AES-256
+    /// round-key schedule on every chunk read/write.
+    cipher: Arc<Aes256Gcm>,
 }
 
 impl EncryptedBlobBackend {
@@ -64,7 +67,8 @@ impl EncryptedBlobBackend {
     ///
     /// `key` must be exactly 32 bytes (AES-256).
     pub fn new(inner: Arc<dyn BlobStorageBackend>, key: &[u8; 32]) -> Self {
-        let cipher = Aes256Gcm::new_from_slice(key).expect("AES-256 key must be 32 bytes");
+        let cipher =
+            Arc::new(Aes256Gcm::new_from_slice(key).expect("AES-256 key must be 32 bytes"));
         Self { inner, cipher }
     }