perf: keyset/LATERAL SQL shapes, auth+blob-cache single-flight, spool buffers, DTO interning

Round 3 of benchmark-gated optimizations (benches/ROUND3.md; every change
gated by a before/after benchmark — an AFTER that did not beat its BEFORE
was to be rolled back; none needed it. Equivalence gates assert identical
row sequences / byte-identical output on every behavior-preserving rewrite):

DB hot paths (local PG16, EXPLAIN-verified):
- Web-UI listing (list_resources_paged): cursor pushed INSIDE the
  folders/files UNION-ALL branches as sargable row-value comparisons with
  per-branch ORDER/LIMIT + two partial expression indexes
  (folder_id, LOWER(name), id). 20k-entry folder: 26.6 -> 1.3 ms/page
  (19.5x); other sort modes at parity or better. New migration
  20260918000000. [benches/LISTING-KEYSET.md section in ROUND3]
- Photos timeline (list_media_files): per-drive CROSS JOIN LATERAL top-N
  on the timeline index, joins moved above the top-N. 50k-photo library:
  97.4 -> 1.6 ms/page (55.7x). The old "LIMIT stops the scan early"
  comment was refuted by EXPLAIN.
- PROPFIND sub-folders (both DAV surfaces): keyset list_folders_batch off
  idx_folders_unique_name replaces COUNT(*) OVER() + LIMIT/OFFSET
  (5k dirs: 79.7 -> 17.9 ms full walk, 4.5x).

Concurrency:
- Basic-auth cache single-flight (moka try_get_with): 8 concurrent DAV
  connections at TTL expiry paid 8 Argon2id runs (2.6 s CPU + 8x64 MiB);
  now 1 (300 ms). Failed verifications remain uncached.
- CachedBlobBackend per-hash single-flight + unique tmp names: 16
  concurrent cold readers = 16 full remote downloads racing truncating
  writes on ONE deterministic .tmp (corruptible cache); now 1 download
  (16x less egress, 2.8x wall on a shared link) and torn files can never
  be renamed into the cache.

I/O and allocations:
- Chunk-assembly reads 64K -> 512K buffers (2.3x, 8x fewer syscalls);
  chunk-spool writes via BufWriter 512K (5.6x, 32x fewer syscalls).
- S3/Azure put_blob_from_bytes_unsynced overrides: dedup settle no longer
  pays a HEAD probe per new chunk (2 RTT -> 1, 1.8x); Azure stops copying
  every chunk (Bytes -> Body, -0.44 ms - 4 MiB alloc per 4 MiB chunk).
- Entity->DTO mapping: Arc<str> interning of closed-set display fields +
  common MIMEs, 1-alloc etag/size formatting, FolderDto moves instead of
  clones. File row: 11 -> 4 allocs; folder row: 11.8 -> 1 (2.1x faster).
- CardDAV REPORT: deleted dead per-contact vCard pre-generation and the
  O(N^2) uid scan whose result was discarded (5k contacts: 55.7 -> 5.7 ms,
  9.8x); byte-identical XML asserted.
- Search-results cache: byte weigher + 32 MiB budget
  (OXICLOUD_SEARCH_CACHE_MAX_BYTES) replaces the 1000-ENTRY cap that let
  ~300 MiB of enriched rows sit in RSS; read latency parity.
- Dropped aws-config + aws-smithy-types (zero references; -82 dep-graph
  nodes, three SDK stacks gone from every build). tokio "process" is now
  an explicit feature (was enabled transitively by aws-config).

Frontend:
- Cached Intl.DateTimeFormat keyed by (locale, options) in formatDate and
  4 sibling callsites: 20k dates 2612 -> 51 ms (51.6x); vitest gate
  asserts output identity across locales and a 3x floor.

Validation: cargo fmt + clippy --all-features --all-targets -D warnings
clean; 518 unit + 548 integration-cfg tests green; new-shape endpoints
smoke-tested end-to-end over HTTP (all 5 listing sort modes with cursor
walks, WebDAV PROPFIND Depth-1, photos timeline, Basic-auth DAV login);
frontend npm run check clean, new vitest gates green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EBsU2qEzny3A8WQUEuMNCr

src/application/services/app_password_service.rs

@@ -304,12 +304,45 @@ impl AppPasswordService {
         let cache_key: [u8; 32] =
             blake3::hash(format!("{}:{}", username, password).as_bytes()).into();
 
-        // ── 2. Cache hit → return immediately ────────────────────────
-        if let Some(cached) = self.auth_cache.get(&cache_key).await {
-            return Ok((cached.user_id, cached.username, cached.email, cached.role));
-        }
+        // ── 2. Single-flight cache lookup ─────────────────────────────
+        // Concurrent misses on the same credential coalesce into ONE
+        // full verification: DAV sync clients hold 4-8 parallel
+        // connections, so an expiring cache entry used to fan out into
+        // K simultaneous Argon2id runs (~100-300 ms CPU + 64 MiB RAM
+        // apiece) every TTL — a recurring p99 spike on every DAV
+        // surface (8 -> 1 verifications, benches/AUTH-HERD.md).
+        // `try_get_with` caches only `Ok` results, so failed
+        // verifications are still never cached, preserving the full
+        // Argon2id cost as a brute-force deterrent.
+        let result = self
+            .auth_cache
+            .try_get_with(
+                cache_key,
+                self.verify_basic_auth_uncached(username, password),
+            )
+            .await
+            .map_err(
+                |e: std::sync::Arc<DomainError>| match std::sync::Arc::try_unwrap(e) {
+                    Ok(err) => err,
+                    // Another coalesced waiter still holds the Arc — rebuild
+                    // an equivalent error (the source chain isn't clonable).
+                    Err(shared) => {
+                        DomainError::new(shared.kind, shared.entity_type, shared.message.clone())
+                    }
+                },
+            )?;
+        Ok((result.user_id, result.username, result.email, result.role))
+    }
 
-        // ── 3. Cache miss → full verification ────────────────────────
+    /// The uncached Basic Auth slow path: user lookup, prefix-scoped
+    /// candidate fetch, Argon2id verification. Runs at most once per
+    /// credential per TTL — `verify_basic_auth` coalesces concurrent
+    /// callers onto a single in-flight instance of this future.
+    async fn verify_basic_auth_uncached(
+        &self,
+        username: &str,
+        password: &str,
+    ) -> Result<CachedBasicAuthResult, DomainError> {
         let user = self
             .user_repo
             .get_user_by_username(username)
@@ -363,15 +396,14 @@ impl AppPasswordService {
             {
                 let _ = self.repo.touch_last_used(ap.id).await;
 
-                let result = CachedBasicAuthResult {
+                // Caching happens in `verify_basic_auth`: `try_get_with`
+                // stores this value under the blake3 key on return.
+                return Ok(CachedBasicAuthResult {
                     user_id: user.id(),
                     username: user.username().unwrap_or("").to_string(),
                     email: user.email().to_string(),
                     role: user.role().to_string(),
-                };
-
-                self.auth_cache.insert(cache_key, result.clone()).await;
-                return Ok((result.user_id, result.username, result.email, result.role));
+                });
             }
         }