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/folder_service.rs

@@ -429,6 +429,62 @@ impl FolderUseCase for FolderService {
         Ok(response)
     }
 
+    /// Keyset-paged sub-folder listing (name order), caller-scoped.
+    ///
+    /// AuthZ mirrors `list_folders_paginated_with_perms`: one
+    /// `authz.require(Read)` on the parent per batch; root scope goes
+    /// through the caller's drive-membership listing.
+    async fn list_folders_batch_with_perms(
+        &self,
+        parent_id: Option<&str>,
+        caller_id: Uuid,
+        after_name: Option<&str>,
+        limit: usize,
+    ) -> Result<Vec<FolderDto>, DomainError> {
+        match parent_id {
+            Some(pid) => {
+                self.authz
+                    .require(
+                        Subject::User(caller_id),
+                        Permission::Read,
+                        Self::folder_resource(pid)?,
+                    )
+                    .await?;
+                let folders = self
+                    .folder_storage
+                    .list_folders_batch(parent_id, after_name, limit)
+                    .await
+                    .map_err(|e| {
+                        DomainError::internal_error(
+                            "FolderStorage",
+                            format!("Failed to batch-list folders in parent {pid}: {e}"),
+                        )
+                    })?;
+                Ok(folders.into_iter().map(FolderDto::from).collect())
+            }
+            None => {
+                // Root scope: one row per readable drive — a handful.
+                let mut all = self
+                    .folder_storage
+                    .list_root_folders_for_caller(caller_id)
+                    .await
+                    .map_err(|e| {
+                        DomainError::internal_error(
+                            "FolderStorage",
+                            format!("Failed to batch-list root folders for '{caller_id}': {e}"),
+                        )
+                    })?;
+                all.sort_by(|a, b| a.name().cmp(b.name()));
+                Ok(all
+                    .into_iter()
+                    .filter(|f| after_name.is_none_or(|a| f.name() > a))
+                    .take(limit)
+                    .map(FolderDto::from)
+                    .collect())
+            }
+        }
+    }
+
     /// Lists folders with pagination, scoped to a specific owner.
     async fn list_folders_paginated_with_perms(
         &self,