perf: round 5 — CalDAV cursor streaming, SPA interning gaps, NC href prefix, per-request micro-allocs

Seven benchmark-gated changes (benches/ROUND5.md; BEFORE/AFTER bench +
equivalence gate each, rollback rule as ROUND2-4 — two intermediate
CalDAV shapes measured worse and were themselves rolled back before
shipping):

- CalDAV whole-calendar responses (REPORT no-range/sync-collection,
  depth-1 collection PROPFIND, .ics GET): buffered double-residency →
  ONE window-ordered scan (MIN(start_time) OVER (PARTITION BY ical_uid))
  streamed through a PG cursor, pages cut at UID boundaries. TTFB
  23.3→11.0 ms (2.1x), peak heap 14.2→8.0 MiB at 4k events / 45→24 MiB
  at 12k, wall +9-15% (documented trade, ZIP-streaming class); both
  multistatus and ICS byte-identical to the buffered output. Rejected
  shapes kept in the doc: per-page GROUP-BY keyset (3-4x wall) and
  per-uid ANY hydration (~20 µs/index descent).
- SPA listing interning gaps: folder/recent/favorites resources handlers
  (and the WebDAV pseudo-root) called raw Arc::from per row for the
  closed display set ROUND3 interned — now intern_display/intern_mime,
  4→0 allocs/row, byte-identical Arc contents.
- NC PROPFIND child hrefs: username + parent path encoded once per
  request instead of per child (543→165 ns/row, 13→4 allocs); native
  WebDAV href drops its intermediate encode String.
- suggest enrichment: entity clone + field re-clones per keystroke row →
  consume + move (166.5→126.8 µs/200 rows, 20→7 allocs/row).
- list_readable_by returns the cache's Arc (246→128 ns warm hit, 4→0
  allocs) — deep Vec clone per DAV-selector request removed.
- CardDAV REPORT: borrowed props, reused href buffer, exact-size etag
  quoting (3.04→2.34 ms per 5k-contact getetag poll).
- Auth span records: user_id.to_string() per request ×3 →
  tracing::field::display.

Checks: cargo fmt, clippy --all-features --all-targets -D warnings,
cargo test --workspace (523 passed). Follow-ups (CardDAV streaming,
&[&str] id batches, ::text UUID casts A/B, share-landing join) recorded
in benches/ROUND5.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017aJu9ghvuT8WqC31ZEGTBA

src/interfaces/nextcloud/webdav_handler.rs

@@ -1526,6 +1526,19 @@ fn build_nc_streaming_propfind(
 
         // ── Children (only if Depth != 0) ────────────────────────────
         if depth != "0" {
+            // Encoded href prefix for every child: username + parent
+            // path encode ONCE here — the old per-row `nc_href` call
+            // re-split and re-encoded the constant prefix for each of
+            // the up-to-500 children of every page.
+            let child_href_prefix = {
+                let base = nc_href(&username, &subpath);
+                if base.ends_with('/') {
+                    base
+                } else {
+                    format!("{base}/")
+                }
+            };
+
             // Files in pages (keyset cursor — O(page) per page instead of
             // the quadratic LIMIT/OFFSET walk).
             let mut after_name: Option<String> = None;
@@ -1563,12 +1576,12 @@ fn build_nc_streaming_propfind(
                     let mut xml = Writer::new(&mut chunk);
                     for file in batch.iter() {
                         let dead = dead_props_for(&file.id, &file_deads);
-                        let child_sub = if subpath.is_empty() {
-                            file.name.clone()
-                        } else {
-                            format!("{}/{}", subpath.trim_end_matches('/'), file.name)
-                        };
-                        let href = nc_href(&username, &child_sub);
+                        // Only the name varies per row — the encoded
+                        // username + parent prefix is computed once
+                        // outside the loops (the old `nc_href` call
+                        // re-encoded both for every child).
+                        let href =
+                            format!("{}{}", child_href_prefix, urlencoding::encode(&file.name));
                         let fid = file_id_map.get(&file.id).copied();
                         let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
                         write_file_response(&mut xml, file, &href, (fid, oc_id.as_deref()), &username, &favs, dead)
@@ -1620,12 +1633,10 @@ fn build_nc_streaming_propfind(
                     let mut xml = Writer::new(&mut chunk);
                     for sf in batch.iter() {
                         let dead = dead_props_for(&sf.id, &sub_deads);
-                        let child_sub = if subpath.is_empty() {
-                            sf.name.clone()
-                        } else {
-                            format!("{}/{}", subpath.trim_end_matches('/'), sf.name)
-                        };
-                        let href = nc_collection_href(&username, &child_sub);
+                        // Collections carry the trailing slash; prefix
+                        // precomputed once like the file loop above.
+                        let href =
+                            format!("{}{}/", child_href_prefix, urlencoding::encode(&sf.name));
                         let fid = sub_id_map.get(&sf.id).copied();
                         let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
                         write_folder_response(&mut xml, sf, &href, (fid, oc_id.as_deref()), &username, &favs, quota, dead)