perf: round 22 — hot-GET HeaderMap borrow, native-WebDAV/CalDAV etag borrowed quotes, FileDto content_hash move, CalendarEvent stamp, ShareItemType case-fold

Benchmark-gated, same rule as ROUND2-21: every change ships with a
BEFORE/AFTER counting-allocator benchmark and a byte/-value equivalence
gate; an AFTER that fails to reduce allocations exits non-zero (rollback).
See benches/ROUND22.md and examples/bench_round22_micro.rs. All arms
no-Postgres.

- H1: the hot GET handlers (get_thumbnail, download_file, list_files_query,
  list_photos, NextCloud preview, public-share download/access) take
  `req: Request` last and read `req.headers()` by borrow instead of axum's
  HeaderMap extractor, whose FromRequestParts impl clones the whole request
  header table just to read 1-3 headers (the ROUND14 §A4 middleware pattern,
  finally propagated to the handlers). 2 -> 0 allocs/req · 9.95x wall.
- W1: native WebDAV write_etag_quoted — the etag emitter for every /webdav/
  PROPFIND row (per file AND per folder, up to 500/page) — emits the quotes
  as borrowed pre-escaped " text events instead of escaping a "{etag}"
  String (the ROUND20 §C1 / ROUND21 §R4 pattern). 3 -> 0 allocs/row.
- C1: CalDAV getetag routed through a shared write_quoted_etag helper across
  all 5 sites (3 per-event + 2 per-calendar); the now-dead etag: &mut String
  buffer threaded through write_event_response/standard/requested props + the
  two per-page buffers removed. 2 -> 0 allocs/row.
- D1: FileDto::from reuses the moved parts.blob_hash instead of cloning it
  via the content_hash() getter (the ROUND19/20 move-not-clone sweep missed
  it — hash/etag are read before into_parts()). Per file row of every
  listing. 1 -> 0 allocs/row.
- E1: CalendarEvent::update_time_range/update_all_day stamp timed
  DTSTART/DTEND via fmt::compact_ical_utc stack render (chrono fallback out
  of range) instead of the %Y%m%dT%H%M%SZ strftime interpreter. 4 -> 0.
- S1: ShareItemType::try_from uses eq_ignore_ascii_case instead of a
  throwaway to_lowercase() String. 1 -> 0 allocs/parse.

Verified: cargo clippy --features bench --all-targets -D warnings clean,
cargo fmt --all --check clean, cargo test --lib --features bench = 529
passed / 0 failed (incl. the OpenAPI-spec-validity test guarding the H1
utoipa-handler signature change).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DKyQ4AnYtgp1JtjzweyMeo

src/application/adapters/webdav_adapter.rs

@@ -809,12 +809,17 @@ impl WebDavAdapter {
 
     fn write_etag_quoted<W: Write>(xml_writer: &mut Writer<W>, etag: &str) -> Result<()> {
         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-        // One exactly-sized allocation instead of format!'s grow-from-empty.
-        let mut quoted = String::with_capacity(etag.len() + 2);
-        quoted.push('"');
-        quoted.push_str(etag);
-        quoted.push('"');
-        xml_writer.write_event(Event::Text(BytesText::new(&quoted)))?;
+        // Borrowed pre-escaped quotes (the ROUND20 §C1 NextCloud / ROUND21 §R4
+        // CardDAV pattern the native WebDAV adapter never got): `BytesText::new`
+        // escapes a literal `"` → `&quot;`, re-allocating an owned `Cow`, so the
+        // old `"{etag}"` String paid TWO allocs/row (the sized buffer + the
+        // escape). Emit the two quotes as borrowed pre-escaped `&quot;` text
+        // events around the escaped body — byte-identical output, 0 allocs/row
+        // on the hottest native-WebDAV PROPFIND path (per file AND per folder,
+        // up to PROPFIND_BATCH_SIZE=500 rows/page).
+        xml_writer.write_event(Event::Text(BytesText::from_escaped("&quot;")))?;
+        xml_writer.write_event(Event::Text(BytesText::new(etag)))?;
+        xml_writer.write_event(Event::Text(BytesText::from_escaped("&quot;")))?;
         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
         Ok(())
     }