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/interfaces/api/handlers/file_handler.rs

@@ -361,9 +361,9 @@ impl FileHandler {
     pub(super) async fn get_thumbnail_impl(
         State(state): State<GlobalState>,
         auth_user: AuthUser,
-        headers: HeaderMap,
+        headers: &HeaderMap,
         Path((id, size)): Path<(String, String)>,
-    ) -> impl IntoResponse {
+    ) -> impl IntoResponse + use<> {
         use crate::application::ports::thumbnail_ports::{ThumbnailFormat, ThumbnailSize};
 
         // check first that user can access this resource
@@ -665,8 +665,8 @@ impl FileHandler {
         auth_user: AuthUser,
         Path(id): Path<String>,
         Query(params): Query<HashMap<String, String>>,
-        headers: HeaderMap,
-    ) -> impl IntoResponse {
+        headers: &HeaderMap,
+    ) -> impl IntoResponse + use<> {
         let retrieval = &state.applications.file_retrieval_service;
 
         // ── Get file metadata (ownership-scoped) ────────────────────────
@@ -705,7 +705,7 @@ impl FileHandler {
         let etag = format!("\"{}\"", file_dto.etag);
 
         // ── ETag (304 Not Modified) ──────────────────────────────────
-        if let Some(resp) = not_modified_response(&headers, &etag) {
+        if let Some(resp) = not_modified_response(headers, &etag) {
             return resp.into_response();
         }
 
@@ -830,9 +830,9 @@ impl FileHandler {
     pub(super) async fn list_files_query_impl(
         State(state): State<GlobalState>,
         auth_user: AuthUser,
-        headers: HeaderMap,
+        headers: &HeaderMap,
         Query(params): Query<HashMap<String, String>>,
-    ) -> impl IntoResponse {
+    ) -> impl IntoResponse + use<> {
         let folder_id = params.get("folder_id").map(|id| id.as_str());
         tracing::info!("API: Listing files with folder_id: {:?}", folder_id);
 
@@ -1217,10 +1217,14 @@ pub(super) fn build_content_disposition(name: &str, mime: &str, force_inline: bo
 pub async fn list_files_query(
     state: State<GlobalState>,
     auth_user: AuthUser,
-    headers: HeaderMap,
     query: Query<HashMap<String, String>>,
+    req: axum::extract::Request,
 ) -> impl IntoResponse {
-    FileHandler::list_files_query_impl(state, auth_user, headers, query).await
+    // Read headers by borrow (`req.headers()`) instead of the `HeaderMap`
+    // extractor, which clones the whole request header table (~2 allocs) just to
+    // read one If-None-Match — the ROUND14 §A4 middleware pattern applied to the
+    // hot listing handler (benches/ROUND22.md §H1).
+    FileHandler::list_files_query_impl(state, auth_user, req.headers(), query).await
 }
 
 #[utoipa::path(
@@ -1299,9 +1303,12 @@ pub async fn download_file(
     auth_user: AuthUser,
     path: Path<String>,
     query: Query<HashMap<String, String>>,
-    headers: HeaderMap,
+    req: axum::extract::Request,
 ) -> impl IntoResponse {
-    FileHandler::download_file_impl(state, auth_user, path, query, headers).await
+    // Borrow the headers (`req.headers()`) instead of the `HeaderMap` extractor's
+    // full clone — every download AND every media Range seek hit this path
+    // (benches/ROUND22.md §H1).
+    FileHandler::download_file_impl(state, auth_user, path, query, req.headers()).await
 }
 
 #[utoipa::path(
@@ -1323,10 +1330,13 @@ pub async fn download_file(
 pub async fn get_thumbnail(
     state: State<GlobalState>,
     auth_user: AuthUser,
-    headers: HeaderMap,
     path: Path<(String, String)>,
+    req: axum::extract::Request,
 ) -> impl IntoResponse {
-    FileHandler::get_thumbnail_impl(state, auth_user, headers, path).await
+    // Borrow the headers (`req.headers()`) instead of the `HeaderMap` extractor's
+    // full clone — thumbnails are the highest-frequency GET (one per grid tile),
+    // and this handler reads only Accept + If-None-Match (benches/ROUND22.md §H1).
+    FileHandler::get_thumbnail_impl(state, auth_user, req.headers(), path).await
 }
 
 #[utoipa::path(