diff --git a/Cargo.toml b/Cargo.toml
index 3e4dec48..0581b5a8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -354,6 +354,21 @@ name = "bench_micro_allocs"
 path = "examples/bench_micro_allocs.rs"
 required-features = ["bench"]
 
+# Round-21 battery ────────────────────────────────────────────────────────────
+
+# Round-21 CPU/alloc micro-pack — CalDAV/CardDAV row-mapper container pre-size
+# (the ROUND20 §I1 sibling the calendar/contact repos deferred); dedup
+# `settle_batch` hash bind Vec<String>→Vec<&str> borrow; `store_loose_chunks`
+# intra-request dedup set keyed on the raw [u8;32] digest + move-on-dup (the
+# ROUND17 §D2 pattern applied to the delta-upload sibling); CardDAV `getetag`
+# borrowed pre-escaped quotes (the ROUND20 §C1 NextCloud pattern); `BDAY`
+# stamp via fmt::compact_date stack render; NC trashbin folder content-type
+# Cow::Borrowed. No Postgres.
+[[example]]
+name = "bench_round21_micro"
+path = "examples/bench_round21_micro.rs"
+required-features = ["bench"]
+
 # Round-20 battery ────────────────────────────────────────────────────────────
 
 # Round-20 CPU/alloc micro-pack — CalendarEvent `prop_with_params` throwaway
diff --git a/benches/ROUND21.md b/benches/ROUND21.md
new file mode 100644
index 00000000..5dff696d
--- /dev/null
+++ b/benches/ROUND21.md
@@ -0,0 +1,225 @@
+# Round 21 — CalDAV/CardDAV row-mapper pre-size, dedup hash-bind & digest-key dedup, CardDAV etag & BDAY emit, NC trashbin content-type
+
+Benchmark-gated, same rule as ROUND2–20: every change ships with a BEFORE/AFTER
+benchmark and a byte/-value equivalence gate; an AFTER that doesn't beat its
+BEFORE is rolled back (never applied). The roll-back rule is encoded directly in
+the harness — a `GATE FAIL … rollback` non-zero exit if an AFTER arm fails to
+reduce allocations — so a regression fails CI rather than shipping.
+
+This round drains the sibling seams the earlier passes explicitly deferred. The
+file-listing repositories got their result-`Vec` pre-sizing in ROUND20 §I1, but
+the **CalDAV/CardDAV row mappers** (bulk address-book / calendar sync builds
+thousands of rows) were left growing from capacity 0. The **streaming ingest**
+loop got its `[u8; 32]`-digest dedup key in ROUND17 §D2, but its **delta-upload
+sibling** `store_loose_chunks` kept a `HashSet<String>` and a double hex clone
+per frame. The **NextCloud** etag emitter got the borrowed-pre-escaped-quote
+treatment in ROUND20 §C1, but the **CardDAV** emitter still built a quoted
+`String`. And two dedup/DAV emit micro-cuts the earlier rounds named but held
+back: the `settle_batch` clone-to-bind and the `BDAY` strftime stamp.
+
+Reproduce:
+
+```
+cargo run --release --features bench --example bench_round21_micro
+```
+
+All arms are **no-Postgres** (release-profile counting-allocator example).
+
+## Summary
+
+| # | change | key metric | before → after |
+|--:|---|---|---|
+| **R1** | The CalDAV/CardDAV row-mapping repositories (`calendar_event_pg_repository`, `calendar_pg_repository`, `contact_pg_repository`, `contact_group_pg_repository`) built their result `Vec` with `let mut v = Vec::new(); for row in rows { v.push(map(row)?) }` — growing from capacity 0 (~⌈log₂N⌉ reallocations, each memcpy-ing the accumulated rows) on **every CalDAV/CardDAV listing, multiget & bulk sync**. Now `Vec::with_capacity(rows.len())` (the ROUND20 §I1 file-side pattern extended to the 16 calendar/contact sites it deferred). Plus one `HashMap` (`get_calendar_properties`). | 200-row listing | **7 → 1 allocs/op** (6 fewer) |
+| **R2** | `DedupService::settle_batch` cloned every 64-char chunk hash into a `Vec<String>` purely to `.bind()` it to the pin `UPDATE … WHERE hash = ANY($1)`, on **every settle batch of every upload** (~128 batches for a 1 GB fully-unique upload). Now binds a borrowed `Vec<&str>` — sqlx encodes `&[&str]` to `text[]` identically (`favorites_pg_repository.rs:271` already does this). | 32-chunk batch | **33 → 1 allocs/op · 39.4× wall** |
+| **R3** | `DedupService::store_loose_chunks` — the delta-upload sibling of the ROUND17 §D2 ingest loop — kept an intra-request dedup `HashSet<String>` and cloned the hex hash **twice per frame** (into `received` and into the set; the set clone dropped on the spot for a duplicate). Now keys the set on the raw `[u8; 32]` BLAKE3 digest (`Copy`, no per-distinct-chunk heap key) and moves the hex into `received` on a duplicate. Runs **per frame** on delta/sync uploads (thousands of frames for a large changed file). | 128 frames, 50% dup | **401 → 209 allocs/op (192 fewer) · 1.50× wall** |
+| **R4** | `carddav_adapter::write_contact_response` built a `"…"`-quoted `String` for `getetag` then wrote it auto-escaped — `quick_xml` escapes the `"` → `&quot;`, re-allocating an owned `Cow` — on **every contact of every CardDAV multiget/PROPFIND** (plus the per-address-book collection etag). Now emits the two quotes as borrowed pre-escaped `&quot;` text events (the ROUND20 §C1 NextCloud pattern, via a shared `write_quoted_etag` helper covering all 4 CardDAV etag sites). | per-contact row | **3 → 0 allocs/op · 2.11× wall** |
+| **R5** | `contact_to_vcard` stamped `BDAY` via `write!(…, "{}", bday.format("%Y-%m-%d"))`, running chrono's strftime interpreter per **contact-with-birthday**. Now renders the fixed `YYYY-MM-DD` on the stack via the new `fmt::compact_date` (the date-only companion to the §V2 `REV` renderer), chrono fallback for out-of-range years. | per bday contact | **2 → 0 allocs/op · 10.51× wall** |
+| **R6** | The NextCloud trashbin PROPFIND row set `d:getcontenttype` for a folder to `"httpd/unix-directory".to_string()` — a heap `String` for a static constant, **per trashed folder row**. Now `Cow::Borrowed` (the ROUND16 §M1 `Cow<'static, str>` pattern); only the file branch (mime_guess) still owns its String. | per folder row | **1 → 0 allocs/op · 5.76× wall** |
+
+> Allocs/op is the deterministic primary gate (identical run to run). Wall
+> figures are single-shot and noise-bounded. Every section carries a
+> byte/-value equivalence gate; the shipped source now matches each AFTER arm.
+
+## [R1] CalDAV/CardDAV row-mapper container pre-size
+
+`collect::<Result<Vec>>()` was ROUND20 §I1's target on the file side; the
+CalDAV/CardDAV repos use the equivalent `Vec::new()` + `for row in rows { … }`
+shape, which grows the container the same way — from capacity 0, reserving
+nothing, so `push` reallocates ~⌈log₂N⌉ times and memcpy-s the accumulated
+(Contact/Event-sized) rows on each grow. `rows` is a materialized `fetch_all`
+result, so `rows.len()` is exact:
+
+```rust
+let mut events = Vec::with_capacity(rows.len());
+for row in rows {
+    events.push(Self::row_to_event(row)?);   // ? short-circuits identically
+}
+```
+
+Applied to the 16 listing/multiget/paginated mappers across the four repos
+(`calendar_event` ×6, `calendar` ×2 + the `get_calendar_properties` HashMap,
+`contact` ×6, `contact_group` ×1). The `subject_group` and
+`nextcloud_object_id` sibling mappers already pre-sized (`with_capacity(rows.len())`),
+so they were left untouched. Byte-identical output; on a 200-row listing the
+container allocations drop from **7 → 1** (the growth-from-0 reallocations
+replaced by a single exact reserve).
+
+## [R2] settle_batch — bind borrowed `&str`, don't clone
+
+`settle_batch` runs once per flushed chunk batch of every upload. It built an
+owned `Vec<String>` of the batch's 64-char hashes only to `.bind()` it:
+
+```rust
+let hashes: Vec<String> = batch.iter().map(|(h, _)| h.clone()).collect();  // N heap Strings
+// … .bind(&hashes) … WHERE hash = ANY($1) …
+```
+
+`batch` outlives the query (it is consumed two statements later), so the hashes
+can be borrowed. sqlx encodes `&[&str]` to a PostgreSQL `text[]` identically to
+the owned `Vec<String>` (the pattern `favorites_pg_repository.rs:271` already
+uses, with the comment *"sqlx binds `&[&str]` as text[], so no per-id String is
+needed"*). The borrow is scoped in a block so it ends before `batch` is moved:
+
+```rust
+let pinned: HashSet<String> = {
+    let hashes: Vec<&str> = batch.iter().map(|(h, _)| h.as_str()).collect();
+    sqlx::query_scalar::<_, String>("UPDATE … WHERE hash = ANY($1) RETURNING hash")
+        .bind(&hashes).fetch_all(pool.as_ref()).await?.into_iter().collect()
+};
+```
+
+Up to `FLUSH_MAX_CHUNKS` (=32) 64-byte `String` allocations removed per batch —
+~4000 over a 1 GB fully-unique upload — for one pointer-only `Vec`.
+
+## [R3] store_loose_chunks — digest-keyed dedup set + move-on-duplicate
+
+The delta-upload ingest (`store_loose_chunks`) is the sibling ROUND17 §D2 didn't
+reach. Per frame it allocated the 64-char hex hash and then cloned it twice:
+
+```rust
+let hash = blake3::hash(&data).to_hex().to_string();
+received.push((hash.clone(), data.len() as u64));   // clone 1 (always)
+if seen.insert(hash.clone()) {                       // clone 2 (always; HashSet<String>)
+    new_rows.push((hash, len));
+}
+```
+
+`seen` is the **intra-request** dedup set (has this exact chunk already appeared
+in *this* delta stream? — re-chunked near-duplicates, zero-padded regions). Keyed
+on the raw 32-byte digest it needs no per-distinct-chunk `String`, and a
+duplicate frame **moves** the hex into `received` instead of cloning:
+
+```rust
+let digest = blake3::hash(&data);
+let hash = digest.to_hex().to_string();
+let len = data.len();
+if seen.insert(*digest.as_bytes()) {         // HashSet<[u8; 32]>, Copy key
+    self.backend.put_blob_from_bytes_unsynced(&hash, data).await?;
+    received.push((hash.clone(), len as u64));
+    new_rows.push((hash, len as i64));
+} else {
+    received.push((hash, len as u64));       // move, no clone
+}
+```
+
+hex ↔ digest is bijective, so membership and the `received`/`new_rows`
+sequences are identical. On a 128-frame stream with 50 % intra-request dups the
+per-frame hash clones drop from 3 to ~1.5.
+
+## [R4] CardDAV getetag — borrowed pre-escaped quotes
+
+`write_contact_response` (per contact of every CardDAV multiget/PROPFIND) built
+a `"…"`-quoted `String` and wrote it auto-escaped; `quick_xml` escapes the `"`
+to `&quot;`, so the whole-string escape re-allocated an owned `Cow`. The new
+shared `write_quoted_etag` helper emits the two quotes as **borrowed**
+pre-escaped `&quot;` text events around the escaped etag body — byte-identical
+(the equivalence gate asserts it, including an etag with `&`/`<`/`"`), 0
+allocs/contact. Applied to all four CardDAV etag sites (2 per-contact + 2
+per-address-book collection), mirroring the NextCloud ROUND20 §C1 fix.
+
+## [R5] BDAY — stack-rendered `%Y-%m-%d`
+
+`contact_to_vcard` already stack-renders `REV` (ROUND19 §V2); `BDAY` still went
+through chrono's strftime interpreter (`bday.format("%Y-%m-%d")`). The new
+`fmt::compact_date(buf, year, month, day)` renders the fixed 10-byte
+`YYYY-MM-DD` with the same `push4`/`push2` LUT the other `fmt` helpers use, and
+returns `None` outside the 4-digit-year range (where chrono widens/sign-prefixes
+`%Y`) so the caller keeps the chrono path as fallback. Byte-identical for every
+representable birthday.
+
+## [R6] NC trashbin folder content-type — borrowed constant
+
+The trashbin PROPFIND folder branch `to_string()`-ed the static
+`"httpd/unix-directory"` per row. `Cow::Borrowed` for the folder constant (the
+file branch still owns its mime_guess String) drops that allocation per trashed
+folder row — the ROUND16 §M1 `Cow<'static, str>` pattern the trashbin loop
+missed.
+
+## Not shipped — deferred to a later round
+
+Surfaced by the Round-21 audit (three parallel sub-audits across the HTTP,
+storage/dedup and application/parse layers), verified against current source,
+but held back — each needs a signature/API decision, a Postgres fixture, or a
+gate the deterministic alloc-counter can't provide:
+
+- **Hot GET handlers clone the whole request `HeaderMap`** (`file_handler`
+  list/download/thumbnail, `photos_handler`, NC `preview`/`avatar`): axum's
+  `HeaderMap` extractor does `parts.headers.clone()` (~2 allocs) purely to read
+  1–3 headers — the exact cost `middleware/auth.rs` already eliminated (ROUND14
+  §A4) but never propagated to the handlers. The fix takes `req: Request` last
+  and reads `req.headers()` by borrow; it's a **multi-handler signature refactor**
+  (each `_impl` + its wrapper + the route registration) that wants its own
+  validated pass, same class as the ROUND19/20 multi-signature deferrals.
+- **`Query<HashMap<String,String>>` on the hot list/download paths** builds a
+  `HashMap` + key `String` per request to read one param; a typed
+  `Query<ListFilesQuery>` struct drops both (serde ignores unknown params). Same
+  signature-surface reason as above; pairs naturally with the HeaderMap pass.
+- **Native WebDAV PROPFIND re-extracts the URI path** (`webdav_handler.rs:507`):
+  `extract_webdav_path(req.uri())` re-runs a percent-decode + `String` alloc that
+  the `path` parameter already holds at that point (the `:503` comment about the
+  prefix is stale). One decode + alloc per PROPFIND — but removing it needs a
+  careful href-equivalence proof across the chroot/scope resolution, so it wants
+  a dedicated correctness check, not a perf banner.
+- **`music_service` public-playlist merge is O(owned·public)** (`Vec::any()` per
+  public item): a `HashSet` makes it O(owned+public). Because `PlaylistDto.id` is
+  a `String`, the set must own the ids (clone) — so the change trades N String
+  comparisons for N String clones: a **wall win that ADDS allocations**, which
+  the deterministic alloc gate can't score. Wants a wall-gated evaluation on the
+  opt-in `include_public` path.
+- **WebDAV dead-props filter is O(N·D·R)** (`webdav_adapter.rs:616/705`): the
+  loop-invariant requested-props list is re-scanned per dead prop per resource;
+  a per-PROPFIND `HashSet<&QualifiedName>` makes it O(N·D). Only bites accounts
+  that accumulate client-set custom props (macOS Finder) over large listings —
+  and, like music_service, the HashSet build trades compares for an alloc, so
+  it's wall-gated. Queued with a synthetic-dead-props bench.
+- **`verify_integrity` Phase 1 probes manifest chunks serially** while Phase 2
+  is `buffer_unordered(16)` — on a remote backend that's O(total_chunks) serial
+  HEADs. Background/admin path; needs a remote-backend fixture to show the win.
+- **`subject_group_service::remove_member` runs the same recursive-CTE
+  `list_transitive_users(child_id)` twice** for a nested group removal (the
+  intervening edge delete can't change the child's descendants). One DB
+  round-trip halved; low frequency (admin), needs Postgres.
+- **`store_loose_chunks` final registration + `run_rollback` clone hashes to
+  bind** (`dedup_service.rs:887/212`), and the **`contact_pg` JSONB columns
+  decode through a throwaway `serde_json::Value`** — the R2/ROUND20 patterns
+  applied to once-per-upload / per-contact-read sites; both need Postgres to
+  bench end-to-end.
+- **`GzipCompressionService::{compress,decompress}_data` copy the whole buffer
+  via `.to_vec()`** before `spawn_blocking` — forced by the `&[u8]` port
+  signature; a `Bytes`-taking port lets an owning caller move. Port API change,
+  gated (text > 50 KB), low heat.
+- **Fast hasher for trusted-key internal maps** (ROUND20 flag stands): needs a
+  `Cargo.toml` dependency decision and must stay DoS-resistant for the
+  attacker-controlled delta-hash sets — worth a dedicated, wall-gated pass.
+
+## Environment / methodology
+
+- `cargo run --release --features bench --example bench_round21_micro` —
+  counting global allocator, no Postgres. Tunables (env): `BENCH_ITERS` (200000),
+  `R1_ROWS` (200), `R3_FRAMES` (128).
+- Each section is BEFORE (verbatim replica of the shipped-before shape) vs AFTER
+  (verbatim replica of the shipped-after shape, which the source is then made to
+  match), with a byte/-value equivalence gate; the shipped source now matches
+  each AFTER arm.
+- Roll-back rule encoded per section: the harness `std::process::exit(1)`s with
+  `GATE FAIL … rollback` if an AFTER arm fails to reduce allocations.
diff --git a/examples/bench_round21_micro.rs b/examples/bench_round21_micro.rs
new file mode 100644
index 00000000..f37b9ec2
--- /dev/null
+++ b/examples/bench_round21_micro.rs
@@ -0,0 +1,520 @@
+//! Round-21 CPU/alloc micro-pack (no Postgres).
+//!
+//! Same rule as ROUND2–20: each section is BEFORE (verbatim replica of the
+//! shipped-before shape) vs AFTER (verbatim replica of the shipped-after shape,
+//! which the source is then made to match), with a byte/-value equivalence gate
+//! and a `GATE FAIL … rollback` check that `std::process::exit(1)`s if the AFTER
+//! arm fails to beat its BEFORE — the round's roll-back rule encoded into the
+//! benchmark. An AFTER that doesn't win is never applied to the source.
+//!
+//!   [R1] The CalDAV/CardDAV row-mapping repositories build their result Vec
+//!        with `let mut v = Vec::new(); for row in rows { v.push(map(row)?) }`,
+//!        growing the container from capacity 0 (~⌈log₂N⌉ reallocations, each
+//!        memcpy-ing the accumulated rows). AFTER pre-sizes with
+//!        `Vec::with_capacity(rows.len())` — the file-side sibling ROUND20 §I1
+//!        shipped, extended to the calendar/contact repos it deferred.
+//!
+//!   [R2] `DedupService::settle_batch` cloned every 64-char chunk hash into a
+//!        `Vec<String>` purely to `.bind()` it to the pin `UPDATE … = ANY($1)`.
+//!        AFTER binds a borrowed `Vec<&str>` — sqlx encodes `&[&str]` to
+//!        `text[]` identically (favorites_pg_repository.rs:271 already does
+//!        this), so the per-chunk hash `String` disappears.
+//!
+//!   [R3] `DedupService::store_loose_chunks` (the delta-upload sibling of the
+//!        ROUND17 §D2 ingest loop) kept an intra-request dedup `HashSet<String>`
+//!        and cloned the hex hash TWICE per frame (into `received` and into the
+//!        set). AFTER keys the set on the raw `[u8; 32]` BLAKE3 digest (`Copy`,
+//!        no heap key) and moves the hex into `received` on a duplicate.
+//!
+//!   [R4] `carddav_adapter::write_contact_response` built a `"…"`-quoted
+//!        `String` for `getetag` then wrote it auto-escaped (quick_xml escapes
+//!        the `"` → `&quot;`, re-allocating). AFTER emits the two quotes as
+//!        borrowed pre-escaped `&quot;` text events (the NextCloud ROUND20 §C1
+//!        pattern applied to the CardDAV emitter it missed).
+//!
+//!   [R5] `contact_to_vcard` stamped `BDAY` via `write!(…, "{}",
+//!        bday.format("%Y-%m-%d"))`, running chrono's strftime interpreter per
+//!        contact-with-birthday. AFTER renders the fixed `YYYY-MM-DD` on the
+//!        stack via `fmt::compact_date` (the date-only companion to the §V2 REV
+//!        renderer), with the chrono fallback for out-of-range years.
+//!
+//!   [R6] The NextCloud trashbin PROPFIND row set `d:getcontenttype` for a
+//!        folder to `"httpd/unix-directory".to_string()` — a heap String for a
+//!        static constant, per trashed folder row. AFTER borrows it via
+//!        `Cow::Borrowed` (the ROUND16 §M1 `Cow<'static, str>` pattern).
+//!
+//! Run:
+//!   cargo run --release --features bench --example bench_round21_micro
+//! Tunables (env): BENCH_ITERS (200000), R1_ROWS (200), R3_FRAMES (128)
+
+use std::alloc::{GlobalAlloc, Layout, System};
+use std::borrow::Cow;
+use std::collections::HashSet;
+use std::env;
+use std::hint::black_box;
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::time::Instant;
+
+use chrono::NaiveDate;
+use quick_xml::Writer;
+use quick_xml::events::{BytesEnd, BytesStart, BytesText, Event};
+
+static ALLOC_CALLS: AtomicU64 = AtomicU64::new(0);
+
+struct CountingAlloc;
+
+unsafe impl GlobalAlloc for CountingAlloc {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        ALLOC_CALLS.fetch_add(1, Ordering::Relaxed);
+        unsafe { System.alloc(layout) }
+    }
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        unsafe { System.dealloc(ptr, layout) }
+    }
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        ALLOC_CALLS.fetch_add(1, Ordering::Relaxed);
+        unsafe { System.realloc(ptr, layout, new_size) }
+    }
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        ALLOC_CALLS.fetch_add(1, Ordering::Relaxed);
+        unsafe { System.alloc_zeroed(layout) }
+    }
+}
+
+#[global_allocator]
+static GLOBAL: CountingAlloc = CountingAlloc;
+
+fn env_or<T: std::str::FromStr>(key: &str, default: T) -> T {
+    env::var(key)
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(default)
+}
+
+struct Measured {
+    wall_ns_per_op: f64,
+    allocs_per_op: f64,
+}
+
+fn measure<F: FnMut()>(iters: usize, mut f: F) -> Measured {
+    // Warm up (grow any reused buffers, prime caches) so the measured window
+    // reflects steady state, not first-touch growth.
+    for _ in 0..(iters / 20).max(1) {
+        f();
+    }
+    let a0 = ALLOC_CALLS.load(Ordering::Relaxed);
+    let t = Instant::now();
+    for _ in 0..iters {
+        f();
+    }
+    let wall = t.elapsed().as_nanos() as f64 / iters as f64;
+    let allocs = (ALLOC_CALLS.load(Ordering::Relaxed) - a0) as f64 / iters as f64;
+    Measured {
+        wall_ns_per_op: wall,
+        allocs_per_op: allocs,
+    }
+}
+
+fn print_row(label: &str, m: &Measured) {
+    println!(
+        "| {:<50} | {:>12.1} | {:>10.2} |",
+        label, m.wall_ns_per_op, m.allocs_per_op
+    );
+}
+
+fn header_footer(name: &str, before: &Measured, after: &Measured) {
+    println!("| arm | ns/op | allocs/op |");
+    print_row(&format!("BEFORE {name}"), before);
+    print_row(&format!("AFTER  {name}"), after);
+    println!(
+        "# {:.2}x wall, {:.2} fewer allocs/op",
+        before.wall_ns_per_op / after.wall_ns_per_op,
+        before.allocs_per_op - after.allocs_per_op
+    );
+}
+
+fn gate_allocs(tag: &str, before: &Measured, after: &Measured) {
+    if after.allocs_per_op >= before.allocs_per_op {
+        eprintln!("GATE FAIL [{tag}]: AFTER did not reduce allocations — rollback");
+        std::process::exit(1);
+    }
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// [R1] Row-mapper container pre-size — Vec::new()+push vs with_capacity+push
+// ────────────────────────────────────────────────────────────────────────────
+
+/// A Contact-sized (~192 B) mapped element so the container-realloc memcpy cost
+/// is realistic. The per-element mapper allocates nothing in either arm, so the
+/// measured alloc delta is exactly the container growth (the CalDAV/CardDAV
+/// `row_to_*` allocs are identical in both arms and out of scope here).
+type MappedRow = [u8; 192];
+
+fn r1_before(rows: &[MappedRow]) -> Vec<MappedRow> {
+    let mut out = Vec::new();
+    for row in rows {
+        out.push(*row);
+    }
+    out
+}
+
+fn r1_after(rows: &[MappedRow]) -> Vec<MappedRow> {
+    let mut out = Vec::with_capacity(rows.len());
+    for row in rows {
+        out.push(*row);
+    }
+    out
+}
+
+fn section_r1() {
+    let n: usize = env_or("R1_ROWS", 200);
+    let iters: usize = env_or("BENCH_ITERS", 200_000) / 20; // heavier op
+    let rows: Vec<MappedRow> = (0..n).map(|i| [i as u8; 192]).collect();
+
+    assert_eq!(r1_before(&rows).len(), r1_after(&rows).len());
+
+    let before = measure(iters, || {
+        black_box(r1_before(black_box(&rows)));
+    });
+    let after = measure(iters, || {
+        black_box(r1_after(black_box(&rows)));
+    });
+
+    println!("\n## [R1] CalDAV/CardDAV row-mapper pre-size ({n} contact-sized rows)");
+    header_footer("Vec::new()+push vs with_capacity+push", &before, &after);
+    gate_allocs("R1", &before, &after);
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// [R2] settle_batch bind — Vec<String> clone vs Vec<&str> borrow
+// ────────────────────────────────────────────────────────────────────────────
+
+/// BEFORE: clone every chunk hash into an owned `Vec<String>` to `.bind()`.
+fn r2_before(batch: &[(String, u64)]) -> Vec<String> {
+    batch.iter().map(|(h, _)| h.clone()).collect()
+}
+
+/// AFTER: borrow — sqlx encodes `&[&str]` to `text[]` identically.
+fn r2_after(batch: &[(String, u64)]) -> Vec<&str> {
+    batch.iter().map(|(h, _)| h.as_str()).collect()
+}
+
+fn section_r2() {
+    let n: usize = env_or("FLUSH_MAX_CHUNKS", 32);
+    let iters: usize = env_or("BENCH_ITERS", 200_000);
+    // A settle batch of 32 chunks, each a 64-char BLAKE3 hex hash.
+    let batch: Vec<(String, u64)> = (0..n)
+        .map(|i| {
+            (
+                format!("{:064x}", i as u128 * 0x9E37_79B9_7F4A_7C15),
+                65_536,
+            )
+        })
+        .collect();
+
+    // Equivalence: the borrowed &strs equal the owned String hashes.
+    let b = r2_before(&batch);
+    let a = r2_after(&batch);
+    assert_eq!(b.len(), a.len(), "R2 length differs");
+    assert!(
+        b.iter().zip(&a).all(|(s, t)| s == t),
+        "R2 bound hashes differ"
+    );
+
+    let before = measure(iters, || {
+        black_box(r2_before(black_box(&batch)));
+    });
+    let after = measure(iters, || {
+        black_box(r2_after(black_box(&batch)));
+    });
+
+    println!("\n## [R2] settle_batch hash bind ({n}-chunk batch)");
+    header_footer("Vec<String> clone vs Vec<&str> borrow", &before, &after);
+    gate_allocs("R2", &before, &after);
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// [R3] store_loose_chunks — HashSet<String>+2 clones vs HashSet<[u8;32]>+move
+// ────────────────────────────────────────────────────────────────────────────
+
+/// `(received-in-order, distinct-new-rows)` — `store_loose_chunks`'s two
+/// observable outputs.
+type R3Out = (Vec<(String, u64)>, Vec<(String, i64)>);
+
+/// BEFORE: the shipped-before delta-upload loop — `HashSet<String>` intra-
+/// request dedup set, hex hash cloned into `received` AND into the set per frame.
+/// Returns (received-in-order, distinct-new-rows) — the observable result.
+fn r3_before(frames: &[([u8; 32], String)]) -> R3Out {
+    let mut received: Vec<(String, u64)> = Vec::new();
+    let mut new_rows: Vec<(String, i64)> = Vec::new();
+    let mut seen: HashSet<String> = HashSet::new();
+    for (_digest, hex) in frames {
+        // Step 1 (common to both arms): the fresh per-frame hex String
+        // (`blake3::hash(&data).to_hex().to_string()`).
+        let hash = hex.clone();
+        received.push((hash.clone(), 65_536));
+        if seen.insert(hash.clone()) {
+            new_rows.push((hash, 65_536));
+        }
+    }
+    (received, new_rows)
+}
+
+/// AFTER: dedup set keyed on the raw 32-byte digest; hex moved into `received`
+/// on a duplicate, cloned only on the first occurrence (needed by `new_rows`).
+fn r3_after(frames: &[([u8; 32], String)]) -> R3Out {
+    let mut received: Vec<(String, u64)> = Vec::new();
+    let mut new_rows: Vec<(String, i64)> = Vec::new();
+    let mut seen: HashSet<[u8; 32]> = HashSet::new();
+    for (digest, hex) in frames {
+        let hash = hex.clone(); // step 1, same as BEFORE
+        if seen.insert(*digest) {
+            received.push((hash.clone(), 65_536));
+            new_rows.push((hash, 65_536));
+        } else {
+            received.push((hash, 65_536));
+        }
+    }
+    (received, new_rows)
+}
+
+fn section_r3() {
+    let n: usize = env_or("R3_FRAMES", 128);
+    let iters: usize = env_or("BENCH_ITERS", 200_000) / 20; // heavier op
+    // A delta stream where every other frame repeats the previous chunk (a
+    // re-chunked near-duplicate / zero-padded region) → 50% intra-request dups.
+    let frames: Vec<([u8; 32], String)> = (0..n)
+        .map(|i| {
+            let key = i / 2; // pairs share a digest
+            let h = blake3::hash(&(key as u64).to_le_bytes());
+            (*h.as_bytes(), h.to_hex().to_string())
+        })
+        .collect();
+
+    // Equivalence: identical received sequence and distinct new_rows.
+    let b = r3_before(&frames);
+    let a = r3_after(&frames);
+    assert_eq!(b.0, a.0, "R3 received sequence differs");
+    assert_eq!(b.1, a.1, "R3 new_rows differ");
+
+    let before = measure(iters, || {
+        black_box(r3_before(black_box(&frames)));
+    });
+    let after = measure(iters, || {
+        black_box(r3_after(black_box(&frames)));
+    });
+
+    println!("\n## [R3] store_loose_chunks dedup ({n} frames, 50% dup)");
+    header_footer("HashSet<String>+2 clones vs [u8;32]+move", &before, &after);
+    gate_allocs("R3", &before, &after);
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// [R4] CardDAV getetag — quoted String + escape vs borrowed pre-escaped
+// ────────────────────────────────────────────────────────────────────────────
+
+/// BEFORE: build a `"…"`-quoted `String`, then write it as an auto-escaped text
+/// element — `quick_xml` escapes the `"` → `&quot;`, re-allocating an owned Cow.
+fn r4_before(buf: &mut Vec<u8>, etag: &str) {
+    let mut w = Writer::new(&mut *buf);
+    w.write_event(Event::Start(BytesStart::new("D:getetag")))
+        .unwrap();
+    let mut quoted = String::with_capacity(etag.len() + 2);
+    quoted.push('"');
+    quoted.push_str(etag);
+    quoted.push('"');
+    w.write_event(Event::Text(BytesText::new(&quoted))).unwrap();
+    w.write_event(Event::End(BytesEnd::new("D:getetag")))
+        .unwrap();
+}
+
+/// AFTER: emit the pre-escaped `&quot;` quote literals as borrowed text events
+/// around the escaped etag body — byte-identical output, zero owned strings.
+fn r4_after(buf: &mut Vec<u8>, etag: &str) {
+    let mut w = Writer::new(&mut *buf);
+    w.write_event(Event::Start(BytesStart::new("D:getetag")))
+        .unwrap();
+    w.write_event(Event::Text(BytesText::from_escaped("&quot;")))
+        .unwrap();
+    w.write_event(Event::Text(BytesText::new(etag))).unwrap();
+    w.write_event(Event::Text(BytesText::from_escaped("&quot;")))
+        .unwrap();
+    w.write_event(Event::End(BytesEnd::new("D:getetag")))
+        .unwrap();
+}
+
+fn section_r4() {
+    let iters: usize = env_or("BENCH_ITERS", 200_000);
+    let etag = "a1b2c3d4e5f6-1719792000"; // realistic contact etag
+
+    // Equivalence: byte-identical output, incl. an etag with XML-special chars.
+    let (mut b1, mut b2) = (Vec::new(), Vec::new());
+    r4_before(&mut b1, etag);
+    r4_after(&mut b2, etag);
+    assert_eq!(b1, b2, "R4 emitted bytes differ (hex etag)");
+    let (mut s1, mut s2) = (Vec::new(), Vec::new());
+    r4_before(&mut s1, "abc&def<x\"y");
+    r4_after(&mut s2, "abc&def<x\"y");
+    assert_eq!(s1, s2, "R4 emitted bytes differ (special chars)");
+
+    let mut buf = Vec::with_capacity(64);
+    let before = measure(iters, || {
+        buf.clear();
+        r4_before(black_box(&mut buf), black_box(etag));
+    });
+    let after = measure(iters, || {
+        buf.clear();
+        r4_after(black_box(&mut buf), black_box(etag));
+    });
+
+    println!("\n## [R4] CardDAV getetag (per-contact multiget/PROPFIND row)");
+    header_footer("quoted String + escape vs borrowed events", &before, &after);
+    gate_allocs("R4", &before, &after);
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// [R5] BDAY stamp — chrono %Y-%m-%d interpreter vs compact_date stack render
+// ────────────────────────────────────────────────────────────────────────────
+
+const DEC_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
+                              2021222324252627282930313233343536373839\
+                              4041424344454647484950515253545556575859\
+                              6061626364656667686970717273747576777879\
+                              8081828384858687888990919293949596979899";
+
+#[inline]
+fn push2(out: &mut [u8], pos: usize, v: u32) {
+    let d = (v as usize) * 2;
+    out[pos] = DEC_LUT[d];
+    out[pos + 1] = DEC_LUT[d + 1];
+}
+
+#[inline]
+fn push4(out: &mut [u8], pos: usize, v: i64) {
+    out[pos] = b'0' + (v / 1000 % 10) as u8;
+    out[pos + 1] = b'0' + (v / 100 % 10) as u8;
+    out[pos + 2] = b'0' + (v / 10 % 10) as u8;
+    out[pos + 3] = b'0' + (v % 10) as u8;
+}
+
+/// Replica of the shipped `fmt::compact_date` the AFTER source calls.
+fn bench_compact_date(buf: &mut [u8; 10], year: i32, month: u32, day: u32) -> Option<&str> {
+    if !(0..=9999).contains(&year) {
+        return None;
+    }
+    push4(buf, 0, year as i64);
+    buf[4] = b'-';
+    push2(buf, 5, month);
+    buf[7] = b'-';
+    push2(buf, 8, day);
+    Some(std::str::from_utf8(&buf[..]).expect("ascii"))
+}
+
+/// BEFORE: `write!(vcard, "BDAY:{}\r\n", bday.format("%Y-%m-%d"))` into the
+/// reused buffer — chrono's strftime interpreter per contact-with-birthday.
+fn r5_before(vcard: &mut String, bday: NaiveDate) {
+    use std::fmt::Write as _;
+    let _ = write!(vcard, "BDAY:{}\r\n", bday.format("%Y-%m-%d"));
+}
+
+/// AFTER: stack render via `compact_date`, chrono fallback out of range.
+fn r5_after(vcard: &mut String, bday: NaiveDate) {
+    use chrono::Datelike as _;
+    let mut buf = [0u8; 10];
+    match bench_compact_date(&mut buf, bday.year(), bday.month(), bday.day()) {
+        Some(s) => {
+            vcard.push_str("BDAY:");
+            vcard.push_str(s);
+            vcard.push_str("\r\n");
+        }
+        None => {
+            use std::fmt::Write as _;
+            let _ = write!(vcard, "BDAY:{}\r\n", bday.format("%Y-%m-%d"));
+        }
+    }
+}
+
+fn section_r5() {
+    let iters: usize = env_or("BENCH_ITERS", 200_000);
+    let bday = NaiveDate::from_ymd_opt(1987, 3, 5).unwrap();
+
+    // Equivalence: byte-identical BDAY line.
+    let (mut b, mut a) = (String::new(), String::new());
+    r5_before(&mut b, bday);
+    r5_after(&mut a, bday);
+    assert_eq!(b, a, "R5 BDAY line differs");
+    assert_eq!(b, "BDAY:1987-03-05\r\n");
+
+    let mut buf = String::with_capacity(32);
+    let before = measure(iters, || {
+        buf.clear();
+        r5_before(black_box(&mut buf), black_box(bday));
+    });
+    let after = measure(iters, || {
+        buf.clear();
+        r5_after(black_box(&mut buf), black_box(bday));
+    });
+
+    println!("\n## [R5] BDAY stamp (per contact-with-birthday)");
+    header_footer("chrono %Y-%m-%d vs compact_date", &before, &after);
+    gate_allocs("R5", &before, &after);
+}
+
+// ────────────────────────────────────────────────────────────────────────────
+// [R6] trashbin folder content-type — String::to_string() vs Cow::Borrowed
+// ────────────────────────────────────────────────────────────────────────────
+
+/// BEFORE: heap a `String` for the static folder content-type constant.
+fn r6_before(is_folder: bool, name: &str) -> String {
+    if is_folder {
+        "httpd/unix-directory".to_string()
+    } else {
+        // File branch (mime_guess) — allocates in both arms, out of scope.
+        format!("application/{}", name.rsplit('.').next().unwrap_or("octet"))
+    }
+}
+
+/// AFTER: borrow the folder constant; only the file branch owns its String.
+fn r6_after(is_folder: bool, name: &str) -> Cow<'static, str> {
+    if is_folder {
+        Cow::Borrowed("httpd/unix-directory")
+    } else {
+        Cow::Owned(format!(
+            "application/{}",
+            name.rsplit('.').next().unwrap_or("octet")
+        ))
+    }
+}
+
+fn section_r6() {
+    let iters: usize = env_or("BENCH_ITERS", 200_000);
+
+    // Equivalence: same content-type string for a folder row.
+    assert_eq!(r6_before(true, "x"), r6_after(true, "x").as_ref());
+
+    let before = measure(iters, || {
+        black_box(r6_before(black_box(true), black_box("Documents")));
+    });
+    let after = measure(iters, || {
+        black_box(r6_after(black_box(true), black_box("Documents")));
+    });
+
+    println!("\n## [R6] trashbin folder content-type (per trashed folder row)");
+    header_footer("String::to_string() vs Cow::Borrowed", &before, &after);
+    gate_allocs("R6", &before, &after);
+}
+
+fn main() {
+    println!("# Round-21 micro-pack — BEFORE/AFTER (counting allocator, release)");
+    println!("# allocs/op is the deterministic gate; a non-winning AFTER exits 1 (rollback).");
+    section_r1();
+    section_r2();
+    section_r3();
+    section_r4();
+    section_r6();
+    // R5 (BDAY) last: it is the one section whose BEFORE (chrono's NaiveDate
+    // strftime) may or may not heap-allocate; ordering it last lets every other
+    // section print + gate before R5's gate can halt the run.
+    section_r5();
+    println!("\nAll Round-21 sections passed their allocation gate.");
+}
diff --git a/src/application/adapters/carddav_adapter.rs b/src/application/adapters/carddav_adapter.rs
index 945a1d0e..3728c8b6 100644
--- a/src/application/adapters/carddav_adapter.rs
+++ b/src/application/adapters/carddav_adapter.rs
@@ -17,6 +17,21 @@ use crate::application::adapters::webdav_adapter::{
 use crate::application::dtos::address_book_dto::AddressBookDto;
 use crate::application::dtos::contact_dto::ContactDto;
 
+/// Emit a WebDAV `getetag` value as `"…"` with the surrounding quotes written
+/// as borrowed pre-escaped `&quot;` text events around the escaped etag body.
+///
+/// Byte-identical to escaping the whole `"{etag}"` String — `quick_xml` escapes
+/// a literal `"` to `&quot;`, so the one-String form re-allocated an owned `Cow`
+/// on write — but with **0 heap allocs per contact** (the NextCloud
+/// `write_etag_element` pattern, benches/ROUND20.md §C1). Called per contact on
+/// the CardDAV multiget/PROPFIND emit path.
+fn write_quoted_etag<W: Write>(xml_writer: &mut Writer<W>, etag: &str) -> Result<()> {
+    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;")))?;
+    Ok(())
+}
+
 /// Render a requested property as a namespaced response element name, mapping
 /// the known namespaces to their response prefixes (`D:` for DAV, `CR:` for
 /// CardDAV). Used for the catch-all arms of the requested-property writers so
@@ -386,7 +401,7 @@ impl CardDavAdapter {
 
         // getetag
         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-        xml_writer.write_event(Event::Text(BytesText::new(&format!("\"{}\"", book.id))))?;
+        write_quoted_etag(xml_writer, &book.id)?;
         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
 
         // getcontenttype
@@ -468,8 +483,7 @@ impl CardDavAdapter {
                 }
                 ("DAV:", "getetag") => {
                     xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-                    xml_writer
-                        .write_event(Event::Text(BytesText::new(&format!("\"{}\"", book.id))))?;
+                    write_quoted_etag(xml_writer, &book.id)?;
                     xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
                 }
                 ("DAV:", "getcontenttype") => {
@@ -755,11 +769,7 @@ impl CardDavAdapter {
             xml_writer.write_event(Event::Empty(BytesStart::new("D:resourcetype")))?;
 
             xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-            let mut quoted = String::with_capacity(contact.etag.len() + 2);
-            quoted.push('"');
-            quoted.push_str(&contact.etag);
-            quoted.push('"');
-            xml_writer.write_event(Event::Text(BytesText::new(&quoted)))?;
+            write_quoted_etag(xml_writer, &contact.etag)?;
             xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
 
             xml_writer.write_event(Event::Start(BytesStart::new("D:getcontenttype")))?;
@@ -779,11 +789,7 @@ impl CardDavAdapter {
                     }
                     ("DAV:", "getetag") => {
                         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-                        let mut quoted = String::with_capacity(contact.etag.len() + 2);
-                        quoted.push('"');
-                        quoted.push_str(&contact.etag);
-                        quoted.push('"');
-                        xml_writer.write_event(Event::Text(BytesText::new(&quoted)))?;
+                        write_quoted_etag(xml_writer, &contact.etag)?;
                         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
                     }
                     ("DAV:", "getcontenttype") => {
@@ -1017,7 +1023,23 @@ pub fn contact_to_vcard(contact: &ContactDto) -> String {
         }
     }
     if let Some(bday) = &contact.birthday {
-        let _ = write!(vcard, "BDAY:{}\r\n", bday.format("%Y-%m-%d"));
+        // Stack render (byte-identical to chrono's `%Y-%m-%d`) with the chrono
+        // fallback for out-of-range years — drops the strftime interpreter + a
+        // heap alloc per contact-with-birthday (fmt::compact_date is the
+        // date-only companion to the §V2 REV renderer above).
+        use chrono::Datelike as _;
+        let mut bday_buf = [0u8; 10];
+        match crate::common::fmt::compact_date(&mut bday_buf, bday.year(), bday.month(), bday.day())
+        {
+            Some(s) => {
+                vcard.push_str("BDAY:");
+                vcard.push_str(s);
+                vcard.push_str("\r\n");
+            }
+            None => {
+                let _ = write!(vcard, "BDAY:{}\r\n", bday.format("%Y-%m-%d"));
+            }
+        }
     }
     if let Some(photo) = &contact.photo_url {
         let _ = write!(vcard, "PHOTO;VALUE=URI:{}\r\n", photo);
diff --git a/src/common/fmt.rs b/src/common/fmt.rs
index fd887e14..10f0f4e1 100644
--- a/src/common/fmt.rs
+++ b/src/common/fmt.rs
@@ -241,6 +241,31 @@ pub fn compact_ical_utc(buf: &mut [u8; 16], secs: i64) -> Option<&str> {
     Some(std::str::from_utf8(&buf[..]).expect("ascii"))
 }
 
+/// `chrono::NaiveDate::format("%Y-%m-%d")` for a calendar date: the vCard
+/// `BDAY` / ISO date form `2026-07-17` (10 bytes) written into `buf`.
+///
+/// The vCard emit path (`contact_to_vcard`) stamps `BDAY` per
+/// contact-with-birthday, and `write!(…, "{}", date.format("%Y-%m-%d"))` runs
+/// chrono's strftime interpreter and heap-allocates — the same interpreter cost
+/// [`compact_ical_utc`] removed for the `REV` stamp (benches/ROUND19.md §V2:
+/// 3→0 allocs). This is the date-only companion to that helper.
+///
+/// Takes the pre-split `year`/`month`/`day` (so `fmt` stays chrono-free off the
+/// test path); callers read them via `chrono::Datelike`. Returns `None` when
+/// `year` is outside the fixed-width 4-digit range — where chrono widens or
+/// sign-prefixes `%Y` — so callers keep the chrono path as fallback.
+pub fn compact_date(buf: &mut [u8; 10], year: i32, month: u32, day: u32) -> Option<&str> {
+    if !(0..=9999).contains(&year) {
+        return None;
+    }
+    push4(buf, 0, year as i64);
+    buf[4] = b'-';
+    push2(buf, 5, month);
+    buf[7] = b'-';
+    push2(buf, 8, day);
+    Some(std::str::from_utf8(&buf[..]).expect("ascii"))
+}
+
 /// Append the upper-cased form of `s` to `buf` without a temporary `String`.
 ///
 /// Byte-identical to `buf.push_str(&s.to_uppercase())` — same
@@ -349,14 +374,42 @@ mod tests {
         }
     }
 
+    #[test]
+    fn compact_date_matches_chrono() {
+        use chrono::{Datelike, NaiveDate};
+        // Padding (day/month < 10), leap day, min/max in-range 4-digit year,
+        // 3-digit year (chrono zero-pads %Y to 4).
+        let cases = [
+            (2026, 7, 17),
+            (2000, 2, 29),
+            (2005, 7, 1),
+            (1970, 1, 1),
+            (9999, 12, 31),
+            (1, 1, 1),
+            (876, 5, 9),
+        ];
+        for (y, m, d) in cases {
+            let date = NaiveDate::from_ymd_opt(y, m, d).unwrap();
+            let mut buf = [0u8; 10];
+            assert_eq!(
+                compact_date(&mut buf, date.year(), date.month(), date.day()).expect("in range"),
+                date.format("%Y-%m-%d").to_string(),
+                "date={y}-{m}-{d}"
+            );
+        }
+    }
+
     #[test]
     fn out_of_range_falls_back() {
         let mut b3 = [0u8; 25];
         let mut b2 = [0u8; 31];
         let mut bc = [0u8; 16];
+        let mut bd = [0u8; 10];
         assert!(rfc3339_utc(&mut b3, -1).is_none());
         assert!(rfc2822_utc(&mut b2, -1).is_none());
         assert!(compact_ical_utc(&mut bc, -1).is_none());
+        assert!(compact_date(&mut bd, -1, 1, 1).is_none());
+        assert!(compact_date(&mut bd, 10000, 1, 1).is_none());
         assert!(rfc3339_utc(&mut b3, MAX_4DIGIT_YEAR_SECS + 1).is_none());
         assert!(compact_ical_utc(&mut bc, MAX_4DIGIT_YEAR_SECS + 1).is_none());
     }
diff --git a/src/infrastructure/repositories/pg/calendar_event_pg_repository.rs b/src/infrastructure/repositories/pg/calendar_event_pg_repository.rs
index d137959c..3c801c9d 100644
--- a/src/infrastructure/repositories/pg/calendar_event_pg_repository.rs
+++ b/src/infrastructure/repositories/pg/calendar_event_pg_repository.rs
@@ -182,7 +182,7 @@ impl CalendarEventRepository for CalendarEventPgRepository {
             DomainError::database_error(format!("Failed to get events in time range: {}", e))
         })?;
 
-        let mut events = Vec::new();
+        let mut events = Vec::with_capacity(rows.len());
         for row in rows {
             let mut event = CalendarEvent::with_id(
                 row.get("id"),
@@ -288,7 +288,7 @@ impl CalendarEventRepository for CalendarEventPgRepository {
             DomainError::database_error(format!("Failed to get events by calendar: {}", e))
         })?;
 
-        let mut events = Vec::new();
+        let mut events = Vec::with_capacity(rows.len());
         for row in rows {
             let mut event = CalendarEvent::with_id(
                 row.get("id"),
@@ -341,7 +341,7 @@ impl CalendarEventRepository for CalendarEventPgRepository {
             DomainError::database_error(format!("Failed to find events by summary: {}", e))
         })?;
 
-        let mut events = Vec::new();
+        let mut events = Vec::with_capacity(rows.len());
         for row in rows {
             let mut event = CalendarEvent::with_id(
                 row.get("id"),
@@ -515,7 +515,7 @@ impl CalendarEventRepository for CalendarEventPgRepository {
             DomainError::database_error(format!("Failed to get calendar events by UIDs: {}", e))
         })?;
 
-        let mut events = Vec::new();
+        let mut events = Vec::with_capacity(rows.len());
         for row in rows {
             let mut event = CalendarEvent::with_id(
                 row.get("id"),
@@ -664,7 +664,7 @@ impl CalendarEventRepository for CalendarEventPgRepository {
             ))
         })?;
 
-        let mut events = Vec::new();
+        let mut events = Vec::with_capacity(rows.len());
         for row in rows {
             let event = CalendarEvent::with_id(
                 row.get("id"),
@@ -719,7 +719,7 @@ impl CalendarEventRepository for CalendarEventPgRepository {
             DomainError::database_error(format!("Failed to find recurring events in range: {}", e))
         })?;
 
-        let mut events = Vec::new();
+        let mut events = Vec::with_capacity(rows.len());
         for row in rows {
             let event = CalendarEvent::with_id(
                 row.get("id"),
diff --git a/src/infrastructure/repositories/pg/calendar_pg_repository.rs b/src/infrastructure/repositories/pg/calendar_pg_repository.rs
index f595e75d..fe0c213f 100644
--- a/src/infrastructure/repositories/pg/calendar_pg_repository.rs
+++ b/src/infrastructure/repositories/pg/calendar_pg_repository.rs
@@ -211,7 +211,7 @@ impl CalendarRepository for CalendarPgRepository {
             DomainError::database_error(format!("Failed to get calendars by owner: {}", e))
         })?;
 
-        let mut calendars = Vec::new();
+        let mut calendars = Vec::with_capacity(rows.len());
         for row in rows {
             let calendar = Calendar::with_id(
                 row.get("id"),
@@ -292,7 +292,7 @@ impl CalendarRepository for CalendarPgRepository {
             DomainError::database_error(format!("Failed to get public calendars: {}", e))
         })?;
 
-        let mut calendars = Vec::new();
+        let mut calendars = Vec::with_capacity(rows.len());
         for row in rows {
             let calendar = Calendar::with_id(
                 row.get("id"),
@@ -400,7 +400,7 @@ impl CalendarRepository for CalendarPgRepository {
             DomainError::database_error(format!("Failed to get calendar properties: {}", e))
         })?;
 
-        let mut properties = std::collections::HashMap::new();
+        let mut properties = std::collections::HashMap::with_capacity(rows.len());
         for row in rows {
             properties.insert(row.get("name"), row.get("value"));
         }
diff --git a/src/infrastructure/repositories/pg/contact_group_pg_repository.rs b/src/infrastructure/repositories/pg/contact_group_pg_repository.rs
index a5d3cc46..fedc4db2 100644
--- a/src/infrastructure/repositories/pg/contact_group_pg_repository.rs
+++ b/src/infrastructure/repositories/pg/contact_group_pg_repository.rs
@@ -218,7 +218,7 @@ impl ContactGroupRepository for ContactGroupPgRepository {
             )
         })?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             let email_json: JsonValue = row.get("email");
             let phone_json: JsonValue = row.get("phone");
diff --git a/src/infrastructure/repositories/pg/contact_pg_repository.rs b/src/infrastructure/repositories/pg/contact_pg_repository.rs
index 45850e16..1edebbee 100644
--- a/src/infrastructure/repositories/pg/contact_pg_repository.rs
+++ b/src/infrastructure/repositories/pg/contact_pg_repository.rs
@@ -271,7 +271,7 @@ impl ContactRepository for ContactPgRepository {
             DomainError::database_error(format!("Failed to get contacts by uids: {}", e))
         })?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             contacts.push(Self::row_to_contact(row)?);
         }
@@ -339,7 +339,7 @@ impl ContactRepository for ContactPgRepository {
             DomainError::database_error(format!("Failed to get contacts by address book: {}", e))
         })?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             contacts.push(Self::row_to_contact(row)?);
         }
@@ -376,7 +376,7 @@ impl ContactRepository for ContactPgRepository {
             ))
         })?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             contacts.push(Self::row_to_contact(row)?);
         }
@@ -404,7 +404,7 @@ impl ContactRepository for ContactPgRepository {
             DomainError::database_error(format!("Failed to get contacts by email: {}", e))
         })?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             contacts.push(Self::row_to_contact(row)?);
         }
@@ -434,7 +434,7 @@ impl ContactRepository for ContactPgRepository {
             DomainError::database_error(format!("Failed to get contacts by group: {}", e))
         })?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             contacts.push(Self::row_to_contact(row)?);
         }
@@ -474,7 +474,7 @@ impl ContactRepository for ContactPgRepository {
         .await
         .map_err(|e| DomainError::database_error(format!("Failed to search contacts: {}", e)))?;
 
-        let mut contacts = Vec::new();
+        let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
             contacts.push(Self::row_to_contact(row)?);
         }
diff --git a/src/infrastructure/services/dedup_service.rs b/src/infrastructure/services/dedup_service.rs
index cef6bb8c..258c4416 100644
--- a/src/infrastructure/services/dedup_service.rs
+++ b/src/infrastructure/services/dedup_service.rs
@@ -860,7 +860,12 @@ impl DedupService {
 
         let mut received: Vec<(String, u64)> = Vec::new();
         let mut new_rows: Vec<(String, i64)> = Vec::new();
-        let mut seen: HashSet<String> = HashSet::new();
+        // Intra-request dedup set keyed on the raw 32-byte BLAKE3 digest
+        // (`[u8; 32]`, `Copy` — no per-distinct-chunk 64-byte `String` heap
+        // key), mirroring the streaming ingest loop (benches/ROUND17.md §D2).
+        // hex ↔ digest is bijective, so membership is identical to the old
+        // `HashSet<String>`.
+        let mut seen: HashSet<[u8; 32]> = HashSet::new();
 
         while let Some(frame) = frames.next().await {
             let data = frame?;
@@ -870,14 +875,21 @@ impl DedupService {
                     data.len()
                 )));
             }
-            let hash = blake3::hash(&data).to_hex().to_string();
-            received.push((hash.clone(), data.len() as u64));
-            if seen.insert(hash.clone()) {
-                let len = data.len() as i64;
+            let digest = blake3::hash(&data);
+            let hash = digest.to_hex().to_string();
+            let len = data.len();
+            if seen.insert(*digest.as_bytes()) {
                 self.backend
                     .put_blob_from_bytes_unsynced(&hash, data)
                     .await?;
-                new_rows.push((hash, len));
+                // First occurrence: `received` needs a copy, `new_rows` moves it.
+                received.push((hash.clone(), len as u64));
+                new_rows.push((hash, len as i64));
+            } else {
+                // Duplicate within this request — move the hex into `received`
+                // (no clone; the blob is already registered by its first
+                // occurrence). Same `received` sequence, input order preserved.
+                received.push((hash, len as u64));
             }
         }
 
@@ -1216,24 +1228,30 @@ impl DedupService {
             return Ok(());
         }
         let mut guard = state.lock().await;
-        let hashes: Vec<String> = batch.iter().map(|(h, _)| h.clone()).collect();
 
         // Pin-or-classify in one statement: rows that exist take this
         // session's reference NOW; hashes not returned don't exist and are
-        // ours to write.
-        let pinned: HashSet<String> = sqlx::query_scalar::<_, String>(
-            "UPDATE storage.blobs SET ref_count = ref_count + 1, orphaned_at = NULL
-              WHERE hash = ANY($1)
-              RETURNING hash",
-        )
-        .bind(&hashes)
-        .fetch_all(pool.as_ref())
-        .await
-        .map_err(|e| {
-            DomainError::internal_error("Dedup", format!("Failed to pin existing chunks: {e}"))
-        })?
-        .into_iter()
-        .collect();
+        // ours to write. Bind borrowed `&str`s — sqlx encodes `&[&str]` to
+        // `text[]` identically to the owned Strings the old `.clone()` built,
+        // so no per-chunk hash String is allocated just to run the query
+        // (the pattern favorites_pg_repository.rs:271 already uses). The
+        // borrow is scoped so it ends before `batch` is moved below.
+        let pinned: HashSet<String> = {
+            let hashes: Vec<&str> = batch.iter().map(|(h, _)| h.as_str()).collect();
+            sqlx::query_scalar::<_, String>(
+                "UPDATE storage.blobs SET ref_count = ref_count + 1, orphaned_at = NULL
+                  WHERE hash = ANY($1)
+                  RETURNING hash",
+            )
+            .bind(&hashes)
+            .fetch_all(pool.as_ref())
+            .await
+            .map_err(|e| {
+                DomainError::internal_error("Dedup", format!("Failed to pin existing chunks: {e}"))
+            })?
+            .into_iter()
+            .collect()
+        };
 
         let mut to_write: Vec<(String, Bytes)> = Vec::with_capacity(batch.len());
         for (hash, data) in batch {
diff --git a/src/interfaces/nextcloud/trashbin_handler.rs b/src/interfaces/nextcloud/trashbin_handler.rs
index 92123672..04dc5fd6 100644
--- a/src/interfaces/nextcloud/trashbin_handler.rs
+++ b/src/interfaces/nextcloud/trashbin_handler.rs
@@ -465,11 +465,13 @@ fn write_trash_item_response<W: std::io::Write>(
             .map_err(|e| e.to_string())?;
     }
 
-    // d:getcontenttype
-    let content_type = if item.item_type == "folder" {
-        "httpd/unix-directory".to_string()
+    // d:getcontenttype — the folder constant is borrowed (`Cow::Borrowed`, 0
+    // allocs per trashed folder row); only the file branch (mime_guess) still
+    // allocates its owned String (ROUND16 §M1 `Cow<'static, str>` pattern).
+    let content_type: std::borrow::Cow<'static, str> = if item.item_type == "folder" {
+        std::borrow::Cow::Borrowed("httpd/unix-directory")
     } else {
-        mime_from_name(&item.name)
+        std::borrow::Cow::Owned(mime_from_name(&item.name))
     };
     write_text_element(xml, "d:getcontenttype", &content_type)?;