perf(round25): in-place encrypted decrypt, dedup hash move, dead folder-Query, playlist N+1 fold, contact vcard over-fetch

Five benchmark-gated optimizations from a fresh six-way audit (benches/ROUND25.md),
each with a BEFORE/AFTER gate that rolls back if AFTER does not beat BEFORE:

- M1 EncryptedBlobBackend::decrypt_bytes: replace split_off (a fresh Vec + full
  ciphertext memcpy on every decrypted chunk, contradicting its own "in place"
  doc) with in-place detached decrypt + a zero-copy Bytes::slice past the nonce.
  Peak RAM per read drops from ~2x to ~1x the payload (-262KB/op at 256KiB;
  scales with blob size). Plaintext byte-identical; tamper/wrong-key tests pass.
- M2 delta commit: move-unzip the owned chunk list instead of a third
  per-occurrence hash clone (-4000 allocs on a 4000-chunk commit).
- M3 folder ZIP download: drop the dead Query<HashMap> extractor it never read
  (byte-identical response; 5->0 allocs/request).
- Q1 public-playlist listing: fold the per-playlist COUNT(*) N+1 into one
  LEFT JOIN ... GROUP BY via a new inherent repo method (101 -> 1 round-trips,
  36x wall on a 100-playlist page).
- Q2 contact REST listings (paginated/search/by-group): stop over-fetching the
  multi-KB vcard TEXT the ContactDto discards, via a shared lite row mapper and
  narrowed SELECTs (6.4x wall on 1000 contacts with 8KiB vcards). The whole-book
  vCard export and CardDAV sync paths keep the column.

Adds bench_round25_micro (counting allocator tracking count+bytes) and
bench_round25_queries (live Postgres), both with equivalence gates and a
rollback exit(1). Verified: cargo fmt clean, cargo clippy -D warnings clean,
cargo test --lib --features bench = 529 passed / 0 failed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L8gs91AhmazoxMsDcNk3KT

src/infrastructure/repositories/pg/contact_pg_repository.rs

@@ -21,8 +21,28 @@ impl ContactPgRepository {
         Self { pool }
     }
 
-    /// Maps a database row to a Contact domain entity
+    /// Maps a database row to a Contact domain entity (reads the `vcard` column).
     fn row_to_contact(row: &sqlx::postgres::PgRow) -> Result<Contact, DomainError> {
+        Self::row_to_contact_with_vcard(row, row.get("vcard"))
+    }
+
+    /// Maps a row whose SELECT omitted the `vcard` column — used by the REST
+    /// listings (paginated / search / by-group) whose `ContactDto` drops vcard
+    /// anyway, so the multi-KB vCard TEXT (which can embed a base64 PHOTO) is
+    /// never SELECTed, shipped over the wire, or allocated (benches/ROUND25.md
+    /// §Q2). The domain `Contact` keeps an empty vcard; these paths never
+    /// re-emit it. Do NOT use for CardDAV sync / whole-book export, which need
+    /// the round-trip vCard.
+    fn row_to_contact_lite(row: &sqlx::postgres::PgRow) -> Result<Contact, DomainError> {
+        Self::row_to_contact_with_vcard(row, String::new())
+    }
+
+    /// Shared row → `Contact` mapper; `vcard` is supplied by the caller so the
+    /// TEXT column can be omitted from listings that don't consume it.
+    fn row_to_contact_with_vcard(
+        row: &sqlx::postgres::PgRow,
+        vcard: String,
+    ) -> Result<Contact, DomainError> {
         // Decode each JSONB column straight into its typed Vec via
         // `sqlx::types::Json<T>` (a single `serde_json::from_slice` pass over
         // the raw JSONB bytes) instead of `row.get::<serde_json::Value>` +
@@ -63,7 +83,7 @@ impl ContactPgRepository {
             row.get::<Option<String>, _>("photo_url"),
             row.get("birthday"),
             row.get("anniversary"),
-            row.get("vcard"),
+            vcard,
             row.get("etag"),
             row.get("created_at"),
             row.get("updated_at"),
@@ -366,7 +386,7 @@ impl ContactRepository for ContactPgRepository {
             SELECT
                 id, address_book_id, uid, full_name, first_name, last_name, nickname,
                 email, phone, address, organization, title, notes, photo_url,
-                birthday, anniversary, vcard, etag, created_at, updated_at
+                birthday, anniversary, etag, created_at, updated_at
             FROM carddav.contacts
             WHERE address_book_id = $1
             ORDER BY full_name, first_name, last_name
@@ -387,7 +407,7 @@ impl ContactRepository for ContactPgRepository {
 
         let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
-            contacts.push(Self::row_to_contact(row)?);
+            contacts.push(Self::row_to_contact_lite(row)?);
         }
         Ok(contacts)
     }
@@ -429,7 +449,7 @@ impl ContactRepository for ContactPgRepository {
             SELECT 
                 c.id, c.address_book_id, c.uid, c.full_name, c.first_name, c.last_name, c.nickname,
                 c.email, c.phone, c.address, c.organization, c.title, c.notes, c.photo_url,
-                c.birthday, c.anniversary, c.vcard, c.etag, c.created_at, c.updated_at
+                c.birthday, c.anniversary, c.etag, c.created_at, c.updated_at
             FROM carddav.contacts c
             INNER JOIN carddav.group_memberships m ON c.id = m.contact_id
             WHERE m.group_id = $1
@@ -445,7 +465,7 @@ impl ContactRepository for ContactPgRepository {
 
         let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
-            contacts.push(Self::row_to_contact(row)?);
+            contacts.push(Self::row_to_contact_lite(row)?);
         }
         Ok(contacts)
     }
@@ -462,9 +482,9 @@ impl ContactRepository for ContactPgRepository {
             SELECT 
                 id, address_book_id, uid, full_name, first_name, last_name, nickname,
                 email, phone, address, organization, title, notes, photo_url,
-                birthday, anniversary, vcard, etag, created_at, updated_at
+                birthday, anniversary, etag, created_at, updated_at
             FROM carddav.contacts
-            WHERE address_book_id = $1 
+            WHERE address_book_id = $1
               AND (
                   full_name ILIKE $2 
                   OR first_name ILIKE $2
@@ -485,7 +505,7 @@ impl ContactRepository for ContactPgRepository {
 
         let mut contacts = Vec::with_capacity(rows.len());
         for row in &rows {
-            contacts.push(Self::row_to_contact(row)?);
+            contacts.push(Self::row_to_contact_lite(row)?);
         }
         Ok(contacts)
     }

src/infrastructure/repositories/pg/playlist_pg_repository.rs

@@ -22,6 +22,21 @@ struct PlaylistRow {
     updated_at: DateTime<Utc>,
 }
 
+/// A public playlist row carrying its aggregated track count, produced by the
+/// single `LEFT JOIN … GROUP BY` that replaces the per-playlist `COUNT(*)` N+1.
+#[derive(FromRow)]
+struct PublicPlaylistCountRow {
+    id: Uuid,
+    name: String,
+    description: Option<String>,
+    owner_id: Uuid,
+    is_public: bool,
+    cover_file_id: Option<Uuid>,
+    created_at: DateTime<Utc>,
+    updated_at: DateTime<Utc>,
+    track_count: i64,
+}
+
 #[derive(FromRow)]
 struct PlaylistItemRow {
     id: Uuid,
@@ -79,6 +94,52 @@ impl PlaylistPgRepository {
     pub fn pool(&self) -> &PgPool {
         &self.pool
     }
+
+    /// Public playlists together with their track counts in a **single**
+    /// round-trip. Replaces the adapter's 1 + N shape (one listing SELECT then
+    /// one `SELECT COUNT(*) FROM audio.playlist_items` per returned playlist —
+    /// up to 101 round-trips at `limit = 100`) with one `LEFT JOIN … GROUP BY`,
+    /// backed by `idx_playlist_items_playlist_id` (benches/ROUND25.md §Q1).
+    pub async fn list_public_playlists_with_counts(
+        &self,
+        limit: i64,
+        offset: i64,
+    ) -> PlaylistRepositoryResult<Vec<(Playlist, i64)>> {
+        let rows = sqlx::query_as::<_, PublicPlaylistCountRow>(
+            "SELECT p.id, p.name, p.description, p.owner_id, p.is_public, p.cover_file_id, \
+                    p.created_at, p.updated_at, COUNT(pi.id) AS track_count \
+             FROM audio.playlists p \
+             LEFT JOIN audio.playlist_items pi ON pi.playlist_id = p.id \
+             WHERE p.is_public = TRUE \
+             GROUP BY p.id \
+             ORDER BY p.updated_at DESC LIMIT $1 OFFSET $2",
+        )
+        .bind(limit)
+        .bind(offset)
+        .fetch_all(&*self.pool)
+        .await
+        .map_err(|e| {
+            DomainError::database_error(format!("Failed to list public playlists: {}", e))
+        })?;
+
+        rows.into_iter()
+            .map(|row| {
+                let track_count = row.track_count;
+                Playlist::with_id(
+                    row.id,
+                    row.name,
+                    row.description,
+                    row.owner_id,
+                    row.is_public,
+                    row.cover_file_id,
+                    row.created_at,
+                    row.updated_at,
+                )
+                .map(|p| (p, track_count))
+                .map_err(|e| DomainError::new(ErrorKind::InternalError, "Playlist", e.to_string()))
+            })
+            .collect()
+    }
 }
 
 impl PlaylistRepository for PlaylistPgRepository {