perf(nextcloud): batch oc:fileid resolution to kill PROPFIND N+1

Resolving the stable numeric oc:fileid for every child in a NextCloud
listing issued one `INSERT ... ON CONFLICT DO UPDATE` per entry — a write
(row rewrite + WAL + dead tuple) even when the mapping already existed.
A Depth:1 PROPFIND of a folder with N children meant N sequential write
round-trips on a read-only operation that sync clients repeat constantly.

- Repository: replace the single `get_or_create` (DO UPDATE) with
  `get_or_create_many` — one idempotent bulk `INSERT ... SELECT unnest(...)
  ON CONFLICT DO NOTHING` (existing rows untouched) plus a single
  `SELECT ... WHERE object_id = ANY(...)`. Two statements instead of N.
- Service: add an Arc-backed moka cache (uuid -> i64; the mapping is
  immutable, so warm entries never go stale) and batch APIs
  `get_or_create_file_ids` / `get_or_create_folder_ids` that only query
  the misses. Warm listings cost zero queries.
- Handlers (PROPFIND, REPORT favorites/search, trashbin, OCS unified
  search): pre-resolve all ids in two batched queries — file and folder
  run concurrently via `tokio::join!` — and turn the XML/JSON emission
  into a synchronous map lookup.

https://claude.ai/code/session_01Dp3oWon5GBMVn4j3QXZdgx

src/infrastructure/repositories/pg/nextcloud_object_id_repository.rs

@@ -1,5 +1,7 @@
 use sqlx::{PgPool, Row};
+use std::collections::HashMap;
 use std::sync::Arc;
+use uuid::Uuid;
 
 use crate::common::errors::{DomainError, ErrorKind, Result};
 
@@ -12,29 +14,73 @@ impl NextcloudObjectIdRepository {
         Self { pool }
     }
 
-    pub async fn get_or_create(&self, object_type: &str, object_id: &str) -> Result<i64> {
-        let row = sqlx::query(
+    /// Resolve — creating when absent — stable numeric IDs for a batch of
+    /// object UUIDs sharing one `object_type`.
+    ///
+    /// Two statements instead of one per id: an idempotent bulk insert that
+    /// leaves existing rows untouched (`ON CONFLICT DO NOTHING` — no row
+    /// rewrite, no WAL churn, no dead tuples, unlike the former `DO UPDATE`),
+    /// followed by a single read of every requested mapping. The insert
+    /// auto-commits before the read, so the read observes both our own rows
+    /// and any created concurrently. Returns a map keyed by object UUID;
+    /// unresolvable inputs are simply absent.
+    pub async fn get_or_create_many(
+        &self,
+        object_type: &str,
+        object_ids: &[Uuid],
+    ) -> Result<HashMap<Uuid, i64>> {
+        if object_ids.is_empty() {
+            return Ok(HashMap::new());
+        }
+
+        // 1. Create missing mappings only. `DO NOTHING` skips the write for
+        //    UUIDs that already map, eliminating the per-listing row rewrite.
+        sqlx::query(
             r#"
             INSERT INTO storage.nextcloud_object_ids (object_type, object_id)
-            VALUES ($1, $2::uuid)
-            ON CONFLICT (object_type, object_id)
-            DO UPDATE SET object_id = EXCLUDED.object_id
-            RETURNING id
+            SELECT $1, u FROM unnest($2::uuid[]) AS u
+            ON CONFLICT (object_type, object_id) DO NOTHING
             "#,
         )
         .bind(object_type)
-        .bind(object_id)
-        .fetch_one(&*self.pool)
+        .bind(object_ids)
+        .execute(&*self.pool)
         .await
         .map_err(|e| {
             DomainError::new(
                 ErrorKind::DatabaseError,
                 "NextcloudFileId",
-                format!("Failed to get/create Nextcloud ID: {}", e),
+                format!("Failed to create Nextcloud IDs: {}", e),
             )
         })?;
 
-        Ok(row.get::<i64, _>("id"))
+        // 2. Read every requested mapping back in a single round-trip.
+        let rows = sqlx::query(
+            r#"
+            SELECT id, object_id
+            FROM storage.nextcloud_object_ids
+            WHERE object_type = $1 AND object_id = ANY($2::uuid[])
+            "#,
+        )
+        .bind(object_type)
+        .bind(object_ids)
+        .fetch_all(&*self.pool)
+        .await
+        .map_err(|e| {
+            DomainError::new(
+                ErrorKind::DatabaseError,
+                "NextcloudFileId",
+                format!("Failed to load Nextcloud IDs: {}", e),
+            )
+        })?;
+
+        let mut map = HashMap::with_capacity(rows.len());
+        for row in rows {
+            let object_id: Uuid = row.get("object_id");
+            let id: i64 = row.get("id");
+            map.insert(object_id, id);
+        }
+        Ok(map)
     }
 
     /// Get the OxiCloud object ID from a Nextcloud numeric ID.