hll: hll_multi_add — batch many (name,items) into one RPC

Mirrors the new waymaker-server HllMultiAdd: one call writes several reserved
HLLs (e.g. a presence flush across scope/bucket sketches), returning per-entry
result codes. Vendored proto synced. Processed locally server-side for now
(multi-name batch can't ring-route).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

proto/sketches.proto

@@ -36,6 +36,9 @@ service WaymakerSketchesService {
   // ----- HyperLogLog -----
   rpc HllReserve (HllReserveRequest) returns (HllReserveResponse);
   rpc HllAdd (HllAddRequest) returns (HllAddResponse);
+  // Batch many (name, items) into ONE call (e.g. a presence flush). Processed
+  // locally today (can't ring-route a multi-name batch) — see the server TODO.
+  rpc HllMultiAdd (HllMultiAddRequest) returns (HllMultiAddResponse);
   rpc HllCount (HllCountRequest) returns (HllCountResponse);
   rpc HllMerge (HllMergeRequest) returns (HllMergeResponse);
   rpc HllDelete (HllDeleteRequest) returns (HllDeleteResponse);
@@ -165,6 +168,20 @@ message HllAddResponse {
   string message = 3;
 }
 
+message HllMultiAddEntry {
+  string name = 1;
+  repeated bytes items = 2;
+}
+message HllMultiAddRequest {
+  repeated HllMultiAddEntry entries = 1;
+}
+message HllMultiAddResponse {
+  bool success = 1;
+  string result_code = 2;
+  string message = 3;
+  repeated string entry_results = 4;
+}
+
 message HllCountRequest { string name = 1; }
 message HllCountResponse {
   bool success = 1;

rust/src/probabilistic/hll.rs

@@ -3,7 +3,8 @@
 use crate::client::Client;
 use crate::error::{Error, Result};
 use crate::sketches_server::{
-    HllAddRequest, HllCountRequest, HllDeleteRequest, HllMergeRequest, HllReserveRequest,
+    HllAddRequest, HllCountRequest, HllDeleteRequest, HllMergeRequest, HllMultiAddEntry,
+    HllMultiAddRequest, HllReserveRequest,
 };
 use tonic::Request;
 
@@ -108,6 +109,28 @@ impl Client {
         Hll::new(self.clone(), name.into())
     }
 
+    /// Batch many `(name, items)` HLL adds into ONE RPC — e.g. a presence flush that
+    /// writes the same id-set into several scope/bucket HLLs. Each name must already
+    /// be reserved (no auto-create); returns the per-entry result codes (`"ok"` /
+    /// `"no_such_hll"`, parallel to `entries`). NOTE: processed locally server-side
+    /// today (a multi-name batch can't ring-route) — single-node use only for now.
+    pub async fn hll_multi_add(&self, entries: Vec<(String, Vec<Vec<u8>>)>) -> Result<Vec<String>> {
+        let mut c = self.sketches_client();
+        let r = c
+            .hll_multi_add(Request::new(HllMultiAddRequest {
+                entries: entries
+                    .into_iter()
+                    .map(|(name, items)| HllMultiAddEntry { name, items })
+                    .collect(),
+            }))
+            .await?
+            .into_inner();
+        if !r.success {
+            return Err(Error::server(r.result_code, r.message));
+        }
+        Ok(r.entry_results)
+    }
+
     pub async fn delete_hll(&self, name: impl Into<String>) -> Result<()> {
         let mut c = self.sketches_client();
         let r = c