rpc: avoid serializing buffers from other servers (#26500)

* rpc: avoid serializing buffers from other servers

Only include remote buffer pointers when the buffer belongs to the RPC dispatcher receiving the graph. Add a two-server regression test for cross-server tensor serialization.

Assisted-by: Codex

* cont : add ref

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

tests/test-rpc-multi-server.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+server=$1
+client=$2
+port_a=$((40000 + $$ % 10000))
+port_b=$((port_a + 1))
+endpoint_a="127.0.0.1:${port_a}"
+endpoint_b="127.0.0.1:${port_b}"
+test_dir=$(mktemp -d)
+
+cleanup() {
+    kill "${pid_a:-}" "${pid_b:-}" 2>/dev/null || true
+    rm -rf "$test_dir"
+}
+trap cleanup EXIT
+
+wait_for_port() {
+    local port=$1
+    for _ in {1..600}; do
+        if (exec 3<>"/dev/tcp/127.0.0.1/$port") 2>/dev/null; then
+            exec 3>&-
+            exec 3<&-
+            return 0
+        fi
+        sleep 0.05
+    done
+    return 1
+}
+
+"$server" --device CPU --host 127.0.0.1 --port "$port_a" >"$test_dir/server-a.log" 2>&1 &
+pid_a=$!
+"$server" --device CPU --host 127.0.0.1 --port "$port_b" >"$test_dir/server-b.log" 2>&1 &
+pid_b=$!
+wait_for_port "$port_a"
+wait_for_port "$port_b"
+
+"$client" "$endpoint_a" "$endpoint_b"
+
+if grep -q "invalid data ptr" "$test_dir/server-b.log"; then
+    cat "$test_dir/server-b.log"
+    exit 1
+fi