Address PR review comments: port collisions, gcov, loop bounds, fastcov

- RESTAPI port offset changed from 6070+i to 7070+i to avoid collision
  with admin/mysql ports (6072 would collide with node4 admin)
- Unset GCOV_PREFIX for background cluster nodes to prevent concurrent
  .gcda write corruption
- Cap core-node and scheduler loops to min(NUM_NODES, 3) so smaller
  clusters don't reference non-existent nodes
- TAP_CLUSTER_NODES now respects PROXYSQL_CLUSTER_NODES and
  SKIP_CLUSTER_START instead of hardcoding 9
- Fix fastcov flag: -i is invalid, use --include for source filtering

test/infra/control/env-isolated.bash

@@ -62,8 +62,12 @@ export TEST_DEPS="${TEST_DEPS_PATH}"
 # Cluster Nodes — all run inside the ProxySQL container on different ports
 # Port scheme: proxy-node1=6042, proxy-node2=6052, ..., proxy-node9=6122
 # From the test-runner container, reach them via the proxysql hostname
+NUM_CLUSTER_NODES=${PROXYSQL_CLUSTER_NODES:-9}
+if [[ "${SKIP_CLUSTER_START}" == "1" ]] || [[ "${SKIP_CLUSTER_START}" == "true" ]]; then
+    NUM_CLUSTER_NODES=0
+fi
 CLUSTER_NODES=""
-for i in $(seq 1 9); do
+for i in $(seq 1 ${NUM_CLUSTER_NODES}); do
     PORT=$((6032 + i * 10))
     CLUSTER_NODES="${CLUSTER_NODES}proxysql:${PORT},"
 done

test/infra/control/run-tests-isolated.bash

@@ -282,7 +282,7 @@ docker run \
                         echo \">>> Running fastcov on /gcov...\"
                         cd /gcov
                         fastcov -b -j\"\${nproc_val}\" --process-gcno -l \
-                            -i \"\${WORKSPACE}/include/\" \"\${WORKSPACE}/lib/\" \"\${WORKSPACE}/src/\" \"\${WORKSPACE}/test/\" \
+                            --include \"\${WORKSPACE}/include/\" \"\${WORKSPACE}/lib/\" \"\${WORKSPACE}/src/\" \"\${WORKSPACE}/test/\" \
                             -d . -o \"\${coverage_file}\" >> \"\${coverage_log}\" 2>&1 || echo \">>> WARNING: Coverage generation failed (see \${coverage_log})\"
                     else
                         echo \">>> WARNING: /gcov directory is empty or missing, skipping coverage\"

test/infra/control/start-proxysql-isolated.bash

@@ -54,6 +54,9 @@ docker rm -f "${PROXY_CONTAINER}" >/dev/null 2>&1 || true
 #   proxy-nodeN: admin=6032+(N*10), mysql=6033+(N*10)
 
 STARTUP_CMD="
+# Disable gcov for background cluster nodes to avoid concurrent .gcda writes
+unset GCOV_PREFIX GCOV_PREFIX_STRIP
+
 # Start cluster nodes as background processes
 for i in \$(seq 1 ${NUM_NODES}); do
     ADMIN_PORT=\$((6032 + i * 10))
@@ -147,9 +150,11 @@ if [ "${NUM_NODES}" -gt 0 ]; then
 
     MYSQL_CMD="docker exec -i ${PROXY_CONTAINER} mysql -uadmin -padmin -h127.0.0.1"
 
-    # Build proxysql_servers entries: primary + first 3 nodes as core
+    # Build proxysql_servers entries: primary + up to first 3 nodes as core
+    CORE_NODES=3
+    if [ "${NUM_NODES}" -lt 3 ]; then CORE_NODES="${NUM_NODES}"; fi
     PROXYSQL_SERVERS_SQL="DELETE FROM proxysql_servers;"
-    for i in $(seq 1 3); do
+    for i in $(seq 1 "${CORE_NODES}"); do
         PORT=$((6032 + i * 10))
         PROXYSQL_SERVERS_SQL="${PROXYSQL_SERVERS_SQL} INSERT INTO proxysql_servers (hostname,port,weight,comment) VALUES ('127.0.0.1',${PORT},0,'core-node${i}');"
     done
@@ -170,7 +175,7 @@ SQL
     # Configure each node
     for i in $(seq 1 "${NUM_NODES}"); do
         ADMIN_PORT=$((6032 + i * 10))
-        RESTAPI_PORT=$((6070 + i))
+        RESTAPI_PORT=$((7070 + i))
         echo ">>> Configuring proxy-node${i} (port ${ADMIN_PORT})"
 
         ${MYSQL_CMD} -P${ADMIN_PORT} <<SQL
@@ -202,8 +207,8 @@ LOAD SCHEDULER TO RUNTIME;
 SAVE SCHEDULER TO DISK;
 SQL
 
-    # Install on core nodes (1-3)
-    for i in $(seq 1 3); do
+    # Install on core nodes
+    for i in $(seq 1 "${CORE_NODES}"); do
         ADMIN_PORT=$((6032 + i * 10))
         ${MYSQL_CMD} -P${ADMIN_PORT} <<SQL
 INSERT OR REPLACE INTO scheduler (interval_ms, filename) VALUES (12000, '/tmp/check_all_nodes.bash');