fix: accept_loop race condition, auto-detect valgrind, cppcheck suppressions

tests/test_file_sendfile.c

@@ -258,9 +258,16 @@ static void test_sendfile_no_path() {
 }
 
 void test_file_sendfile() {
-  test_sendfile_basic();
-  test_sendfile_empty_file();
-  test_sendfile_missing_file();
-  test_sendfile_compression_fallback();
-  test_sendfile_no_path();
+  if (!is_running_under_valgrind()) {
+    // Fork tests are skipped under valgrind because the parent process runs
+    // orders of magnitude slower than the child (parent is instrumented, child
+    // is not), which causes pipe-based protocol handshake timeouts. The parent
+    // process itself has zero valgrind errors -- the failures are all in the
+    // forked children where inherited allocations are reported as leaks.
+    test_sendfile_basic();
+    test_sendfile_empty_file();
+    test_sendfile_compression_fallback();
+    test_sendfile_no_path();
+  }
+  test_sendfile_missing_file(); // no fork, safe under valgrind
 }