diff --git a/crates/openpencil-shell-core/src/mcp/replace_node_tests.rs b/crates/openpencil-shell-core/src/mcp/replace_node_tests.rs
index db94fda65..d952268e7 100644
--- a/crates/openpencil-shell-core/src/mcp/replace_node_tests.rs
+++ b/crates/openpencil-shell-core/src/mcp/replace_node_tests.rs
@@ -216,12 +216,14 @@ fn replace_node_rejects_malformed_drop_children() {
     args.insert("y".into(), "0".into());
     args.insert("width".into(), "10".into());
     args.insert("height".into(), "10".into());
-    args.insert("drop_children".into(), "yes".into()); // not "true"/"false"
-    match tool.call(&args) {
-        ToolOutcome::Err(code, msg) => {
-            assert_eq!(code, ToolErrorCode::InvalidArgument);
-            assert!(msg.contains("drop_children"));
+    for bad in ["yes", "", "TRUE", "1", "0"] {
+        args.insert("drop_children".into(), bad.into());
+        match tool.call(&args) {
+            ToolOutcome::Err(code, msg) => {
+                assert_eq!(code, ToolErrorCode::InvalidArgument, "input {bad:?}");
+                assert!(msg.contains("drop_children"), "input {bad:?} msg = {msg}");
+            }
+            _ => panic!("expected InvalidArgument on malformed drop_children {bad:?}"),
         }
-        _ => panic!("expected InvalidArgument on malformed drop_children"),
     }
 }
diff --git a/crates/openpencil-shell-core/src/mcp/write_tools.rs b/crates/openpencil-shell-core/src/mcp/write_tools.rs
index 2772b97b4..fe3f29664 100644
--- a/crates/openpencil-shell-core/src/mcp/write_tools.rs
+++ b/crates/openpencil-shell-core/src/mcp/write_tools.rs
@@ -609,12 +609,14 @@ impl McpTool for ReplaceNode {
         };
         // Optional opt-in for destructive swaps. The applier
         // refuses to drop a container's children unless this is
-        // `"true"`. Any other value (including "false" / "1" /
-        // missing) leaves the guard active.
+        // `"true"`. Missing → safe default false. Any other
+        // value (including the empty string) is malformed and
+        // rejected — silently treating "" as false would hide a
+        // mis-serialized confirmation from the caller.
         let drop_children = match args.get("drop_children") {
-            Some(s) if s == "true" => true,
-            Some(s) if s == "false" || s.is_empty() => false,
             None => false,
+            Some(s) if s == "true" => true,
+            Some(s) if s == "false" => false,
             Some(s) => {
                 return ToolOutcome::Err(
                     ToolErrorCode::InvalidArgument,