From 398131b9ccda7ed5be2516b9ea7436a9b56fea70 Mon Sep 17 00:00:00 2001
From: dotCooCoo <RobertLeeLW@gmail.com>
Date: Thu, 5 Nov 2026 19:04:43 -0800
Subject: [PATCH] Reject invalid Transparency Grid parameters

---
 crates/engine/src/cmd/views.rs              |  4 ++--
 crates/engine/src/tests/transparencygrid.rs | 15 +++++++++++++++
 docs/mcp.md                                 |  1 +
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/crates/engine/src/cmd/views.rs b/crates/engine/src/cmd/views.rs
index 8597a0963..fd9e11bcf 100644
--- a/crates/engine/src/cmd/views.rs
+++ b/crates/engine/src/cmd/views.rs
@@ -5,7 +5,7 @@ use serde_json::{Value, json};
 use vectorcraft_doc::SavedView;
 use vectorcraft_geom::Point;
 
-use super::{CommandSpec, Result, Session, always, bad, bool_or, cmd, f64_req, finite_numbers, has_doc, str_param};
+use super::{CommandSpec, Result, Session, always, bad, bool_or, cmd, f64_req, finite_numbers, has_doc, str_param, switch_or};
 
 pub fn specs() -> Vec<CommandSpec> {
     vec![
@@ -64,7 +64,7 @@ fn caps_lock(s: &mut Session, p: &Value) -> Result<Value> {
 
 fn transparency_grid(s: &mut Session, p: &Value) -> Result<Value> {
     let st = s.doc_mut()?;
-    st.transparency_grid = p.get("on").and_then(Value::as_bool).unwrap_or(!st.transparency_grid);
+    st.transparency_grid = switch_or(p, "on", !st.transparency_grid, "view.transparencyGrid")?;
     Ok(json!({ "on": st.transparency_grid }))
 }
 
diff --git a/crates/engine/src/tests/transparencygrid.rs b/crates/engine/src/tests/transparencygrid.rs
index 974fb0343..06efa70fb 100644
--- a/crates/engine/src/tests/transparencygrid.rs
+++ b/crates/engine/src/tests/transparencygrid.rs
@@ -26,3 +26,18 @@ fn transparency_grid_is_per_document_view_state() {
     s.execute("document.activate", &json!({"index": 1})).unwrap();
     assert!(!grid(&s));
 }
+
+#[test]
+fn invalid_transparency_grid_parameters_leave_the_view_unchanged() {
+    let mut s = Session::new();
+    s.execute("file.new", &json!({})).unwrap();
+    for params in [json!({"on": "false"}), json!({"on": 1})] {
+        assert!(s.execute("view.transparencyGrid", &params).is_err(), "accepted {params}");
+        let st = s.doc().unwrap();
+        assert!(!st.transparency_grid, "changed the grid for {params}");
+        assert!(st.history.undo.is_empty() && !st.is_dirty(), "recorded an edit for {params}");
+    }
+    // Left out, or null as for every command, it toggles.
+    assert_eq!(s.execute("view.transparencyGrid", &json!(null)).unwrap(), json!({"on": true}));
+    assert_eq!(s.execute("view.transparencyGrid", &json!({"on": null})).unwrap(), json!({"on": false}));
+}
diff --git a/docs/mcp.md b/docs/mcp.md
index 5c9c5cb45..4934da0c7 100644
--- a/docs/mcp.md
+++ b/docs/mcp.md
@@ -1359,6 +1359,7 @@ mask first". Pattern editing mode does not count as isolation mode here.
 `view.transparencyGrid {on?}` (View → Show Transparency Grid; default: toggle) is view state of each open document,
 like the mask view: the grid shows behind the artboards of the documents that turn it on, on the canvas and in
 `ui.screenshot`, never in exports. It returns `{on}`, isn't undoable and doesn't mark the document changed.
+The command rejects an `on` value that is not a boolean. Omitting `on` toggles the current value.
 
 `view.globalRulers {global?}` (View → Rulers → Change to Global / Artboard Rulers, Cmd+Alt+R; default: toggle) is
 saved with the document and undoable. With artboard rulers (a new document's) the rulers count from the active