Perspective grid: coming back from a temporary tool keeps a hidden grid hidden (review of #333)

Choosing a perspective tool shows the grid, but the canvas also re-selected the tool after a
Cmd-drag with the borrowed Selection tool, so a grid hidden with the tool chosen came back after
any Cmd-drag. `Session::switch_tool` (and the app's `restore_tool`) switch without choosing; the
temporary-tool return uses it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/tests_distort.rs

@@ -267,6 +267,22 @@ fn the_grid_hides_while_a_perspective_tool_is_chosen() {
     }
 }
 
+#[test]
+fn a_hidden_grid_stays_hidden_back_from_a_temporary_tool() {
+    // Cmd-dragging with a perspective tool borrows the Selection tool; going back to the
+    // perspective tool is not choosing it, so the grid hidden meanwhile stays hidden.
+    let mut s = session();
+    let v = ViewInfo::default();
+    s.select_tool("perspectiveGrid", v).unwrap();
+    s.execute("perspective.grid.show", &json!({"visible": false})).unwrap();
+    s.switch_tool("selection", v).unwrap();
+    s.switch_tool("perspectiveGrid", v).unwrap();
+    assert!(s.overlays(v).is_empty());
+    s.select_tool("selection", v).unwrap();
+    s.select_tool("perspectiveGrid", v).unwrap();
+    assert!(s.overlays(v).len() > 20, "choosing it shows the grid");
+}
+
 #[test]
 fn grid_preset_and_set_are_undoable() {
     let mut s = session();

crates/engine/src/tooling.rs

@@ -56,7 +56,7 @@ impl Session {
         self.tool.id()
     }
 
-    /// Switch tools (finishing any pending tool work first).
+    /// Choose a tool (the toolbar, its shortcut, MCP), finishing any pending tool work first.
     pub fn select_tool(&mut self, id: &str, view: ViewInfo) -> Result<()> {
         // Choosing a perspective tool shows the document's perspective grid; Hide Grid hides it
         // again, the tool staying chosen.
@@ -65,6 +65,12 @@ impl Session {
         {
             crate::cmd::distortcmds::silent(self, |g| g.visible = true)?;
         }
+        self.switch_tool(id, view)
+    }
+
+    /// Switch to tool `id` without choosing it afresh (back from a temporary tool: a hidden
+    /// perspective grid stays hidden), finishing any pending tool work first.
+    pub fn switch_tool(&mut self, id: &str, view: ViewInfo) -> Result<()> {
         if self.tool.id() == id {
             return Ok(());
         }

crates/ui-egui/src/canvas.rs

@@ -560,7 +560,7 @@ fn handle_input(app: &mut VectorcraftApp, ui: &Ui, resp: &egui::Response, rect:
                     if matches!(d, Drag::TempSelect | Drag::Art { temp: true })
                         && let Some(prev) = ui.data(|dd| dd.get_temp::<String>(temp_tool_id()))
                     {
-                        app.select_tool(&prev);
+                        app.restore_tool(&prev);
                     }
                 }
                 Drag::Pan { .. } | Drag::RotateView { .. } => {}

crates/ui-egui/src/lib.rs

@@ -510,8 +510,19 @@ impl VectorcraftApp {
 
     /// Select a tool (also used by the toolbar and shortcuts).
     pub fn select_tool(&mut self, id: &str) {
+        self.change_tool(id, true);
+    }
+
+    /// Go back to tool `id` after a temporary one, without choosing it afresh
+    /// ([`vectorcraft_engine::Session::switch_tool`]).
+    pub fn restore_tool(&mut self, id: &str) {
+        self.change_tool(id, false);
+    }
+
+    fn change_tool(&mut self, id: &str, choose: bool) {
         let v = self.view_info();
-        if let Err(e) = self.session.select_tool(id, v) {
+        let r = if choose { self.session.select_tool(id, v) } else { self.session.switch_tool(id, v) };
+        if let Err(e) = r {
             self.ui.status = e.to_string();
         }
         if let Some(g) = vectorcraft_tools::catalog::group_of(id)