fix(mcp-server): review fixes for the shell's sync core

A recovery loads the server's diagram in full and waits for draw.io's
load report, as the classic page does: whether the canvas takes a write
in place is decided inside DiagramProvider, and an autosave of the
canvas being replaced went to the server as an edit when the decision
was wrong. A paper size change alone is pushed again: autosaves are
compared as documents only for draw.io's own copy of a committed write.
A projection stays on screen until draw.io reports the restore load
(5 s at most), the whole export ends in 15 s even when its result POST
hangs, and an export in flight is dropped when draw.io starts over. A
refused poll shows the tab offline. With several pages and the page on
screen unknown, a write loads in full. hasLoadOnlySettings and the
highlight of an AI change are shared with the editor bridge.

lib/drawio/editor-bridge.ts

@@ -262,19 +262,19 @@ function hasShapes(xml: string): boolean {
     })
 }
 
-// Page settings draw.io applies on a full load only: replacing the page in
-// place (Editor.readGraphState) keeps the old ones. (Its adaptive colors and
-// theme stay too: a diagram the AI writes does not set them.)
-function hasLoadOnlySettings(model: string): boolean {
-    const page = new DOMParser().parseFromString(
-        model,
-        "text/xml",
-    ).documentElement
+/**
+ * Page settings draw.io applies on a full load only: replacing the page in
+ * place (Editor.readGraphState) keeps the old ones. (Its adaptive colors and
+ * theme stay too: a diagram the AI writes does not set them.) Takes the
+ * page's mxGraphModel element; the MCP shell's sync asks the same question
+ * of a document before it reaches the editor.
+ */
+export function hasLoadOnlySettings(model: Element): boolean {
     return (
-        page.hasAttribute("backgroundImage") ||
-        page.hasAttribute("extFonts") ||
-        page.getAttribute("math") === "1" ||
-        page.getAttribute("shadow") === "1"
+        model.hasAttribute("backgroundImage") ||
+        model.hasAttribute("extFonts") ||
+        model.getAttribute("math") === "1" ||
+        model.getAttribute("shadow") === "1"
     )
 }
 
@@ -322,7 +322,9 @@ export function canReplaceDiagram(xml: string): boolean {
     // A document with them, or replacing one with them, loads in full
     return (
         model !== null &&
-        !hasLoadOnlySettings(model) &&
+        !hasLoadOnlySettings(
+            new DOMParser().parseFromString(model, "text/xml").documentElement,
+        ) &&
         !canvasHasLoadOnlySettings()
     )
 }
@@ -547,6 +549,19 @@ export function highlightCells(ids: string[], color: string) {
     }
 }
 
+/**
+ * Marks the cells an AI change touched in the page's marker color, once
+ * draw.io has drawn them (the web app's versions and the MCP shell share it)
+ */
+export function highlightChangedCells(ids: string[]) {
+    setTimeout(() => {
+        const marker = getComputedStyle(document.documentElement)
+            .getPropertyValue("--marker")
+            .trim()
+        highlightCells(ids, marker || "#ffd84d")
+    }, 60)
+}
+
 // ---------------------------------------------------------------------------
 // Selection
 // ---------------------------------------------------------------------------