refactor(web): edit and wrap diagrams with the MCP server's code

- edit_diagram runs the MCP server's editDiagram: every new_xml is checked
  first, one cell per operation, and after the edit only the target page
  is checked, rejecting only errors this edit introduced. An unrelated
  problem elsewhere in the document no longer blocks every edit. The
  error lists each failed operation
- The streaming edit preview uses the MCP applyDiagramOperations
- Delete applyDiagramOperations (292 lines) and wrapWithMxFile from
  lib/utils.ts, and the unused hand-copied scripts/test-diagram-operations.mjs
- One blank document (BLANK_MXFILE) for the web app and the MCP preview,
  replacing four copies
- Saving a .drawio wraps a bare model with normalizeToMxfile
- The empty-diagram check uses hasCells, which also counts cells wrapped
  in a UserObject/object
- DiagramOperation is the MCP type
- The wrapped-cell and empty-diagram tests now run against the MCP code
- New e2e test: edit_diagram changes the canvas, and a failing edit
  leaves it as it was

hooks/use-diagram-tool-handlers.ts

@@ -7,6 +7,7 @@ import type {
 import type { ValidationResult } from "@/lib/diagram-validator"
 import { formatValidationFeedback } from "@/lib/diagram-validator"
 import { isMxCellXmlComplete } from "@/lib/utils"
+import { editDiagram } from "@/packages/mcp-server/src/edit-diagram.ts"
 import { prepareNewDiagram } from "@/packages/mcp-server/src/new-diagram.ts"
 
 const DEBUG = process.env.NODE_ENV === "development"
@@ -401,27 +402,19 @@ ${finalXml}
                 }
             }
 
-            const { applyDiagramOperations } = await import("@/lib/utils")
-            const { result: editedXml, errors } = applyDiagramOperations(
-                currentXml,
-                operations,
-            )
-
-            // Check for operation errors
-            if (errors.length > 0) {
-                const errorMessages = errors
-                    .map(
-                        (e) =>
-                            `- ${e.type} on cell_id="${e.cellId}": ${e.message}`,
-                    )
-                    .join("\n")
-
+            // All or nothing, checked like the MCP server's edit_diagram.
+            // The model sees the first page, so edits target it.
+            const outcome = editDiagram(currentXml, operations, {})
+            if (!outcome.ok) {
+                const reason = outcome.pageError
+                    ? outcome.errors[0]
+                    : `No changes were made because ${outcome.errors.length} operation(s) failed:\n${outcome.errors.map((e) => `- ${e}`).join("\n")}`
                 restoreOriginal()
                 addToolOutput({
                     tool: "edit_diagram",
                     toolCallId: toolCall.toolCallId,
                     state: "output-error",
-                    errorText: `Some operations failed:\n${errorMessages}
+                    errorText: `${reason}
 
 Current diagram XML:
 \`\`\`xml
@@ -435,36 +428,12 @@ Please check the cell IDs and retry.`,
                 return
             }
 
-            // loadDiagram validates and returns error if invalid
-            const validationError = onDisplayChart(editedXml)
-            if (validationError) {
-                console.warn(
-                    "[edit_diagram] Validation error:",
-                    validationError,
-                )
-                restoreOriginal()
-                addToolOutput({
-                    tool: "edit_diagram",
-                    toolCallId: toolCall.toolCallId,
-                    state: "output-error",
-                    errorText: `Edit produced invalid XML: ${validationError}
-
-Current diagram XML:
-\`\`\`xml
-${currentXml}
-\`\`\`
-
-Please fix the operations to avoid structural issues.`,
-                })
-                // Clean up the shared original XML ref
-                editDiagramOriginalXmlRef.current.delete(toolCall.toolCallId)
-                return
-            }
+            onDisplayChart(outcome.xml, true)
             onExport()
             addToolOutput({
                 tool: "edit_diagram",
                 toolCallId: toolCall.toolCallId,
-                output: `Successfully applied ${operations.length} operation(s) to the diagram.`,
+                output: `Successfully applied ${outcome.applied} operation(s) to the diagram.`,
             })
             // Clean up the shared original XML ref
             editDiagramOriginalXmlRef.current.delete(toolCall.toolCallId)