refactor(web): validate and repair diagram XML with the MCP server's engine

- Delete the web app's own copy of the XML checks and repairs from
  lib/utils.ts (1,074 lines). loadDiagram now uses the MCP server's
  validateAndFixXml without the strict checks, because the XML may hold
  the user's own diagram
- display_diagram and append_diagram prepare the model's XML with the new
  shared prepareNewDiagram, also used by the MCP create_new_diagram: wrap,
  validate strictly and auto-fix while it is still a bare model (where
  duplicate ids are renamed), then turn it into an mxfile
- The streaming preview of display_diagram no longer redraws the model's
  raw cells after the tool handler loaded the checked diagram, and drops
  a queued preview once the input is complete. That redraw lost
  auto-fixes and UserObject/object wrappers, so a linked cell lost its
  label; it also showed a second error toast
- The web repair regression tests now run against the MCP functions
- New e2e test checks the canvas content after display_diagram
- Fix the e2e upload tests, whose file input locator also matched the
  template import input

tests/unit/utils.test.ts

@@ -1,12 +1,9 @@
 import { describe, expect, it } from "vitest"
 import {
     applyDiagramOperations,
-    autoFixXml,
     cn,
     extractCompleteMxCells,
     isMxCellXmlComplete,
-    validateAndFixXml,
-    validateMxCellStructure,
     wrapWithMxFile,
 } from "@/lib/utils"
 
@@ -136,92 +133,6 @@ describe("extractCompleteMxCells", () => {
     })
 })
 
-const page = (id: string, cells: string) =>
-    `<diagram name="${id}" id="${id}"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/>${cells}</root></mxGraphModel></diagram>`
-
-describe("duplicate ids in multi-page documents", () => {
-    const shape = (id: string, value = "Box") =>
-        `<mxCell id="${id}" value="${value}" vertex="1" parent="1"><mxGeometry x="0" y="0" width="80" height="40" as="geometry"/></mxCell>`
-
-    it("accepts the same ids on different pages", () => {
-        const xml = `<mxfile>${page("p1", shape("2"))}${page("p2", shape("2"))}</mxfile>`
-        expect(validateMxCellStructure(xml)).toBeNull()
-    })
-
-    it("still reports duplicate ids within one page", () => {
-        const xml = `<mxfile>${page("p1", shape("2") + shape("2"))}${page("p2", "")}</mxfile>`
-        expect(validateMxCellStructure(xml)).toContain("duplicate ID")
-    })
-
-    it("does not rename the root cells of other pages when fixing", () => {
-        const xml = `<mxfile>${page("p1", shape("2", "R&D"))}${page("p2", shape("3"))}</mxfile>`
-        const result = validateAndFixXml(xml)
-        expect(result.valid).toBe(true)
-        expect(result.fixed).not.toContain("_dup")
-        expect(result.fixed).toContain("R&amp;D")
-    })
-
-    it("renames a duplicate id within a page", () => {
-        const xml = `<mxfile>${page("p1", shape("d") + shape("d"))}</mxfile>`
-        const { fixed } = autoFixXml(xml)
-        expect(fixed).toContain('<mxCell id="d" ')
-        expect(fixed).toContain('<mxCell id="d_dup1" ')
-    })
-})
-
-describe("autoFixXml", () => {
-    it("does not insert a space at the start of style values", () => {
-        const xml = `<mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><mxCell id="2" value="R&D" style="rounded=1;whiteSpace=wrap;" vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell></root></mxGraphModel>`
-        const { fixed } = autoFixXml(xml)
-        expect(fixed).toContain('style="rounded=1;whiteSpace=wrap;"')
-    })
-
-    it("adds a missing space between attributes", () => {
-        const xml = `<mxCell id="2" vertex="1"parent="1"/>`
-        expect(autoFixXml(xml).fixed).toContain('vertex="1" parent="1"')
-    })
-
-    it("keeps &quot; inside rich text labels", () => {
-        const label = "&lt;font color=&quot;#ff0000&quot;&gt;Hello&lt;/font&gt;"
-        const xml = `<mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><mxCell id="2" value="${label}" style="html=1;" vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell><mxCell id="3" value="Q&A" vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell></root></mxGraphModel>`
-        const result = validateAndFixXml(xml)
-        expect(result.valid).toBe(true)
-        expect(result.fixed).toContain(`value="${label}"`)
-    })
-
-    it("fixes an attribute delimited by &quot;", () => {
-        const xml = `<mxCell id="2" dashPattern=&quot;1 1;&quot; vertex="1" parent="1"/>`
-        expect(autoFixXml(xml).fixed).toContain('dashPattern="1 1;"')
-    })
-
-    it("keeps cells written on one line next to multi-line cells", () => {
-        const xml = `<mxGraphModel><root>
-<mxCell id="0"/>
-<mxCell id="1" parent="0"/>
-<mxCell id="2" value="Q&A" vertex="1" parent="1">
-  <mxGeometry x="0" y="0" width="80" height="40" as="geometry"/>
-</mxCell>
-<mxCell id="e1" edge="1" parent="1" source="2" target="3"><mxGeometry relative="1" as="geometry"/></mxCell>
-<mxCell id="3" value="B" vertex="1" parent="1">
-  <mxGeometry x="200" y="0" width="80" height="40" as="geometry"/>
-</mxCell>
-</root></mxGraphModel>`
-        const result = validateAndFixXml(xml)
-        expect(result.valid).toBe(true)
-        for (const id of ["2", "e1", "3"]) {
-            expect(result.fixed).toContain(`<mxCell id="${id}"`)
-        }
-    })
-
-    it("keeps object and UserObject wrappers", () => {
-        const xml = `<mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><UserObject id="2" label="Docs" link="https://example.com"><mxCell vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell></UserObject><object id="3" label="A&B" owner="me"><mxCell vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell></object></root></mxGraphModel>`
-        const result = validateAndFixXml(xml)
-        expect(result.valid).toBe(true)
-        expect(result.fixed).toContain('<UserObject id="2"')
-        expect(result.fixed).toContain('<object id="3"')
-    })
-})
-
 describe("applyDiagramOperations with wrapped cells", () => {
     const xml = `<mxfile><diagram id="p1"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><UserObject id="5" label="Docs" link="https://example.com"><mxCell vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell></UserObject><mxCell id="6" value="B" vertex="1" parent="1"><mxGeometry as="geometry"/></mxCell><mxCell id="e1" edge="1" parent="1" source="5" target="6"><mxGeometry relative="1" as="geometry"/></mxCell></root></mxGraphModel></diagram></mxfile>`