fix(mcp-server): count a one-page view only for that page, and more review fixes

Found by the second PR review:
- get_diagram with a page selector, or a rejected edit's error, counted
  the whole document as seen, so an edit on another page could overwrite
  the user's change there. A one-page view now counts for all pages only
  if the others are unchanged; otherwise the reply says to get them.
- add_page accepted shapes with the root cell ids "0" and "1" and renamed
  them, breaking their edges. The check also missed ids on UserObject
  wrappers and ids written with spaces around the "=".
- Root cells written over two lines were kept as an extra layer, cells
  with id = "a" did not count as cells, and CDATA text before a page's
  model passed the check although draw.io cannot open the page.
- Auto-save cleanup deleted the user's own files that start with mcp-.
  Only names in the session id format are removed now.
- Restoring a history entry dropped edits made in the browser since the
  last entry. They are added to history first.
- A session whose state expired showed a blank page, and the next change
  overwrote its auto-save file. The saved file is loaded instead.
- An edit on a page export's one-page projection, made before the real
  document was back, replaced the whole document.
- A late sync reply could overwrite a newer edit: each sync export is
  numbered, and the server ignores replies older than the current state.
- screenshot_diagram could return another session's image after
  start_session ran during its retries.

packages/mcp-server/tests/http-server.test.ts

@@ -11,6 +11,7 @@ import { afterAll, beforeAll, describe, expect, it } from "vitest"
 import { addHistory, getHistory } from "../src/history.ts"
 import {
     getState,
+    onSessionRecreate,
     requestExport,
     requestSync,
     setState,
@@ -242,6 +243,27 @@ describe("POST /api/state", () => {
         expect(getHistory(id)).toHaveLength(before)
         expect(await waitForSync(id, 200)).toBe(true)
     })
+
+    it("ignores a sync reply older than a user edit saved meanwhile", async () => {
+        const id = "mcp-late-sync"
+        const version = setState(id, "<mxfile>A</mxfile>", undefined, true)
+        requestSync(id)
+        // The user's edit is saved before the sync reply arrives
+        const edit = await postJson("/api/state", {
+            sessionId: id,
+            xml: "<mxfile>B</mxfile>",
+            baseVersion: version,
+        })
+        expect(edit.status).toBe(200)
+        const late = await postJson("/api/state", {
+            sessionId: id,
+            xml: "<mxfile>A</mxfile>",
+            baseVersion: version,
+            source: "sync",
+        })
+        expect(late.status).toBe(409)
+        expect(getState(id)?.xml).toBe("<mxfile>B</mxfile>")
+    })
 })
 
 describe("export requests", () => {
@@ -283,6 +305,19 @@ describe("export requests", () => {
 })
 
 describe("preview page", () => {
+    it("shows the saved diagram of a session whose state expired", async () => {
+        const saved = `<mxfile><diagram id="p" name="P"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><mxCell id="kept" vertex="1" parent="1"/></root></mxGraphModel></diagram></mxfile>`
+        onSessionRecreate((id) => (id === "mcp-expired" ? saved : null))
+        try {
+            await request("/?mcp=mcp-expired")
+            expect(getState("mcp-expired")?.xml).toBe(saved)
+            await request("/?mcp=mcp-never-saved")
+            expect(getState("mcp-never-saved")?.xml).not.toContain("kept")
+        } finally {
+            onSessionRecreate(() => null)
+        }
+    })
+
     it("serves scripts that parse, with every placeholder filled", async () => {
         const res = await request("/?mcp=mcp-test-script")
         expect(res.body).not.toContain("{{")
@@ -314,4 +349,24 @@ describe("history restore", () => {
         expect(res.status).toBe(200)
         expect(getState(id)?.xml).toBe("<mxfile>5</mxfile>")
     })
+
+    it("keeps manual edits in history before restoring", async () => {
+        const id = "mcp-history-manual"
+        const doc = (cellId: string) =>
+            `<mxfile><diagram id="p" name="P"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><mxCell id="${cellId}" vertex="1" parent="1"/></root></mxGraphModel></diagram></mxfile>`
+        const version = setState(id, doc("ai"))
+        addHistory(id, doc("ai"))
+        // An edit in the browser is not a history entry by itself
+        const push = await postJson("/api/state", {
+            sessionId: id,
+            xml: doc("manual"),
+            baseVersion: version,
+        })
+        expect(push.status).toBe(200)
+
+        const [entry] = getHistory(id)
+        await postJson("/api/restore", { sessionId: id, id: entry.id })
+        expect(getState(id)?.xml).toBe(doc("ai"))
+        expect(getHistory(id).map((e) => e.xml)).toContain(doc("manual"))
+    })
 })